An Irf6-Esrp1/2 regulatory axis controls midface morphogenesis in vertebrates

ABSTRACTIrf6 and Esrp1 are important for palate development across vertebrates. In zebrafish, we found that irf6 regulates the expression of esrp1. We detailed overlapping Irf6 and Esrp1/2 expression in mouse orofacial epithelium. In zebrafish, irf6 and esrp1/2 share expression in periderm, frontonasal ectoderm and oral epithelium. Genetic disruption of irf6 and esrp1/2 in zebrafish resulted in cleft of the anterior neurocranium. The esrp1/2 mutant also developed cleft of the mouth opening. Lineage tracing of cranial neural crest cells revealed that the cleft resulted not from migration defect, but from impaired chondrogenesis. Analysis of aberrant cells within the cleft revealed expression of sox10, col1a1 and irf6, and these cells were adjacent to krt4+ and krt5+ cells. Breeding of mouse Irf6; Esrp1; Esrp2 compound mutants suggested genetic interaction, as the triple homozygote and the Irf6; Esrp1 double homozygote were not observed. Further, Irf6 heterozygosity reduced Esrp1/2 cleft severity. These studies highlight the complementary analysis of Irf6 and Esrp1/2 in mouse and zebrafish, and identify a unique aberrant cell population in zebrafish expressing sox10, col1a1 and irf6. Future work characterizing this cell population will yield additional insight into cleft pathogenesis.

STUDIES ON RABBIT LYMPHOCYTES IN VITRO

Specific antisera directed against all six of the well characterised allotypic determinants of rabbit IgG (As1, 2, 3, 4, 5, and 6) are capable of inducing blast transformation and DNA synthesis when added to lymphocyte cultures obtained from donor rabbits having the appropriate IgG allotype. Mixtures of antisera directed against two different allotypic determinants induce a "summation" of transformation and DNA synthesis over and above the effect of mixtures of two antisera directed against the same allotypic determinant. This summation effect is observed regardless of whether the antisera which have been mixed are directed against allotypic determinants controlled by the same locus or by different loci. The finding that summation occurs with mixtures of two antisera directed against both the allotypic determinants of a double homozygote rabbit (As1, 6) suggests that lymphocytes from the peripheral blood may be primed to produce only one or the other of the two polypeptide chains of IgG, but not both.