Identification of a Novel Gene Product, Sertoli Cell Gene with a Zinc Finger Domain, That Is Important for FSH Activation of Testicular Sertoli Cells
Sertoli cells provide the cytoarchitectural support and microenvironment necessary for the process of spermatogenesis. A novel, ubiquitously expressed cDNA clone was isolated from Sertoli cells and termed Sertoli cell gene with a zinc finger domain (SERZ). A significant homology of SERZ was found with a mouse genomic sequence that suggested the presence of at least 10 exons. An open reading frame at the 5-end of the cDNA, termed SERZ-␣, had a cryptic basic helixloop-helix (bHLH) domain, but no
... tart codon. When a start codon was engineered into the 5-end of the cDNA, an in vitro translation product of SERZ-␣ was obtained. The longest second open reading frame with an ATG start site at 304 bp from the 5-end coded for a 308-amino acid SERZ-␤ polypeptide. Motif analysis and BLAST search of SERZ-␤ showed signifi- cant homology to the DHHC domain of conserved zinc finger proteins. A number of potential phosphorylation sites were observed in the SERZ-␤ polypeptide sequence. The long 5untranslated region of SERZ-␤ prompted an investigation of both potential alternate polypeptide products, SERZ-␣ and SERZ-␤. Both SERZ-␣ and SERZ-␤ proteins were detected with specific antibodies to SERZ-␤ and the 5-end open reading frame SERZ-␣ in a Western blot analysis of total Sertoli cell proteins. The presence of the SERZ-␤ polypeptide was also confirmed by in vitro translation of the cDNA, but SERZ-␣ was not translated in vitro in the absence of an engineered start codon. The expression pattern of SERZ mRNA was observed in all tissues examined. The transcript size of SERZ as determined by Northern blot analysis is approximately 2.7 kb. An antisense oligonucleotide to SERZ was found not to influence basal levels of transferrin promoter activation, but significantly blocked FSH-induced transferrin promoter activation. SERZ mRNA expression was not regulated by FSH treatment of Sertoli cell cultures. In summary, a novel gene product, SERZ, was identified that appears to have a role in maintaining Sertoli cell differentiated functions and mediating FSH actions. Translation of SERZ may give rise to two gene products; however, the SERZ-␤ containing the zinc finger domain is probably the principal product of the SERZ gene. (Endocrinology 143: 426 -435, 2002) Abbreviations: bHLH, Basic helix-loop-helix; CAT, chloramphenicol acetyltransferase; MMLV, Moloney murine leukemia virus; RACE, rapid amplification of cDNA ends; SERZ, Sertoli cell gene with a zinc finger domain.