Myosin Va and kinesin II motor proteins are concentrated in ribosomal domains (periaxoplasmic ribosomal plaques) of myelinated axons

Abstract

Periaxoplasmic ribosomal plaques (PARPs) are discrete ribosome-containing domains distributed intermittently along the periphery of axoplasm in myelinated fibers. Thus, they are structural formations in which translational machinery is spatially organized to serve as centers of protein synthesis for local metabolic requirements and perhaps repair as well. Because of evidence that RNA is transported to putative PARP domains, involving both microtubule- and actin-based mechanisms, it was of interest to investigate whether cytoskeletal motor proteins exhibit a nonrandom localization within PARP domains. Axoplasm, from large Mauthner fibers and rat or rabbit spinal ventral nerve root fibers, removed from the myelin sheath in the form of an "axoplasmic whole-mount" was used for this analysis. PARP domains were identified either by specific immunofluorescence of rRNA, ribosomal P antigen, or by nonspecific RNA fluorescence using RNA binding dyes YOYO-1 or POPO-1. A polyclonal antibody (pAb) against the motor domain of myosin Va showed prominent nonrandom immunofluorescence labeling in PARP domains. Similarly, monoclonal antibodies (mAb) against kinesin KIF3A and a pan-specific antikinesin (mAb IBII) also showed a preponderant immunofluorescence in PARP domains. On the other hand, H2, a mAb antikinesin KIF5A, exhibited only random immunofluorescence labeling in axoplasm, as was also the case with pAb antidynein heavy chain immunofluorescence. Several possible explanations for these findings are considered, primary among which is targeted trafficking of translational machinery that results in local accumulation of motor proteins. Additional possibilities are trafficking functions intrinsic to the domain, and/or functions that govern dynamic organizational properties of PARPs.

A novel 65 kDa RNA-binding protein in squid presynaptic terminals

“…Also, periaxoplasmic ribosomal plaques, discrete ribosome-containing domains found along myelinated axons, contain both MVa protein and its mRNA (Calliari et al, 2002;Sotelo-Silveira et al, 2004).…”

“…MVa and its mRNA have been identified in periaxoplasmic ribosomal plaques in axons (Calliari et al, 2002;Sotelo-Silveira et al, 2004) and, perhaps most remarkably, members of the myosin V class have been implicated in the transport and cytoplasmic localization of mRNA (Jansen et al, 1996;Yoshimura et al, 2006;Chang et al, 2008;Salerno et al, 2008). The exact function of MVa at the synapse has yet to be clarified.…”

Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit

“…Myosin Va and kinesin II proteins also coincide with PARPs (285). Besides these molecular motor proteins, axoplasmic plaques appear to contain BC1 RNA, a brain-specific transcript of RNA polymerase III.…”

Myo2p, a class V myosin in budding yeast, associates with a large ribonucleic acid–protein complex that contains mRNAs and subunits of the RNA-processing body

“…Translational machinery is spatially organized in PARPS to serve as centers for protein synthesis (Sotelo-Silveira et al 2006). Myosin Va is thought to accumulate in PARPS as a result of targeted transport of translational machinery and/or mRNAs into these structures (Sotelo-Silveira et al 2004). Myosin Va is also found to associate with translocation in liposarcoma (TLS), an RNA-binding protein in neurons (Yoshimura et al 2006).…”