Effects of endosulfan and nonylphenol on the primordial germ cell population in pre-larval zebrafish embryos.

A variety of chemicals released into the aquatic environment are capable of targeting the reproductive system in fish and other vertebrates. Some of the effects observed in exposed adults may arise by permanent organizational changes that occur during embryogenesis, including changes in gonad structure and function. Little work has addressed the effects of pesticides and industrial chemicals, many of which are recognized as endocrine disrupting chemicals, on early embryos. The recent cloning of the vasa gene in zebrafish, the mRNA of which is found in fertilized eggs and is later segregated into the primordial germ cells (PGCs), has provided a unique opportunity to examine PGC migration and positioning in early embryos. We utilized antisense RNA probes to vasa mRNA in whole mount in situ hybridization analysis in order to examine the early migration and distribution of PGCs in embryos exposed to endosulfan and nonylphenol. The data reveal that these chemicals cause alterations in the distribution of PGCs along the anterior-posterior axis in 24-h-old embryos. This suggests that the previously reported alterations in juvenile and adult gonad structure of various aquatic vertebrates following exposure to pesticides and industrial chemicals could be related in part to alterations in early PGC distribution.