Mutation of Vsx genes in zebrafish highlights the robustness of the retinal specification network.
Genetic studies in human and mice have established a dual role for Vsx genes in retina development: an early function in progenitors specification, and a later requirement for bipolar-cells fate determination. Despite their conserved expression patterns, it is currently unclear to which extent Vsx functions are also conserved across vertebrates, as mutant models are available only in mammals. To gain insight into vsx function in teleosts, we have generated vsx1 and vsx2 CRISPR-Cas9 double knockouts (vsxKO) in zebrafish. Our electrophysiological and histological analyses indicate severe visual impairment and bipolar cells depletion in vsxKO larvae, with retinal precursors being rerouted towards photoreceptor or Muller glia fates. Surprisingly, neural retina is properly specified and maintained in mutant embryos, which do not display microphthalmia. We show that although important cis-regulatory remodelling occurs in vsxKO retinas during early specification, this has little impact at a transcriptomic level. Our observations point to genetic redundancy as an important mechanism sustaining the integrity of the retinal specification network, and to Vsx genes regulatory weight varying substantially among vertebrate species. Brief Summary Statement for use in emailed and online tables of content alertsThe mutation of vsx genes in zebrafish confirms a conserved role in bipolar cells specification across vertebrates, but do not interfere with the specification of the neural retina domain. Our data reveal the unexpected robustness of the genetic network sustaining the identity of the neural retina.