Imprinting the Gnas locus

Gnas is an enigmatic and rather complex imprinted gene locus. A single transcription unit encodes three, and possibly more, distinct proteins. These are determined by overlapping transcripts from alternative promoters with different patterns of imprinting. The canonical Gnas transcript codes for Gs alpha, a highly conserved signalling protein and an essential intermediate in growth, differentiation and homeostatic pathways. Monoallelic expression of Gnas is highly tissue-restricted. The alternative transcripts encode XL alpha s, an unusual variant of Gsa, and the chromogranin-like protein Nesp55. These transcripts are expressed specifically from the paternal and maternal chromosomes, respectively. Their existence in the Gnas locus might imply functional connections amongst them or with Gs alpha. In this review, we consider how imprinting of Gnas was discovered, the phenotypic consequences of mutations in each of the gene products, both in the mouse and human, and provide some conjectures to explain why this elaborate imprinted locus has evolved in this manner in mammals. Copyright (c) 2006 S. Karger AG, Basel.