Dogmas and controversies in the handling of nitrogenous wastes: osmoregulation during early embryonic development in the marine little skate Raja erinacea; response to changes in external salinity.
TLDR
The data indicate that little skate embryos synthesize and retain urea, as well as a suite of other osmolytes, in order to regulate osmotic balance with the external environment.Abstract:
SUMMARY Marine elasmobranchs retain relatively high levels of urea to
counterbalance the osmotic strength of seawater. Oviparous species, such as
the little skate Raja erinacea , release encapsulated embryos that
hatch after about 9 months on the seafloor. To study the ureosmotic capability
of skate embryos, we measured a variety of possible osmolytes and
ornithine–urea cycle (OUC) enzyme activities in little skate embryos,
and determined their physiological response to dilute seawater (75% SW)
exposure relative to controls (100% SW). The urea:trimethylamine oxide (TMAO)
+ other osmolytes ratio was 2.3–2.7:1. At the earliest stage of
development investigated (4 months), there were significant levels of the key
OUC enzyme, carbamoyl phosphate synthetase III, as well as ornithine
transcarbamoylase, arginase and glutamine synthetase, providing evidence for a
functional OUC. Embryos (4 and 8 months) survived and recovered from exposure
to 5 days of 75% SW. There was a significant increase in the rate of urea
excretion (five- to tenfold), no change in OUC enzyme activities, and
significant decreases in the tissue content of urea, TMAO and other osmolytes
in embryos exposed to 75% SW compared to 100% SW. Taken together, the data
indicate that little skate embryos synthesize and retain urea, as well as a
suite of other osmolytes, in order to regulate osmotic balance with the
external environment. Interestingly, these ureosmotic mechanisms are in place
as early as 4 months, around the time at which the egg capsule opens and the
embryo is in more direct contact with the external environment.read more
Citations
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Vertebrate vitellogenin gene duplication in relation to the "3R hypothesis": correlation to the pelagic egg and the oceanic radiation of teleosts.
TL;DR: Bayesian analysis is used to examine the evolution of vertebrate Vtg genes in relation to the “3R hypothesis” of whole genome duplication (WGD) and the functional end points of LvH degradation during oocyte maturation to find that teleost Vtgs have experienced a post-R3 lineage-specific gene duplication to form paralogous clusters that correlate to the pelagic and benthic character of the eggs.
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Osmoregulation in elasmobranchs: a review for fish biologists, behaviourists and ecologists
TL;DR: A broad review of osmoregulation in elasmobranchs for non-specialists, focusing on recent advances, is provided, highlighting the contribution of drinking and eating processes in maintaining osmotic consistency.
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SkateBase, an elasmobranch genome project and collection of molecular resources for chondrichthyan fishes.
Jennifer T. Wyffels,Benjamin L. King,James J. Vincent,Chuming Chen,Cathy H. Wu,Shawn W. Polson +5 more
TL;DR: This study summarizes available data for chondrichthyes and describes resources for one of the largest projects to characterize one of these fish, Leucoraja erinacea, the little skate, serving as the skate genome project portal linking data, research tools, and teaching resources.
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Variability and Conservation in Late Chondrichthyan Development: Ontogeny of the Winter Skate (Leucoraja ocellata)
TL;DR: Despite the similarities of early events related to development of the branchial region and initial outgrowth of the fins, later stages are increasingly characterized by taxon‐specific morphologies making a universal staging table for chondrichthyans less applicable.
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The Little Skate Raja erinacea Exhibits an Extrahepatic Ornithine Urea Cycle in the Muscle and Modulates Nitrogen Metabolism during Low‐Salinity Challenge
TL;DR: Data suggest that a functional OUC may be present in the skeletal muscle tissues of R. erinacea and that enhanced urea excretion rates and the downregulation of the anchor OUC enzyme, arginase, in the liver may be critical in regulating tissue urea content under dilute‐seawater stress.
References
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Methylamine osmoregulatory solutes of elasmobranch fishes counteract urea inhibition of enzymes
Paul H. Yancey,George N. Somero +1 more
TL;DR: The relief from urea perturbation afforded by these methylamines may have precluded the requirement for widespread modifications in the sequences of elasmobranch proteins to allow these proteins to function in the presence of perturbing urea concentrations.
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Water Stress, Osmolytes and Proteins1
TL;DR: Organic osmolytes are small solutes used by cells of numerous water-stressed organisms and tissues to maintain cell volume and have led to proposed uses in biotechnology, agriculture and medicine, including improved biochemical methods, in vitro rescue of misfolded proteins in cystic fibrosis and prion diseases, and plants engineered for drought and salt tolerance.
Journal ArticleDOI
Biochemical and environmental perspectives on nitrogen metabolism in fishes
TL;DR: This review focuses on aspects of the formation, transport, detoxification and excretion of the two most important nitrogenous products of fishes: ammonia and urea.
Journal ArticleDOI
Intracellular osmoregulatory role of amino acids and urea in marine elasmobranchs.
RP Forster,L Goldstein +1 more
TL;DR: The osmoregulatory importance of the free amino acid pool in erythrocytes and muscle was a particularly prominent feature in both species and regulation of muscle cell volume was associated with sharp declines in cellular concentrations of total amino acids (ninhydrin-positive materials) and urea.
Journal ArticleDOI
Growth, aerobic metabolism, and dissolved oxygen requirements of embryos and alevins of steelhead, Salmo gairdneri
TL;DR: Indirect calorimetry was used to estimate metabolic rates and critical dissolved oxygen concentrations for steelhead at intervals between fertilization and complete yolk exhaustio...