Subterranean Fishes of the World

5610

2022

AIM 2022

17

Understanding how animal adapted to new environment and evolved new shapes is a central question of EVO-DEVO. It is well accepted that morphological evolution is driven by changes in gene expression rather than changes in protein function. Gene expression is tightly regulated through cis-regulatory elements (non-coding DNA sequences) and trans-acting factors binding them. Any change in these regulatory processes will influence spatial and temporal gene expression that can in turn modulate development and lead to morphological changes. Thus looking at change in gene regulation is critical to understand how species evolve and adapt to new environment. To disentangle cis- from trans- regulatory divergences in Astyanax mexicanus developmental evolution, we generated transcriptomes of pools of Pachón cave and Texas surface embryos as well as reciprocal F1 hybrid embryos, at neural plate stage (10 hours post-fertilization). This stage corresponds to the end of gastrulation, a time when extensive variations in gene expression occur to set out neurulation and brain/eye development. We identified 26390 fixed single nucleotide polymorphism on 5573 genes in the two morphs. Comparing allelic expression ratio in F1 hybrids allowed us to identify 108 genes whose change in expression levels are due to changes in cis-regulation. Among them we focused on Rx3, a critical gene for eye development, down-regulated in cavefish. Using reciprocal transplantation experiments, we demonstrated that the level of expression of Rx3 is regulated in a cell-autonomous manner. On the contrary, the size of the Rx3 expression domain depended on external signaling (Wnt), thus showing the uncoupling of the control of the level of expression and of the spatial expression for a single gene.

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