Regional distribution of the leucine-rich glioma inactivated (LGI) gene family transcripts in the adult mouse brain

The leucine-rich glioma inactivated (LGI) gene subfamily contains four highly conserved members (LGI1, 2, 3 and 4), which have been described in human, mouse and other mammalians. Although their main roles remain unknown, LGI1 gene mutations have been found in human partial temporal lobe epilepsy. Moreover, previous studies showed that the products of these genes exert their function in the nervous system. The anatomical distribution of these gene transcripts in the brain might give some insight to elucidate their possible function. In this study, the pattern of expression of the four LGI genes was assessed in the brain of C57BL/6J adult mice by in situ hybridization. We found that the LGI1 transcript is mainly expressed in the dentate gyrus and CA3 field of the hippocampus. LGI2 and LGI4 genes, which showed a similar pattern of distribution with minor differences, were mostly expressed in the medial septal area, thalamic reticular nucleus and substantia nigra pars compacta. LGI3-expressing cells were distributed widespread, but were more consistently observed in the hippocampal formation, thalamic and hypothalamic nuclei, substantia nigra and reticular formation. In summary, LGI1 gene expression is very restricted to intrahippocampal circuitry, which might be related to its involvement in temporal lobe epilepsy. The patterns of expression of LGI2 and LGI4 genes are very similar and their distribution in the vertical limb of the diagonal band and in putative hippocampal interneurons suggests that the function of these genes might be related to the generation of hippocampal theta rhythm. Finally, LGI3 gene widespread expression in the brain suggests that its transcripts might be involved in a common cellular process present in different neuronal types.