Differential expression of the two GH genes during embryonic development of rainbow trout oncorhynchus mykiss in relation with the IGFs system

Abstract

The Growth hormone (GH)/insulin-like growth factor (IGF) system promotes embryonic growth in higher vertebrates. Such a system exists in salmonids, but exhibits an additional level of complexity resulting from a recent whole genome tetraploidisation. Thus, two nonallelic GH genes are present in the trout genome. Although the two GH genes are similar, the possibility remains that the two genes have evolved separately, acquiring a distinct expression pattern. In this study, using whole mounted in situ hybridisation, we observed a one stage delay between the appearance of GH-2 (Stage 22) and GH-1 (Stage 23) soon after pituitary formation (Stage 21). In addition, by double in situ hybridisation, we clearly evidenced two types of somatotroph, one expressing only GH-2 and the other type both GH-1 and GH-2 at Stage 24. Consequently, at this stage more cells expressed GH-2 than GH-1 as confirmed by quantitative RT-PCR. However at hatching, as in adult, the difference between the expression of the two GH genes was no longer observed. In addition, our immunohistochemical studies did not show any delay between the expression of the mRNA and its translation as a protein at Stage 24. A comparison of the expression pattern of the IGF system components (IGF-1, IGF-2, and the receptor type I) determined by real time RT-PCR, have shown an IGF-1 mRNA increase concomitantly to the appearance of GH expression. On the whole, our results demonstrate a differential regulation of GH-1 and GH-2 genes in rainbow trout embryo. The relationship observed between the expression of different component of the GH/IGF system seems to indicate that this system could be functional early on during embryonic development.

Sexual dimorphism in hepatic gene expression and the response to dietary carbohydrate manipulation in the zebrafish (Danio rerio)

“…As pepck is transcriptionally regulated by several other hormones in addition to insulin, interpretation of its regulation and its relative response in male and female zebrafish requires careful consideration. The IGF axis genes, igf-1, igf-2 and igfbp-5 were up-regulated in males, suggesting increased mitogenic activity similar to previous results in rainbow trout (Gabillard et al, 2003). It is possible that increased expression of components of the IGF axis in males is associated with protein economy, as one mechanism of IGF is to decrease protein degradation (Hill et al, 1999;Bell and McDermott, 2000).…”

The pro-opiomelanocortin genes in rainbow trout (Oncorhynchus mykiss): duplications, splice variants, and differential expression

“…It could be that many of the duplicated genes that have been discovered have significant physiological roles and thus it is advantageous to have redundancy or there could be other reasons why these genes persist. Evolution of novel function is one suggested reason why duplicate genes would persist, but the novelty could be subtle, such as tissue-specific expression (Coon et al 1999) or development stage-specific expression (Gabillard et al 2003) and may not be influenced by the coding sequence itself, but by promoter or regulatory elements upstream of the gene or, in genes such as the POMC gene, in its post-translational processing.…”

Differential expression of two GH receptor mRNAs following temperature change in rainbow trout (Oncorhynchus mykiss)

“…Quantitative real-time RT-PCR was performed as previously described (Gabillard et al 2003a). Briefly, 1 mg total RNA was used to perform the RT reaction (Applied Biosystems kit no.…”

“…Indeed, in rainbow trout, two GH and IGFR-I genes have been described (Agellon et al 1988, Greene & Chen 1999, Gabillard et al 2003a, while there is no evidence of IGF-I or -II duplicates. Several works have reported a weak differential expression of both GH genes according to the physiological state (Salam et al 1999, Mori et al 2001, Gabillard et al 2003a, while no obvious difference was observed between the two IGFR-I genes (Gabillard et al 2003b(Gabillard et al , 2003c. Recently, the GHR gene was found to be duplicated in salmon (Fukada et al 2004), but the regulation of both GHR genes has not yet been studied.…”