PARENT SESSION
MINISYMPOSIUM VI: Regulation of Gene Expression in Gametogenesis
Tuesday, July 31, 2001, 10:30 AM-12:00 PM
Westin-Confederation I
Chair: Norman B. Hecht
Speakers: Norman B Hecht, Clinton C MacDonald, Daniel L Kilpatrick

GERM CELL-SPECIFIC mRNA POLYADENYLATION.

MacDonald, Clinton¹, ¹

ABSTRACT- Messenger RNA 3' end polyadenylation is essential for gene expression in all cells. In somatic cells, the canonical signal AAUAAA is required for efficient polyadenylation. However, many mRNAs in male germ cells (as many as 60%) do not contain AAUAAA in their 3' ends, yet are efficiently polyadenylated. We are investigating the mechanism of this "testis-specific polyadenylation." A key protein in polyadenylation is the 64,000 Mr protein of the cleavage stimulation factor (CstF-64). We found that there were two immunologically distinct forms of CstF-64 expressed in mouse male germ cells: a somatic form (of ~64,000 Mr) is found in all tissues including testis. A variant form (~70,000 Mr) is found only in testis and to a lesser extent in brain. In testis, the variant CstF-64 is found exclusively in meiotic and postmeiotic spermatocytes and spermatids, so it is a strong candidate to control meiosis-specific polyadenylation. We also mapped the gene for the somatic form of CstF-64 to the X chromosome in both mouse and human, suggesting it is absent in spermatocytes because of X-chromosomal inactivation. We propose that the gene for the somatic form of CstF-64 is inactivated during male meiosis creating the need for a variant autosomal source of the protein which is capable of polyadenylating AAUAAA-deficient mRNAs. We named the variant form of CstF-64 "CstF-64." The cDNA for CstF-64 from mouse (mCstF-64) encodes a protein that is only 69.8% similar to mouse CstF-64. It does, however, have many unique features that are different from the somatic CstF-64, and that make it a very strong candidate for the protein responsible for testis-specific mRNA polyadenylation.

KEY WORDS: polyadenylation, gene expression, testis, germ cells