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EXPRESSION AND FUNCTIONAL ANALYSIS OF AN OOCYTE-SPECIFIC NOVEL GENE, c-1, IN THE MOUSE.
Minami, Naojiro1, Miyamoto, Masakazu1, Aizawa, Akira2, Imai, Hiroshi1, 1 2
ABSTRACT- In the present study, we report the full-length sequencing, tissue-specific expression, and mRNA localization of c-1, a novel gene expressed in mouse oocytes. The gene was first isolated based on its elevated expression in 2-cell embryos developed without oviductal tissue, in which embryos cannot develop beyond the 2-cell stage. The full length of the gene was constructed from a set of homologous clones obtained from the EST (Expressed Sequence Tag) database and a 5' RACE analysis. Expression analysis of a novel cDNA isolated from various stages of embryos revealed that c-1 expression disappeared after the 2-cell stage. RT-PCR analysis of the cDNA obtained from various somatic tissues demonstrated that the expression of the novel gene was confined to ovary and testis. In addition, there were two types of cDNA, one of which was expressed only in the ovary (Type I) and the other was dominant in the testis (Type II: 634 base pairs larger than type I cDNA). However, a Northern blot analysis of RNA from multiple mouse tissues demonstrated that the gene was expressed only in the ovary, in which it was expressed as a single transcript of approx. 1.8 kb. Sequence analysis of Type I and Type II cDNAs revealed that only Type I cDNA has a single open reading frame of 326 amino acids corresponding to a predicted molecular mass of 37 kDa with no significant homology to the sequences previously reported. A remarkable characteristic of the gene is that it contains a leucine zipper at positions 131-152. In situ hybridization using an RNA probe in sections of the adult ovary resulted in distinct signals in the oocyte and surrounding cumulus cells. However, an RT-PCR analysis of cDNA obtained from cumulus cells of ovulated oocytes demonstrated that the gene is not expressed in the cumulus cells. This indicates that the novel gene is expressed specifically in the oocytes. An RT-PCR experiment using various stages of fetal ovary revealed that de novo expression of the novel gene starts at 15.5 dpc ovary. This time coincides with the start of meiosis of the ovarian oocytes, suggesting that the novel gene is involved in regulating meiosis in the oocytes.
KEY WORDS: novel gene, mouse, oocyte, meiosis
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