The Presence of Two MyoD Genes in a Subset of Acanthopterygii Fish Is Associated with a Polyserine Insert in MyoD1.

The MyoD gene was duplicated during the teleost whole genome duplication and, while a second MyoD gene (MyoD2) was subsequently lost from the genomes of some lineages (including zebrafish), many fish lineages (including Alcolapia species) have retained both MyoD paralogues. Here we reveal the expression patterns of the two MyoD genes in Oreochromis (Alcolapia) alcalica using in situ hybridisation. We report our analysis of MyoD1 and MyoD2 protein sequences from 54 teleost species, and show that O. alcalica, along with some other teleosts, include a polyserine repeat between the amino terminal transactivation domains (TAD) and the cysteine-histidine rich region (H/C) in MyoD1. The evolutionary history of MyoD1 and MyoD2 is compared to the presence of this polyserine region using phylogenetics, and its functional relevance is tested using overexpression in a heterologous system to investigate subcellular localisation, stability, and activity of MyoD proteins that include and do not include the polyserine region.