Function of conserved transcription factors in the C. elegans somatic gonad and pharynx
Clary, Lynn M.
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Mammalian EGR-family genes and T-box family genes are broadly expressed and mutants result in a variety of defects and diseases (O'Donovan et al., 1999). To aid in our understanding of how these transcription factor families regulate gene expression we analyzed the function of C. elegans egrh-1 and tbx-2 in the somatic gonad and pharynx respectively. We found that the C. elegans Early Growth Response factor family member egrh-1 inhibits oocyte maturation and ovulation until sperm are available. C. elegans is an important system for addressing the fundamental events of oocyte meiotic maturation, ovulation and fertilization, complementing studies in vertebrate systems (Hubbard and Greenstein, 2000). In C. elegans oocyte production, maturation and ovulation must be coordinated with sperm availability for successful fertilization. egrh-1 mutants exhibit ectopic oocyte differentiation in the distal gonadal arm and accumulate abnormal and degraded oocytes proximally. These defects result in reduced brood size and partially penetrant embryonic lethality. Results of tissue-specific egrh-1(RNAi) experiments and genetic mosaic analyses revealed EGRH-1 function is necessary in the soma, and surprisingly this function is required in both the gut and the somatic gonad. Through transformation rescue experiments we show EGRH-1 in the somatic gonad inhibits oocyte maturation, ovulation and sperm recruitment. The T-box family member TBX-2 is the sole C. elegans member of the conserved Tbx2 sub-family. It has been previously shown that C. elegans TBX-2 is required for the development of ABa-derived pharyngeal muscles; however it is not known how TBX-2 specifically regulates the development of these cells. We are interested in identifying TBX-2 targets that function in pharyngeal muscle development, and in determining if TBX-2 is a transcriptional activator or repressor. To identify targets of TBX-2, we have compared mRNA expression levels in wild-type and tbx-2(bx59) mutant embryos using Affymetrix microarrays. Of 19,885 probe sets examined, we found 980 mRNAs that were significantly up-regulated in tbx-2(bx59) relative to wild-type and 175 mRNAs that were significantly down-regulated. Using clustering analysis, comparisons to existing data sets on pharyngeal gene expression, and phylogenetic foot-printing to identify promoters with consensus T-box factor binding sites, we have analyzed a subset of genes and identified D2096.6 as a direct target of TBX-2. Our data indicate that D2096.6 is directly repressed by TBX-2 at a variant T-box binding site in the D2096.6 promoter.
early growth response