The Drosophila homeobox genes zfh-1 and even-skipped are required for cardiac-specific differentiation of a numb-dependent lineage decision

A series of inductive signals are necessary to subdivide the mesoderm in or der to allow the formation of the progenitor cells of the heart. Mesoderm-e ndogenous transcription factors, such as those encoded by twist and tinman, seem to cooperate with these signals to confer correct context and compete nce for a cardiac cell fate. Additional factors are likely to be required f or the appropriate specification of individual cell types within the formin g heart. Similar to tinman, the zinc finger- and homeobox-containing gene, zfh-1, is expressed in the early mesoderm and later in the forming heart, s uggesting a possible role in heart development. Here, we show that Zfh-1 is specifically required for formation of the even-skipped (eve)-expressing s ubset of pericardial cells (EPCs), without affecting the formation of their siblings, the founders of a dorsal body wall muscle (DA1). In addition to zfh-1, mesodermal eve itself appears to be needed for correct EPC different iation, possibly as a direct target of Zfh-1. Epistasis experiments show th at zfh-1 specifies EPC development independently of numb, the lineage gene that controls DA1 founder versus EPC cell fate. We discuss the combinatoria l control mechanisms that specify the EPC cell fate in a spatially precise pattern within the embryo.