Subterranean Fishes of the World

4324

2019

AIM 2019

74

In animals the basic body plan is determined at early stages of embryogenesis. In fish and amphibians dorso-ventral polarity is established by maternal factors present in the oocyte. Downstream to the dorsalizing effect of maternal factors and the establishment of the organizer, the antero-posterior axis is specified during gastrulation, leading to the induction and regionalization of the neural tube. Subtle modifications in such early events are susceptible to have a major impact in later morphogenesis that can be deleterious or bring along morphological diversification. Here we used cave and surface morphotypes of the fish Astyanax mexicanus to study early embryonic events that could account for phenotypic evolution. First, we found differences in patterns, levels and dynamics of dkk1b (a Wnt pathway antagonist) expression in the prechordal plate from early gastrulation to somitogenesis. Our analyses of axial and paraxial mesodermal markers indicate that those differences might stem from heterochronic hypoblast internalization and convergent extension movements, which occur earlier in cavefish. Further, interfering with Wnt signaling in surface fish embryos reduced the size of the eye. Using F1 hybrid embryos obtained by reciprocal crosses of the two inter-fertile morphotypes we found that observed gastrulation differences depend fully on the maternal contribution. Later phenotypic differences in neural development became progressively hidden when zygotic genes take the control over development. Our work strongly suggests that maternal effect genes and developmental heterochronies occurring during gastrulation have impacted morphological brain change during cavefish evolution.

1

Astyanax Interrnational Meeting