Islet-1 marks the early heart rudiments and is asymmetrically expressed during early rotation of the foregut in the chick embryo

Islet-1 (Isl-1), the LIM domain homeobox gene, is a well-known early marker of neuronal specification. Here, we show its spatial and temporal patterns of expression during early heart and gut development in the chick embryo. Isl-1 transcripts are first detected in the early cardiac progenitors and u nderlying endoderm at late stage 4. By stages 5-6, it is also expressed in the prechordal plate. From stage 6 onward, transcripts are also detected in the endoderm forming the anterior intestinal portal and floor of the cauda l foregut. With progressive rostrocaudal fusion of the paired cardiac rudim ents, Isl-1 expression is maintained in the cardiac mesoderm and associated endoderm. By the onset of heart beating, transcripts become restricted to the dorsal mesocardium and more caudal medial splanchnic mesoderm flanking the open gut. Within the foregut, Isl-1 is expressed in the endoderm of the oral membrane, thyroid rudiment, and second pharyngeal pouches, as well as within the second branchial grooves adjacent to the secondary pouches. int erestingly, with the onset of gut rotation, Isl-1 expression is detected un ilaterally in the splanchnic mesodermal wall of the future greater curvatur e of the caudal stomach/rostral duodenum. Thus, Isl-1 is a novel and useful marker of the early cardiac rudiments and of the original left side of the rotating foregut. During early organogenesis, Isl-1 is also expressed in s everal other discrete domains as reported previously. Additionally, it is e xpressed at the interface between the hind limbs and trunk, Anat Rec 260:20 4-207, 2000. (C) 2000 Wiley-Liss, Inc.