A Broad but Restricted Requirement for TAF-5 (Human TAFII100) for Embryonic Transcription inCaenorhabditis elegans

Abstract

As conserved components of the transcription factor (TF) IID-and TFTC/SAGA-related complexes, TATAbinding protein-associated factors (TAF II s) are important for eukaryotic mRNA transcription. In yeast, genetic analyses suggest that, although some individual TAF II s are required for transcription of most genes, others have highly specialized functions. Much less is known about the functions of TAF II s in metazoans, which have more complex genomes that include many tissue-specific genes. TAF-5 (human (h) TAF II 100) is of particular interest because it is predicted to have an important structural role. Here we describe the first genetics-based analysis of TAF-5 in a metazoan. By performing RNA interference in Caenorhabditis elegans embryos, which can survive for several cell generations without transcription, we found that taf-5 is important for a significant fraction of transcription. However, TAF-5 is apparently not essential for the expression of multiple developmental and other metazoan-specific genes. This phenotype remarkably resembles the previously described effects of similarly depleting two C. elegans histone fold TAF II s, TAF-9 (hTAF II 31/32) and TAF-10 (hTAF II 30), but is distinct from the widespread transcription block caused by TAF-4 (hTAF II 130) depletion. Our findings suggest that TAF-5, TAF-9, and TAF-10 are part of a functional module of TFIID-and TFTC/ SAGA-related complexes that can be bypassed in many metazoan-specific genes.Eukaryotic mRNA transcription requires the coordinate activity of gene-specific activators, coactivator proteins, general transcription factors (TFIIA, 1 TFIIB, TFIID, TFIIE, TFIIF, and TFIIH), Mediator complexes, and RNA polymerase II (pol II) (1-3). This complexity allows the transcription machinery to communicate with gene-specific regulators through an extraordinary diversity of combinatorial interactions. Genetic studies performed in yeast indicate that, although many transcription machinery components are essential, others seem to perform more specialized roles in regulating subgroups of genes (4 -6). In general, genes involved in maintenance of cell viability are shared by all eukaryotes, suggesting that aspects of their regulation are likely to be conserved between yeast and metazoans. However, most metazoan genes, including those controlling development and differentiation, are not conserved in single cell eukaryotes and may require alternative regulatory strategies (7,8).The general transcription factor TFIID is composed of the TATA-binding protein along with 12-14 additional polypeptides, the TATA-binding protein-associated factors (TAF II s) 2 (5, 9, 10). The TAF II s are generally conserved in eukaryotes (11). TFIID has various functions during initiation; it appears to possess enzymatic activities, and TAF II s have been implicated in essential interactions with gene-specific activators and with core promoter sequences located near the transcription start site (5, 9, 12, 13). Many TAF II s contain a domain that is related to the histone fold, through w...

An Extensive Requirement for Transcription Factor IID-specific TAF-1 in Caenorhabditis elegans Embryonic Transcription

“…The level of antiphospho-Ser-2 staining in these RNAi embryos was only slightly higher than the background seen in transcriptionally silent ama-1(RNAi) or taf-4(RNAi) embryos and was significantly lower than in taf-5, taf-9, or taf-10(RNAi) embryos (Fig. 4A) (22,23), suggesting that most pol II transcription had been prevented. Accordingly, in taf-1(RNAi) embryos nucleoplasmic anti-phospho-Ser-5 staining was decreased proportionally to anti-phospho-Ser-2 staining, except that two anti-phosphoSer-5 foci like those normally present in the germ line were prominent in somatic cells (Fig.…”

“…elegans embryonic development is initially sustained by maternally provided gene products (30). Interference with maternal and zygotic expression of other TAF II s or PIC components such as ama-1 and ttb-1 (TFIIB) arrests embryonic development at about 100 cells without signs of differentiation, a phenotype that is characteristic of a broad zygotic transcription defect (21)(22)(23)31). taf-1(RNAi) embryos arrested development at a similar stage, apparently without differentiation (Fig.…”

“…In the C. elegans embryo, the levels and patterns of antiphospho-Ser-5 and anti-phospho-Ser-2 staining parallel overall transcription activity (22,23,31,37,38). Nuclear staining with these antibodies first appears at the three-to four-cell stage, when new mRNA transcription begins.…”

“…A unique advantage of this system is that it allows analysis of de novo gene expression in individual living embryos. Each of these reporters is fully dependent upon taf-4, but in taf-5, taf-9, and taf-10(RNAi) embryos the metazoan-specific reporters we have analyzed are expressed at WT levels (22,23). Second, we used RT-PCR to measure the expression of endogenous genes in control and RNAi embryos.…”

“…Using this strategy, we determined previously that TAF-4 is required for essentially all early embryonic transcription (22). In contrast, TAF-5, TAF-9, and TAF-10 were required for significant and comparable fractions of early transcription but appeared to be dispensable at most metazoan-specific promoters (22,23). Each of the TAF II s we have analyzed is shared between TFIID and SAGA-like complexes, leaving open the question of how broadly TFIID is required in the embryo.…”