poky/chuk/ikk1 is required for differentiation of the zebrafish embryonic epidermis

Abstract

An epidermis surrounds all vertebrates, forming a water barrier between the external environment and the internal space of the organism. In the zebrafish, the embryonic epidermis consists of an outer enveloping layer (EVL) and an inner basal layer that have distinct embryonic origins. Differentiation of the EVL requires the maternal effect gene poky/ikk1 in EVL cells prior to establishment of the basal layer. This requirement is transient and maternal Ikk1 is sufficient to allow establishment of the EVL and formation of normal skin in adults. Similar to the requirement for Ikk1 in mouse epidermis, EVL cells in poky mutants fail to exit the cell cycle or express specific markers of differentiation. In spite of the similarity in phenotype, the molecular requirement for Ikk1 is different between mouse and zebrafish. Unlike the mouse, EVL differentiation requires functioning Poky/Ikk1 kinase activity but does not require the HLH domain. Previous work suggested that the EVL was a transient embryonic structure, and that maturation of the epidermis required replacement of the EVL with cells from the basal layer. We show here that the EVL is not lost during embryogenesis but persists to larval stages. Our results show that while the requirement for poky/ikk1 is conserved, the differences in molecular activity indicate that diversification of an epithelial differentiation program has allowed at least two developmental modes of establishing a multilayered epidermis in vertebrates.

Requirement of Npc1 and availability of cholesterol for early embryonic cell movements in zebrafish

“…Epiboly defects may be in part due to abnormal cytoskeletal structures, as we observed disruptions in the actin cytoskeleton in npc1 morphants. Unlike some zebrafi sh mutants and morphants that have epiboly delay, Npc1-morphant zebrafi sh did not show a reduction in EVL integrity ( 45,46 ) or any decline to the ability of the leading cells to undergo necessary shape changes during epiboly ( 47 ). The phenotype cannot be attributed to cell death during early developmental stages as we did not detect any increases in apoptosis in these morphant embryos.…”

“…We constructed riboprobes from plasmids containing a selected region of ntl ( 53 ), fkd6 ( 54 ), papc ( 55 ), gsc ( 56 ), krt4 ( 57 ), krt18 ( 58 ), cldnE ( 59 ), krt8 ( 45,46,60,61 ), and sox32 ( 62 ) zebrafi sh genes. Embryos were visualized on a Leica MZ16F microscope equipped with a Leica DFC 490 digital camera.…”

αE-catenin regulates cell-cell adhesion and membrane blebbing during zebrafish epiboly

“…It has been reported that defects in EVL differentiation can induce defects in epiboly (Fukazawa et al, 2010). In order to rule out the possibility that the defect in EVL morphology and the delay in epiboly were caused by a defect in EVL differentiation, we performed ISH for keratin4 (krt4) mRNA at the dome stage (supplementary material Fig.…”

A toolbox to study epidermal cell types in zebrafish

“…1) and acts similarly in oxygen exchange (McLeish et al, 2010;Schwerte, 2010). The basal layer consists of cells that express the epithelial stem cell marker p63 (Bakkers et al, 2002;Lee and Kimelman, 2002), whereas the periderm is an outer superficial layer of differentiated cytokeratin-positive cells (Gong et al, 2002;Wang et al, 2006) that are derived from the enveloping layer (Fukazawa et al, 2010) (Fig. 1A,B).…”

“…Additionally, the epidermis of the developing zebrafish contains several specialized cell types that allow for the exchange of oxygen, ions and macromolecules, similar to mammalian bilayered epithelia (Hwang, 2009;Jevtov et al, 2014;Schwerte, 2010). Mammalian genes involved in epithelial morphogenesis, maintenance and disease conditions are conserved in zebrafish (de la Garza et al, 2013;Fukazawa et al, 2010;Lee and Kimelman, 2002;Li et al, 2011;Sabel et al, 2009;Sonawane et al, 2009). Further, gene function within the epidermis can be readily probed using mutations, morpholinos and chemical inhibitors.…”