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Fig. 5 Juvenile gonads of fancl mutants contain oocytes that fail to progress through meiosis.
Histological comparison of germ cell development in fancl homozygous mutants (fancl) and wild-type sibling controls (WT), by hematoxylin and eosin staining of gonads at different stages of development: undifferentiated, 19–22 dpf (A,B), transitional juveniles, 26 dpf (C–F), post-transitional juveniles, 32 dpf (G–I) and adults (J–L). At 19–22 dpf, no morphological differences were observed between WT (n = 10) and fancl animals (n = 10) and both genotypes showed early stage IB perinucleolar oocytes (epo in A,B). At 26 dpf, the first histological differences between WT and fancl became apparent. Most WT controls (7 out of 9 individuals) had abundant enlarged perinucleolar oocytes that had progressed from early stage IB to late stage IB (lpo in C), and only two lacked late stage IB oocytes (E). In contrast, only one of twelve fancl mutant animals had enlarged oocytes at late stage IB (lpo in D), while the majority (11 out of 12) lacked late stage IB oocytes (F). Both wild-type and fancl mutant gonads that lacked oocytes possessed spermatogonia (sg in E,F). Remarkably, in contrast to wild types, fancl mutants showed abundant pyknotic cells (pc) at 26 dpf (D,F). At 32 dpf, gonads showed unmistakably the morphology of either ovary or testis, and in wild-type controls, approximately half of the animals (6 out of 11) had ovaries with perinucleolar oocytes at late stage IB (lpo in G) and the other half (5 out of 11) showed the typical testis morphology with abundant spermatogonia (sg) and spermatocytes (sc) arranged in cysts (dashed line in H). In contrast to controls, all fancl mutants (n = 8) had gonads that lacked perinucleolar oocytes, and showed testis morphology with groups of spermatogonia (sg) and spermatocytes (sc) (I). Finally, in adults, half of the WT controls (5 out of 10) had mature ovaries filled with oocytes at different stages of oogenesis: stage IA, IB, II, III and IV (J), and the other half (5 out of 10) had mature testes (K), in contrast to fancl mutants in which all animals (n = 7), had mature testes filled with germ cells at different stages of spermatogenesis: spermatogonia (sg), spermatocytes (sc) and sperm (sp) (L), and none of the seven fancl mutants had ovaries. Oocyte stages described according to [49]; Spermatogenesis stages described according to [28]. Scale bar: 0.02 mm (as in A, except for J).