Birth of normal offspring from mouse eggs activated by a phospholipase Czeta protein lacking three EF-hand domains.

Sperm-specific phospholipase C, PLCzeta, is a candidate for the Ca(2+) oscillation-inducing factor that is introduced into the ooplasm upon sperm-egg fusion. In addition to the 647-residue full-length PLCzeta, s-PLCzeta lacking the N-terminal 110 amino acids is known to be present in the mouse testis. In this study, we attempted to obtain full-term offspring from s-PLCzeta-activated eggs by round spermatid injection. Metaphase II-arrested eggs injected with a high RNA concentration of s-PLCzeta RNA normally developed to blastocysts. When the round spermatid nucleus was injected into telophase II-stage eggs previously activated by s-PLCzeta RNA, three live offspring were successfully obtained by transfer of the developed 4-cell embryos to pseudopregnant mice. These three offspring all grew to be normal adults and reproduced healthy second-generation mice.

Possible role of mouse poly(A) polymerase mGLD-2 during oocyte maturation.

Cytoplasmic polyadenylation of mRNAs is involved in post-transcriptional regulation of genes, including translational activation. In addition to yeast Cid1 and Cid13 and mouse TPAP, GLD-2 has been recently identified as a cytoplasmic poly(A) polymerase in Caenorhabditis elegans and Xenopus oocytes. In this study, we have characterized mouse GLD-2, mGLD-2, in adult tissues, meiotically maturing oocytes, and NIH3T3 cultured cells. mGLD-2 was ubiquitously present in all tissues and cells tested. mGLD-2 was localized in the nucleus as well as in the cytoplasm of somatic, testicular, and cultured cells. Transfection of expression plasmids encoding mGLD-2 and the mutant proteins into NIH3T3 cells revealed that a 17-residue sequence in the N-terminal region of mGLD-2 probably acts as a localization signal required for the transport into the nucleus. Analysis of reverse transcriptase-polymerase chain reaction indicated the presence of mGLD-2 mRNA in the oocytes throughout meiotic maturation. However, 54-kDa mGLD-2 was found in the oocytes only at the metaphases I and II after germinal vesicle breakdown, presumably due to translational control. When mGLD-2 synthesis was artificially inhibited and enhanced by injection of double-stranded and polyadenylated RNAs into the germinal vesicle-stage oocytes, respectively, oocyte maturation was significantly arrested at the metaphase-I stage. These results suggest that mGLD-2 may act in the ooplasm on the progression of metaphase I to metaphase II during oocyte maturation.