Myosin regulatory light chain expression in trout muscle

Abstract

Muscle's contractile properties can vary along different trajectories, including between muscle fiber types, along the body (within a muscle fiber type), and between developmental stages. This study explores the role of the regulatory myosin light chain (MLC2) in modulating contractile properties in rainbow trout myotomal muscle. Rainbow trout show longitudinal variations in muscle activation and relaxation, with faster contractile properties in the anterior myotome. The expression of two muscle proteins, troponin T and parvalbumin, vary along the length of trout in concert with shifts in muscle activation and relaxation. However, there is no longitudinal variation in myosin heavy chain in trout. This study explores the role of MLC2 (or regulatory light chain), part of the myosin hexamer, in contributing to longitudinal variations in contractile properties of trout swimming muscle. We cloned and sequenced two isoforms of MLC2 from trout muscle and used real-time quantitative polymerase chain reaction to assess the relative expression of these two isoforms in red and white muscle from different body positions of two ages of rainbow trout: parr and smolt. Longitudinal variations in slow (sMLC2) but not fast (fMLC2) regulatory light chain isoforms were observed in young trout parr but not older trout smolts. The differences in sMLC2 expression correlated with shifts in muscle contractile properties in the parr.

Expression and functional analyses of two essential myosin light chains from the fast white muscle of the spotted mandarin fish Siniperca scherzeri

“…The expression patterns of the fish MyHC and MLCs are environmentally and developmentally regulated [31][32]. In this study we showed that MLC1 and MLC3 were differentially expressed in developing somites and skeletal muscles of fish embryos.…”

“…The MLCs exist in two forms, the essential light chain (MLC1/3) and the regulatory light chain (MLC2) [3]. The relative content of MyHC and MLC in muscle fiber determines the muscle properties.…”

Characterization and ontogenetic expression analysis of the myosin light chains from the fast white muscle of mandarin fish Siniperca chuatsi

“…Myosin, the major protein component of muscle tissue, is a hexameric protein composed of two heavy chain (myosin heavy chain, MyHC ) subunits with molecular mass c. 220 kDa (kilo‐Dalton) and four light‐chain subunits c. 16–20 kDa, that are the primary determinants of contractile performance (Kikuchi et al , 1999; Bryson‐Richardson et al , 2005; Nihei et al , 2006). The myosin light chains ( MLC ) belong to the EF‐hand (helix‐loop‐helix) superfamily (Trybus, 1994) and the four MLC s are classified into two classes: two essential light chains released from heavy chains by alkaline treatment and the other two regulatory light chains dissociated with the alkali and dinitrobenzoic acid (DTNB), which are all expressed in slow and fast muscles (Ochiai et al , 1990; Donato et al , 2008). These two types of essential light chain, MLC1 and MLC3 , are ontogenetically differentially expressed from lower vertebrates to higher vertebrates (Trybus, 1994; Thiebaud et al , 2001).…”

“…The complementary DNA (cDNA) clone analysis indicates a similar situation in the amphibian Xenopus laevis (Periasamy et al , 1984). The DTNB‐removable light chain, MLC2 , also known as myosin regulatory light chain ( MRLC or RLC ), has many isoforms depending on its distribution (Lowey & Trybus, 1995; Donato et al , 2008). In smooth muscle, MLC2 is phosphorylated at Thr18 and Ser19 by myosin light chain kinase (MLCK) in a Ca 2+ –calmodulin‐dependent manner (Ikebe & Hartshorne, 1985; Ikebe et al , 1998, 1999).…”

“…Both MLC s and MLC s exist in multiple isoforms with tissue‐specific and developmental‐stage‐specific distribution, and their expression is regulated under environmental and hormonal factors (Yamano et al , 1994; Xu et al , 1999, 2000; Moutou et al , 2001). In rainbow trout Oncorhynchus mykiss (Walbaum 1792), the myosin isoform expression is developmentally regulated, in which the younger parr has faster contractile properties than older fish (Donato et al , 2008). Oncorhynchus mykiss also show longitudinal variation in rates of muscle activation and relaxation, and its anterior red and white muscles have faster rates of both muscle activation and relaxation with differential expression of the MLC chain (Thiebaud et al , 2001; Donato et al , 2008; Dou et al , 2008).…”