Basic mechanisms of ovarian function: germ cells

Recent work is reviewed on several molecular aspects of gene expression during oocyte maturation and early development. Several analyses have been carried out on protein synthesis patterns using the high resolution two-dimensional polyacrylamide gel electrophoresis technique. The protein pattern of some 400–500 spots in sea urchin oocytes before and just after fertilization are quite similar. By gastrula, major stage specific protein changes have been noted. In a similar study major protein changes are noted during the meiotic maturation process in mammals. With the use of the single-copy DNA hybridization technique, the quantitative levels of rare mRNA sequence expression have been determined during oogenesis and early development in the sea urchin model. The mature oocyte sequence set of some 37 × 10(6) nucleotides of information (or potentially 18,500 different proteins) is synthesized during oogenesis and slowly utilized during development. The sea urchin gastrula mRNA is predominantly synthesized by the embryo genome; however, essentially all those gastrula mRNA sequences can also be found in the mature oocyte (maternal) set. It is proposed by Hough-Evans et al. that this maternal sequence set, which is made during oogenesis and both utilized (translated in 10,000–20,000 proteins), and in part, continually synthesized by all stages of the embryo, plays a critical role in the morphogenic formation of a sea urchin embryo.