Evidence for two distinct waves of epidermal ionocyte differentiation during medaka embryonic development

Abstract

Background: The fish epidermis contains specific cells, or ionocytes, that are specialized in ion transport and contribute to the osmoregulatory function. Besides the zebrafish model, the medaka (Oryzias latipes) has recently emerged as an important model for osmoregulation studies because it possesses a particularly high adaptability to salinity changes. However, hindering the progress of research on embryonic ionocytes is the lack of a comprehensive view of their developmental dynamic. Results: Using EdU integrations and the foxi3 and NKA markers, we characterized the proliferating progenitors of ionocytes (here called ionoblastes) and we quantified them, along with ionocytes, during embryogenesis. While progenitors of the vitellin zone promptly differentiate in a synchronous manner, progenitors of the lateral zone differentiate progressively and asynchronously. Furthermore, we evidenced that nhe3 is expressed in differentiated ionocytes of both zones, whereas ecac, ncc, and gcm2 are strictly specific of the lateral zone. We also evidenced that the two zones are differentially regulated in distilled water and seawater. Conclusions: Our data led us to propose a model timeline, which provides evidence for the expansion of two successive and distinct populations of ionocytes. This model opens the way for new studies related to epidermal development, plasticity and osmoregulation ontogeny. Developmental Dynamics 244:888-902, 2015. V C 2015 Wiley Periodicals, Inc.

A mesenchymal to epithelial switch in Fgf10 expression specifies an evolutionary-conserved population of ionocytes in salivary glands

“…We discovered an unexpected switch of FGF10 expression during the second postnatal week from mesenchymal cells to epithelial duct cells. Furthermore, the adult epithelial FGF10 pos population resembles Ascl3 -expressing (ASCL3 pos ) duct cells ( Bullard et al, 2008 ; Rugel-Stahl et al, 2012 ) and expresses molecular signatures that are characteristic of an ancient ionocyte cell type found in fish and frog, conserved into mouse and human ( Chen et al, 2017 , 2019 ; Hsu et al, 2014 ; Trayer et al, 2015 ). Importantly, FGF10 pos cells highly express Cftr , which is critical for exocrine secretion ( Noel et al, 2008 ; Shin et al, 2016 ; Yokoyama et al, 2019 ; Zeng et al, 2017 ).…”