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Fig. 3 Zebrafish germ cells express fancl during gonad development.
In situ hybridizations with fancl probe were performed on cryo-sections of wild-type animals at different stages of gonad development. Weak fancl expression signal (arrows) was detected in undifferentiated gonads at 17 days post-fertilization (dpf) (A) and 23 dpf (B). Signal became stronger in germ cells (arrows) of transitioning and immature ovaries (ooplasm of oocytes, arrows in C,E,G) and transitioning and immature testes (D,F,H) at 26, 33, and 37 dpf. In adults, fancl expression was restricted to germ cells, but signal intensity depended on the stage of germ cell differentiation. In adult ovaries (I), early stage IB oocytes (eIB) already showed low fancl expression and late stage IB oocytes (lIB) showed strong fancl signal in the ooplasm, suggesting that fancl expression initiated in early stage IB oocytes. As oogenesis progressed, ooplasm volume increased, cortical alveoli appeared (stage II), yolk accumulated (stage III), and fancl expression signal became diluted. In adult testes (J), fancl expression signal was detected in a subset of cells with large nuclei and morphology consistent with primary spermatocytes (sc), but signal was not detected in cells with small nuclei in an advanced stage of spermatogenesis (i.e. spermatids and sperm (sp)). Oocyte staging is according to [49] and [29]. Scale bar: 0.1 mm.