Substantial Downregulation of Myogenic Transcripts in Skeletal Muscle of Atlantic Cod during the Spawning Period

Gonadal maturation is an extremely energy consuming process for batch spawners and it is associated with a significant decrease in growth and seasonal deterioration in flesh quality. Our knowledge about the molecular mechanisms linking sexual maturation and muscle growth is still limited. In the present study, we performed RNA-Seq using 454 GS-FLX pyrosequencing in fast skeletal muscle sampled from two-year-old Atlantic cod (Gadus morhua) at representative time points throughout the reproductive cycle (August, March and May). In total, 126,937 good quality reads were obtained, with 546 nucleotide length and 52% GC content on average. RNA-Seq analysis using the CLC Genomics Workbench with the Atlantic cod reference UniGene cDNA data revealed 59,581 (46.9%) uniquely annotated reads. Pairwise comparison for expression levels identified 153 differentially expressed UniGenes between time points. Notably, we found a significant suppression of myh13 and myofibrillar gene isoforms in fast skeletal muscle during the spawning season. This study uncovered a large number of differentially expressed genes that may be influenced by gonadal maturation, thus representing a significant contribution to our limited understanding of the molecular mechanisms regulating muscle wasting and regeneration in batch spawners during their reproductive cycle

Structure-Function of Serotonin in Bivalve Molluscs

It has been observed that 5-HT excites the heart nerves in hard clam and regulates contraction and relaxation of the anterior byssus retractor muscle in the blue mussel. It is now known that 5-HT regulates several neurobehavioral systems such as mood, appetite, sleep, learning, and memory. It also plays critical roles in the physiological functions of peripheral organs involved in stress, growth, and reproduction in the animal kingdom. The present study reviews conserved 5-HT biosynthesis and its localization in the nervous system, and its physiological contribution to regulate reproduction in bivalves. In the cytosol of neurons, tryptophan hydroxylase catalyzes hydroxylation of l-tryptophan to 5-hydroxytryptophan, which is converted to 5-HT by aromatic l-amino acid decarboxylase. A 5-HT transporter and a monoamine oxidase reuptakes and metabolizes 5-HT to control the amount of released 5-HT in the nervous system and peripheral organs. Perikarya and fibers of 5-HT neurons are mostly located in the cortices and neuropil of ganglia, respectively, and innervate the gonad. However, distribution and 5-HT content differ among species and sexes and undergo seasonal variations associated with gonadal development. The present review pays a special attention to future research perspectives to better understand 5-HT regulation of reproduction in bivalves

Pharmacology and Molecular Identity of Serotonin Receptor in Bivalve Mollusks

It is now known that 5-HT regulates several neurobehavioral systems such as mood, appetite, sleep, learning, and memory. It also plays critical roles in the physiological functions of peripheral organs involved in stress, growth, and reproduction in the animal kingdom. 5-HT content has seen to be higher in the nervous system of bivalves than those of other examined invertebrates and vertebrates. Thus, bivalves have been considered as an excellent model to investigate 5-HT functions in neurological and peripheral systems. The present study reviews knowledge on 5-HT signaling mediated through 5-HT receptor and its physiological contribution to regulate reproduction in bivalves. Two G-protein-coupled 5-HT1-like receptors have been cloned in bivalve species. However, binding affinities of the 5-HT agonists and antagonists to the isolated plasma membrane proteins and their effects on spawning in bivalves suggest the presence of a single or mixed 5-HT1-, 5-HT2-, and 5-HT3-like receptors. It has suggested that the 5-HT-like receptors in bivalves are distinct from those of mammalian 5-HT receptors due to pharmacological properties. The present review pays a special attention to future research perspectives to better understand 5-HT regulation of reproduction in bivalves, which can provide us with satisfactory knowledge to elucidate reproductive disorders associated with dysfunctions of the neurotransmitter system

Circadian rhythmicity and photic plasticity of myosin gene transcription in fast skeletal muscle of Atlantic cod (Gadus morhua)

Author's accepted version (post-print).NOTICE: this is the author’s version of a work that was accepted for publication in Marine Genomics (2014). Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Marine Genomics (2014), 18(A). doi: http://dx.doi.org/10.1016/j.margen.2014.04.011.The circadian rhythm is a fundamental adaptive mechanism to the daily environmental changes experienced by many organisms, including fish. Myosins constitute a large family of contractile proteins that are essential functional components of skeletal muscle. They are known to display thermal plasticity but the influence of light on myosin expression remains to be investigated in fish. In the present study, we have examined the circadian rhythmicity and photoperiodic plasticity of myosin gene transcription in Atlantic cod (Gadus morhua) fast skeletal muscle. In silico mining of the Atlantic cod genome resulted in the identification of 76 myosins representing different classes, many of which were hitherto uncharacterized. Among the 23 skeletal muscle-expressed myosin genes, myh_tc, myh_n1, myh_n4, myo18a_2, and myo18b_2 displayed circadian rhythmicity and contained several circadian-related transcription factor binding sites (Creb, Mef2 and E-box motifs) within their putative promoter regions. Also, the circadian expression of these 5 myosins strongly correlated with the transcription pattern of clock genes in fast skeletal muscle. Under ex vivo conditions, myosin transcript levels lost their circadian rhythmicity. Nonetheless, different photoperiod regimes influenced the mRNA levels of myh_n4, myo18a_2 and myo18b_2 in fast skeletal muscle explants. Photoperiod manipulation in Atlantic cod juveniles revealed that continuous light significantly elevated mRNA levels of several myosins in fast skeletal muscle when compared to natural photoperiod. The circadian rhythmicity observed in some fast skeletal muscle myosin genes suggests that they may be under circadian clock regulation. In addition, the influence of photoperiod on their expression implies that myosins may be involved in the photic plasticity of muscle growth observed in Atlantic cod

Molecular characterization of an estrogen receptor and estrogen-related receptor and their autoregulatory capabilities in two Mytilus species

Vertebrate-like sex steroid hormones have been widely detected in mollusks, and numerous experiments have shown the importance of steroids in gonad development. Nevertheless, their signaling pathways in invertebrates have not been uncovered yet. Steroid receptors are an ancient class of transcription factors with multiple roles in not only vertebrates but also invertebrates. Estrogen signaling is thought to have major roles in mollusk physiology, but the full repertoire of estrogen receptors is unknown. We presented the successful cloning of two novel forms of estrogen receptor-like genes. These receptors are present in two closely related species of Mytilus: Mytilus edulis and Mytilus galloprovincialis, commonly known and widely distributed sentinel species. Our phylogenetic analysis revealed that one of these receptors is an estrogen receptor (ER) and the other one is an estrogen-related receptor (ERR). Studies of expression analysis showed that both receptor mRNAs were localized in the oocytes and follicle cells in contact with developing oocytes in the ovary and Sertoli cells in the testis, and in the ciliated cells of the gill. In addition, we have evidence that one (ER) of these may have a capacity to autoregulate its own expression in the gonadal cells by estrogen (E2) and that this gene is responsive to estrogenic compounds