Maturation of a large neurofilament protein (NF 150K) in rat postnatal development

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Abstract
The mammalian neurofilament is made of three neu‐ron‐specific proteins with approximate molecular weights of 70 kilodaltons (kDa) (NF 70K), 150 kDa (NF 15OK), and 200 kDa (NF 200K) by SDS‐PAGE. As previously reported in the rat by Strocchi et al (J Neurochem 39:1132–1141,1982) and Nixon et al (J Cell Biol) 94:150–58, 19821, NF 150K comprises three molecular weight variants with the same isoelectric point. A fourth lower molecular weight and slightly less acidic variant was identified by monoclonal and polyclonal antibodies reacting with the a‐helical middle domain of NF 150K. With few exceptions, this lower molecular weight variant did not stain with monoclonal antibodies reacting with the peripheral carboxyterminal domain. Staining with these antibodies was abolished or markedly reduced following neurofilament dephosphorylation. The distribution of the NF 150K variants varied in different regions of the nervous system. The higher molecular weight variant (component a) was less prominent in brain compared to spinal cord, optic nerve, and sciatic nerve. Further‐more, the lower molecular weight variant (component d) was not identified in optic nerve and sciatic nerve. All four variants were identified in brain and spinal cord extracts of newborn rats with monoclonal and polyclonal antibodies reacting with the a‐helical middle domain of NF 150K. As a general rule (see Results for exceptions) monoclonal antibodies reacting with the carboxy‐terminal region of NF 150K did not stain the variants in newborn rat brain extracts until day 10 when immunoreactivity of component a first appeared. The adult pattern was first observed on postnatal day 15. With the same antibodies component a was already stained at birth in spinal cord extracts while the adult pattern first appeared on day 10. The delayed appearance of immunoreactivity of the NF 150K variants in development suggests the occurrence of post‐translational modifications probably related to axonal maturation.