Retinal degenerative diseases are a major cause of untreatable blindness. Stem cell therapy to replace lost photoreceptors represents a feasible future treatment. We previously demonstrated that postmitotic photoreceptor precursors expressing an NrlGFP transgene integrate into the diseased retina and restore some light sensitivity. As genetic modification of precursor cells derived from stem cell cultures is not desirable for therapy, we have tested cell selection strategies using fluorochrome-conjugated antibodies recognizing cell surface antigens to sort photoreceptor precursors. Microarray analysis of postnatal NrlGFP-expressing precursors identified four candidate genes encoding cell surface antigens (Nt5e, Prom1, Podxl, and Cd24a). To test the feasibility of using donor cells isolated using cell surface markers for retinal therapy, cells selected from developing retinae by fluorescence-activated cell sorting based on Cd24a expression (using CD24 antibody) and/or Nt5e expression (using CD73 antibody) were transplanted into the wild-type or Crb1rd8/rd8 or Prph2rd2/rd2 mouse eye. The CD73/CD24-sorted cells migrated into the outer nuclear layer, acquired the morphology of mature photoreceptors and expressed outer segment markers. They showed an 18-fold higher integration efficiency than that of unsorted cells and 2.3-fold higher than cells sorted based on a single genetic marker, NrlGFP, expression. These proof-of-principle studies show that transplantation competent photoreceptor precursor cells can be efficiently isolated from a heterogeneous mix of cells using cell surface antigens without loss of viability for the purpose of retinal stem cell therapy. Refinement of the selection of donor photoreceptor precursor cells can increase the number of integrated photoreceptor cells, which is a prerequisite for the restoration of sight.
Retina; Cell transplantation; Cell surface markers; fluorescence-activated cell sorting; Stem cell transplantation; Fluorescent protein reporter genes; Microarray; Embryonic stem cells
Retinal degenerative disease causing loss of photoreceptor cells is the leading cause of untreatable blindness in the developed world, with inherited degeneration affecting 1 in 3000 people. Visual acuity deteriorates rapidly once the cone photoreceptors die, as these cells provide daylight and colour vision. Here, in proof-of-principle experiments, we demonstrate the feasibility of cone photoreceptor transplantation into the wild-type and degenerating retina of two genetic models of Leber congenital amaurosis, the Crb1rd8/rd8 and Gucy2e−/− mouse. Crx-expressing cells were flow-sorted from the developing retina of CrxGFP transgenic mice and transplanted into adult recipient retinae; CrxGFP is a marker of cone and rod photoreceptor commitment. Only the embryonic-stage Crx-positive donor cells integrated within the outer nuclear layer of the recipient and differentiated into new cones, whereas postnatal cells generated a 10-fold higher number of rods compared with embryonic-stage donors. New cone photoreceptors displayed unambiguous morphological cone features and expressed mature cone markers. Importantly, we found that the adult environment influences the number of integrating cones and favours rod integration. New cones and rods were observed in ratios similar to that of the host retina (1:35) even when the transplanted population consisted primarily of cone precursors. Cone integration efficiency was highest in the cone-deficient Gucy2e−/− retina suggesting that cone depletion creates a more optimal environment for cone transplantation. This is the first comprehensive study demonstrating the feasibility of cone transplantation into the adult retina. We conclude that flow-sorted embryonic-stage Crx-positive donor cells have the potential to replace lost cones, as well as rods, an important requirement for retinal disease therapy.
Direct placement restorative materials must interface with tooth structures that are often compromised by caries or trauma. The material must seal the interface while providing sufficient strength and wear resistance to assure function of the tooth for, ideally, the lifetime of the patient. Needed are direct restorative materials that are less technique-sensitive than current resin-based composite systems while having improved properties. The ideal material could be successfully used in areas of the world with limited infrastructure. Advances in our understanding of the interface between the restoration adhesive system and the stages of carious dentin can be used to promote remineralization. Application of fracture mechanics to adhesion at the tooth-restoration interface can provide insights for improvement. Research in polymer systems suggests alternatives to current composite resin matrix systems to overcome technique sensitivity, while advances in nano- and mesoparticle reinforcement and alignment in composite systems can increase material strength, toughness, and wear resistance, foreshadowing dental application.
nanocomposites; cross-link density; remineralization; biomimetics; dentin bonding; aligned composites
Cell transplantation is a novel therapeutic strategy to restore visual responses to the degenerate adult neural retina and represents an exciting area of regenerative neurotherapy. So far, it has been shown that transplanted postmitotic photoreceptor precursors are able to functionally integrate into the adult mouse neural retina. In this review, we discuss the differentiation of photoreceptor cells from both adult and embryonic-derived stem cells and their potential for retinal cell transplantation. We also discuss the strategies used to overcome barriers present in the degenerate neural retina and improve retinal cell integration. Finally, we consider the future translation of retinal cell therapy as a therapeutic strategy to treat retinal degeneration.
stem cell; progenitor cell; photoreceptor; retina; transplantation; degeneration
Retinal degeneration is the leading cause of untreatable blindness in the developed world. Cell transplantation strategies provide a novel therapeutic approach to repair the retina and restore sight. Previously, we have shown that photoreceptor precursor cells can integrate and form functional photoreceptors after transplantation into the subretinal space of the adult mouse. In a clinical setting, however, it is likely that far greater numbers of integrated photoreceptors would be required to restore visual function. We therefore sought to assess whether the outer limiting membrane (OLM), a natural barrier between the subretinal space and the outer nuclear layer (ONL), could be reversibly disrupted and if disruption of this barrier could lead to enhanced numbers of transplanted photoreceptors integrating into the ONL. Transient chemical disruption of the OLM was induced in adult mice using the glial toxin, dl-alpha-aminoadipic acid (AAA). Dissociated early post-natal neural retinal cells were transplanted via subretinal injection at various time-points after AAA administration. At 3 weeks post-injection, the number of integrated, differentiated photoreceptor cells was assessed and compared with those found in the PBS-treated contralateral eye. We demonstrate for the first time that the OLM can be reversibly disrupted in adult mice, using a specific dose of AAA administered by intravitreal injection. In this model, OLM disruption is maximal at 72 h, and recovers by 2 weeks. When combined with cell transplantation, disruption of the OLM leads to a significant increase in the number of photoreceptors integrated within the ONL compared with PBS-treated controls. This effect was only seen in animals in which AAA had been administered 72 h prior to transplantation, i.e. when precursor cells were delivered into the subretinal space at a time coincident with maximal OLM disruption. These findings suggest that the OLM presents a physical barrier to photoreceptor integration following transplantation into the subretinal space in the adult mouse. Reversible disruption of the OLM may provide a strategy for increasing cell integration in future therapeutic applications.
retinal transplantation; Müller cell; outer limiting membrane; cell integration; photoreceptor; stem cells; mouse
Episodes of depression and anxiety (D&A) during the transition from late
adolescence to adulthood, particularly when persistent, are predictive of long-term
disorders and associated public health burden. Understanding risk factors at this time
is important to guide intervention. The current objective was to investigate the
associations between maternal symptoms of D&A with offspring symptoms during
their transition to adulthood.
Data from a large population-based birth cohort study, in South Brazil, were used.
Prospective associations between maternal D&A and offspring risk of these
symptoms during the transition to adulthood (18/19, 24 and 30 years) were estimated.
Maternal D&A in adolescence was associated with offspring symptoms across the
transition to adulthood, associations were consistently stronger for females than for
males. Daughters whose mothers reported D&A were 4.6 times (95% confidence
interval 2.71–7.84) as likely to report D&A at all three time-points, than
daughters of symptom-free mothers.
Maternal D&A is associated with persistent D&A during the daughter's
transition to adulthood. Intervention strategies should consider the mother's mental
Cohort study; common mental disorder; intergenerational; mental health; offspring
Cognitive theories of depression suggest that beliefs of low self-worth and the tendency to attribute negative events to causes that are global (widespread rather than specific) and stable (will persist rather than change in the future) are associated with the development of depressed mood. Such theories are supported by evidence from prospective studies and have guided the development of successful treatment and prevention strategies such as CBT. However, the relative importance of different psychological constructs within cognitive theories is unknown. This is important to refine cognitive theories and develop more efficient prevention strategies.
We used prospective data from over 3500 young adults from the Avon Longitudinal Study for Parents and Children (ALSPAC) cohort in the UK to investigate the association between cognitive style, measured by short forms of the Dysfunctional Attitudes Scale (DAS) and Cognitive Styles Questionnaire-Short Form (CSQ-SF) at age 18, and future depressed mood at age 19. Structural equation modelling techniques were used to separate cognitive style constructs.
Cognitive styles were associated with future depressed mood, independently of baseline mood, both as measured by the DAS-SF and the CSQ-SF. Of the different CSQ-SF constructs, only global attributions were associated with both baseline and future mood independently of other constructs.
The study was subject to attrition and the follow-up was relatively short (10 months).
The findings suggest that the tendency to attribute negative events specifically to global causes could be particularly important for depression. Reducing global attributions is potentially important in the prevention and treatment of depression.
ALSPAC; Depression; Cognitive styles; Latent traits; Global attribution
The activation of the Akt signalling in response to cytokine receptor signalling promotes protein synthesis, cellular growth and proliferation. To determine the role of Akt in interleukin-3 (IL-3) signalling, we generated IL-3-dependent myeloid cell lines from mice lacking Akt1, Akt2 or Akt3. Akt1 deletion resulted in accelerated apoptosis at low concentrations of IL-3. Expression of constitutively active Akt1 was sufficient to delay apoptosis in response to IL-3 withdrawal, but not sufficient to induce proliferation in the absence of IL-3. Akt1 prolonged survival of Bim- or Bad-deficient cells, but not cells lacking Puma, indicating that Akt1-dependent repression of apoptosis was in part dependent on Puma and independent of Bim or Bad. Our data show that a key role of Akt1 during IL-3 signalling is to repress p53-dependent apoptosis pathways, including transcriptional upregulation of Puma. Moreover, our data indicate that regulation of BH3-only proteins by Akt is dispensable for Akt-dependent cell survival.
Akt; Bcl-2; interleukin-3; puma
RNA polymerase I transcription; ribosomopathies; cancer; hypertrophy; atrophy; oncogene; tumour suppressor; Treacher Collins Syndrome; Blooms Syndrome; Werner Syndrome; Human Cockayne Syndrome; Siderius-X-linked mental retardation; cohesinopathy; Filamin A
Some relatively small studies suggest that maternal postnatal depression is a risk factor for offspring adolescent depression. However no large cohort studies have addressed this issue. Furthermore only one small study has examined the association between antenatal depression and later offspring depression. Understanding these associations is important to inform prevention.
To investigate the hypothesis that there are independent associations between antenatal and postnatal depression with offspring depression; and that the risk pathways are different, such that the risk associated with postnatal depression is moderated by disadvantage (low maternal education) but the risk associated with antenatal depression is not.
Prospective investigation of associations between symptoms of antenatal and postnatal parental depression with offspring depression at age 18.
UK community based birth cohort (ALSPAC).
Data from over 4,500 parents and their adolescent offspring.
Main Outcome Measure
Diagnosis of offspring major depression, aged 18, using ICD-10.
Antenatal depression was an independent risk factor. Offspring were 1.28 times (95% CI 1.08 to 1.51, p=0.003) more likely to have depression at 18 for each s.d increase in maternal depression score antenatally, independently of later maternal depression. Postnatal depression was also a risk factor for mothers with low education, with offspring 1.26 times (95% CI 1.06 to 1.50, p=0.009) more likely to have depression for each s.d increase in postnatal depression score. However, for more educated mothers, there was little association (OR 1.09, 95% CI 0.88 to 1.36, p=0.420). Moderation analyses found that maternal education moderated the effects of postnatal but not antenatal depression. Paternal depression antenatally was not associated with offspring depression, while postnatally paternal depression showed a similar pattern to maternal depression.
The findings suggest that treating maternal depression antenatally could prevent offspring depression during adulthood and that prioritising less advantaged mothers postnatally may be most effective.
ALSPAC; depression; antenatal; postnatal; mechanisms; moderation
Most asthma exacerbations are triggered by virus infections, the majority being caused by human rhinoviruses (RV). In mouse models, γδT cells have been previously demonstrated to influence allergen-driven airways hyper-reactivity (AHR) and can have antiviral activity, implicating them as prime candidates in the pathogenesis of asthma exacerbations. To explore this, we have used human and mouse models of experimental RV-induced asthma exacerbations to examine γδT-cell responses and determine their role in the immune response and associated airways disease. In humans, airway γδT-cell numbers were increased in asthmatic vs. healthy control subjects during experimental infection. Airway and blood γδT-cell numbers were associated with increased airways obstruction and AHR. Airway γδT-cell number was also positively correlated with bronchoalveolar lavage (BAL) virus load and BAL eosinophils and lymphocytes during RV infection. Consistent with our observations of RV-induced asthma exacerbations in humans, infection of mice with allergic airways inflammation increased lung γδT-cell number and activation. Inhibiting γδT-cell responses using anti-γδTCR (anti-γδT-cell receptor) antibody treatment in the mouse asthma exacerbation model increased AHR and airway T helper type 2 cell recruitment and eosinophilia, providing evidence that γδT cells are negative regulators of airways inflammation and disease in RV-induced asthma exacerbations.
Degeneration of the neural retina is the leading cause of untreatable blindness in the developed world. Stem cell replacement therapy offers a novel strategy for retinal repair. Postmitotic photoreceptor precursors derived from the early postnatal (P) retina are able to migrate and integrate into the adult mouse retina following transplantation into the subretinal space, but it is likely that a large number of these cells would be required to restore vision. The adult recipient retina presents a very different environment to that from which photoreceptor precursor donor cells isolated from the developing postnatal retina are derived. Here we considered the possibility that modulation of the recipient environment by ectopic expression of developmentally regulated growth factors, normally present during photoreceptor development, might enhance the migration and integration of transplanted cells into the adult neural retina. Adeno-associated viral (AAV) vectors were used to introduce three growth factors previously reported to play a role in photoreceptor development, IGF1, FGF2, and CNTF, into the adult retina, prior to transplantation of P4 cells derived from the Nrl.GFP+ve neural retina. At 3 weeks posttransplantation the number of integrated, differentiated photoreceptor cells present in AAV-mediated neurotrophic factor-treated eyes was assessed and compared to control treated contralateral eyes. We show, firstly, that it is possible to manipulate the recipient retinal microenvironment via rAAV-mediated gene transfer with respect to these developmentally relevant growth factors. Moreover, when combined with cell transplantation, AAV-mediated expression of IGF1 led to significantly increased levels of cell integration, while overexpression of FGF2 had no significant effect on integrated cell number. Conversely, expression of CNTF led to a significant decrease in cell integration and an exacerbated glial response that led to glial scarring. Together, these findings demonstrate the importance of the extrinsic environment of the recipient retina for photoreceptor cell transplantation and show for the first time that it is possible to manipulate this environment using viral vectors to influence photoreceptor transplantation efficiency.
Photoreceptor; Retina; Transplantation; Neurotrophic factors; Gene therapy; Stem cell
HIV has become increasingly prevalent in the Northeast region of Brazil where Leishmania infantum chagasi is endemic, and concurrent AIDS and visceral leishmaniasis (VL) has emerged. In this study, persons with HIV/AIDS and VL (n = 17) had a mean age of 37.3 years (range 29–53 years) compared with 12.5 years (1–80 years) for persons with VL alone (n = 2836). Males accounted for 88% of cases versus 65%. The mean CD4 count and antileishmanial antibody titre were lower and recurrence of VL and death were more likely with co-infection. Considering the prevalences of L.i. chagasi and HIV in the region, this may herald the emergence of an important public health problem.
Visceral leishmaniasis; HIV; AIDS; Leishmania chagasi infection; Brazil
In recent years, vigorous debate has developed concerning how conflicts contribute to the spread of infectious diseases, and in particular, the role of post-conflict situations in the epidemiology of HIV/AIDS. This study details the age-specific mortality patterns among the population in the central provincial capital of Beira, Mozambique, during and after the Mozambican civil war which ended in 1992.
Data was collected from the death register at Beira's Central Hospital between 1985 and 2003 and descriptively analyzed.
The data show two distinct periods: before and after the peace agreements in 1992. Before 1992 (during the civil war), the main impact of mortality was on children below 5 years of age, including still births, accounting for 58% of all deaths. After the war ended in 1992, the pattern shifted dramatically and rapidly to the 15-49 year old age group which accounted for 49% of all deaths by 2003.
As under-5 mortality rates were decreasing at the end of the conflict, rates for 24-49 year old adults began to dramatically increase due to AIDS. This study demonstrates that strategies can be implemented during conflicts to decrease mortality rates in one vulnerable population but post-conflict dynamics can bring together other factors which contribute to the rapid spread of other infectious diseases in other vulnerable populations.
Diseases culminating in photoreceptor loss are a major cause of untreatable blindness. Transplantation of rod photoreceptors is feasible, provided donor cells are at an appropriate stage of development when transplanted. Nevertheless, the proportion of cells that integrate into the recipient outer nuclear layer (ONL) is low. The outer limiting membrane (OLM), formed by adherens junctions between Müller glia and photoreceptors, may impede transplanted cells from migrating into the recipient ONL. Adaptor proteins such as Crumbs homologue 1 (Crb1) and zona occludins (ZO-1) are essential for localization of the OLM adherens junctions. We investigated whether targeted disruption of these proteins enhances donor cell integration. Transplantation of rod precursors in wild-type mice achieved 949 ± 141 integrated cells. By contrast, integration is significantly higher when rod precursors are transplanted into Crb1rd8/rd8 mice, a model of retinitis pigmentosa and Lebers congenital amaurosis that lacks functional CRB1 protein and displays disruption of the OLM (7,819 ± 1,297; maximum 15,721 cells). We next used small interfering (si)RNA to transiently reduce the expression of ZO-1 and generate a reversible disruption of the OLM. ZO-1 knockdown resulted in similar, significantly improved, integration of transplanted cells in wild-type mice (7,037 ± 1,293; maximum 11,965 cells). Finally, as the OLM remains largely intact in many retinal disorders, we tested whether transient ZO-1 knockdown increased integration in a model of retinitis pigmentosa, the rho−/− mouse; donor cell integration was significantly increased from 313 ± 58 cells without treatment to 919 ± 198 cells after ZO-1 knockdown. This study shows that targeted disruption of OLM junctional proteins enhances integration in the wild-type and degenerating retina and may be a useful approach for developing photoreceptor transplantation strategies.
Stem cell; Migration; Transplantation; Degeneration; Müller glia
Visceral leishmaniasis (VL) in northeast Brazil is a disease caused by infection with the protozoan Leishmania chagasi. Infection leads to variable clinical outcomes ranging from asymptomatic infection to potentially fatal disease. Prior studies suggest the genetic background of the host contributes to the development of different outcomes after infection, although it is not known if ancestral background itself influences outcomes. VL is endemic in peri-urban areas about the city of Natal in northeast Brazil. The population of northeast Brazil is a mixture of distinct racial and ethnic groups. We hypothesized that some sub-populations may be more susceptible than others to develop different clinical outcomes after L. chagasi infection. Using microsatellite markers, we examined whether admixture of the population as a whole, or markers likely inherited from a distinct ethnic background, differed between individuals with VL, individuals with an asymptomatic infection, or individuals with no infection. There was no apparent significant difference in overall population admixture proportions among the three clinical phenotype groups. However, one marker on Chr. 22 displayed evidence of excess ancestry from putative ancestral populations among different clinical phenotypes, suggesting this region may contains genes determining the course of L. chagasi infection.
leishmaniasis; Brazil; admixture; STRUCTURE; susceptibility; variation
Neuronal network output in the cortex as a function of synapse density during development has not been explicitly determined. Synaptic scaling in cortical brain networks seems to alter excitatory and inhibitory synaptic inputs to produce a representative rate of synaptic output. Here, we cultured rat hippocampal neurons over a three-week period to correlate synapse density with the increase in spontaneous spiking activity. We followed the network development as synapse formation and spike rate in two serum-free media optimized for either (a) neuron survival (Neurobasal/B27) or (b) spike rate (NbActiv4). We found that while synaptophysin synapse density increased linearly with development, spike rates increased exponentially in developing neuronal networks. Synaptic receptor components NR1, GluR1 and GABA-A also increase linearly but with more excitatory receptors than inhibitory. These results suggest that the brain’s information processing capability gains more from increasing connectivity of the processing units than increasing processing units, much as Internet information flow increases much faster than the linear number of nodes and connections.
BACKGROUND: Violence involving the use of firearms has increased in the UK over the past decade. This study assesses the implications of such injuries for service provision and training by reviewing the experience at one hospital. METHODS: Accident and emergency triage data were searched for patients presenting with gunshot wounds over a 54-month period. Case notes were reviewed and patterns of care established. The resources required for clinical management were ascertained, and the financial consequences determined at contemporary full cost. RESULTS: There were 187 attendances with 247 wounds. Mean age was 21 years (range, 8-63 years). Of the attendances, 69% were out of normal working hours. Of the 187 cases, 97 patients were admitted to one hospital (83 of whom required surgery) and 10 patients were transferred to other hospitals (6 for plastic surgery not available at the Manchester Royal Infirmary and 4 due to lack of beds). Of the 80 patients who were not admitted, 4 died in accident and emergency, the rest were either air gun wounds or relatively simple higher calibre injuries. A wide range of surgical specialties was involved (limb injury, 53; thoraco-abdominal and vascular, 28; head and neck, 5; and orbit, 2), and combinations of injuries transgressed specialty and sub-specialty boundaries. The total cost of patient care was pound 267,000. CONCLUSIONS: Gunshot wounds present a heavy demand on the clinical and financial resources of the receiving hospital, and surgeons responsible for unselected acute admissions in "general surgery" should be capable of dealing with these indiscriminate injuries. Current training and service trends towards increasing sub-specialisation may mitigate against them achieving or retaining this capability.
The spatial patterns in the distributions of vertebrates in the rainforests of the wet tropics biogeographic region of north-eastern Australia were examined to form hypotheses on the processes that have shaped vertebrate assemblages and patterns of species richness and regional endemism. These rainforests occur in a relatively narrow and discontinuous strip along the coast of north-eastern Australia. We found that the number of regionally endemic species and the proportion of regional endemics present in each subregion are both strongly related to the geographic shape of subregional patches of rainforest, independent of rainforest area, within Australian tropical rainforests. Shape has a more significant influence on regional endemism than area, and area has a stronger influence on species richness. These patterns were congruent for all terrestrial vertebrate classes manuals, birds, reptiles and frogst, and for the four groups combined. Our results suggest that the combination of current rainforest area and shape are an index of the relative susceptibility of each area of rainforest to historical contractions, with the implication that historical habitat fluctuations, coupled with subsequent localized extinctions species sifting; have been extremely important processes in determining current patterns of endemism in Australia's wet tropical rainforests. This hypothesis is supported by the highly nested structure of the subregional distribution patterns.
A prospective comparison of metabolic and inflammatory responses after laparoscopic and open inguinal hernia operations was undertaken. There were 10 patients in each group. Plasma levels of cortisol, growth hormone, prolactin, C-reactive protein (CRP) and interleukin-6 (IL-6) were measured preoperatively and at fixed intervals up to 120 h postoperatively. In vitro, endotoxin stimulated whole blood tumour necrosis factor alpha (TNF alpha) was measured in preoperative and 24 h postoperative blood samples. Changes in the plasma levels of cortisol, growth hormone and prolactin showed no statistically significant difference between the groups. No significant change in IL-6 levels were recorded in any group. Changes in CRP levels were significantly higher (P < 0.006) in open hernia patients. Endotoxin stimulated TNF alpha production was suppressed in both groups. The degree of suppression in open hernia patients was significantly higher (P < 0.005). This study has shown that both these operations produce similar stress responses. However, open hernia operation results in a higher acute phase response and induces a greater endotoxin tolerance.
The activation of p70s6k is associated with multiple phosphorylations at two sets of sites. The first set, S411, S418, T421, and S424, reside within the autoinhibitory domain, and each contains a hydrophobic residue at -2 and a proline at +1. The second set of sites, T229 (in the catalytic domain) and T389 and S404 (in the linker region), are rapamycin sensitive and flanked by bulky aromatic residues. Here we describe the identification and mutational analysis of three new phosphorylation sites, T367, S371, and T447, all of which have a recognition motif similar to that of the first set of sites. A mutation of T367 or T447 to either alanine or glutamic acid had no apparent effect on p70s6k activity, whereas similar mutations of S371 abolished kinase activity. Of these three sites and their surrounding motifs, only S371 is conserved in p70s6k homologs from Drosophila melanogaster, Arabidopsis thaliana, and Saccharomyces cerevisiae, as well as many members of the protein kinase C family. Serum stimulation increased S371 phosphorylation; unlike the situation for specific members of the protein kinase C family, where the homologous site is regulated by autophosphorylation, S371 phosphorylation is regulated by an external mechanism. Phosphopeptide analysis of S371 mutants further revealed that the loss of activity in these variants was paralleled by a block in serum-induced T389 phosphorylation, a phosphorylation site previously shown to be essential for kinase activity. Nevertheless, the substitution of an acidic residue at T389, which mimics phosphorylation at this site, did not rescue mutant p70s6k activity, indicating that S371 phosphorylation plays an independent role in regulating intrinsic kinase activity.