Anti-cdc2 and anti-cyclin B immunoblots of suc1 precipitates from immature (I) and mature (M) zebrafish oocyte extracts. The positions of protein markers are shown on the left. Cyclin B forming a complex with cdc2 is found only in mature oocytes.

Changes in cdc2 and cdk7 protein levels during zebrafish oogenesis. (A) Anti-cdc2 and anti-cdk7 immunoblots of oocytes in stages 1 – 5. The oocyte diameter in each stage is indicated below the blots. Proteins derived from 90nl of stage 1 oocytes and 180nl of stage 2 – 5 oocytes were applied in each lane. The numbers of oocytes corresponding to the volume applied on each lane were 12.5, 7, 3, 1.5, and 1 for stages 1 – 5, respectively. (B) Changes in the protein content of cdc2 and cdk7 during oogenesis. The protein content was calculated from the density of the bands of cdc2 and cdk7 in A, using E.coli-produced cdc2 and cdk7 as standards. Mean ± standard deviations for three independent measurements. (C) Changes in the concentration of cdc2 and cdk7 during oogenesis. The values obtained in B were divided by the cytoplasmic volume of each stage of oocytes. Means ± standard deviations (n = 3).

Previtellogenic (A) and fully grown (B) oocytes centrifuged on a Ficoll density gradient. The centrifugation segregated the cytoplasm (CY), including the germinal vesicle, from the metaplasm which consists mainly of cortical alveoli (CA) in previtellogenic stage 1 oocytes and yolk (Y) in fully grown stage 5 oocytes. Scale, 100 μm.

Fully grown (A, B) and previtellogenic (C, D) oocytes microinjected with BSA (A, C) or recombinant cyclin B protein (B, D). Microinjection of cyclin B protein induced GVBD in both fully grown and previtellogenic oocytes. GV, germinal vesicle. Scale, 100 μm.

Northern blots of 5 μg of total RNA isolated from previtellogenic (P) and fully grown (F) zebrafish oocytes, as probed with DIG-labeled zebrafish cyclin B antisense RNA. The positions of RNA markers are shown on the right.