The gene <i>tinman</i> is required for specification of the heart and visceral muscles in <i>Drosophila</i>

TLDR

Tinman, a homeobox gene, is expressed in the mesoderm primordium and later restricted to visceral mesoderm and heart, a pattern that depends on the mesoderm determinant twist. The study demonstrates that tinman is required for the development of visceral muscle and heart. Ubiquitous expression of tinman cDNA via a heat‑shock promoter partially restores heart cells and visceral mesoderm in tinman‑mutant embryos. tinman mutants lack visceral mesoderm and heart primordia, exhibit impaired endoderm fusion, yet somatic body‑wall muscles develop abnormally, showing that tinman is one of the earliest genes essential for heart development and early mesodermal subdivision.

Abstract

ABSTRACT The homeobox-containing gene tinman (msh-2, Bodmer et al., 1990Development 110, 661-669) is expressed in the mesoderm primordium, and this expression requires the function of the mesoderm determinant twist. Later in development, as the first mesodermal subdivisions are occurring, expression becomes limited to the visceral mesoderm and the heart. Here, I show that the function of tinman is required for visceral muscle and heart development. Embryos that are mutant for the tinman gene lack the appearance of visceral mesoderm and of heart primordia, and the fusion of the anterior and posterior endoderm is impaired. Even though tinman mutant embryos do not have a heart or visceral muscles, many of the somatic body wall muscles appear to develop although abnormally. When the tinman cDNA is ubiquitously expressed in tinman mutant embryos, via a heatshock promoter, formation of heart cells and visceral mesoderm is partially restored. tinman seems to be one of the earliest genes required for heart development and the first gene reported for which a crucial function in the early mesodermal subdivisions has been implicated.