Global gene expression in muscle from fasted/refed trout reveals up-regulation of genes promoting myofibre hypertrophy but not myofibre production

Abstract

Background: Compensatory growth is a phase of rapid growth, greater than the growth rate of control animals, that occurs after a period of growth-stunting conditions. Fish show a capacity for compensatory growth after alleviation of dietary restriction, but the underlying cellular mechanisms are unknown. To learn more about the contribution of genes regulating hypertrophy (an increase in muscle fibre size) and hyperplasia (the generation of new muscle fibres) in the compensatory muscle growth response in fish, we used high-density microarray analysis to investigate the global gene expression in muscle of trout during a fasting-refeeding schedule and in muscle of control-fed trout displaying normal growth.

Results: The compensatory muscle growth signature, as defined by genes up-regulated in muscles of refed trout compared with control-fed trout, showed enrichment in functional categories related to protein biosynthesis and maturation, such as RNA processing, ribonucleoprotein complex biogenesis, ribosome biogenesis, translation and protein folding. This signature was also enriched in chromatin-remodelling factors of the protein arginine N-methyl transferase family. Unexpectedly, functional categories related to cell division and DNA replication were not inferred from the molecular signature of compensatory muscle growth, and this signature contained virtually none of the genes previously reported to be up-regulated in hyperplastic growth zones of the late trout embryo myotome and to potentially be involved in production of new myofibres, notably genes encoding myogenic regulatory factors, transmembrane receptors essential for myoblast fusion or myofibrillar proteins predominant in nascent myofibres.

Conclusion: Genes promoting myofibre growth, but not myofibre formation, were up-regulated in muscles of refed trout compared with continually fed trout. This suggests that a compensatory muscle growth response, resulting from the stimulation of hypertrophy but not the stimulation of hyperplasia, occurs in trout after refeeding. The generation of a large set of genes up-regulated in muscle of refed trout may yield insights into the molecular and cellular mechanisms controlling skeletal muscle mass in teleost and serve as a useful list of potential molecular markers of muscle growth in fish.

Keywords: Gene expression; Muscle growth; Muscle hyperplasia; Muscle hypertrophy; Teleost; Transcriptome.

Fig. 1

Change in body mass and condition factor over the time course of the experiment. Body weight (a) and condition factor (b) curves of trout in experimental (fasted-refed) and control (normally fed) groups. Bars indicate standard error of the mean

Fig. 2

Hierarchical clustering of differentially expressed genes in muscle during a fasting-refeeding schedule and in control-fed trout displaying usual growth. Hierarchical clustering of differentially expressed genes led to the formation of three distinct clusters: I, IIa and IIb. Cluster IIb, which includes genes up-regulated in muscles of refed trout compared with control-fed trout, defines the specific molecular signature of compensatory muscle growth following refeeding. Each row represents the expression pattern of a single gene, and each column corresponds to a single sample: columns 1 to 5, muscles from fasted trout; columns 6 to 10, 11 to 15 and 16 to 19, muscles from 4-, 11- and 36-days refed trout respectively; columns 20 to 23, muscles of control-fed trout. The expression levels are represented by colored tags, with red representing the highest levels of expression and green representing the lowest levels of expression

Fig. 3

Supervised clustering of chromatin-remodeling factors present in compensatory muscle growth signature. Columns are as in Fig. 2

Fig. 4

The compensatory muscle growth response involves only a subpart of the molecular signature of the hyperplastic growth zone. Venn diagram representing the distribution of genes of the compensatory muscle growth signature and genes up-regulated in the superficial hyperplastic growth zone of the late trout embryo. Functional categories inferred from genes common to the compensatory muscle growth and the hyperplastic growth zone signatures are detailed and major functional categories specific to hyperplastic growth zones are mentioned. The 312 genes specific of the compensatory muscle growth response were mostly related to translation, protein folding, RNA processing and ribosome biogenesis