Abstract
Chinese mitten crab (Eriocheir sinensis) is an economically important freshwater aquaculture species and is a model species for research on the mechanism of molting. This study aimed to identify important candidate genes associated with the molting process and to determine the role of gills in the regulation of molting with the help of transcriptomic analysis. The transcriptomes of crabs at different molting stages—postmolt (PoM), intermolt (InM), premolt (PrM) and ecdysis (E)—were de novo assembled to generate 246,232 unigenes with a mean length of 851 bp. A total of 86,634 unigenes (35.18% of the total unigenes) were annotated against reference databases. Significantly upregulated genes were identified in postmolt compared to intermolt (1,475), intermolt compared to premolt (65), premolt compared to ecdysis (1,352), and ecdysis compared to postmolt (153), and the corresponding numbers of downregulated genes were 1,276, 32, 1,573 and 171, respectively. Chitin synthase, endochitinase, chitinase A, chitinase 3, chitinase 6 and chitin deacetylase 1 were upregulated during the postmolt and ecdysis stages, while phosphoglucomutase 3 (PGM3), glucosamine 6-phosphate deaminase (GNPDA) and glucosamine glycoside hydrolase (nagZ) were upregulated during the intermolt and premolt stages compared to the other stages. The upregulated genes were enriched in several lipid-related metabolic pathways, such as “fatty acid elongation”, “glycerophospholipid metabolism” and “sulfur metabolism”. Meanwhile, three signaling pathways, including the “phosphatidylinositol signaling system”, the “calcium signaling pathway” and the “GnRH signaling pathway” were also enriched. Tetraspanin-18, an important effector gene in the lysosomal pathway involved in cell apoptosis, up-regulate with the beginning of molting (in premolt stage) and reach the top in the ecdysis stage, and barely expressed in the intermolt stage. The expression variations in the tetraspanin-18 gene indicated that it may play an important role in the beginning of molting cycle, which might be regulated by the stress of salinity. This study revealed that the gills could participate in chitin degradation, in reestablishment of the exoskeleton and the signaling process. Based on transcriptomic analysis of the gills, we not only explored novel molecular mechanisms of molting in E. sinensis but also acquired foundational genetic data for E. sinensis.
Highlights
Eriocheir sinensis or Chinese mitten crab, a kind of crab named for its furry claw feature, belongs to the taxa Arthropoda, Crustacea, Decapoda, Grapsidae and Eriocheir (Veilleux & De Lafontaine, 2007)
From 12 gill samples at four molting stages, namely, postmolt, intermolt, premolt and ecdysis, we obtained a total of 1,712,109,230 clean reads from 1,826,272,782 raw pairedend reads (93.75%) after quality trimming using QC-Chain
We found that genes involved in chitin metabolism exhibited distinctly different expression patterns in different molting stages (Fig. 3)
Summary
Eriocheir sinensis or Chinese mitten crab, a kind of crab named for its furry claw feature, belongs to the taxa Arthropoda, Crustacea, Decapoda, Grapsidae and Eriocheir (Veilleux & De Lafontaine, 2007). E. sinensis originated from east Asia (Herborg et al, 2003) but is found in Europe and North America, where it is considered an invasive species, damaging river walls and embankments and competing with native species (Dittel & Epifanio, 2009; Ruiz et al, 2006) This species can live in freshwater and seawater, and the unique physiological characteristics of E. sinensis allow this species to inhabit rice fields by the sea and inland rivers; this species is a perfect model for research on osmoregulation. The crabs abandon the old crab shell and grow a new shell, and this entire essential biological process is known as molting. The crab is frail and unprotected; the molting process is strictly regulated
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