Rispoli, R. | bioRxiv Science

bioRxiv2019

A zebrafish model for MonoMAC syndrome identifies an earlier role for gata2 in haemogenic endothelium programming and generation of haematopoietic stem cells

Haematopoietic stem and progenitor cells (HSPCs) maintain the vertebrate blood system throughout life and their emergence from haemogenic endothelium (HE) is regulated by transcription factors such as Gata2. Here we deleted a conserved enhancer (i4 enhancer) driving pan-endothelial expression of gata2a and showed that Gata2a is required for HE programming by regulating expression of runx1 and of the second zebrafish Gata2 orthologue, gata2b. By 5 days, homozygous gata2a{Delta}i4/{Delta}i4 larvae showed normal numbers of HSPCs, a recovery mediated by Notch signalling driving gata2b and runx1 expression in HE. However, gata2a{Delta}i4/{Delta}i4 adults showed oedema, susceptibility to infections and marrow hypo-cellularity, consistent with bone marrow failure found in GATA2 deficiency syndromes. Thus, gata2a expression driven by the i4 enhancer is required for HE programming in embryos and maintenance of steady-state haematopoietic stem cell output in the adult. These enhancer mutants are a new paradigm to explore the pathophysiology of GATA2-related deficiencies in vivo.

developmental biology↗

bioRxiv2018

Vegfa expression is activated through positive and negative transcriptional regulatory networks controlled by the ETS factor Etv6 in vivo

VEGFA signaling is crucial for physiological and pathological angiogenesis and hematopoiesis. Although many context-dependent signaling pathways downstream of VEGFA have been uncovered, vegfa transcriptional regulation in vivo remains unclear. Here we show that the ETS transcription factor, Etv6, positively regulates vegfa expression during Xenopus blood stem cell development through multiple transcriptional inputs. In agreement with its established repressive functions, Etv6 directly inhibits the expression of the vegfa repressor, foxo3. Surprisingly, it also directly activates the expression of the vegfa activator, klf4. Finally, it indirectly binds to the vegfa promoter where it co-localizes with Klf4. Klf4 deficiency downregulates vegfa expression and significantly decreases Etv6 binding to the vegfa promoter, indicating that Klf4 recruits Etv6 to the vegfa promoter. Thus, our work uncovers a dual function for Etv6, as both a transcriptional repressor and activator, in controlling a major signaling pathway involved in blood and endothelial development in vivo. Given the established relationships between development and cancer, this elaborate gene regulatory network may inform new strategies for the treatment of VEGFA-dependent tumorigenesis.

developmental biology↗