EXPRESSION OF LOW-MOLECULAR-WEIGHT NEUROFILAMENT (NF-L) MESSENGER-RNADURING POSTNATAL-DEVELOPMENT OF THE MOUSE-BRAIN

A regional Northern blot analysis demonstrated that the highest levels of NF-L mRNA in the adult mouse brain are present in brain stem follo wed by mid-brain, with lower levels found in neocortex, cerebellum, an d hippocampus. The study was extended to the cellular level over the t ime course of postnatal development using in situ hybridization. This developmental analysis revealed that the expression of NF-L mRNA close ly follows the differentiation pattern of many large neurons during po stnatal neurogenesis. Neurons which differentiate early such as Purkin je, mitral, pyramidal, and large neurons of brain stem and thalamic nu clei, expressed high levels of NF-L mRNA at postnatal day 1. Early exp ression of NF-L mRNA may be required for the maintenance of the extens ive neurofilament protein networks that are detected within the axons of larger neurons. Smaller neurons which differentiate later, such as dentate gyms granule cells, small pyramidal and granule cells of the n eocortex, and granule cells of the cerebellum, exhibit a delayed expre ssion of NF-L mRNA.