TRITON-SOLUBLE PHOSPHOVARIANTS OF THE HEAVY NEUROFILAMENT SUBUNIT IN DEVELOPING AND MATURE MOUSE CENTRAL-NERVOUS-SYSTEM

The low abundance of soluble neurofilament (NF) subunits in mature axo ns has suggested that newly synthesized NF proteins rapidly assemble i nto highly stable polymers and associate with the Triton X-100-insolub le cytoskeleton, The dynamic nature of these subunit associations in v ivo remains unresolved, and the applicability of this assembly model t o NFs in other neuronal compartments or to developing neurons is unkno wn, Here, we report that a unique pool of Triton X-100-soluble, extens ively phosphorylated, high molecular weight NF subunits (NF-H, or H-20 0) are abundantly expressed in the mouse CNS during early postnatal de velopment and persist in the perikaryal compartment of some mature neu rons, Triton-soluble H-200 subunits appeared at postnatal day 1.4 (P14 ) and remained high through P60, beyond which the percentage declined to marginal levels by P120, Medium and low molecular weight NF (NF-M a nd NF-L, respectively) were at all times only detectable within the cy toskeleton, Comparison of soluble and cytoskeleton-associated H-200 im munoreactivity indicated that certain phosphorylation-dependent epitop es were confined to the cytoskeleton, Pulse-chase radiolabeling analys es in optic pathway demonstrated that some Triton-soluble NF-H subunit s are extensively phosphorylated within retinal perikarya before they are incorporated into Triton-insoluble structures, These findings indi cate that the assembly behaviors of NF-H differ substantially from tho se of NF-M and IVF-L, and that the interaction of NF-H with NFs may be more dynamic than is generally recognized, especially during brain de velopment and within specific compartments of mature neurons. (C) 1997 Wiley-Liss, Inc.