Expression and localisation of IGF‐binding protein mRNAs in regenerating rat skeletal muscle

Abstract

The expression of the insulin-like growth factor-binding proteins (IGFBP) -3, -4, -5 and -6 was investigated in neonatal, in normal adult and in regenerating rat skeletal muscle. Semi-quantification was done by densitometric scannings of Northern blots. The expression of all investigated IGFBPs, with the exception of IGFBP-5, was higher in neonatal than in adult muscle. During postischaemic regeneration the expression of all IGFBPs increased, but with different time schedules. IGFBP-3 increased transiently during the early phase of regeneration, while IGFBP-4, -5 and -6 increased during the later phase of regeneration. In situ hybridisation on regenerating muscle showed that the expression of the various IGFBPs was cell specific; thus, IGFBP 3 was mainly expressed in macrophages, IGFBP-4 in connective tissue, IGFBP-5 in regenerating muscle cells, and IGFBP-6 in muscle cells, connective tissue and endothelium. Ligand blotting, using 125I-IGF-I as the ligand, showed a number of bands ranging between 24 and 44 kDa. Samples from neonatal and regenerating muscle contained much higher levels of all IGFBPs than those from normal adult muscle. An ordered and cell-specific expression of IGFBPs, allowing a strict regulation of IGF actions, is probably necessary to ensure an optimal regeneration process.

Coordinated regulation of the GH/IGF system genes during refeeding in rainbow trout (Oncorhynchus mykiss)

“…IGFBP-4 has a unique expression profile consisting of a lower mRNA abundance in starved fish, followed by a transitory but strong increase 1 day after refeeding. Given that in muscle, IGFBP-4 mRNA has been detected in connective tissue instead of muscle fibers (Jennische & Hall 2000), our observations suggest that the transitory increase of IGFBP-4 mRNA does not participate in myogenesis resumption.…”

Switching to fast growth: the insulin-like growth factor (IGF) system in skeletal muscle of Atlantic salmon

“…Expression of IGFBP-4 was correlated with that of IGF-I, and IGFBP-4 expression was the highest of all the binding proteins measured in fast muscle. IGFBP-4 is also known to be highly expressed in mammalian connective tissue (Boes et al, 1992;Jennische and Hall, 2000). Knudtson and colleagues reported that a C-terminal basic region of 20 amino acids was required for targeting the rat IGFBP-4 to connective tissue (Knudtson et al, 2001).…”

IGF-binding protein-4: biochemical characteristics and functional consequences

“…Northern blot analysis revealed that IGFBP-4 mRNA is widely expressed in adult rat tissues, including adrenal gland, testis, spleen, heart, liver, lung, kidney, stomach, hypothalamus and brain cortex, with liver being the site of the highest expression (Shimasaki et al 1990). The expression of IGFBP-4 was also examined in rat small intestine (Shoubridge et al 2001), smooth muscle (Smith et al 2001), skeletal muscle ( Jennische & Hall 2000), pancreas (Hill et al 1999), uterus and placenta (Cerro & Pintar 1997), mouse spinal cord (Arnold et al 2000), mouse and human thymus (Li et al 1996), human prostate (Thomas et al 2000), bone (Mohan et al 1995a) and ovary (Zhou & Bondy 1993, el Roeiy et al 1994) of several species. In the mouse embryo, IGFBP-4 transcripts were detected as early as 11 days postcoitum (dpc) in different regions, including telencephalon, mesencephalon, snout, tongue and differentiating sclerotomes.…”