Novel spikey ionocytes are regulated by cortisol in the skin of an amphibious fish

• Published in: Proceedings of the Royal Society. B, Biological sciences Vol. 288; no. 1965; p. 20212324
• Main Authors: Ridgway, Megan R, Tunnah, Louise, Bernier, Nicholas J, Wilson, Jonathan M, Wright, Patricia A
• Format: Journal Article
• Language: English
• Published: England The Royal Society 22.12.2021
• Subjects: Animals; Cyprinodontiformes - physiology; Development and Physiology; Gills - anatomy & histology; Hydrocortisone; Metyrapone; Skin; Water; Kryptolebias marmoratus; metyrapone; gill; ions; ionoregulation; fish
• ISSN: 0962-8452; 1471-2954
• DOI: 10.1098/rspb.2021.2324

Cortisol is a major osmoregulatory hormone in fishes. Cortisol acts upon the gills, the primary site of ionoregulation, through modifications to specialized ion-transporting cells called ionocytes. We tested the hypothesis that cortisol also acts as a major regulator of skin ionocyte remodelling in the amphibious mangrove rivulus ( ) when gill function ceases during the water-to-land transition. When out of water, demonstrated a robust cortisol response, which was linked with the remodelling of skin ionocytes to increase cell cross-sectional area and Na -K -ATPase (NKA) content, but not when cortisol synthesis was chemically inhibited by metyrapone. Additionally, we discovered a novel morphology of skin-specific ionocyte that are spikey with multiple cell processes. Spikey ionocytes increased in density, cell cross-sectional area and NKA content during air exposure, but not in metyrapone-treated fish. Our findings demonstrate that skin ionocyte remodelling during the water-to-land transition in amphibious fish is regulated by cortisol, the same hormone that regulates gill ionocyte remodelling in salinity-challenged teleosts, suggesting conserved hormonal function across diverse environmental disturbances and organs in fishes.