Exploring the Expression of Cardiac Regulators in a Vertebrate Extremophile: The Cichlid Fish Oreochromis (Alcolapia) alcalica

Although it is widely accepted that the cellular and molecular mechanisms of vertebratecardiac development are evolutionarily conserved, this is on the basis of data from only a fewmodel organisms suited to laboratory studies. Here, we investigate gene expression during cardiacdevelopment in the extremophile, non-model fish species, Oreochromis (Alcolapia) alcalica. Wefirst characterise the early development of O. alcalica and observe extensive vascularisation across the yolk prior to hatching. We further investigate heart development by identifying andcloning O. alcalica orthologues of conserved cardiac transcription factors gata4, tbx5, and mef2cfor analysis by in situ hybridisation. Expression of these three key cardiac developmentalregulators also reveals other aspects of O. alcalica development, as these genes are expressed indeveloping blood, limb, eyes, and muscle, as well as the heart. Our data support the notion that O.alcalica is a direct-developing vertebrate that shares the highly conserved molecular regulation ofthe vertebrate body plan. However, the expression of gata4 in O. alcalica reveals interestingdifferences in the development of the circulatory system distinct from that of the well-studiedzebrafish. Understanding the development of O. alcalica embryos is an important step towardsproviding a model for future research into the adaptation to extreme conditions; this is particularlyrelevant given that anthropogenic-driven climate change will likely result in more freshwaterorganisms being exposed to less favourable conditions