Guest Talk - Spatial Patterning of the Lateral Plate Mesoderm in Xenopus

The transcription factor hand1 is expressed in the heart, lateral plate mesoderm (LPM) and neural crest cells during development. Hand1-null mice die early in embryogenesis due to defects in the heart and placenta. Due to this lethality, our understanding of the range of functions for HAND1 in early development remains incomplete. In Xenopus, we observed that changes in the hand1 expression patterns correlate very closely with development of specific LPM derivatives, leading us to hypothesize that these changes in hand1 expression are required for normal development of specific LPM lineages. We compared the development of different LPM lineages in hand1 knockdown and overexpression models in Xenopus. As in the mouse, we found that Hand1 is required for proper heart morphogenesis. Hand1 is also required for the formation of a complex vascular plexus within embryos by maintaining early endothelial cell populations, however, hand1 overexpression is not sufficient to induce endothelial cell differentiation. Furthermore, downregulation of hand1 is critical for expansion of the hematopoietic lineages. These findings confirm a conserved role of Hand1 in heart morphogenesis and suggest regulation of Hand1 levels is critical for normal lineage development in the LPM.