No abstract

The SIN3 corepressor and RPD3 histone deacetylase are components of the evolutionarily conserved SIN3/RPD3 transcriptional repression complex. Here we show that the SIN3/RPD3 complex and the corepressor SMRTER are required for Drosophila G 2 phase cell cycle progression. Loss of the SIN3, but not the p55, SAP18, or SAP30, component of the SIN3/RPD3 complex by RNA interference (RNAi) causes a cell cycle delay prior to initiation of mitosis. Loss of RPD3 reduces the growth rate of cells but does not cause a distinct cell cycle defect, suggesting that cells are delayed in multiple phases of the cell cycle, including G 2 . Thus, the role of the SIN3/RPD3 complex in G 2 phase progression appears to be independent of p55, SAP18, and SAP30. SMRTER protein levels are reduced in SIN3 and RPD3 RNAi cells, and loss of SMRTER by RNAi is sufficient to cause a G 2 phase delay, demonstrating that regulation of SMRTER protein levels by the SIN3/RPD3 complex is a vital component of the transcriptional repression mechanism. Loss of SIN3 does not affect global acetylation of histones H3 and H4, suggesting that the G 2 phase delay is due not to global changes in genome integrity but rather to derepression of SIN3 target genes.Posttranslational acetylation of evolutionarily conserved lysine residues within the N-terminal tails of histones has been implicated in the regulation of transcription (33). In general, histone acetylation levels are correlated with transcription levels; nucleosomes located near active genes contain hyperacetylated histones, while those located near inactive genes contain hypoacetylated histones (5,20). Histone acetylation levels are determined by the relative activities of various histone acetyltransferases (HATs) and histone deacetylases (HDACs) that display specificity for particular lysine residues (33). Thus, targeting of an HDAC to a given promoter provides a mechanism for transcriptional repression (29,55). Histone deacetylation may repress transcription by strengthening histone tail-DNA interactions and thereby blocking access of transcriptional regulators to the DNA template or by removing acetyl moieties on histone tails that are important for the interaction of transcriptional regulators with chromatin (17,25,37,63,67).SIN3 and the RPD3 deacetylase are components of a multiprotein complex that represses the transcription of many eukaryotic genes (3). The SIN3/RPD3 complex does not directly bind DNA but is targeted to specific genes through proteinprotein interactions between SIN3 and DNA-binding proteins or corepressors that interact with DNA-binding proteins. The mammalian SIN3/RPD3 complex (which we refer to as the SIN3/HDAC1 complex and which contains SIN3A and/or SIN3B and HDAC1 and/or HDAC2) is involved in the regulation of transcription by nuclear hormone receptors (NHRs), the Myc/Mad/Max family of transcription factors, and a variety of other transcription factors (12,18,21,28,35,44). NHRs and Myc/Mad/Max proteins participate in both activation and repression of genes. In the absence of horm...

Context: Type 1 diabetes (T1D) complications are responsible for much of the disease morbidity. Evidence suggests that familial factors exert an influence on susceptibility to complications. Objectives:We investigated familial risk factors and gender differences for retinopathy, nephropathy, and neuropathy. Design and Setting:This study was a case-control design nested on a cohort of T1D families. We collected data (questionnaire, medical records) starting in 1988. Follow-up has been ongoing since 2004.Patients: There were 8114 T1D patients among 6707 families. All patients had T1D onset age younger than 30 yr and required insulin treatment. Patients who remained without a complication after more than 15 yr of diabetes were considered to be without that complication for our analyses. Results:A complication in a sibling increased the risk for that complication among probands: odds ratio 9.9 (P Ͻ 0.001) for retinopathy, 6.2 for nephropathy (P Ͻ 0.001), and 2.2 for neuropathy (P Ͻ 0.05). Compared with male probands, a female T1D proband had 1.7-fold higher retinopathy risk (P Ͻ 0.001) and 2-fold higher neuropathy risk (P Ͻ 0.001). T1D cases with onset between ages 5 and 14 yr had an increased complications risk compared with subjects diagnosed either at a very young age or after puberty. The presence of one complication significantly increased the risk for others. If a parent had type 2 diabetes, the risk for nephropathy increased (odds ratio 1.9, P Ͻ 0.01, but T1D in a parent did not increase the risk). Conclusions:We confirmed that familial factors influence T1D microvascular pathologies, suggesting a shared genetic basis for complications, perhaps independent of T1D susceptibility. We also found an unexpected increased female risk for complications. R ETINOPATHY, NEPHROPATHY, and neuropathy are long-term microvascular complications responsible for much of the morbidity in type 1 diabetes and type 2 diabetes. Retinopathy, a major cause of blindness (1), occurs in up to 50% of type 1 diabetes patients and in about 10% of patients with type 2 diabetes who have had the disease for 15 or more years (2). Ten to 20% (cumulative prevalence) of type 1 diabetes patients have established nephropathy (3-7), a leading cause of end-stage renal failure and the primary cause of excess mortality in type 1 diabetes patients (8). Diabetic neuropathies affect different parts of the nervous system and present with diverse clinical manifestations. Evidence suggests that familial factors exert a strong influence on susceptibility to complications (8 -11); and a family history of type 2 diabetes has been reported to be a risk factor for diabetic nephropathy in type 1 diabetes patients (12).Our goals were to identify familial risk factors for diabetic microvascular complications and to examine how these risk factors influence retinopathy, nephropathy, and neuropathy onset. We analyzed data from the large cohort of type 1 diabetes patients and families assembled over 25 yr by the Human Biological Data Interchange (HBDI), a program of the...

The TFIID transcription initiation complex is composed of TBP and multiple TAFs. Studies in unicellular systems indicate that TAF250 is required for progression through G1͞S of the cell cycle and repression of apoptosis. Here we extend these in vivo studies by determining the developmental requirements for TAF250 in a multicellular organism, Drosophila. TAF250 mutants were isolated in a genetic screen that also yielded TAF60 and TAF110 mutants, indicating that TAFs function coordinately to regulate transcription. Null alleles of TAF250 are recessive larval lethal. However, combinations of weak loss-of-function TAF250 alleles survive to adulthood and reveal requirements for TAF250 during ovary, eye, ocelli, wing, bristle, and terminalia development as well as overall growth of the fly. These phenotypes suggest roles for TAF250 in regulating the cell cycle, cell differentiation, cell proliferation, and cell survival. Finally, molecular analysis of TAF250 mutants reveals that the observed phenotypes are caused by mutations in a central region of TAF250 that is conserved among metazoan organisms. This region is contained within the TAF250 histone acetyltransferase domain, but the mutations do not alter the histone acetyltransferase activity of TAF250 in vitro, indicating that some other aspect of TAF250 function is affected. Because this region is not conserved in the yeast TAF250 homologue, TAF145, it may define an activity for TAF250 that is unique to higher eukaryotes. T FIID is a transcription initiation factor that nucleates the assembly of RNA polymerase II and other initiation factors (TFIIA, TFIIB, TFIIE, TFIIF, and TFIIH) at the core promoter of protein-coding genes (1). The most abundant form of Drosophila melanogaster TFIID is composed of TBP and eight TAFs: TAF250, TAF150, TAF110, TAF80, TAF60, TAF40, TAF30␣, and TAF30␤ (2). Similar stable multimeric TFIID complexes exist in all eukaryotic organisms investigated to date (3). In the yeast Saccharomyces cerevisiae, almost all TAFs are essential for viability (4). In Drosophila, TAF40, TAF60, and TAF110, the only TAFs that have been examined, are recessive embryonic or larval lethal and cell lethal, indicating the critical role that TAFs play in vivo (5, 6). However, it remains to be determined whether all TAFs or only subsets of TAFs are required for the transcription of TAF-dependent genes in vivo, whether TAFs are required for developmental events that are particular to multicellular organisms, and whether biochemical activities attributed to TAFs in vitro are required in vivo.TAF250 (also designated TAF230 in Drosophila, CCG1 in humans, and TAF145͞135 in yeast), is required for progression through the G 1 ͞S boundary of the cell cycle. Mammalian or yeast cells carrying temperature-sensitive alleles of TAF250 arrest in G 1 at the nonpermissive temperature (7,8). Furthermore, following growth arrest, mammalian cells undergo apoptosis (9). In addition to serving as a scaffold on which other TAFs and TBP are assembled, TAF250 possesses enzymatic, promoter r...