Regulation of germ layer mesoderm specification

Regulation of germ layer mesoderm specification

Trithorax proteins and long-intergenic noncoding RNAs are critical regulators of embryonic stem cell pluripotency; however, how they cooperatively regulate germ layer mesoderm specification remains elusive.

Authors report that HoxBlinc RNA first specifies Flk1+ mesoderm and then promotes hematopoietic differentiation through regulation of hoxb pathways. 

HoxBlinc binds to the hoxb genes, recruits Setd1a/MLL1 complexes, and mediates long-range chromatin interactions to activate transcription of the hoxb genes.

Depletion of HoxBlinc by shRNA-mediated knockdown or CRISPR-Cas9-mediated genetic deletion inhibits expression of hoxbgenes and other factors regulating cardiac/hematopoietic differentiation.

Reduced hoxbexpression is accompanied by decreased recruitment of Set1/MLL1 and H3K4me3 modification, as well as by reduced chromatin loop formation. Re-expression of hoxb2–b4 genes in HoxBlinc-depleted embryoid bodies rescues Flk1+ precursors that undergo hematopoietic differentiation.

Thus, HoxBlinc plays an important role in controlling hoxb transcription networks that mediate specification of mesoderm-derived Flk1+ precursors and differentiation of Flk1+ cells into hematopoietic lineages.