NUCLEUS BASALIS MAGNOCELLULARIS AND HIPPOCAMPUS ARE THE MAJOR SITES OF FMR-1 EXPRESSION IN THE HUMAN FETAL BRAIN

The expression of the FMR-1 gene, which is implicated in fragile-X syn drome was investigated in human fetuses by in situ hybridization. In 8 and 9 week-old fetuses, FMR-1 mRNAs are expressed in proliferating an d migrating cells of the nervous system, in the retina, and in several non-nervous tissues. In the brain of 25 week-old fetuses, FMR-1 mRNAs are produced in all nearly differenciated structures, with the highes t level in cholinergic neurons of the nucleus basalis magnocellularis and in pyramidal neurons of hippocampus. The early transcription of FM R- 1 gene and the distribution of FMR-1 mRNAs in human fetuses suggest that alterations of FMP-1 gene expression may contribute to the patho genesis of fragile-X syndrome and especially the mental retardation.