Comparison between oogenesis and related ovarian structures in a reptile, Pseudemys scripta elegans (turtle) and in a bird Coturnix coturnix japonica (quail).

Abstract

The aspect of the oogonia during their premitotic DNA synthesis and of the premeiocytes during their premeiotic DNA synthesis was studied in turtles by autoradiography, after injection of 3H-thymidine. As in the adult laying quail, the intrafollicular oocytes of the adult turtle go through three successive stages: prelampbrush, lampbrush and postlampbrush. During the prelampbrush and lampbrush stage two kinds of nucleoli exist: peripheral and central. In contrast to avian yolk, during its final rapid growth, no polyhedric protein yolk units were found in turtle yolk. As in the yellow yolk of quail, highly osmiophilic alcohol insoluble satellite yolk (egg oil) accumulates between the protein globular yolk of Pseudemys. Turtle yolk globules increase in volume by fusion. The penetration of peripherally assembled yolk in the turtle germinal disc is analogous to what we have described in the quail. Also in postlampbrush germinal discs subcortical ooplasmic organelles are present. Below the turtle germinal disc no structure comparable to the avian nucleus of Pander could be observed. No pyriform cells (as in squamate reptiles) and no pyriform-like cells (as in birds: Callebaut, 1991 b) were found in the chelonian ovarian granulosa layer. We could not demonstrate functional lacunoperitoneal communications via openings in the hilus ovarii of the turtle as is the case in birds.