Primordial germ cell proliferation in the salamander Pleurodeles waltl: genetic control before gonadal differentiation.

PGC counts were carried out on larvae of Pleurodeles waltl (urodele amphibia) issued from standard, monosexual male and monosexual female offspring while the genital ridges were settling. During this period, which is characterized by a zero mitotic index (and is therefore called the Po period), and which lasts from stage 35 to stage 41, no PGC proliferation occurs. A statistical analysis indicated that PGC counts per larva are sex genotype independent and that offspring may be divided into three groups with average PGC counts of 96.9, 51.0 and 31.1, respectively. A fourth group with an average of 18.3 PGCs has been identified using experimental larvae reared at 30 degrees C from stage 30. The PGC count of 96.9 would result from at least three mitotic cycles. Before the Po period, germ cells are not identifiable. A hypothesis concerning genetic control of PGC proliferation before Po was deduced from this analysis.