Origin of variation in isogenic, gynogenetic, and androgenetic strains of common carp,Cyprinus carpio

Production and verification of a 2nd generation clonal group of Japanese flounder, Paralichthys olivaceus

Clonal fishes are useful tools in biology and aquaculture studies due to their isogenicity. In Japanese flounder (Paralichthys olivaceus), a group of homozygous clones was created by inducing meiogynogenesis in eggs from a mitogynogenetic homozygous diploid. As the clones reached sexual maturity, meiogynogenesis was again induced in order to produce a 2^nd generation clonal group of Japanese flounder. After 3 months, there were 611 healthy, surviving individuals. Twenty-four microsatellite markers, that covered all the linkage groups of Japanese flounder, were used to identify the homozygosity of the 2^nd generation clones; no heterozygous locus was detected. This indicates that the production of a 2^nd generation clonal group of Japanese flounder was successful. Restriction-site DNA associated sequencing at the genomic level also confirmed the homozygosity and clonality of the 2^nd generation clonal group. Furthermore, these 2^nd generation clones had a small coefficient of variation for body shape indices at 210 days of age and showed a high degree of similarity in body characteristics among individuals. The successful production of 2^nd generation clones has laid the foundation for the large-scale production of clonal Japanese flounder.

ACTH, α-MSH, and control of cortisol release: cloning, sequencing, and functional expression of the melanocortin-2 and melanocortin-5 receptor in Cyprinus carpio

Cortisol release from fish head kidney during the acute phase of the stress response is controlled by the adrenocorticotropic hormone (ACTH) from the pituitary pars distalis (PD). Alpha-melanocyte-stimulating hormone (α-MSH) and β-endorphin, from the pars intermedia (PI), have been implicated in cortisol release during the chronic phase. The present study addresses the regulation of cortisol release by ACTH and α-MSH in common carp ( Cyprinus carpio) and includes characterization of their receptors, namely, the melanocortin-2 and melanocortin-5 receptors (MC2R and MC5R). We could not demonstrate corticotropic activity of α-MSH, β-endorphin, and combinations of these. We do show a corticotrope in the PI, but its identity is as yet uncertain. Carp restrained for 1 and 7 days showed elevated plasma cortisol and α-MSH levels; cortisol is still elevated but lower at day 7 than day 1 of restraint. Interrenal response capacity is unaffected, as estimated by stimulation with a maximum dose ACTH in a superfusion setup. MC2R and MC5R appear phylogenetically well conserved. MC2R is predominantly expressed in head kidney; a low abundance was found in spleen and kidney. MC5R is expressed in brain, pituitary PD, kidney, and skin. Quantitative PCR analysis of MC2R and MC5R expression in the head kidney of restrained fish reveals MC2R mRNA downregulation after 7 days restraint, in line with lower plasma cortisol levels seen. We discuss regulation of corticosteroid production from a phylogenetic perspective. We propose that increased levels of α-MSH exert a positive feedback on hypothalamic corticotropin-releasing hormone release to sustain a mild stress axis activity.

Regulation of branchial Na(+)/K(+)-ATPase in common carp Cyprinus carpio L. acclimated to different temperatures

Isogenic carp Cyprinus carpio L. were acclimated to water temperatures of 15, 22 and 29 degrees C for at least 8 weeks. The acclimations consistently resulted in slightly, but significantly, different plasma osmolality, sodium, potassium and chloride concentrations between the groups studied. Plasma total and ionic calcium levels were unaffected, indicating successful adaptation. The apparent changes in set point for plasma ion levels are explained by altered sodium pump activity and hormonal control of branchial permeability to water and ions. It appears that in 15 degrees C-acclimated fish, a lower apparent Na(+)/K(+)-ATPase activity is compensated by strongly enhanced Na(+)/K(+)-ATPase expression (determined biochemically and immunohistochemically). In 29 degrees C-acclimated fish, the higher ambient temperature activates the enzyme. Arrhenius plots for branchial Na(+)/K(+)-ATPase preparations of the three groups of fish suggest the occurrence of different enzyme isoforms or protein (in)stability as explanations for differences in apparent enzyme activities, rather than temperature-dependent changes in membrane fluidity. As for hormonal control over permeability, prolactin mRNA expression (and anticipated production and release) is lower in fish kept at 29 degrees C, suggesting that control over branchial permeability to water and ions needs to be downregulated at higher temperatures. In so doing, enhanced sodium pump activity is balanced by a controlled passive ion loss to fine-tune plasma sodium levels. Basal plasma cortisol levels did not correlate positively with Na(+)/K(+)-ATPase expression, but doubling plasma cortisol levels in control fish by administering exogenous cortisol (for 7 days, using implanted minipumps and thus stress-free) enhanced Na(+)/K(+)-ATPase expression. This effect must be the result of a glucocorticoid action of the steroid: in fish, mineralocorticoid receptors have higher affinity for cortisol than glucocorticoid receptors. At a lower ambient temperature, branchial Na(+)/K(+)-ATPase expression is upregulated to counteract the temperature-inhibited activity of the sodium pump, perhaps via a mineralocorticoid receptor.

Differential expression and haplotypic variation of two interleukin-1beta genes in the common carp (Cyprinus carpio L.)

Interleukin-1beta (IL-1beta) is a central component in innate immunity and the inflammatory response of mammals. Only recently, the first non-mammalian IL-1beta sequences were published. In this study, we describe a second IL-1beta sequence (IL-1beta2) in carp with 74% amino acid identity to the carp IL-1beta1 sequence. The existence of two IL-1beta copies in the carp genome probably originates from the tetraploid nature of the species. In contrast to the first carp IL-1beta sequence, IL-1beta2 is represented by multiple genes with 95-99% identity. Detection of several IL-1beta2 sequences within individual homozygous fish suggests the presence of multiple copies of the IL-1beta2 gene in the carp genome, possibly as a result of subsequent gene duplication of IL-1beta2. In vivo, constitutive mRNA expression of both IL-1beta genes was found in healthy carp. IL-1beta2 mRNA expression could be up-regulated in head kidney cells similar to carp IL-1beta1, in vivo by infection with Trypanoplasma borreli and in vitro by stimulation with lipopolysaccharide (LPS). Cortisol, the major glucocorticoid in fish, is an endocrine-derived fator mediating IL-1beta expression. Although constitutive IL-1beta expression was inhibited by a physiological dose of cortisol, cortisol synergistically enhanced LPS-induced IL-1beta expression in carp. Involvement of the transcription factor nuclear factor (NF)-kappaB in expression of IL-1beta1 and IL-1beta2 was demonstrated. Ratio of IL-1beta expression was determined and this showed IL-1beta1 mRNA expression to be at least tenfold higher compared with IL-1beta2. The possibilities of IL-1beta2 being a functional gene or approaching pseudogene status are discussed.

Corticosteroids affect the testicular androgen production in male common carp (Cyprinus carpio L.)

Our previous experiments to study the effect of stress adaptation on pubertal development in carp showed that repeated temperature stress and prolonged feeding with cortisol-containing food pellets, which mimics the endocrine stress effects, retarded the first waves of spermatogenesis and decreased 11-ketotestosterone (11KT) plasma levels. The objective of the present study was to investigate whether the decrease in plasma 11KT is caused by a direct effect of cortisol on the steroid-producing capacity of the testis or by an indirect effect, such as a decrease in plasma LH. Pubertal and adolescent isogenic male common carp (Cyprinus carpio L.) were fed with either cortisol-containing food pellets or control food pellets over a prolonged period. Our results indicate that cortisol has a direct inhibitory effect on the testicular androgen secretion independent of the LH secretion. Furthermore, the pubertal period is critical to the influence of cortisol regarding testicular androgen secretion, because the effect is no longer observed at adolescence.

Long-term cortisol treatment inhibits pubertal development in male common carp, Cyprinus carpio L

The onset and regulation of puberty is determined by functional development of the brain-pituitary-gonad (BPG) axis. Stress has been shown to interfere with reproduction and the functioning of the BPG axis. The response to chronic and severe stress may require much energy and force the organism to make adaptive choices. Energy that is normally available for processes like growth, immune response, or reproduction will be channeled into restoration of the disturbed homeostasis. Cortisol plays a key role in the homeostatic adaptation during or after stress. In the present study, immature common carp were fed with cortisol-containing food pellets covering the pubertal period. We showed that cortisol caused an inhibition of pubertal development, by affecting directly or indirectly all components of the BPG axis. The salmon GnRH content of the brain was decreased. Luteinizing hormone- and FSH-encoding mRNA levels in the pituitary and LH plasma levels were diminished by long-term cortisol treatment, as was the testicular androgen secretion. Testicular development, reflected by gonadosomatic index and the first wave of spermatogenesis, was retarded.

Major histocompatibility genes in cyprinid fishes: theory and practice

The first teleostean MHC sequences were described for carp. Subsequent studies in a number of cyprinid fishes showed that the class I sequences of these fishes are of particular interest. Two distinct lineages (Cyca-Z and Cyca-U) are found in the common and ginbuna crucian carp, but only the U lineage is present in zebrafish and other non-cyprinid species. The presence of the Z lineage is hypothesised to be the result of an allotetraploidisation event. Both phylogenetic analyses and amino acid sequence comparisons suggest that Cyca-Z sequences are non-classical class I sequences, probably similar to CD1. The comprehensive phylogenetic analyses of these sequences revealed different phylogenetic histories of the exons encoding the extracellular domains. The MHC genes were studied in laboratory and natural models. The natural model addressed the evolution of MHC genes in a Barbus species flock. Sequence analysis of class I and class II supported the species designation of the morphotypes present in the lake, and as a consequence the trans-species hypothesis of MHC polymorphism. The laboratory model involves the generation of gynogenetic clones, which can be divergently selected for traits such as high and low antibody response. The role of MHC molecules can be investigated further by producing a panel of isogenic lines.

Induction of oral tolerance in carp (Cyprinus carpio L.) after feeding protein antigens

Induction of oral tolerance against ferritin, recombinant surface glycoprotein of viral haemorrhagic septicemia virus (KLG18) and ovalbumin (OVA) was studied in carp. Feeding of ferritin or KLG18 resulted in lower Ab titres compared to unprimed controls when animals were intramuscularly (i.m.) injected with protein 10 weeks later and sampled 21 days after this injection. After administration of OVA by different routes (oral, anal, i.m.) and i.m. injection with OVA + Freund's incomplete adjuvant 2 months later, only a few fish responded to OVA as measured by serum Ab titres. Responsiveness to OVA appeared to be carp strain dependent. When an isogenic carp strain was selected for an optimal response to i.m. injection with OVA, this carp strain did not develop oral tolerance after feeding. In contrast, 6 x feeding high doses of OVA on subsequent days, resulted in immunological memory formation. Oral tolerance can be induced in carp, but differences in tolerance induction may depend on the protein used. A possible role of genetic factors in the induction of oral tolerance in fish is discussed.