| This study was designed to investigate molt-induced responses affecting muscle growth in the pacific white shrimp Litopenaeus vannamei. Cellular, molecular and genetic analyses were carried out in abdominal muscle. Clear images of uropod setogenesis and muscle myofibers were presented. Water, total soluble proteins, DNA, and RNA levels presented specific variations during the molt cycle. A reverse transcriptase multiplex PCR method for semi-quantitative detection of mRNA from muscle genes was developed. Five genes (muscle actin, beta-actin, myosin heavy chain, ubiquitin and heat shock protein 70) were studied and mRNA levels were normalized to an internal control housekeeping gene. Results confirmed that there are specific regulations of gene expressions during molt cycle. A shrimp abdominal muscle cDNA library was constructed and screened to investigate the diversity of expressed sequence tags and to identify new sequences that may play a role in regulation of muscle growth. Direct sequence of 311 randomly picked clones revealed 109 sequences with high homology (blastn score >100 bits) to annotated sequences from DNA databases. Homologous genes were grouped in 8 major functional categories. Sixty three sequences were considered unknowns. Contig creation grouped 77 sequences in 37 contigs with 430nt of average length of insert. These results illustrate the diversity of genes expressed in shrimp muscle, and also revealed that EST analysis is a suitable methodology for gene discovery in shrimps. Overall results of this project enhanced our understanding of muscle growth in shrimp. As shrimp aquaculture is becoming an important sector of world production of seafood, the knowledge generated by this work supports further studies that will favor genetic selection of fast growing shrimp lines, which can decrease growout cycles, productions costs, and reduce the time of exposure to diseases. |
