Zebrafish mll Gene Is Essential for Hematopoiesis

Abstract

Studies implicate an important role for the mixed lineage leukemia (Mll) gene in hematopoiesis, mainly through maintaining Hox gene expression. However, the mechanisms underlying Mll-mediated hematopoiesis during embryogenesis remain largely unclear. Here, we investigate the role of mll during zebrafish embryogenesis, particularly hematopoiesis. Mll depletion caused severe defects in hematopoiesis as indicated by a lack of blood flow and mature blood cells as well as a significant reduction in expression of hematopoietic progenitor and mature blood cell markers. Furthermore, mll depletion prevented the differentiation of hematopoietic progenitors. In addition, we identified the N-terminal mini-peptide of Mll that acted as a dominant negative form to disrupt normal function of mll during embryogenesis. As expected, mll knockdown altered the expression of a subset of Hox genes. However, overexpression of these down-regulated Hox genes only partially rescued the blood deficiency, suggesting that mll may target additional genes to regulate hematopoiesis. In the mll morphants, microarray analysis revealed a dramatic up-regulation of gadd45␣a. Multiple assays indicate that mll inhibited gadd45␣a expression and that overexpression of gadd45␣a mRNA led to a phenotype similar to the one seen in the mll morphants. Taken together, these findings demonstrate that zebrafish mll plays essential roles in hematopoiesis and that gadd45␣a may serve as a potential downstream target for mediating the function of mll in hematopoiesis.

The epigenetic factor Kmt2a/Mll1 regulates neural progenitor proliferation and neuronal and glial differentiation

“…The sequence and expression of kmt2a have been reported previously (Robinson et al, ; Wan et al, ). We performed expression analysis with more focus on the developing nervous system and found that kmt2a was ubiquitously expressed in the entire embryo from four‐cell stage but later restricted in the brain from 48‐hours postfertilization (hpf), as previously described [Fig.…”

“…Mice harboring a truncation of Kmt2a exhibit various phenotypes, such as failure of preimplantation (Ayton et al, ), fetal liver hematopoiesis (Yagi et al, ), and acute leukemia (Dobson et al, ), depending on the particular allele knocked out and the tissues in, which Kmt2a was deleted. Furthermore, knockdown of Kmt2a expression in zebrafish embryos resulted in hematopoietic defects, which is a conserved phenotype observed in mammals (Wan et al, ). These studies demonstrated the important role of KMT2A in hematopoiesis at both physiological and pathological levels.…”

Eafs Control Erythroid Cell Fate by Regulating c-myb Expression through Wnt Signaling

“…In the late stage, in eaf s morphants at 2 dhf, we observed significant defects including heart edema, reduced circular blood cells, and a lack of blood flow or clumps of blood cells located in front of the beating heart in embryos knockdown both of eaf1 and eaf2 (data not shown), suggesting that the eaf s morphants displayed hematopoietic defects, as observed in mll morphants [30]. Here, in order to further test the molecular characters underlying the phenotypes, we applied blood markers to detect the hematopoietic defects in eafs morphants.…”

Zebrafish hoxd4a Acts Upstream of meis1.1 to Direct Vasculogenesis, Angiogenesis and Hematopoiesis

“…DIG- labeled antisense RNA probes were transcribed from linearized template using T3, T7 or SP6 RNA polymerase (Roche). Probes for hoxb6b and hoxb7a were derived by RT-PCR-mediated amplification from RNA from 26–28 hpf embryos using primers described in Wan et al [42]. Embryos were incubated with anti-DIG antibody (Roche) and probes were detected using NBT/BCIP (nitro blue tetrazolium chloride/5-bromo-4-chloro-3-indolyl phosphate, toluidine salt) from Roche.…”