Common genetic control of haemangioblast and cardiac development in zebrafish

Abstract

Over the past few years it has become clear that over half of the mammalian heart derives from outside the heart field as originally defined. Such a second heart field, however, has not been described in zebrafish, which could explain its smaller, two-chambered heart. Instead, zebrafish have a population of haemangioblasts, which is absent in mammalian embryos, raising the possibility that these cells represent the evolutionary ancestor of the second heart field. Here, we show for the first time that the genetic programmes of these anterior haemangioblasts and the adjacent heart field are co-regulated, by transcription factors previously associated with heart but not blood or endothelial development. We demonstrate that gata4, gata5 and gata6 are essential for anterior haemangioblast specification, and for subsequent myelopoiesis, acting as early as cloche and upstream of scl. The requirement for gata4, gata5 and gata6 in myeloid, endothelial and cardiac specification is in the mesoderm, but these factors also control, from within the endoderm and the yolk syncytial layer, the migration of the cardiac precursors as they differentiate. This genetic link between the blood/endothelial and cardiac programmes supports the notion that this haemangioblast population in zebrafish is an evolutionary antecedent of the second heart field, and has implications for the differentiation of haemangioblasts and cardiomyocytes from pluripotent cells, and for the origins of stem cells in the adult heart. KEY WORDS: Myelopoiesis, Cardiogenesis, GATA factors, Second heart field, Haemangioblasts, Transcriptional regulation, Evolution, Adult stem cells, Zebrafish Development 136, 1465Development 136, -1474Development 136, (2009 DEVELOPMENT 1466 the first time that they are crucial for anterior haemangioblast formation and subsequent myelopoiesis. This requirement is within the mesoderm, although we also show that gata5 and gata6 are required in the yolk syncytial layer (YSL) and the endoderm for the correct migration of cardiac precursors. The ablation of both cardiac and haemangioblast programmes within the ALM suggests that these GATA factors lie at the top of a genetic cascade that is initially common to both of these two lineages. This is confirmed by the continued expression of gata4, gata5 and gata6 in scl morphants and cloche mutants, suggesting that these GATA factors lie upstream of, or parallel to, these well-described blood and endothelial regulatory factors. These data genetically link the anterior haemangioblast and cardiac fields, and are consistent with the former being the evolutionary ancestor of the latter. MATERIALS AND METHODS In situ hybridisation of zebrafish embryosWild-type and cloche [Clo m39 ] (Stainier, 2001) zebrafish were bred, maintained, and embryos raised and staged using standard conditions (Westerfield, 1993). In situ hybridisations on zebrafish embryos were carried out as previously described (Jowett, 2001). All RNA probes used were labelled with digoxigenin (DIG) and detection of the antibody-...

A short history of hemogenic endothelium

“…These hematopoietic cells resembled the transient population of erythromyeloid progenitors also found in the yolk sac [13], indicating their transient nature. In this the cardiac endothelium bears reminiscence of the anterior hemangioblast-derived cells in zebrafish [68] and Drosophila [69].…”

Ncor1 and Ncor2 play essential but distinct roles in zebrafish primitive myelopoiesis

“…Given that spi1b þ cells are derived from anterior hemangioblasts that are the precursors of myeloid cells, head endothelium and endocardium (Lieschke et al, 2002;Peterkin et al, 2009;Xu et al, 2012), we next examined expressions of tal1, lmo2, and etv2, the master regulators that control the development of hemangioblasts (Sumanas et al, 2008;Ellett and Lieschke, 2010), in the ncor morphants. Performing whole-mount in situ hybridization, we found that the expressions of tal1, lmo2, and etv2 were not affected in either ncor2 or ncor1 morphants at 10-somite stage (Fig.…”

“…Zebrafish tal1 and lmo2 are known the master regulators that control the development of anterior hemangioblasts that give rise to myeloid cells (Sumanas et al, 2008;Peterkin et al, 2009;Ellett and Lieschke, 2010). To examine whether overexpressions of tal1 and lmo2 could rescue the depleted myeloid cells in ncor2 morphants, we microinjected tal1 and lmo2 mRNAs into zebrafish embryos together with ncor2 MO.…”

“…In zebrafish primitive myelopoieses, spi1b 1 myeloid cells are derived from tal1 1 cells (Lieschke et al, 2002;Rhodes et al, 2005;Peterkin et al, 2009;Ellett and Lieschke, 2010;Xu et al, 2012). spi1b has been reported to be directly regulated by nuclear protein Gata1a and Gata2a in hematopoietic development (Chou et al, 2009).…”

“…gata4/5/6 are known to lie on the top position of the genetic hierarchy above cloche and tal1 controlling primitive myelopoiesis. Depleted expressions of gata4/5/6 blocked the formation of anterior hemangioblasts by abolishing the expressions of tal1 and lmo2, the two master regulators of hemangioblasts, in the rostral end of ALPM (anterior lateral plate mesoderm) (Peterkin et al, 2009). Retinoic acid (RA), a derivative of vitamin A, has been demonstrated to play a variety of crucial roles in vertebrate early development (Niederreither and Dolle, 2008).…”