Co-expression of IGFs and GH receptors (GHRs) in gilthead sea bream (Sparus aurata L.): sequence analysis of the GHR-flanking region

Abstract

The tissue-specific expression of IGFs and GH receptors (GHRs) was analyzed in gilthead sea bream (Sparus aurata L.) as an attempt to understand the functional partitioning of duplicated GHRs on the regulation of fish growth by season and aging. Gene transcripts were measured in liver, muscle, and adipose tissue by means of quantitative real-time PCR assays. In juvenile fish, concurrent increases in circulating levels of GH and IGF-I and hepatic mRNA levels of IGF-I and GHR-I were evidenced with the summer growth spurt. Conversely, muscle and adipose tissue expression of GHR-I and IGF-II were significantly upregulated by overwintering. The aging decrease of growth rates was accompanied by a reduced activity of the liver GH/IGF axis, and parallel increases in muscle IGF expression would be dictated at the local tissue level by the enhanced expression of GHR-I. Extra-hepatic expression of IGFs and GHR-II did not correlate seasonally in juvenile fish, and nonsignificant effects of aging were found on the summer expression of GHR-II in any analyzed tissue. One transcription start site was identified by RLM-RACE in GHR-I and GHR-II. Sequence analyses indicated that both genes have TATA-less promoters containing consensus initiator sequences and downstream promoter elements surrounding the transcription start site. Conserved CCAAT-boxes and GC-rich regions were retrieved in the GHR-I promoter, whereas stress-and redoxsequence elements (cAMP-responsive element-binding protein, activator proteins; AP-1, and AP-4) were characteristic features of GHR-II. All this supports the functional partitioning of fish GHRs regardless of fish species differences.

Chronic exposure to the parasite Enteromyxum leei (Myxozoa: Myxosporea) modulates the immune response and the expression of growth, redox and immune relevant genes in gilthead sea bream, Sparus aurata L.

“…Of note, in the present study, the HK expression of GHR-II and IGF-II was not altered in both parasitized and non-parasitized R fish. This is in accordance with the recent notion that GHR-I and II have evolved as duplicated GHR subtypes having different patterns of tissue distribution, post-receptor signalling and hormonal transcriptional regulation [79,80].…”

Correlation with larval body size of mRNA levels of growth hormone, growth hormone receptor I and insulin-like growth factor I in larval torafugu Takifugu rubripes

“…On the other hand, the mRNA level of ghr2 was not correlated to the L T or D B of T. rubripes in the present study. These results are consistent with previous reports that the hepatic mRNA levels of ghr1 , rather than ghr2 , correlated with body growth and plasma Igf‐I levels in S. aurata (Benedito‐Palos et al , 2007; Saera‐Vila et al , 2007). Furthermore, it has been reported that S. aurata Ghr2 lacks certain amino acid residues that are essential for the formation of dimeric structure and downstream signalling such as cysteine and tyrosine, respectively, located at extracellular and intracellular regions in the case of Ghr‐1, respectively (Saera‐Vila et al , 2005).…”

Identification and expression analysis of two growth hormone receptors in zanzibar tilapia (Oreochromis hornorum)

“…These models include season (Wargelius et al 2005;Nilsen et al 2008), age (Saera-Vila et al 2007), dietary composition (Gómez-Requeni et al 2004a, b), stress confinement (Saera-Vila et al 2009) and parasite challenges (Sitjà-Bobadilla et al 2008), which cover a wider range of physiological conditions rather than fasting alone. So it cannot be adequately determined here whether the increases in GHR1 and GHR2 are solely attributed to fasting or a combination of handling, confinement and fasting.…”