Embryonic Ontogeny And Postembryonic Development Of Slow Skeletal Muscle Of Mandarin Fish Siniperca Chuatsi

The skeletal muscle of fish accounts for about40-60%of body weight, andcomposed by three types: slow-twitch muscle, fast-twitch muscle and pink muscle.The myosin is the essential component of skeletal muscle thick filament, which iscomposed by two heavy chains and two pair of light chains. The different musclefibers in fish occur in distinct different area, while in mammal different muscle fibercross with each other. There are different development features for different musclefibers. MyoD is one of the MRFs family, it is one of the main factors in regulatingmuscle development at embryonic stage, the expression of MyoD gene play animportant role in maintaining the muscle cell differentiation. To fully understand theontogeny and development feature of Mandarin fish Siniperca chuatsi skeletal muscle,the following were carried out in this paper:RT-PCR and RACE (Rapid Amplification of cDNA Ends) were used to clonethe S2and LMM domain of slow myosin heavy chain (MHC) of Mandarin fish. Aftersplicing with the S1domain (2520bp) cloned earlier in our laboratory, the5891bpslow myosin heavy chain was obtained, which contains5751bp open reading frameand140bp3’ non-coding region. Nucleotide sequence and amino acid sequencesimilarity between the slow MyHC and the fast MyHC was80%and88%,respectively. Specific primers of fast muscle and slow muscle were designed based ontheir cDNA sequence, synthetized specific mRNA probes were digoxigenin labeled.Ontogeny of slow muscle and fast muscle at embryonic stage were investigated by insitu hybridization, the result showed slow muscle signal was detected at32hour afterfertilization, while the fast muscle signal at34hour, the slow muscle wasdifferentiated earlier than the fast muscle. In addition, fragments of MyoD1and MyoD2gene in slow muscle and fast muscle were cloned by RT-PCR, two types ofslow muscle MyoD (sMyoD1, sMyoD2) and one type of fast muscle MyoD1(fMyoD)were obtained at present.In most fish, slow and fast muscle fibers occupy distinct regions of the axialmuscle and display different growth characteristics. To fully understand thepostembryonic development feature of slow muscle fibers of Mandarin Fish, paraffinsections at the beginning of the dorsal fin of1–33days after hatching individuals werecarried out and identifed by immunohistochemistry, the numbers and area of slowmuscle fibers were also measured by image analysis software. The results showed thatslow muscle fibers located near the horizontal septum after hatching and appeared likewedge shape, later they extended to the dorsal and ventral. During the1–9daysafter hatching, the slow muscle fibers were monolayers, then they became multilayersafter11days. At the19days after hatching, slow muscle fibers covered across thelateral line. The slow muscle fibers extended up to the second dorsal myotome anddown to2/3of ventral myotome at33days after hatching, and two populations ofslow muscle fibers were formed at the horizontal septum and lateral line, respectively.The superficial, spindle cells of skeletal muscle maybe were the main source of slowmuscle fibres hyperplasia growth. The total numbers of slow muscle fibers increasedfrom6to315after hatching, and the total fiber area increased from13.18μm~2to7839.58μm~2. Hyperplasia growth was dominant at the13days after hatching, whereashypertrophic growth was dominant at the other stages.