Epithelial signals regulate pigpen expression during craniofacial morphogenesis
Description
Peptide growth factors mediate epithelial-mesenchytnal interactions during organogenesis. In vitro, the expression of Pigpen, a nuclear protein, was shown to correlate with growth factor-mediated changes in proliferation and differentiation in bovine endothelial cells (Alliegro and Alliegro, 1996b). Although a number of functions have been proposed for Pigpen, the role Pigpen might play during growth factor-mediated inductive events during embryogenesis has not been determined. To begin to elucidate the role of pigpen in mouse embryogenesis. I cloned the mouse homologue of pigpen and investigated the regulation of its expression during embryogenesis. Sequence analysis of the mouse cDNA indicated that it was 89% and 95% identical to the bovine homologue at the nucleotide and amino acid levels, respectively. Immunocytochemical studies demonstrated that pigpen expression was concentrated in large nuclear granules in mouse embryonic cells, and CAT assays showed that the putative transcriptional activation domain in the 5 ' end of the protein was active in vitro. In situ hybridization analyses demonstrated that pigpen showed a ubiquitous expression pattern early in postimplantation development [on embryonic day 9.5 (E9.5)], which was followed by a pattern of more restricted expression during later organogenesis. At E10.5 pigpen expression was elevated in the mandible, other facial primordia, the limbs, and in the neural epithelium, and by E13.5 pigpen was strongly expressed in the retina, trigeminal ganglion, and dorsal root ganglion. The pattern of pigpen expression was striking in a number of organ primordia including the tooth, vibrissae, eye, lung, and kidney. Because growth factor-mediated epithelial-mesenchymal interactions are vital for the formation of all these organs, I asked how such interactions might regulate pigpen expression at a specific site, that is, in the developing mandible. In vitro assays indicated that epithelial signals were required to maintain pigpen expression in the mandibular mesenchyme and bead implantation assays demonstrated that FGF-8, and to a lesser extent FGF-9, positively regulated pigpen expression in the mesenchyme. In contrast, BMP-4 repressed the expression of pigpen. These data suggest that mouse pigpen operates downstream of specific growth factors and could activate genetic pathways that regulate proliferation and/or differentiation during craniofacial morphogenesis in the mouse embryo