Differential expression of FMR1, FXR1 and FXR2 proteins in human brain and testis

Lack of expression of the fragile X mental retardation protein (FMRP)results in mental retardation and macroorchidism, seen as the majorpathological symptoms in fragile X patients. FMRP is a cytoplasmic RNA-binding protein which cosediments with the 60S ribosomal subunit. Recently,two proteins homologous to FMRP were discovered: FXR1 and FXR2. These novelproteins interact with FMRP and with each other and they are alsoassociated with the 60S ribosomal subunit. Here, we studied the expressionpattern of the three proteins in brain and testis by immunohistochemistry.In adult brain, FMR1, FXR1 and FXR2 proteins are coexpressed in thecytoplasm of specific differentiated neurons only. However, we observed adifferent expression pattern in fetal brain as well as in adult and fetaltestis, suggesting independent functions for the three proteins in thosetissues during embryonic development and adult life.