Cold-induced muscle atrophy in zebrafish: Insights from swimming activity and gene expression analysis.

The investigation into the effects of cold acclimation on fish skeletal muscle function and its potential implications for muscle atrophy is of great interest to us. This study examines how rearing zebrafish at low temperatures affects their locomotor activity and the expression of genes associated with muscle atrophy. Zebrafish were exposed to temperatures ranging from 10 °C to 25 °C, and their swimming distance was measured. The expression levels of important muscle atrophy genes, Atrogin-1 and MuRF1, were also evaluated. Our findings show that swimming activity significantly decreases when the water temperature ranges from 10 °C to 15 °C, indicating a decrease in voluntary movement. Additionally, gene expression analysis shows a significant increase in the expression of Atrogin-1 and MuRF1 at 10 °C. This up-regulation could lead to muscle atrophy caused by decreased activity in cold temperatures. To investigate the effects of exercise on reducing muscle atrophy, we subjected zebrafish to forced swimming at a temperature of 8 °C for ten days. This treatment significantly reduced the expression of Atrogin-1 and MuRF1, emphasizing the importance of muscle stimulation in preventing muscle atrophy in zebrafish. These findings suggest that zebrafish can serve as a valuable model organism for studying muscle atrophy and can be utilized in drug screening for muscle atrophy-related disorders. Cold-reared zebrafish provide a practical and ethical approach to inducing disuse muscle atrophy, providing valuable insights into potential therapeutic strategies for addressing skeletal muscle atrophy.

Global gene expression analysis of the muscle tissues of medaka acclimated to low and high environmental temperatures.

Medaka (Oryzias latipes) is a temperate eurythermal fish that is able to survive over a wide range of water temperatures ranging from near zero to over 30°C throughout the year; it maintains its normal physiological and biochemical processes through temperature acclimation. To determine the mechanisms involved in temperature acclimation of fish, the fast skeletal muscle tissues of medaka underwent global gene expression analysis using next-generation sequencing. Ten individuals were placed into two aquariums at 24°C. While the water temperature of one aquarium was decreased to 10°C, that of the other aquarium was increased to 30°C; these temperatures were subsequently maintained for 5weeks. RNA sequencing (RNA-Seq) analyses revealed that 11 genes involved in energy metabolism and muscle atrophy were significantly highly expressed in the 10°C-acclimated fish. Meanwhile, significantly higher expression levels were observed for 20 genes encoding myofibrillar proteins and heat shock proteins in the 30°C-acclimated fish. Moreover, 1103 genes had at least fourfold differential expression between the acclimation groups. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses provided important information: although the expression of genes related to metabolic processes were activated, muscle atrophy occurred in the 10°C-acclimated fish, and muscle cells divided actively in the 30°C-acclimated fish and avoided thermal stress by expressing heat shock proteins. Therefore, RNA-Seq analyses with the available genome database will be useful for better understanding the molecular mechanisms involved in the temperature acclimation of fish.

Lampreys have a single gene cluster for the fast skeletal myosin heavy chain gene family.

Muscle tissues contain the most classic sarcomeric myosin, called myosin II, which consists of 2 heavy chains (MYHs) and 4 light chains. In the case of humans (tetrapod), a total of 6 fast skeletal-type MYH genes (MYHs) are clustered on a single chromosome. In contrast, torafugu (teleost) contains at least 13 fast skeletal MYHs, which are distributed in 5 genomic regions; the MYHs are clustered in 3 of these regions. In the present study, the evolutionary relationship among fast skeletal MYHs is elucidated by comparing the MYHs of teleosts and tetrapods with those of cyclostome lampreys, one of two groups of extant jawless vertebrates (agnathans). We found that lampreys contain at least 3 fast skeletal MYHs, which are clustered in a head-to-tail manner in a single genomic region. Although there was apparent synteny in the corresponding MYH cluster regions between lampreys and tetrapods, phylogenetic analysis indicated that lamprey and tetrapod MYHs have independently duplicated and diversified. Subsequent transgenic approaches showed that the 5'-flanking sequences of Japanese lamprey fast skeletal MYHs function as a regulatory sequence to drive specific reporter gene expression in the fast skeletal muscle of zebrafish embryos. Although zebrafish MYH promoters showed apparent activity to direct reporter gene expression in myogenic cells derived from mice, promoters from Japanese lamprey MYHs had no activity. These results suggest that the muscle-specific regulatory mechanisms are partially conserved between teleosts and tetrapods but not between cyclostomes and tetrapods, despite the conserved synteny.

Purification, characterization, and cDNA cloning of opine dehydrogenases from the polychaete rockworm Marphysa sanguinea.

Alanopine dehydrogenase (AlDH) and three isoforms of strombine/alanopine dehydrogenase (St/AlDH) were purified from muscle tissue of the polychaete rockworm Marphysa sanguinea. The four enzymes, which can be distinguished by the isoelectric point, are monomeric 42 kDa proteins, possess similar pH-activity profiles, and display specificity for pyruvate and NAD(H). The three isoforms of St/AlDH show equivalent Km and Vmax for glycine and L-alanine and for D-strombine and meso-alanopine. Free amino acid levels in the muscle and D-strombine accumulation in vivo during muscle activity suggest that St/AlDHs function physiologically as StDH. AlDH shows specificity for L-alanine and meso-alanopine, but not for glycine or D-strombine. The amino acid sequences of AlDH and one of the St/AlDH isoforms were determined by a combination of amino acid sequence analysis and cDNA cloning. St/AlDH cDNA consisted of 1586 bp nucleotides that encode a 399-residue protein (43,346.70 Da), and AlDH cDNA consisted of 1587 bp nucleotides that encode a 399-residue protein (43,886.68 Da). The two amino acid sequences deduced from the cDNA displayed 67% amino acid identity, with greatest similarity to that of tauropine dehydrogenase from the polychaete Arabella iricolor.

Tauropine dehydrogenase from the marine sponge Halichondria japonica is a homolog of ornithine cyclodeaminase/mu-crystallin.

The partial amino acid sequence including the N- and C-terminal portions of tauropine dehydrogenase (EC 1.5.1.23) from the marine sponge Halichondria japonica was determined by enzymatic cleavages followed by peptide sequencing. This information was used to design degenerate primers for amplification of cDNA encoding the tauropine dehydrogenase. The cDNA included 1231 nucleotides with an open reading frame of 1002 nucleotides that encodes a protein of 334 amino acid residues. From the peptide and nucleotide sequencing, the mature tauropine dehydrogenase was estimated to consist of 333 amino acid residues with an acetylated N-terminal serine residue and no intrachain disulfide bonds. The primary structure of the H. japonica enzyme showed apparent similarity with a homolog of ornithine cyclodeaminase from Rhizobium meliloti and other proteins of the ornithine cyclodeaminase/mu-crystallin family, but it showed no significant similarity with the known sequences of octopine dehydrogenases and tauropine dehydrogenases from marine invertebrates. These findings indicate that opine dehydrogenases in marine invertebrates are not all homologous.

The amino acid sequence of tauropine dehydrogenase from the polychaete Arabella iricolor.

The amino acid sequence of tauropine dehydrogenase (EC 1.5.1.23) from the polychaete Arabella iricolor was determined by automated sequencing of fragments obtained by cleavage with lysyl endopeptidase, endoproteinase Glu-C, and cyanogen bromide. The purified enzyme contained two isoforms that differ only in the 41st amino acid residue (Thr or Ile). Although the sequence contained eight Cys residues, intrachain disulfide bonds were not found. Two possible N-linked glycosylation sites occur in the sequences, but the enzyme does not appear to contain bound carbohydrates. Based on these data, the two isoforms of Arabella tauropine dehydrogenase are simple proteins consisted of 396 amino acid residues with calculated molecular masses of 43,085.7 Da (Thr41 isoform) and 43,097.8 Da (Ile41 isoform).

Complementary DNA cloning and molecular evolution of opine dehydrogenases in some marine invertebrates.

The complete complementary DNA sequences of genes presumably coding for opine dehydrogenases from Arabella iricolor (sandworm), Haliotis discus hannai (abalone), and Patinopecten yessoensis (scallop) were determined, and partial cDNA sequences were derived for Meretrix lusoria (Japanese hard clam) and Spisula sachalinensis (Sakhalin surf clam). The primers ODH-9F and ODH-11R proved useful for amplifying the sequences for opine dehydrogenases from the 4 mollusk species investigated in this study. The sequence of the sandworm was obtained using primers constructed from the amino acid sequence of tauropine dehydrogenase, the main opine dehydrogenase in A. iricolor. The complete cDNA sequence of A. iricolor, H. discus hannai, and P. yessoensis encode 397, 400, and 405 amino acids, respectively. All sequences were aligned and compared with published databank sequences of Loligo opalescens, Loligo vulgaris (squid), Sepia officinalis (cuttlefish), and Pecten maximus (scallop). As expected, a high level of homology was observed for the cDNA from closely related species, such as for cephalopods or scallops, whereas cDNA from the other species showed lower-level homologies. A similar trend was observed when the deduced amino acid sequences were compared. Furthermore, alignment of these sequences revealed some structural motifs that are possibly related to the binding sites of the substrates. The phylogenetic trees derived from the nucleotide and amino acid sequences were consistent with the classification of species resulting from classical taxonomic analyses.

Presence of free D-amino acids in microalgae.

Several species of microalgae (phytoplankton), 4 species of freshwater algae and 4 species of marine diatoms, were cultured germ-free in the laboratory. The presence of free D-amino acids was verified in these species by a reversed-phase HPLC analysis. D-Aspartate was detected in all the microalgae examined, but D-alanine was only present in the marine diatoms. The D-amino acid content in Asterionella sp. of the marine diatoms increased from the exponential phase to the stationary phase and then decreased to the phase of decline.