Subspecies of protein kinase C in the rat spinal cord

In this review, the developmental expression of alpha-, beta- and gamma-subspecies of protein kinase C (PKC) in the rat spinal cord was summarized, and possible roles of this protein for neuronal differentiation were discussed. Faint immunoreactivity (IR) for PKCs was first demonstrated in the cervical spinal cord on embryonic day 13 (E-13). It gradually became stronger, and between E-18 and postnatal day 0 (P-0), strong IR for these three subspecies was uniformly distributed throughout the spinal cord. While thereafter, it irregularly declined, and reached the adult pattern around P-28 or P-35. The motor neurons began to express these three subspecies of PKC in the nucleus, perikaryal cytoplasm, dendrites and axons, soon after they began to differentiate. In the perikaryal cytoplasm, the IR was expressed mainly on ribosomes, and in the dendrites, mainly on cytoskeletal elements. At the late embryonic and early postnatal stages, IR for these PKCs was expressed both in the presynaptic terminals and on the postsynaptic densities. While thereafter, the IR in the former declined, and was detected only on the postsynaptic densities. The dorsal corticospinal tract transiently expressed strong IR for these PKCs at the early postnatal developmental stages, but thereafter, the IR rapidly declined. The developing corticospinal tract fibers expressed strong IR mainly on cytoskeletal elements. In contrast, in the mature fibers, IR for alpha-PKC was detected on some cytoskeletal elements, and for beta-PKC on almost all cytoskeletal elements, but IR for gamma-PKC, mainly on smooth surfaced endoplasmic reticulum. These findings suggest that PKC might be involved in several aspects of neuronal differentiation such as gene expression, protein synthesis, morphological maturation and synapse formation.