Thymus development in the zebrafish (Danio rerio) from an ecoimmunology perspective

15 pág.

The thymus is present in all gnathostome vertebrates and is an essential organ for the adaptive immune system via the generation of functional mature T-cells. Over the life span of mammals, the thymus undergoes morphological and functional alterations, including an age-related involution, which in humans starts in early life. Life history tradeoffs have been suggested as possible reasons for thymus involution. While in teleost fish, only a few studies have investigated alterations of thymus structure and function over different life stages, resulting in a fragmented database. Here, we investigated the thymus growth of zebrafish (Danio rerio) from early life, throughout puberty and reproductive stage, up to 1-year-old. We assessed thymus growth by histological and morphometric analyses and thymocyte numbers. Thymus function was assessed by measuring the transcripts of the thymocyte marker genes, ikaros, tcrα, and tcrδ. Additionally, we analyzed gonad maturity and tail homogenate vitellogenin concentrations to align thymus status with the status of the reproductive system. Our results showed that the zebrafish thymus, in contrast to the human thymus, grew strongly during early life and puberty but started to undergo involution when the fish reached the reproductive age. The involution was characterized by reduced thymus area and thymocyte number, altered histoarchitecture, and decreasing thymocyte marker gene transcript levels. Our findings suggest that age-related changes of the zebrafish thymus do exist and could be partly explained in terms of resource tradeoffs, but also in terms of the ontogenetically late development of a functional adaptive immune system in teleosts.

We would like to acknowledge Audrey Phan, for her technical advice and practical support during sampling, and Elio Herzog and John Huynh for practical support during sampling and molecular analysis. This study was supported by the grant 310030E‐164266 to Helmut Segner from the Swiss National Science Foundation. It was part of the grant ANR‐CE32‐2015 to Tiphaine Monsinjon, Université Le Havre, France, from the Agence Nationale de La Recherche. Christyn Bailey was funded by SNSF Post‐Doc Mobility grant P400PB_183824.

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