Urea-based osmoregulation in the developing embryo of oviparous cartilaginous fish (Callorhinchus milii): contribution of the extraembryonic yolk sac during the early developmental period
posted on 2023-05-18, 01:03authored byTakagi, W, Kajimura, M, Tanaka, H, Hasegawa, K, Bell, JD, Toop, T, Donald, JA, Hyodo, S
Marine cartilaginous fish retain a high concentration of urea to maintain the plasma slightly hyperosmotic to the surrounding seawater. In adult fish, urea is produced by hepatic and extrahepatic ornithine urea cycles (OUCs). However, little is known about the urea retention mechanism in developing cartilaginous fish embryos. In order to address the question as to the mechanism of urea-based osmoregulation in developing embryos, the present study examined the gene expression profiles of OUC enzymes in oviparous holocephalan elephant fish (Callorhinchus milii) embryos. We found that the yolk sac membrane (YSM) makes an important contribution to the ureosmotic strategy of the early embryonic period. The expression of OUC enzyme genes was detectable in the embryonic body from at least stage 28, and increased markedly during development to hatching, which is most probably due to growth of the liver. During the early developmental period, however, the expression of OUC enzyme genes was not prominent in the embryonic body. Meanwhile, we found that the mRNA expression of OUC enzymes was detected in the extra-embryonic YSM; the mRNA expression of cmcpsIII in the YSM was much higher than that in the embryonic body during stages 28–31. Significant levels of enzyme activity and the existence of mitochondrial-type cmgs1 transcripts in the YSM supported the mRNA findings. We also found that the cmcpsIII transcript is localized in the vascularized inner layer of the YSM. Taken together, our findings demonstrate for the first time that the YSM is involved in urea-based osmoregulation during the early to mid phase of development in oviparous cartilaginous fish.
History
Publication title
Journal of Experimental Biology
Volume
217
Issue
10
Pagination
1353-1362
ISSN
0022-0949
Department/School
Institute for Marine and Antarctic Studies
Publisher
Company Of Biologists Ltd
Place of publication
Bidder Building Cambridge Commercial Park Cowley Rd, Cambridge, England, Cambs, Cb4 4Dl
Rights statement
Copyright 2014 The Company of Biologists Ltd-distributed under Creative Commons Attribution 3.0 Unported license (CC BY 3.0)