Spatio-temporal expression of a DAZ-like gene in the Japanese newt Cynops pyrrhogaster that has no germ plasm.

To investigate the germ cell specification in urodeles, we cloned a DAZ-like sequence from the Japanese newt Cynops pyrrhogaster, Cydazl, and raised antibodies specific to Cydazl. Cydazl is a homologue of the human DAZ (deleted in azoospermia), DAZL, and Xenopus dazl genes, which are involved in gametogenesis or germ cell specification. During gametogenesis, expression of Cydazl mRNA and Cydazl protein was detected at first in the small previtellogenic oocytes in females but was not localized as seen in Xenopus and was restricted to secondary spermatogonia prior to meiosis in males. During early embryogenesis, maternal stores of the Cydazl transcript and protein were present in the entire embryos, not localized in any specific region. The zygotic expression was detected in hatching larvae (stage 50) by RT-PCR analysis whereas specific cells expressing Cydazl could not be determined by in situ hybridization at this stage. Strong expression of Cydazl and Cydazl were detected in primordial germ cells (PGCs) that had entered the gonadal rudiment at late stage 59. These results suggest that Cydazl does not function early in development, for the specification of germ cells, but functions later for differentiation of germ cells in the developing gonads during embryogenesis and for meiotic regulation, supporting the previous idea of an intermediate germ cell formation mode in urodeles.