Ugo Coppola

Craniofacial malformations arise from developmental defects in the head, face, and neck with phenotypes such as 22q11.2 deletion syndrome illustrating a developmental link between cardiovascular and craniofacial morphogenesis. NKX2-5 is a key cardiac transcription factor associated with congenital heart disease and mouse models of Nkx2-5 deficiency highlight roles in cardiac development. In zebrafish, nkx2.5 and nkx2.7 are paralogues in the NK4 family expressed in cardiomyocytes and pharyngeal arches. Despite shared cellular origins of cardiac and craniofacial tissues, the function of NK4 factors in head and neck patterning has not been elucidated. Molecular evolutionary analysis of NK4 genes shows that nkx2.5 and nkx2.7 are ohnologs resulting from whole genome duplication events. Nkx2.7 serves as a previously unappreciated regulator of branchiomeric muscle and cartilage formation for which nkx2.5 cannot fully compensate. Mechanistically, our results highlight that Nkx2.7 patterns the cranial neural crest and functions upstream of Endothelin1 to inhibit Notch signals. Together, our studies shed light on an evolutionarily conserved Nkx transcription factor with unique functions in vertebrate craniofacial development, advancing our understanding of congenital head and neck deformities.

Nr2f transcription factors (TFs) are conserved regulators of vertebrate atrial cardiomyocyte (AC) differentiation. However, little is known about the mechanisms directing Nr2f expression in ACs. Here, we identified a conserved enhancer 3' to the nr2f1a locus, which we call 3'reg1-nr2f1a (3'reg1), that can promote Nr2f1a expression in ACs. Sequence analysis of the enhancer identified putative Lef/Tcf and Foxf TF binding sites. Mutation of the Lef/Tcf sites within the 3'reg1 reporter, knockdown of Tcf7l1a, and manipulation of canonical Wnt signaling support that Tcf7l1a is derepressed via Wnt signaling to activate the transgenic enhancer and promote AC differentiation. Similarly, mutation of the Foxf binding sites in the 3'reg1 reporter, coupled with gain- and loss-of-function analysis supported that Foxf1 promotes expression of the enhancer and AC differentiation. Functionally, we find that Wnt signaling acts downstream of Foxf1 to promote expression of the 3'reg1 reporter within ACs and, importantly, both Foxf1 and Wnt signaling require Nr2f1a to promote a surplus of differentiated ACs. CRISPR-mediated deletion of the endogenous 3'reg1 abrogates the ability of Foxf1 and Wnt signaling to produce surplus ACs in zebrafish embryos. Together, our data support that downstream members of a conserved regulatory network involving Wnt signaling and Foxf1 function on a nr2f1a enhancer to promote AC differentiation in the zebrafish heart.