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.
15 May 2004-The Journal of Experimental Biology (The Company of Biologists Ltd)-Vol. 207, Iss: 12, pp 2021-2031
TL;DR: 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.
Citations
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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.
Abstract: The spiny ray-finned teleost fishes (Acanthomorpha) are the most successful group of vertebrates in terms of species diversity. Their meteoric radiation and speciation in the oceans during the late Cretaceous and Eocene epoch is unprecedented in vertebrate history, occurring in one third of the time for similar diversity to appear in the birds and mammals. The success of marine teleosts is even more remarkable considering their long freshwater ancestry, since it implies solving major physiological challenges when freely broadcasting their eggs in the hyper-osmotic conditions of seawater. Most extant marine teleosts spawn highly hydrated pelagic eggs, due to differential proteolysis of vitellogenin (Vtg)-derived yolk proteins. The maturational degradation of Vtg involves depolymerization of mainly the lipovitellin heavy chain (LvH) of one form of Vtg to generate a large pool of free amino acids (FAA 150–200 mM). This organic osmolyte pool drives hydration of the ooctye while still protected within the maternal ovary. In the present contribution, we have used Bayesian analysis 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. We 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. Neo-functionalization allowed one paralogue to be proteolyzed to FAA driving hydration of the maturing oocytes, which pre-adapts them to the marine environment and causes them to float. The timing of these events matches the appearance of the Acanthomorpha in the fossil record. We discuss the significance of these adaptations in relation to ancestral physiological features, and propose that the neo-functionalization of duplicated Vtg genes was a key event in the evolution and success of the teleosts in the oceanic environment.
197 citations
Cites background from "Dogmas and controversies in the han..."
...Interestingly, this adaptation is analogous to the oviparous Chondrichthyes that store the organic endproducts of protein metabolism (urea and trimethylamine oxides) in their eggs [143–145]....
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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.
Abstract: This article provides a broad review of osmoregulation in elasmobranchs for non-specialists, focusing on recent advances. Marine and euryhaline elasmobranchs in seawater regulate urea and other body fluid solutes (trimethylamine oxide (TMAO), Na+, Cl−) such that they remain hyper-osmotic to their environment. Salt secretions of the rectal gland and excretions in the urine compensate for continuous inward diffusion of environmental salts. Freshwater and euryhaline elasmobranchs in fresh water synthesise less urea and retain less urea and other body fluid solutes compared to marine elasmobranchs and thus have relatively lower osmolarity. Electrolyte uptake at the gills and kidney reabsorption of salts maintain acid–base balance and ionic consistency. The role of the gills, kidney, liver and rectal gland in elasmobranch osmoregulation is reviewed. The ontogeny of osmoregulatory systems in elasmobranchs and the contribution of drinking and eating processes in maintaining osmotic consistency are discussed. Rec...
69 citations
Cites background from "Dogmas and controversies in the han..."
...Raja erinacea embryos contain significant levels of OUC enzymes as well as synthesise and retain urea, as well as other osmolytes, in order to osmoregulate with changes in external salinity (Steele et al. 2004)....
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...erinacea are in place as early as 4 months, around the time at which the egg capsule opens and the embryo becomes bathed by the external environment (Steele et al. 2004)....
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...These osmoregulatory mechanisms in R. erinacea are in place as early as 4 months, around the time at which the egg capsule opens and the embryo becomes bathed by the external environment (Steele et al. 2004)....
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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.
Abstract: Chondrichthyan fishes are a diverse class of gnathostomes that provide a valuable perspective on fundamental characteristics shared by all jawed and limbed vertebrates. Studies of phylogeny, species diversity, population structure, conservation, and physiology are accelerated by genomic, transcriptomic and protein sequence data. These data are widely available for many sarcopterygii (coelacanth, lungfish and tetrapods) and actinoptergii (ray-finned fish including teleosts) taxa, but limited for chondrichthyan fishes. In this study, we summarize available data for chondrichthyes and describe resources for one of the largest projects to characterize one of these fish, Leucoraja erinacea, the little skate. SkateBase ( http://skatebase.org) serves as the skate genome project portal linking data, research tools, and teaching resources.
65 citations
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.
Abstract: The ontogeny of the northwestern Atlantic batoid, Leucoraja ocellata, is described with special focus on the development of skate specific morphologies and the development of the fins. The results show that the sequence of events involving the early outgrowth of the paired fins and the initial development of the pharyngeal region is remarkably constant in skates, holocephalians, and sharks. However, differences exist in timing of the reshaping of the mandibular arch region, development of branchial filaments, median fins, denticles, and the order of branchial cleft formation. 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. The staging table presented in this study represents an important resource for future studies on batoid embryology.
61 citations
Cites background from "Dogmas and controversies in the han..."
...This need would be caused by factors such as an earlier opening of the egg case to seawater, an event that necessitates having functional osmoregulatory mechanisms in elasmobranchs (Mellinger et al., 1986; Steele et al., 2004)....
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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.
Abstract: Urea synthesis via the hepatic ornithine urea cycle (OUC) has been well described in elasmobranchs, but it is unknown whether OUC enzymes are also present in extrahepatic tissues. Muscle and liver urea, trimethylamine oxide (TMAO), and other organic osmolytes, as well as selected OUC enzymes (carbamoyl phosphate synthetase III, ornithine transcarbamoylase, arginase, and the accessory enzyme glutamine synthetase), were measured in adult little skates (Raja erinacea) exposed to 100% or 75% seawater for 5 d. Activities of all four OUC enzymes were detected in the muscle. There were no changes in muscle OUC activities in skates exposed to 75% seawater; however, arginase activity was significantly lower in the liver, compared to controls. Urea, TMAO, and several other osmolytes were significantly lower in the muscle of little skates exposed to 75% seawater, whereas only glycerophosphorylcholine was significantly lower in the liver. Urea excretion rates were twofold higher in skates exposed to 75% seaw...
53 citations
Cites background from "Dogmas and controversies in the han..."
...Alternatively, the OUC in the muscle may simply be a vestige of an important pathway during early development (Steele et al. 2004)....
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...Similarly, urea excretion rates were elevated within the first 3 h after embryonic R. erinacea were exposed to 75% SW (Steele et al. 2004)....
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...Raja erinacea embryos downregulate tissue urea, TMAO, and/or other organic solutes after 5 d of exposure to 75% seawater (SW; Steele et al. 2004)....
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...Moreover, CPSase III and other OUC-related enzymes have been detected in the muscle of Raja erinacea embryos (Steele et al. 2004)....
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References
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TL;DR: The data indicate that trout embryos have an efficient system to prevent ammonia accumulation in embryonic tissue, by conversion of ammonia to urea in embryonic tissues and through elevation of ammonia levels in the yolk.
Abstract: The present study investigated the role of ammonia as a trigger for hatching, mechanisms of ammonia detoxification and the localization of urea cycle enzymes in the early life stages of freshwater rainbow trout (Oncorhynchus mykiss). The key urea cycle enzyme carbamoyl phosphate synthetase III was found exclusively in the embryonic body (non-hepatic tissues); related enzymes were distributed between the liver and embryonic body. 'Eyed-up' trout embryos were exposed either acutely (2h) to 10 mmol l(-1) NH(4)Cl or chronically (4 days) to 0.2 mmol l(-1) NH(4)Cl. Time to hatching was not affected by either acute or chronic NH(4)Cl exposure. Urea levels, but not ammonia levels in the embryonic tissues, were significantly higher than in controls after both acute and chronic NH(4)Cl exposure, whereas there were no significant changes in urea cycle enzyme activities. Total amino acid levels in the embryonic tissues were unaltered by chronic ammonia exposure, but levels of most individual amino acids and total amino acid levels in the yolk were significantly lower (by 34-58%) than in non-exposed controls. The data indicate that trout embryos have an efficient system to prevent ammonia accumulation in embryonic tissue, by conversion of ammonia to urea in embryonic tissues and through elevation of ammonia levels in the yolk.
60 citations
"Dogmas and controversies in the han..." refers background or methods in this paper
...Skeletal muscle CPSase III has been reported in teleost fish (Julsrud et al., 1998; Kong et al., 1998; Lindley et al., 1999; Todgham et al., 2001; Steele et al., 2001), but to our knowledge never in elasmobranchs....
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...All tissue and yolk samples were prepared for urea analysis as described by Steele et al. (2001), with the following exceptions....
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...Enzyme reactions for GSase, CPSase III, OTCase and arginase were run according to Steele et al. (2001), except that GSase, OTCase and arginase activities were determined by the amount of product produced from 0 to 6·min, while the CPSase III reaction was stopped after 18·min....
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TL;DR: Most marine osmoconformer appear to be stenohaline (unable to cope with large salinity changes, but some are euryhaline, able to adapt), and there should be little cost to maintain internal ion balances, at least for extracellular fluids.
Abstract: Publisher Summary The basic dissolved constituents of cells-potassium yield an osmotic pressure of roughly 300 milliosmolar (mOsm) in most organisms. Because seawater is about 1000 mOsm, marine organisms must have adaptations to maintain cell volume in the face of this potentially dehydrating force. Most marine organisms (invertebrates, protists, and bacteria) are “pure” osmoconformer, with internal osmotic pressures that are equal to or slightly higher than the environment. Thus, there is no tendency to lose water to the environment, Extracellular fluids typically resemble seawater, at least in having similar concentrations of NaCl, and they typically change passively with external changes. Thus, there should be little cost to maintain internal ion balances, at least for extracellular fluids. Most marine osmoconformer appear to be stenohaline (unable to cope with large salinity changes), but some are euryhaline, able to adapt.
46 citations
TL;DR: The results showed that urea-N accounts for about 30% of the total nitrogen excreted under control conditions, and the total units of CPSase III and OCTase in muscle, intestine, and liver appear to be sufficient to account for the observed rate of urea excretion.
45 citations
"Dogmas and controversies in the han..." refers background in this paper
...Skeletal muscle CPSase III has been reported in teleost fish (Julsrud et al., 1998; Kong et al., 1998; Lindley et al., 1999; Todgham et al., 2001; Steele et al., 2001), but to our knowledge never in elasmobranchs....
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TL;DR: It is found that forty-eight hours is required for skate serum to acclimate osmotically to a salinity change as small as 2.4% while a change of 10.0% requires 70 hr.
40 citations
"Dogmas and controversies in the han..." refers background in this paper
...%) seawater (Price and Creaser, 1967; Goldstein et al., 1968; Goldstein and Forster, 1971; Cooper and Morris, 1998)....
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...They suggested that urea synthesis may be diminished in dilute seawater (although this has not been tested in adults), which 2030 would explain the significantly lower tissue urea levels under these conditions (e.g. Price and Creaser, 1967; Goldstein and Forster, 1971)....
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TL;DR: It is concluded that tail beating is required to supply sufficient oxygen to the embryonic skate, consistent with the proposal that actively pumping water through the capsule, by tail beating, has played an evolutionary role in the shape of the capsule.
Abstract: Near-hatching embryonic little skates, Raja erinacea, are highly active within their egg capsules, displaying a characteristic tail beating, which pumps water through the cap- sule. We measured the metabolic rate of late-stage embryos to determine whether oxygen suffi- cient for the embryo's needs will diffuse through the egg capsule, and to assess the energetic cost of tail beating. Metabolic rate was inferred from oxygen consumption rates while embryos were in the capsules, unencapsulated, and anesthetized and unencapsulated. Anesthesia inhibited volun- tary movements, including tail wagging, allowing an estimate of the standard metabolic rate (SMR). Averaged over five embryos, the SMR was 0.032 ± 0.004 ml O2 g -1 hr -1 . There was no significant difference in metabolic rate between encapsulated (0.058 ± 0.009 ml O2 g -1 hr -1 ) and unencapsu- lated (0.049 ± 0.009 ml O2 g -1 hr -1 ) skates. Tail beating was found to be energetically expensive, requiring a 53%-81% increase over the SMR. From literature values for the oxygen permeability of the egg capsule we conclude that tail beating is required to supply sufficient oxygen to the embryonic skate. This observation is consistent with the proposal that actively pumping water through the capsule, by tail beating, has played an evolutionary role in the shape of the capsule. J. Exp. Zool. 283:13n18, 1999. © 1999 Wiley-Liss, Inc.
40 citations
"Dogmas and controversies in the han..." refers background in this paper
...Furthermore, Leonard et al. (1999) compared metabolic rate (i.e. oxygen consumption) in late term intact versusdecapsulated embryos and found no significant differences....
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