Figure 5:

Shift in the balance of pro-male and pro-female pathways will determine direction of gonad differentiation in zebrafish. Three major developmental pathways (Tp53-apoptosis, NF-кB and canonical Wnt) have been shown to participate in the process. The number of germ cells also has a profound effect on the final outcome (data not shown). In the males (left), numbers of primary oocytes originating from the ‘juvenile ovary’ are low, tp53 is upregulated, apoptotic processes are fully active and the NF-кB as well as canonical Wnt signaling pathways are both downregulated. The hormonal balance is shifted toward maleness. In the females (right), the number of primary oocytes originating from the ‘juvenile ovary’ is high, the NF-кB pathway and canonical Wnt signaling pathways are both upregulated, whereas tp53 is downregulated. Apoptosis is inhibited and the hormonal balance is shifted toward femaleness. The timing and causative effects of these processes are not fully understood.