The <i>Iroquois</i> Complex Is Required in the Dorsal Mesoderm to Ensure Normal Heart Development in <i>Drosophila</i>

<div><p><i>Drosophila</i> heart development is an invaluable system to study the orchestrated action of numerous factors that govern cardiogenesis. Cardiac progenitors arise within specific dorsal mesodermal regions that are under the influence of temporally coordinated actions of multiple signaling pathways. The <i>Drosophila Iroquois</i> complex (<i>Iro-C</i>) consists of the three homeobox transcription factors <i>araucan</i> (<i>ara</i>), <i>caupolican (caup</i>) and <i>mirror (mirr</i>). The <i>Iro-C</i> has been shown to be involved in tissue patterning leading to the differentiation of specific structures, such as the lateral notum and dorsal head structures and in establishing the dorsal-ventral border of the eye. A function for <i>Iro-C</i> in cardiogenesis has not been investigated yet. Our data demonstrate that loss of the whole <i>Iro</i> complex, as well as loss of either <i>ara/caup</i> or <i>mirr</i> only, affect heart development in <i>Drosophila</i>. Furthermore, the data indicate that the GATA factor Pannier requires the presence of <i>Iro-C</i> to function in cardiogenesis. Furthermore, a detailed expression pattern analysis of the members of the <i>Iro-C</i> revealed the presence of a possibly novel subpopulation of Even-skipped expressing pericardial cells and seven pairs of heart-associated cells that have not been described before. Taken together, this work introduces <i>Iro-C</i> as a new set of transcription factors that are required for normal development of the heart. As the members of the <i>Iro-C</i> may function, at least partly, as competence factors in the dorsal mesoderm, our results are fundamental for future studies aiming to decipher the regulatory interactions between factors that determine different cell fates in the dorsal mesoderm.</p>