The pioneer gene, apontic, is required for morphogenesis and function of the Drosophila heart

In an effort to isolate genes required for heart development and to further our understanding of cardiac specification at the molecular level, we scre ened PlacZ enhancer trap lines for expression in the Diosophila heart. One of the lines generated in this screen, designated B2-2-15, was particularly interesting because of its early pattern of expression in cardiac precurso r cells, which is dependent on the homeobox gene tinman, a key determinant of heart development in Drosophila. We isolated and characterized a gene in the vicinity of B2-2-15 that exhibits an identical expression pattern than the reporter gene of the enhancer trap. The product of his gene, apontic ( npt; see also Gellon et al., 1997), does not appear to have any homology wi th known genes. apt mutant embryos show distinct abnormalities in heart mor phology as early as mid-embryonic stages when the heat tube assembles, in t hat segments of heart cells (those of myocardial and pericardial identity) are often missing. Most strikingly, however, apr mutant embryos or larvae o nly develop a much reduced heart rate, perhaps because of defects in the as sembly of an intact heart tube and/or because of defects in the function or physiological control of the myocardial cells, which normally mediate hear t contractions. These cardiac defects may be the cause of death of these mu tants during late embryonic or early larval stages. (C) 1999 Elsevier Scien ce Ireland Ltd. All rights reserved.