Prepubertal gonad investment modulates thymus function: evidence in a teleost fish

Area of Science:

• Comparative immunology
• Endocrinology
• Fish biology

Background:

• Sex hormones influence immune system plasticity in vertebrates.
• The interplay between gonads and thymus, especially during development, is poorly understood.
• Teleost fish offer a model to study immune-endocrine interactions due to their environmental sensitivity.

Purpose of the Study:

• Investigate if thymus plasticity in European sea bass involves trade-offs with growth and reproduction.
• Determine if gonad-thymus interaction occurs during gonadal differentiation and development.
• Examine the role of environmental factors (photoperiod, temperature) in modulating this interaction.

Main Methods:

• Studied juvenile European sea bass (Dicentrarchus labrax) over one year.
• Maintained fish under constant or fluctuating photoperiod and temperature conditions.
• Assessed thymus changes, including foxn1 gene expression, thymocyte, and T cell counts, alongside gonadal and somatic growth.

Main Results:

• Gonadal development during prepuberty coincided with a cessation of thymus growth in both environmental conditions.
• Somatic growth continued despite the halt in thymus development.
• The impact of reproductive effects on the thymus varied with ecophysiological conditions.

Conclusions:

• This study provides the first evidence that gonadal development in prepubertal fish regulates thymus plasticity.
• The findings suggest a potential mechanism for thymus involution observed with aging in mammals.
• Environmental conditions significantly modulate the reproductive effects on the thymus, independent of direct sexual maturity or hormone levels.