Localization of the acetylcholine receptor γ subunit gene to human chromosome 2q32→qter

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Abstract
The nicotinic acetylcholine receptor of skeletal muscle (CHRN in man, Acr in mouse) is a transmembrane protein composed of four different subunits (α, β, γ, and δ) assembled into the pentamer α2βγδ. These subunits are encoded by separate genes which derive from a common ancestral gene by duplication. We have used a murine full-length 1,900-bp-long cDNA encoding the γ subunit subcloned into M13 (clone γ18) to prepare single-stranded probes for hybridization to EcoRI-digested DNA from a panel of human × rodent somatic cell hybrids. Using conditions of low stringency to favor cross-species hybridization, and prehybridization with rodent DNA to prevent rodent background, we detected a single major human band of 30–40 kb. The pattern of segregation of this 30–40 kb band correlated with the segregation of human chromosome 2 within the panel and the presence of a chromosomal translocation in the distal part of the long arm of this t(X;2)(p22;q32.1) chromosome allowing the localization of the γ subunit gene (CHRNG) to 2q32→qter. The human genes encoding the γ and δ subunits have been shown to be contained in an EcoRl restriction fragment of approximately 20 kb (Shibahara et al., 1985). Consequently, this study also maps the δ subunit gene (CHRND) to human chromosome 2q32.1→qter. In the mouse, the Acrd and Acrg genes have been shown to be linked to Idh-1, Mylf(lDHI and MYL1 in humans, respectively) and to the gene encoding villin on chromosome 1. Interestingly, we have recently localized the human MYL1 gene to the same chromosomal fragment of human chromosome 2. These results clearly demonstrate a region of chromosomal homoeology between mouse chromosome 1 and human chromosome 2.