Molt cycle regulation of protein synthesis in skeletal muscle of the blackback land crab, Gecarcinus lateralis, and the differential expression of a myostatin-like factor during atrophy induced by molting or unweighting

Abstract

SUMMARYIn decapod crustaceans, claw muscle undergoes atrophy in response to elevated ecdysteroids while thoracic muscle undergoes atrophy in response to unweighting. The signaling pathways that regulate muscle atrophy in crustaceans are largely unknown. Myostatin is a negative regulator of muscle growth in mammals, and a myostatin-like cDNA is preferentially expressed in muscle of the land crab, Gecarcinus lateralis (Gl-Mstn). Contrary to prediction, levels of Gl-Mstn mRNA decreased dramatically in both the claw closer and weighted thoracic muscles when molting was induced by either eyestalk ablation (ESA) or multiple limb autotomy (MLA). However, the effect of molt induction was greater in the claw muscle. By late premolt, Gl-Mstn mRNA in the claw muscle decreased 81% and 94% in ESA and MLA animals, respectively, and was negatively correlated with ecdysteroids. Gl-Mstn mRNA in thoracic muscle decreased 68% and 82% in ESA and MLA animals, respectively, but was only weakly correlated with ecdysteroid. Claw and thoracic muscles also differed to varying extents in the expression of ecdysteroid receptor (Gl-EcR and Gl-RXR), elongation factor-2 (Gl-EF-2), and calpain T (Gl-CalpT) in response to molt induction, but levels of the four transcripts were not correlated with ecdysteroid. The downregulation of Gl-Mstn expression in premolt claw muscle coincided with 11-and 13-fold increases in protein synthesis in the myofibrillar and soluble protein fractions, respectively. Furthermore, the rate of the increase in the synthesis of soluble proteins was greater than that of myofibrillar proteins during early premolt (1.4:1, soluble:myofibrillar), but the two were equivalent during late premolt. By contrast, Gl-Mstn mRNA increased 3-fold and Gl-CalpT mRNA decreased 40% in unweighted thoracic muscle; there was little or no effect on Gl-EF-2, Gl-EcR, and Gl-RXR mRNA levels. These data indicate that Gl-Mstn expression is negatively regulated by both ecdysteroids and load-bearing contractile activity. The downregulation of GlMstn in claw muscle may induce the elevated protein turnover associated with remodeling of the contractile apparatus during molt-induced atrophy. The upregulation of Gl-Mstn in unweighted thoracic muscle suggests that this factor is also involved in disuse atrophy when hemolymph ecdysteroid levels are low.

Growing backwards: an inverted role for the shrimp ortholog of vertebrate myostatin and GDF11

“…Loss-offunction mutations of the MSTN gene in vertebrates result in heavily muscled phenotypes (McPherron and , whereas increasing circulating levels of MSTN induces muscle atrophy (Ma et al, 2003;Shao et al, 2007;Wehling et al, 2000). Recently, invertebrate orthologs of genes similar to Mstn have been reported in a number of species, including decapod crustaceans (Covi et al, 2008;Covi et al, 2010;Kim et al, 2010;MacLea et al, 2010); however, the function of these gene orthologs has not been specifically investigated.…”

Molt regulation in green and red color morphs of the crab,Carcinus maenas: gene expression of molt-inhibiting hormone signaling components

“…The differences in the effect of ESA on NOS and GC-Iβ gene expression in the two species can be attributed to whether ESA induces molting. Both C. maenas color morphs were resistant to ESA (Figs 4, 5), while G. lateralis enter premolt immediately and molt by 3 weeks post-ESA (Covi et al, 2010).…”

“…ESA removes the primary source of MIH and results in an immediate activation of the YO and an increase in hemolymph ecdysteroid titers (Covi et al, 2010;Lee et al, 2007b;Lee and Mykles, 2006;reviewed by Lachaise et al, 1993). In Gecarcinus lateralis, ESA increases Gl-NOS, Gl-GC-Iβ and Gl-GC-III expression in the YO by 7 days post-ESA, which indicates that YOs are responsive to acute withdrawal of eyestalk neuropeptides (Lee et al, 2007b;McDonald et al, 2011).…”

Rheb, an activator of target of rapamycin, in the blackback land crab,Gecarcinus lateralis: cloning and effects of molting and unweighting on expression in skeletal muscle

“…RNA isolation from G. lateralis skeletal muscles and cDNA synthesis were the same as described in Covi et al (Covi et al, 2010). PCR K. S. MacLea and others used 0.5l of the first-strand cDNA as a template and forward and reverse primers (10pmol each; Table1) synthesized by Integrated DNA Technology (IDT; Coralville, IA, USA).…”