Primary ciliary dyskinesia (PCD) is an inherited disorder characterized by recurrent infections of the upper and lower respiratory tract, reduced fertility in males and situs inversus in about 50% of affected individuals (Kartagener syndrome). It is caused by motility defects in the respiratory cilia that are responsible for airway clearance, the flagella that propel sperm cells and the nodal monocilia that determine left-right asymmetry1. Recessive mutations that cause PCD have been identified in genes encoding components of the outer dynein arms, radial spokes and cytoplasmic pre-assembly factors of axonemal dyneins, but these mutations account for only about 50% of cases of PCD. We exploited the unique properties of dog populations to positionally clone a new PCD gene, CCDC39. We found that loss-of-function mutations in the human ortholog underlie a substantial fraction of PCD cases with axonemal disorganization and abnormal ciliary beating. Functional analyses indicated that CCDC39 localizes to ciliary axonemes and is essential for assembly of inner dynein arms and the dynein regulatory complex.

The planar cell polarity (PCP) signaling pathway governs collective cell movements duringvertebrate embryogenesis, and certain PCP proteins are also implicated in the assembly ofcilia. The septins are cytoskeletal proteins controlling behaviors such as cell division and migration. Here, we identified control of septin localization by the PCP protein Fritz as a crucial control point for both collective cell movement and ciliogenesis in Xenopus embryos. We also linked mutations in human Fritz to Bardet-Biedl and Meckel-Gruber syndromes, a notable link given that other genes mutated in these syndromes also influence collective cell movement and ciliogenesis. These findings shed light on the mechanisms by which fundamental cellular machinery, such as the cytoskeleton, is regulated during embryonic development and human disease.

Limb-girdle muscular dystrophy type 1D (LGMD1D) was linked to 7q36 over a decade ago1, but its genetic cause has remained elusive. We have studied nine LGMD families from Finland, the U.S., and Italy, and identified four dominant missense mutations leading to p.Phe93Leu or p.Phe89Ile changes in the ubiquitously expressed co-chaperone DNAJB6. Functional testing in vivo showed that the mutations have a dominant toxic effect mediated specifically by the cytoplasmic isoform of DNAJB6. In vitro studies demonstrated that the mutations increase the half-life of DNAJB6, extending this effect to the wild-type protein, and reduce its protective anti-aggregation effect. Further, we show that DNAJB6 interacts with members of the CASA complex, including the myofibrillar-myopathy-causing protein BAG3. Our data provide the genetic cause of LGMD1D, suggest that the pathogenesis is mediated by defective chaperone function, and highlight how mutations expressed ubiquitously can exert their effect in a tissue-, cellular compartment-, and isoform-specific manner.

Endoglin interacts with PI3K via GIPC to recruit and activate PI3K/Akt at the cell membrane. TGF-β1 attenuates, whereas BMP-9 enhances, endoglin/GIPC-mediated membrane scaffolding of PI3K/Akt to alter endothelial capillary tube stability in vitro, and GIPC mediates endoglin function during developmental angiogenesis in vivo.

Endoglin (CD105) is an endothelial-specific transforming growth factor β (TGF-β) coreceptor essential for angiogenesis and vascular homeostasis. Although endoglin dysfunction contributes to numerous vascular conditions, the mechanism of endoglin action remains poorly understood. Here we report a novel mechanism in which endoglin and Gα-interacting protein C-terminus–interacting protein (GIPC)–mediated trafficking of phosphatidylinositol 3-kinase (PI3K) regulates endothelial signaling and function. We demonstrate that endoglin interacts with the PI3K subunits p110α and p85 via GIPC to recruit and activate PI3K and Akt at the cell membrane. Opposing ligand-induced effects are observed in which TGF-β1 attenuates, whereas bone morphogenetic protein-9 enhances, endoglin/GIPC-mediated membrane scaffolding of PI3K and Akt to alter endothelial capillary tube stability in vitro. Moreover, we employ the first transgenic zebrafish model for endoglin to demonstrate that GIPC is a critical component of endoglin function during developmental angiogenesis in vivo. These studies define a novel non-Smad function for endoglin and GIPC in regulating endothelial cell function during angiogenesis.

Two common variants within CFH, the Y402H1–4 and the rs1410996 SNPs5,6, explain 17% of age-related macular degeneration (AMD) liability. However, proof for the involvement of CFH, as opposed to a neighboring transcript, and the potential mechanism of susceptibility alleles are lacking. Assuming that rare functional variants might provide mechanistic insights, we used genotype data and high throughput sequencing to discover a rare high-risk CFH haplotype containing an R1210C mutation. This allele has been implicated previously in atypical hemolytic uremic syndrome, and abrogates C-terminal ligand binding7,8. Genotyping R1210C in 2,423 AMD cases and 1,122 controls demonstrated high penetrance (present in 40 cases versus 1 control, p=7.0×10−6) and six year earlier onset of disease (p=2.3×10−6). This result suggests that loss of function alleles at CFH likely drive AMD risk. This finding represents one of the first instances where a common complex disease variant has led to discovery of a rare penetrant mutation.

Bardet–Biedl syndrome (BBS; OMIM no. 209 900) and Alström syndrome (ALMS; OMIM no. 203 800) are rare, multisystem genetic disorders showing both a highly variable phenotype and considerable phenotypic overlap; they are included in the emerging group of diseases called ciliopathies. The genetic heterogeneity of BBS with 14 causal genes described to date, serves to further complicate mutational analysis. The development of the BBS–ALMS array which detects known mutations in these genes has allowed us to detect at least one mutation in 40.5% of BBS families and in 26.7% of ALMS families validating this as an efficient and cost-effective first pass screening modality. Furthermore, using this method, we found two BBS families segregating three BBS alleles further supporting oligogenicity or modifier roles for additional mutations. We did not observe more than two mutations in any ALMS family.

Bardet–Biedl syndrome (BBS) and Laurence–Moon syndrome (LMS) have a similar phenotype, which includes retinal dystrophy, obesity, and hypogenitalism. They are differentiated by the presence of spasticity and the absence of polydactyly in LMS. The aims of this study were to describe the epidemiology of BBS and LMS, further define the phenotype, and examine genotype–phenotype correlation. The study involved 46 patients (26 males, 20 females) from 26 families, with a median age of 44 years (range 1–68 years). Assessments were performed in 1986, 1993, and 2001 and included neurological assessments, anthropometric measurements, and clinical photographs to assess dysmorphic features. The phenotype was highly variable within and between families. Impaired co-ordination and ataxia occurred in 86% (18/21). Thirty percent (14/46) met criteria for psychiatric illness; other medical problems included cholecystectomy in 37% (17/46) and asthma in 28% (13/46). Dysmorphic features included brachycephaly, large ears, and short, narrow palpebral fissures. There was no apparent correlation of clinical or dysmorphic features with genotype. Two patients were diagnosed clinically as LMS but both had mutations in a BBS gene. The features in this population do not support the notion that BBS and LMS are distinct. The lack of a genotype–phenotype correlation implies that BBS proteins interact and are necessary for the development of many organs.

Mutations in genes encoding ciliary components cause ciliopathies, but how many of these mutations disrupt ciliary function is unclear. We investigated Tectonic1 (Tctn1), a regulator of mouse Hedgehog signaling, and found that it is essential for ciliogenesis in some, but not all, tissues. Cell types that do not require Tctn1 for ciliogenesis require it to localize select membrane-associated proteins to the cilium, including Arl13b, AC3, Smoothened and Pkd2. Tctn1 forms a complex with multiple ciliopathy proteins associated with Meckel (MKS) and Joubert (JBTS) syndromes, including Mks1, Tmem216, Tmem67, Cep290, B9d1, Tctn2, and Cc2d2a. Components of the Tectonic ciliopathy complex colocalize at the transition zone, a region between the basal body and ciliary axoneme. Like Tctn1, loss of complex components Tctn2, Tmem67 or Cc2d2a causes tissue-specific defects in ciliogenesis and ciliary membrane composition. Consistent with a shared function for complex components, we identified a mutation in TCTN1 that causes JBTS. Thus, a transition zone complex of MKS and JBTS proteins regulates ciliary assembly and trafficking, suggesting that transition zone dysfunction is the cause of these ciliopathies.

The authors describe the screening of 55 families of European, Tunisian, and Arab descent for mutations in 15 BBS and 5 additional ciliopathy genes. The spectrum of mutations is described with a discussion of possible third-allele effects.

Purpose.

Bardet-Biedl syndrome (BBS) is genetically heterogeneous with 15 BBS genes currently identified, accounting for approximately 70% of cases. The aim of our study was to define further the spectrum of BBS mutations in a cohort of 44 European-derived American, 8 Tunisian, 1 Arabic, and 2 Pakistani families (55 families in total) with BBS.

Methods.

A total of 142 exons of the first 12 BBS-causing genes were screened by dideoxy sequencing. Cases in which no mutations were found were then screened for BBS13, BBS14, BBS15, RPGRIP1L, CC2D2A, NPHP3, TMEM67, and INPP5E.

Results.

Forty-three mutations, including 8 frameshift mutations, 10 nonsense mutations, 4 splice site mutations, 1 deletion, and 20 potentially or probably pathogenic missense variations, were identified in 46 of the 55 families studied (84%). Of these, 21 (2 frameshift mutations, 4 nonsense mutations, 4 splice site mutations, 1 deletion, and 10 missense variations) were novel. The molecular genetic findings raised the possibility of triallelic inheritance in 7 Caucasian families, 1 Arabian family, and 1 Tunisian patient. No mutations were detected for BBS4, BBS11, BBS13, BBS14, BBS15, RPGRIP1L, CC2D2A, NPHP3, TMEM67, or INPP5E.

Conclusions.

This mutational analysis extends the spectrum of known BBS mutations. Identification of 21 novel mutations highlights the genetic heterogeneity of this disorder. Differences in European and Tunisian patients, including the high frequency of the M390R mutation in Europeans, emphasize the population specificity of BBS mutations with potential diagnostic implications. The existence of some BBS cases without mutations in any currently identified BBS genes suggests further genetic heterogeneity.

Purpose

To investigate the phenotypic variability of patients bearing the heterozygous R124H mutation in the TGFBI (transforming growth factor-beta-induced) gene that causes granular corneal dystrophy type 2 (GCD2).

Methods

We describe the phenotypic range of GCD2 heterozygotes for the common R124H mutation in TGFBI; seven with an extremely mild phenotype and six with an extremely severe phenotype. Detailed slit-lamp photographs of these patients were generated. All patients had no history of ocular surgery and were diagnosed as being heterozygous for GCD2 by DNA analysis from peripheral blood. Expression levels of transforming growth factor-beta-induced protein (TGFBIp) were compared among cultured corneal fibroblasts from ten normal donors.

Results

We report profound differences in the severity of the phenotype across our case series. Two patients with a mild phenotype were diagnosed as unaffected at presentation; however follow-up examinations revealed granular deposits. Importantly, we also observed familial clustering of phenotypic variance; five patients from two families with a mild phenotype showed a similarly mild phenotype within family members. Similarly, six patients from two families with severe phenotypes showed corneal deposits with similar patterns and severity within each distinct family, but distinct patterns between families. TGFBIp expressions from different donor derived cultured corneal fibroblasts were different between one another.

Conclusions

GCD2 heterozygotes have extremely varied phenotypes between individual patients. However phenotypes were broadly consistent within families, suggesting that the observed variable expressivity might be regulated by other genetic factors that could influence the abundance of TGFBIp or the function of the pathway. From a clinical perspective, our data also highlighted that genetic analysis and meticulous slit-lamp examination in both eyes at multiple time intervals is necessary.

Regulatory mechanisms governing the sequence from progenitor cell proliferation to neuronal migration during corticogenesis are poorly understood1–10. Here we report that phosphorylation of DISC1, a major susceptibility factor for several mental disorders, acts as a molecular switch from maintaining proliferation of mitotic progenitor cells to activating migration of postmitotic neurons. Unphosphorylated DISC1 regulates canonical Wnt signaling via an interaction with GSK3β, whereas specific phosphorylation at Serine 710 (S710) triggers the recruitment of Bardet-Biedl-Syndrome (BBS) proteins to the centrosome. In support of this model, loss of BBS1 leads to defects in migration, but not proliferation, while DISC1 knockdown leads to deficits in both. A phospho-dead mutant can only rescue proliferation, while a phospho-mimic mutant rescues exclusively migration defects. These data highlight a dual role for DISC1 in corticogenesis and suggest that phosphorylation of this protein at S710 activates a key developmental switch.

Homozygous mutations in the sodium-bicarbonate transporter SLC4A11 cause two early onset corneal dystrophies: congenital hereditary endothelial dystrophy (CHED) and Harboyan syndrome. More recently, four sporadic patients with late onset Fuchs corneal dystrophy (FCD), a common age-related disorder, were also reported to harbor heterozygous mutations at this locus. We therefore tested the hypothesis that SLC4A11 contributes to FCD and asked whether mutations in SLC4A11 are responsible for familial cases of late onset FCD. We sequenced SLC4A11 in 192 sporadic and small nuclear late-onset FCD families and found seven heterozygous missense novel variations that were absent from ethnically matched controls. Familial data available for one of these mutations showed segregation under a dominant model in a three-generational family. In silico analyses suggested that most of these substitutions are intolerant, while biochemical studies of the mutant protein indicated that these alleles impact the localization and/or post-translational modification of the protein. These results suggest that heterozygous in SLC4A11 are modest contributors to the pathogenesis of adult FCD, suggesting a causality continuum between FCD and CHED. Taken together with a recent model between FCD and yet another early onset corneal dystrophy, PPCD, our data suggest a shared pathomechanism and genetic overlap across several corneal dystrophies.

Ciliopathies are pleiotropic and genetically heterogeneous disorders caused by defective development and function of the primary cilium. Bardet-Biedl syndrome (BBS) proteins localize to the base of cilia and undergo intraflagellar transport, and the loss of their functions leads to a multisystemic ciliopathy. Here we report the identification of mutations in guanylate cyclases (GCYs) as modifiers of Caenorhabditis elegans bbs endophenotypes. The loss of GCY-35 or GCY-36 results in suppression of the small body size, developmental delay, and exploration defects exhibited by multiple bbs mutants. Moreover, an effector of cGMP signalling, a cGMP-dependent protein kinase, EGL-4, also modifies bbs mutant defects. We propose that a misregulation of cGMP signalling, which underlies developmental and some behavioural defects of C. elegans bbs mutants, may also contribute to some BBS features in other organisms.

Author Summary

Bardet-Biedl syndrome (BBS) is a genetically heterogeneous, multisystemic disorder. Defects to the cilium, an evolutionarily conserved organelle, cause ciliopathies, a growing class of diseases that includes BBS. BBS proteins are involved in the vesicular transport of proteins to the cilium and in the process of intraflagellar transport. Here we show that, in addition to sensory defects, Caenorhabditis elegans bbs mutants exhibit reduced body size and delayed developmental timing. The reduced body size phenotype is not fully recapitulated by IFT mutants, suggesting that BBS proteins may have additional functions beyond bridging IFT motors. We further identified that the loss of function mutations in the soluble guanylate cyclase complex, GCY-35/GCY-36, results in a suppression of these defects. Interestingly, GCY-35/GCY-36 influences the body size through a cGMP-dependent protein kinase EGL-4 in a group of body cavity neurons. BBS proteins, on the other hand, function through a non-overlapping set of ciliated sensory neurons to influence cGMP signalling in the body cavity neurons. In conclusion, this study reveals a non-cell autonomous role for sensory cilia in regulating cGMP signalling during development. We propose that aberrant cGMP signalling, essential for a number of cellular processes, may also contribute to some ciliopathy features in other systems.

The primary cilium is an antenna-like organelle that is dynamically regulated during the cell cycle. Ciliogenesis is initiated as cells enter quiescence, while cilium resorption precedes mitosis. The mechanisms coordinating ciliogenesis with the cell cycle are unknown. Here we identify the centrosomal protein, Nde1, as a negative regulator of ciliary length. Nde1 is expressed at high levels in mitosis, low levels in quiescence and localizes at the mother centriole, which nucleates the primary cilium. Cells depleted of Nde1 show longer cilia and a delay in cell cycle re-entry that correlates with ciliary length. Knockdown of Nde1 in zebrafish embryos results in increased ciliary length, suppression of cell division, reduction of the number of cells forming the Kupffer’s vesicle, and left-right patterning defects. These data suggest that Nde1 is an integral component of a network coordinating ciliary length with cell cycle progression and have implications in the transition from quiescence to a proliferative state.

The authors report the first independent replication of rs613872, an intronic SNP of TCF4 associated with late-onset Fuchs corneal dystrophy.

Purpose.

Fuchs corneal dystrophy (FCD) is an autosomal dominant disease of the corneal endothelium with variable penetrance and expressivity. Recently, rs613872, an intronic variation of TCF4 associated with late-onset FCD, was reported. The present study was undertaken to examine this association in our cohort of FCD patients, to assess the significance of this finding, and to investigate the candidacy of TCF4 in the context of the mapped FCD2 locus.

Methods.

The authors recruited 170 patients with late-onset FCD and 180 age-matched controls. Blood samples were collected, and genomic DNA was extracted. A panel of nine SNPs spanning the entire TCF4 locus was genotyped both on this cohort and on three previously reported FCD2-linked families. The association of an individual SNP with late-onset FCD was evaluated with the Fisher exact test, and the coding exons and exon-intron boundaries of TCF4 were sequenced in 96 affected persons.

Results.

The risk allele G of rs613872 is associated significantly with late-onset FCD (odds ratio, 4.2; P = 4.28 × 10−15) and was present in male and female affected persons without any sex bias, replicating recent findings, though the authors found no apparent correlation with the severity of the disease phenotype. Moreover, the risk allele did not cosegregate with the disease phenotype in any of the three FCD2-linked families. The authors did not identify any pathogenic variants in the coding region of TCF4.

Conclusions.

The authors report the first independent replication of rs613872 conferring risk of late-onset FCD. Their data suggest that this risk factor is likely independent of the FCD2 locus, whose causality remains unknown.

Ligand-dependent activation of the Hedgehog (Hh) signaling pathway has been implicated in both tumor initiation and metastasis of pancreatic ductal adenocarcinoma (PDAC). Prior studies in genetically engineered mouse models (GEMMs) have assessed the role of Hh signaling by cell autonomous expression of a constitutively active Gli2 within epithelial cells. On the contrary, aberrant pathway reactivation in the human exocrine pancreas occurs principally as a consequence of Sonic Hh ligand (Shh) overexpression from epithelial cells. To recapitulate the cognate pathophysiology of Hh signaling observed in the human pancreas, we examined GEMM where Hh ligand is conditionally overexpressed within the mature exocrine pancreas using a tamoxifen-inducible Elastase-Cre promoter (Ela-CreERT2;LSL-mShh). We also facilitated potential cell autonomous epithelial responsiveness to secreted Hh ligand by generating compound transgenic mice with concomitant expression of the Hh receptor Smoothened (Ela-CreERT2;LSL-mShh;LSL-mSmo). Of interest, none of these mice developed intraductal precursor lesions or PDAC during the follow-up period of up to 12 months after tamoxifen induction. Instead, all animals demonstrated marked expansion of stromal cells, consistent with the previously described epithelial-to-stromal paracrine Hh signaling. Hh responsiveness was mirrored by the expression of primary cilia within the expanded mesenchymal compartment and the absence within mature acinar cells. In the absence of cooperating mutations, Hh ligand overexpression in the mature exocrine pancreas is insufficient to induce neoplasia, even when epithelial cells coexpress the Smo receptor. This autochthonous model serves as a platform for studying epithelial stromal interactions in pancreatic carcinogenesis.

Fuchs corneal dystrophy (FCD) is a common ocular disorder that affects approximately 4% of the United States population over the age of 40. This study examines the age-severity relationship in families with late-onset FCD through the use of retroillumination photography.

Purpose.

Fuchs corneal dystrophy (FCD) is a progressive disorder of the corneal endothelium and is pathologically defined by the presence of guttae, which are excrescences of the Descemet membrane. The present study was undertaken to investigate the age-severity relationship of the FCD2-linked disease phenotype using retroillumination photography and to compare it with the characteristics of FCD1.

Methods.

Two large families with multiple affected members were recruited. Exclusion analyses of the known late-onset FCD loci were completed with closely spaced STR markers, whereas genes associated with early- and late-onset FCD were investigated by bidirectional sequencing. Haplotypes were constructed, and two-point LOD scores were calculated. To document age-severity relationships, retroillumination photographs were acquired from members of both families.

Results.

Parametric linkage and haplotype analysis mapped both families to FCD2 with significant two-point LOD scores. A total of 70,249 guttae were counted in 14 persons from both families. A significant increase in guttae density in the inferotemporal region (P = 0.016) was observed, a pattern similarly observed in a family linked to FCD1. Similarly, FCD2-linked families display an exponential trend in severity with age, as was observed in a family linked to FCD1. Finally, comparison of FCD1 and FCD2 exponential models suggested that the FCD1 phenotype is significantly more severe (P = 0.01).

Conclusions.

A combination of genetic mapping and retroillumination photography was used to quantify the severity of the disease phenotype associated with FCD2 and to compare it to the disease characteristics of FCD1. These data suggest that this approach might have sufficient resolution to discriminate between discrete genetic FCD backgrounds, which will potentially aid in patient management.

Fuchs endothelial corneal dystrophy (FECD) is a common, late-onset disorder of the corneal endothelium. Although progress has been made in understanding the genetic basis of FECD by studying large families in which the phenotype is transmitted in an autosomal dominant fashion, a recently reported genome-wide association study identified common alleles at a locus on chromosome 18 near TCF4 which confer susceptibility to FECD. Here, we report the findings of our independent validation study for TCF4 using the largest FECD dataset to date (450 FECD cases and 340 normal controls). Logistic regression with sex as a covariate was performed for three genetic models: dominant (DOM), additive (ADD), and recessive (REC). We found significant association with rs613872, the target marker reported by Baratz et al.(2010), for all three genetic models (DOM: P = 9.33×10−35; ADD: P = 7.48×10−30; REC: P = 5.27×10−6). To strengthen the association study, we also conducted a genome-wide linkage scan on 64 multiplex families, composed primarily of affected sibling pairs (ASPs), using both parametric and non-parametric two-point and multipoint analyses. The most significant linkage region localizes to chromosome 18 from 69.94cM to 85.29cM, with a peak multipoint HLOD = 2.5 at rs1145315 (75.58cM) under the DOM model, mapping 1.5 Mb proximal to rs613872. In summary, our study presents evidence to support the role of the intronic TCF4 single nucleotide polymorphism rs613872 in late-onset FECD through both association and linkage studies.

Nephronophthisis-related ciliopathies (NPHP-RC) are recessive disorders featuring dysplasia or degeneration preferentially in kidney, retina, and cerebellum. Here we combine homozygosity mapping with candidate gene analysis by performing “ciliopathy candidate exome capture” followed by massively-parallel sequencing. We detect 12 different truncating mutations of SDCCAG8 in 10 NPHP-RC families. We demonstrate that SDCCAG8 is localized at both centrioles and directly interacts with NPHP-RC-associated OFD1. Depletion of sdccag8 causes kidney cysts and a body axis defect in zebrafish and induces cell polarity defects in 3D renal cell cultures. This work identifies SDCCAG8 loss of function as a novel cause of a retinal-renal ciliopathy and validates exome capture analysis for broadly heterogeneous single-gene disorders.

Bardet-Biedl syndrome (BBS) is primarily an autosomal recessive disorder characterized by the five cardinal features retinitis pigmentosa, postaxial polydactyly, mental retardation, obesity and hypogenitalism. In addition, renal cysts and other anomalies of the kidney and urinary tract can be present. To date, mutations in 12 BBS genes as well as in MKS1 and CEP290 have been identified as causing BBS. The vast genetic heterogeneity of BBS renders molecular genetic diagnosis difficult in terms of both the time and cost required to screen all 204 coding exons. Here, we report the use of genome-wide homozygosity mapping as a tool to identify homozygous segments at known BBS loci in BBS individuals from inbred and outbred background. In a worldwide cohort of 45 families, we identified, via direct exon sequencing, causative homozygous mutations in 20 families. Eleven of these mutations were novel, thereby increasing the number of known BBS mutations by 5% (11/218). Thus, in the presence of extreme genetic locus heterogeneity, homozygosity mapping provides a valuable approach to the molecular genetic diagnosis of BBS and will facilitate the discovery of novel pathogenic mutations.

Cilia are complex structures that have garnered interest because of their roles in vertebrate development and their involvement in human genetic disorders. In contrast to multicellular invertebrates in which cilia are restricted to specific cell types, these organelles are found almost ubiquitously in vertebrate cells, where they serve a diverse set of signaling functions. Here, we highlight properties of vertebrate cilia, with particular emphasis on their relationship with other subcellular structures, and explore the physiological consequences of ciliary dysfunction.

The actin depolymerizing factors (ADFs) play important roles in several cellular processes that require cytoskeletal rearrangements, such as cell migration, but little is known about the in vivo functions of ADFs in developmental events like branching morphogenesis. While the molecular control of ureteric bud (UB) branching during kidney development has been extensively studied, the detailed cellular events underlying this process remain poorly understood. To gain insight into the role of actin cytoskeletal dynamics during renal branching morphogenesis, we studied the functional requirements for the closely related ADFs cofilin1 (Cfl1) and destrin (Dstn) during mouse development. Either deletion of Cfl1 in UB epithelium or an inactivating mutation in Dstn has no effect on renal morphogenesis, but simultaneous lack of both genes arrests branching morphogenesis at an early stage, revealing considerable functional overlap between cofilin1 and destrin. Lack of Cfl1 and Dstn in the UB causes accumulation of filamentous actin, disruption of normal epithelial organization, and defects in cell migration. Animals with less severe combinations of mutant Cfl1 and Dstn alleles, which retain one wild-type Cfl1 or Dstn allele, display abnormalities including ureter duplication, renal hypoplasia, and abnormal kidney shape. The results indicate that ADF activity, provided by either cofilin1 or destrin, is essential in UB epithelial cells for normal growth and branching.

Author Summary

Development of the ureter and collecting ducts of the kidney requires extensive growth and branching of an epithelial tube, the ureteric bud. While many genes that control this process are known, the cellular events that underlie renal morphogenesis remain poorly understood. Many cellular changes that might contribute to ureteric bud morphogenesis, such as migration and changes in shape, involve the actin cytoskeleton. Actin depolymerizing factors (ADFs) are important for changes in the organization of the cytoskeleton in cultured cells, but the roles of the ADF genes in vivo remain to be fully elucidated. Here, we examine the importance of the ADFs cofilin1 and destrin in ureteric bud branching and find that lack of both genes arrests this process at an early stage, while lesser reductions in ADF gene dosage cause more subtle defects in kidney development. This finding may help us to understand the origins of certain congenital malformations in humans.

Peripheral sensory perception is established through an elaborate network of specialized neurons that mediate the translation of extraorganismal stimuli through the use of a broad array of receptors and downstream effector molecules. Studies of human genetic disorders, as well as mouse and other animal models, have identified some of the key molecules necessary for peripheral innervation and function. These findings have, in turn, yielded new insights into the developmental networks and homeostatic mechanisms necessary for the transformation of external stimuli into interpretable electrical impulses. In this review, we will summarize and discuss some of the genes/proteins implicated in two particular aspects of sensory perception, thermosensation and mechanosensation, highlighting pathways whose perturbation leads to both isolated and syndromic sensory deficits.

LRRK2 plays an important role in Parkinson's disease (PD), but its biological functions are largely unknown. Here, we cloned the homolog of human LRRK2, characterized its expression, and investigated its biological functions in zebrafish. The blockage of zebrafish LRRK2 (zLRRK2) protein by morpholinos caused embryonic lethality and severe developmental defects such as growth retardation and loss of neurons. In contrast, the deletion of the WD40 domain of zLRRK2 by morpholinos targeting splicing did not induce severe embryonic developmental defects; rather it caused Parkinsonism-like phenotypes, including loss of dopaminergic neurons in diencephalon and locomotion defects. These neurodegenerative and locomotion defects could be rescued by over-expressing zLRRK2 or hLRRK2 mRNA. The administration of L-dopa could also rescue the locomotion defects, but not the neurodegeneration. Taken together, our results demonstrate that zLRRK2 is an ortholog of hLRRK2 and that the deletion of WD40 domain of zLRRK2 provides a disease model for PD.

Author Summary

Parkinson's disease (PD) is a degenerative disease of the brain (central nervous system) that often impairs motor skills, speech, and other functions. PD was long thought to be caused by environmental factors, but the discovery of several gene mutations in the patients (mostly with familial form of PD) clearly demonstrated the involvement of genetic factors in the development of PD. Among the identified genes, LRRK2 was discovered to be one of the most important genetic causes of PD. The biological function of LRRK2 was, however, largely unknown. In this study, we studied the function of LRRK2 in zebrafish by blocking the normal function of LRRK2. The zebrafish showed features of neurodegeneration and locomotion defects, similar to those of PD patients. The defects of the fish could be rescued by expressing the normal protein of LRRK2, and the locomotion defect could also be rescued by the administration of L-dopa that is commonly used for treating PD patients. We have therefore developed a zebrafish model for PD that can be used for understanding the mechanism underlying the development of PD and will be helpful for future screening of new drugs to treat PD.