The vomeronasal organ (VNO) is a chemosensory organ specialized in the detection of pheromones in higher vertebrates. In mouse and rat, two gene superfamilies, V1r1, 2 and V2r3, 4, 5 vomeronasal receptor genes, are expressed in sensory neurons whose cell bodies are located in, respectively, the apical and basal layers of the VNO epithelium [6]. Here, we report that neurons of the basal layer express another multigene family, termed H2-Mv, representing nonclassical class I genes of the major histocompatibility complex. The nine H2-Mv genes are expressed differentially in subsets of neurons. More than one H2-Mv gene can be expressed in an individual neuron. In situ hybridization with probes for H2-Mv and V2r genes reveals complex and nonrandom combinations of coexpression. While neural expression of Mhc class I molecules is increasingly being appreciated, the H2-Mv family is distinguished by variegated expression across seemingly similar neurons and coexpression with a distinct multigene family encoding neural receptors. Our findings suggest that basal vomeronasal sensory neurons may consist of multiple lineages or compartments, defined by particular combinations of V2r and H2-Mv gene expression.
