BMP/Ventx1.1 axis modulates the multiciliogenesis in the early Xenopus epidermis

In Xenopus laevis, multiciliated cells (MCCs) in epidermis produce coordinated motile cilia to promote fluid flow across epithelial surfaces. In a previous study, it has been reported that Bmp signaling negatively regulates the multiciliated cell formation. However, Bmp signaling is required for the early ectodermal patterning and epidermal specification.

In the present study, the requirement of Bmp signaling was examined in ectoderm specification including multiciliogenesis of epidermis. Inhibition of Bmp signaling using a dominant-negative Bmp receptor (Dnbr) decreased MCC formation both in animal cap explants and whole embryos.

Differentially expressed MCC-associated transcripts were confirmed by transcriptome and RT-qPCR analysis of Bmp-inhibited and control animal cap explants. The promoters of multicilia-associated genes including mcidas, foxj1, deup1 and ccno were cloned to examine how Bmp signaling regulated MCC gene expression.

Dnbr-injected embryos consistently showed the reduced promoter activity. However, a direct target gene of Bmp signaling ventx1.1 restored MCC gene expression and promoter activity as well as epidermal marker expression in Dnbr-injected embryos.

Together, the results support a model in which early BMP/Ventx1.1 axis positively modulates epidermal multiciliogenesis at least in part by establishing epidermal competence through ventx1.1 associated transcriptional programs.