Tilapia, a good model for studying reproductive endocrinology

Area of Science:

• Reproductive Biology
• Endocrinology
• Genetics

Background:

• Nile tilapia (Oreochromis niloticus) possess XX/XY sex determination and are globally farmed, offering a rapid sexual maturation and year-round propagation advantage.
• Established genome sequencing and gene editing platforms, coupled with a moderate body size suitable for hormone level analysis, make tilapia an ideal model organism.
• Previous research highlights the critical role of estrogen in female development and the influence of various steroid hormones on fish reproduction.

Approach:

• Investigated the effects of mutations in genes involved in estrogen synthesis (e.g., cyp19a1a) and estrogen receptors (esr2a/esr2b) on sex determination and reversal in XX tilapia.
• Examined the impact of mutations in genes related to androgen, cortisol, and DHP synthesis on fertility in XY tilapia.
• Explored the potential for transdifferentiation of gonads by manipulating estrogen synthesis and receptor activity, and analyzed the roles of male (amhy, dmrt1, gsdf) and female (foxl2, sf-1, foxl3) pathway genes in sex determination.

Key Points:

• Estrogen is crucial for female development; its deficiency or mutated receptors cause sex reversal in XX tilapia.
• Mutations in genes regulating androgen, cortisol, and DHP impact fertility in XY tilapia.
• Gonadal differentiation can be reversed by altering estrogen synthesis and receptor signaling, with specific genes like foxl3 mediating female germ cell fate.

Conclusions:

• Tilapia is an excellent model for studying fish reproductive endocrinology due to its genetic tractability and clear hormonal influences on sex determination.
• Estrogen plays a central role in directing female development and germ cell fate, while other steroid hormones are critical for male fertility.
• Manipulating key hormonal pathways offers insights into the complex mechanisms governing sex determination and reproduction in fish.