Figure 4. Phenotype analysis of the npr^+/+ and npr^−/− female zebrafish at 75 dpf.

(a) Gross morphology of the npr^+/+ and npr^−/− fish. (b,c) Body length (b) and body weight (c) of npr^+/+ and npr^−/− mutants (n = 6). (d) Ovary morphology of the npr^+/+ and npr^−/− fish. (e), Microscopic examination of follicles from npr^+/+ and npr^−/− mutants. Follicles were collected at 15:00 pm and matured oocytes (red arrows) could be observed in the npr^−/− mutant. (f) The gonado somatic index (GSI) of npr^+/+ and npr^−/− fish (n = 6). (g) Spawning assay. No npr^−/− fish succeeded in spawning (n = 30). (h) Ovary histology of the npr^+/+ and npr^−/− fish. The outer layer cells of the matured follicles (indicated by arrow) failed to breakdown in the npr^−/− fish. (i) Oocyte maturation assay. FG stage follicles from npr^+/+ and npr^−/− fish were treated with IGF3 or 17α, 20β-DHP, and the percentages of follicles that underwent germinal vesicle breakdown (GVBD) were recorded. Each value represents the mean value ± SEM (n = 4) of three independent experiments (*P < 0.05; ***P < 0.001 vs npr^+/+).