FMR1 gene expression in olfactory neuroblasts from two males with fragile X syndrome.

The fragile X mental retardation 1 gene (FMR1) mutation is strongly correlated with specific and marked neurobehavioral and neuroanatomical abnormalities. The protein product, FMRP, is highly expressed in neurons of the normal mammalian brain, and absent or in low levels in leukocytes from individuals with fragile X (FraX)-associated mental impairment. Inferences which arise from these findings are that FMRP has a critical role in the development and functioning of the brain, and that leukocyte-derived molecular assessments provide a good indicator of FMR1 expression in that organ. This latter conclusion appears true in most cases even though the typical FMR1 mutation is an unstable triplet repeat expansion which demonstrates somatic heterogeneity within and across tissues. Blood to brain correspondence in FraX patients has only rarely been confirmed by the direct study of human brain specimens and, to our knowledge, it has never been studied in living individuals with the FMR1 mutation. In this report, we describe the FMR1 patterns in olfactory neuroblasts (ON) from two living brothers with expansion mutations in their leukocytes who are mentally retarded and autistic. ON were chosen for study because they are accessible neurons closely linked to the brain. In both subjects, the ON genotype was highly, but not perfectly, consistent with that observed in leukocytes. Protein phenotypes across tissues were completely consistent showing the absence of FMRP-immunoreactivity (-ir). These results augment the limited amount of direct evidence which indicates that FMR1 mutation patterns in leukocytes are a good, albeit potentially fallible, reflection of such patterns in the brain. This report further demonstrates the feasibility of using ON samples to evaluate the FMR1 mutation in humans in vivo.

Immunoblotting patterns of cytoskeletal dendritic protein expression in human neocortex.

Qualitative and quantitative evaluations of cytoskeletal proteins are critical for understanding physiological and pathological processes affecting the nervous system. Most of such studies on human samples have only used immunohistochemical techniques. We describe a complementary immunoblotting approach, for the assessment of neuronal cytoskeletal proteins, which employs fresh frozen postmortem tissues. We found that cytosolic fractions are suitable for qualitative and quantitative evaluations of four major dendritic cytoskeletal proteins: microtubule-associated protein (MAP)-2, MAP-5, and high- and medium-molecular-weight nonphosphorylated neurofilaments. The enhanced chemiluminescence (ECL) technique revealed consistent and distinctive immunoblotting patterns for all four proteins in both monkey (no postmortem delay) and human (17-34 h postmortem interval) samples, some of which differed from those found in rodents. Quantitations of blots, by tissue protein-optical density curves that demonstrated linearity of the measurements in the 0- to 100-microgram range, support the feasibility of these immunoassays for the study of neurologic disorders.