Characterization of GPR101 transcript structure and expression patterns

Abstract

We recently showed that Xq26.3 microduplications cause X-linked acrogigantism (X-LAG). X-LAG patients mainly present with growth hormone and prolactin-secreting adenomas and share a minimal duplicated region containing at least four genes. GPR101 was the only gene highly expressed in their pituitary lesions, but little is known about its expression patterns. GPR101 transcripts were characterized in human tissues by 5’-RACE and RNAseq, while the putative promoter was bioinformatically predicted. We investigated GPR101 mRNA and protein expression by RT-qPCR, whole-mount in situ hybridization, and immunostaining, in human, rhesus monkey, rat, and zebrafish. We identified four GPR101 isoforms characterized by different 5’ untranslated regions (UTRs) and a common 6.1 kb-long 3’UTR. GPR101 expression was very low or absent in almost all adult human tissues examined, except for specific brain regions. Strong GPR101 staining was observed in human fetal pituitary and during adolescence, whereas very weak/absent expression was detected during childhood and adult life. In contrast to humans, adult pituitaries of monkey and rat expressed GPR101, but in different cell types. Gpr101 is expressed in the brain and pituitary during rat and zebrafish development; in rat pituitary Gpr101 is expressed only after birth and showed sexual dimorphism. This study shows that different GPR101 transcripts exist and that the brain is the major site of GPR101 expression across different species, although divergent species- and temporal-specific expression patterns are evident. These findings suggest an important role for GPR101 in brain and pituitary development and likely reflect the very different growth, development and maturation patterns among species.

Germline and mosaic mutations causing pituitary tumours: genetic and molecular aspects

“…While GPR101 was found to be significantly overexpressed in the pituitary tumours of XLAG patients, it was not expressed in sporadic somatotroph PAs or in the adult human pituitary gland (Trivellin et al 2014). On the contrary, GPR101 protein expression was described using immunohistochemistry in the foetal human pituitary and in pituitary samples obtained from adolescents, suggesting that its expression, at least in the pituitary gland, could be age dependent and induced during development and adolescence (Trivellin et al 2016a). The expression pattern of GPR101 in the pituitary gland also seems to be species specific.…”

“…The expression pattern of GPR101 in the pituitary gland also seems to be species specific. In the pituitary of the rhesus monkey, for example, GPR101 was uniquely expressed, at the protein level, in gonadotroph cells, while in the rat pituitary gland, GPR101 was found to be expressed only in a subpopulation of somatotroph cells (Trivellin et al 2016a).…”

“…In mice, Gpr101 mRNA was identified primarily in the central nervous system, and particularly in the hypothalamus and amygdala (Bates et al 2006). In humans, GPR101 was found to be highly expressed at the mRNA level in the nucleus accumbens, as well as in the medulla and the occipital lobe (Trivellin et al 2016a). Interestingly, Gpr101 was found to be expressed in about half of the neuronal cells expressing the anorexigenic neuropeptide pro-opiomelanocortin in mice (Nilaweera et al 2007).…”

Somatic mosaicism underlies X-linked acrogigantism syndrome in sporadic male subjects

“…GHRH is a very potent physiological stimulator of GH, and GHRH secretion by a discreet population of hypothalamic neurons is tightly regulated by integrated central and peripheral signals (Gahete, et al 2009; Veldhuis, et al 2012). GPR101 is specifically expressed in regions of the hypothalamus and brain that are involved in integrating such signals, the dysregulation of GHRH secretion and pituitary pathology in XLAG syndrome (Bates, et al 2006; Trivellin, et al 2016; Trivellin et al 2014). Taken together these findings suggest a mechanism by which even modestly increased copy number of GPR101 could lead to the severe pituitary gigantism observed in XLAG syndrome patients with an Xq26.3 duplication; some of these mosaicism levels may be beyond that which can currently be detected by our techniques.…”

AIP and the somatostatin system in pituitary tumours

“…Most of the cases result from de novo germline or embryonic mosaic somatic mutations (Beckers et al 2015, Daly et al 2016a,b, Iacovazzo et al 2016b, Trivellin et al 2016.…”