Busulfan-mediated germ cell depletion does not alter gonad differentiation in the urodele amphibian Pleurodeles waltl.

It is not known in urodele amphibians whether germ cells (GCs) are indispensable for gonadal differentiation. In order to address this question in the newt Pleurodeles waltl, we first cloned the ortholog of VASA which is known as a GC marker in many species. Male (ZZ) and female (ZW) larvae were then exposed to the alkylating agent busulfan (25 μg/ml for 3 days) just after hatching (stage 36). In the main body of busulfan-treated larvae, PwVASA mRNA expression decreased before gonad differentiation in both sexes (at stage 50). This suggested GC depletion which was confirmed by histology, with a complete absence of GCs observed slightly earlier in females (stage 54) than in males (stage 54 + 60 days). In busulfan-treated ZW larvae, the presence of the typical central cavity and expression of a high level of aromatase mRNA confirmed the ovarian phenotype. In busulfan-treated ZZ larvae, the presence of a medulla surrounded by a thin cortex and a low level of aromatase mRNA confirmed the testis phenotype. At the juvenile stage, efferent ducts and lobules were present in the first testis lobe. Taken together, these data suggest that GC depletion does not alter gonad differentiation in P. waltl.