Aromatase, brain sexualization and plasticity: the fish paradigm

Area of Science:

• Neuroendocrinology
• Comparative Neurobiology
• Fish Biology

Background:

• Teleost fish exhibit labile sex determination, influenced by hormonal, social, and environmental factors, leading to hermaphroditism.
• Unlike mammals, fish brains are not irreversibly sexualized early in life, maintaining plasticity throughout adulthood.
• This plasticity is linked to unique features of brain sexualization in teleosts.

Purpose of the Study:

• To highlight unique features of fish brains that contribute to their sexual plasticity.
• To explain the role of aromatase genes and their expression in adult fish brains.
• To explore how these features allow for sex changes and varied reproductive strategies.

Main Methods:

• Review of existing literature on teleost fish sex determination, brain sexualization, and aromatase function.
• Analysis of aromatase gene expression (cyp19a1a and cyp19a1b) in adult fish brains.
• Correlation of brain aromatase activity with sex steroid levels and neurogenic activity.

Main Results:

• Adult teleosts show intense aromatase activity from two genes, cyp19a1a and cyp19a1b, with aromatase B expressed in radial glial cells (RGCs).
• Radial glial cells in fish persist throughout life and function as neural progenitors.
• High expression of cyp19a1b is maintained by an autoregulatory loop involving estrogens and androgens, similar to embryonic mammalian brains.

Conclusions:

• Fish brains retain embryonic characteristics, including high neurogenic activity and aromatase expression in progenitor cells, throughout life.
• This permanent brain-gonad dialogue facilitates sex changes and diverse reproductive strategies in teleosts.
• These findings offer insights into the evolution of brain sexualization and reproductive plasticity.