| Research Abstract |
Our project has focused on the 2-cell stage of mouse preimplantation embryo. In mouse embryogenesis, zygotic genes are activated around the 2-cell stage, and interaction of the zygotic gene products with maternally-inherited products are critical for further development of the embryo. In order to identify genes that are highly expressed at the 2-cell stage, we have taken two approaches.
One approach was to identify cDNAs containing B1 repetitive sequences, which are over-represented in genes expressed in early embryos. From a mouse 2-cell cDNA Iibrary, we have identified and characterized around 100 independent clones. General characteristics of the B1 sequences identified in these cDNAs are that(i) the B1 sequences are present within non-coding regions of mRNA in most cases, (ii) the orientation of the B1 sequences relative to the orientation of transcripts are quite random. In addition, characterization of these cDNA clones led to identification of M31 and M32, which appear to be involved in heterochromatin modification, and tsec-1, which are also expressed in adult testis.
The other approach employed the subtraction technique, and we have identified the SSEC-D (Stage-Specific Embryonic Clone-D) gene, which is highly expressed at the 2-cell stage. Characterization of the SSEC-D gene and its products has revealed that (i) it is a novel gene, highly conserved among rodent and primate, (ii) many mouse strains have one pseudo gene, (iii) it is expressed in every adult tissues tested, and (iv) at about 15 hours post fertilization, its maternally inherited products become elongated for about 400 ntds, probably by poly A extension. The last characteristics・・・stage-specific elongation of the SSEC-D transcripts・・・is particularly intriguing, and we are currently examining the molecular alterations more in details to understand the developmental program that causes this peculiar phenomenon.
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