A Feasible Role of Neuropilin Signaling in Pharyngeal Pouch Formation in Zebrafish

Abstract

Pharyngeal pouches are an important epithelial structure controlling facial skeletal development in vertebrates. A series of pouches arise sequentially in the pharyngeal endoderm through collective cell migration followed by rearrangement of pouch-forming cells. While crucial transcription factors and signaling molecules have been identified in pouch formation, a role for Neuropilins (Nrps) in pouch development has not yet been analyzed in any vertebrates. Nrps are cell surface receptors essential for angiogenesis and axon guidance. In all vertebrates, the two Nrp family members, Nrp1 and Nrp2, are conserved in the genome, with two paralogs for Nrp1 (Nrp1a and Nrp1b) and Nrp2 (Nrp2a and Nrp2b) being identified in zebrafish. Here, I report a potential requirement of Nrp signaling in pouch development in zebrafish. nrp1a and nrp2b were expressed in the developing pouches, with sema3d, a ligand for Nrps, being expressed in the pouches. Knocking down Nrps signaling in the pharyngeal endoderm led to severe defects in pouches and facial cartilages. In addition, blocking Mitogen-activated protein kinase (MAPK) activities, a downstream effector of Nrp signaling, in the pharyngeal endoderm caused similar defects in pouches and facial skeleton to those by knocking down Nrps signaling. My results suggest that Nrp signaling acts for pouch formation through MAPK.

A Potential Role of fgf4, fgf24, and fgf17 in Pharyngeal Pouch Formation in Zebrafish

“…Loss of Tbx1, Pax1, and Foxi1 transcription factors and Fgf ligands led to loss or malformation of pouches and facial skeletons in mice and zebrafish ( Lindsay et al, 2001 ; Nissen et al, 2003 ; Piotrowski et al, 2003 ; Tran et al, 2011 ; Okada et al, 2016 ; Jin et al, 2018 ; Liu et al., 2020 ). In zebrafish, Wnt, Ephrin, and VEGF-C signaling molecules are also required for pouch formation, with Neuropilin signaling being implied in pouch formation ( Crump et al, 2004 ; Ober et al, 2004 ; Choe et al, 2013 ; Choe & Crump, 2014 ; Choe, 2023 ). To control pouch formation, Pax1 regulates the expression of tbx1 and fgf3 in the pharyngeal endoderm in medaka and zebrafish, with Foxi1 regulating wnt4a expression in zebrafish ( Okada et al, 2016 ; Jin et al, 2018 ; Liu et al, 2020 ).…”