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

Gemma Sutton,Kanchon K Dasmahapatra,Antonia G.P Ford,Julia J Day,Asilatu Shechonge,Mary E Pownall,Lewis J White

doi:10.3390/jdb8040022

Abstract

Although it is widely accepted that the cellular and molecular mechanisms of vertebrate cardiac development are evolutionarily conserved, this is on the basis of data from only a few model organisms suited to laboratory studies. Here, we investigate gene expression during cardiac development in the extremophile, non-model fish species, Oreochromis (Alcolapia) alcalica. We first characterise the early development of O. alcalica and observe extensive vascularisation across the yolk prior to hatching. We further investigate heart development by identifying and cloning O. alcalica orthologues of conserved cardiac transcription factors gata4, tbx5, and mef2c for analysis by in situ hybridisation. Expression of these three key cardiac developmental regulators also reveals other aspects of O. alcalica development, as these genes are expressed in developing 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 of the vertebrate body plan. However, the expression of gata4 in O. alcalica reveals interesting differences in the development of the circulatory system distinct from that of the well-studied zebrafish. Understanding the development of O. alcalica embryos is an important step towards providing a model for future research into the adaptation to extreme conditions; this is particularly relevant given that anthropogenic-driven climate change will likely result in more freshwater organisms being exposed to less favourable conditions.

Highlights

Aquatic ectotherms, such as fish, are significantly impacted by the changes or stressors in their environment, as they rely on the surrounding water for maintaining homeostasis [1,2].Despite this restriction, fish have evolved morphological, biochemical, physiological, behavioural, and developmental mechanisms allowing them to colonise most aquatic environments, including a variety of extreme habitats [3,4]
The network of cardiac transcription factors that regulate embryonic heart development displays a high degree of evolutionary conservation across vertebrates; here, we identify and describe the expression of a subset of these regulators, GATA-binding protein 4 (GATA4), T-box 5 (Tbx5), and Myocyte enhancer factor 2c (Mef2c) in Oreochromis (Alcolapia) alcalica
We report here the expression of three evolutionarily conserved regulators of cardiogenesis in the context of a direct-developing extremophile fish, Oreochromis (Alcolapia) alcalica

Summary

Introduction

Aquatic ectotherms, such as fish, are significantly impacted by the changes or stressors in their environment, as they rely on the surrounding water for maintaining homeostasis [1,2]. Despite this restriction, fish have evolved morphological, biochemical, physiological, behavioural, and developmental mechanisms allowing them to colonise most aquatic environments, including a variety of extreme habitats [3,4]. Most fish species are unable to survive extremes of temperature, pH, salinity, and environments which seasonally dry out, some specialised species have adapted to thrive in such conditions, making them useful subjects for studying the molecular and developmental mechanisms underpinning adaptation to imposed stressors [5].

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