Association between microtubules and mitochondria in myelinated axons of Lacerta muralis

Abstract

The spatial relationship between microtubules and mitochondria was studied in myelinated axons of the ventral and dorsal spinal roots of the lizard Lacerta muralis by use of quantitative methods in single and serial sections. Microtubules mainly occurred in groups of 3 to 10. The mean density of microtubules was found to be significantly higher close to mitochondria than in the rest of the axoplasm. In single sections, 59-62% (according to the root region examined) of the microtubule groups were found to be 'associated' with mitochondria; this percentage rose to 74-76% in serial sections. The examination in serial sections of progressively longer segments of the same microtubule groups showed that the longer the segments of microtubule groups examined the higher was the percentage of microtubule groups 'associated' with mitochondria. The results obtained show that in the axons studied in the present research a non-accidental spatial association exists between microtubule groups and mitochondria. This evidence supports the suggestion that the microtubule groups play a role in the movement of mitochondria along the axon, even though it does not clarify the precise nature of this role.

Mitochondrial transport and docking in axons

“…SNPH likely acts as a docking receptor specific for axonal mitochondria through a unique interaction with the microtubule-based cytoskeleton. These findings provide a molecular explanation for the previously identified biochemical interactions between neuronal mitochondria and microtubules (Linden et al, 1989; Jung et al, 1993; Leterrier et al, 1994), and morphological observations of axonal ultrastructures, which revealed cross-bridges between mitochondria and microtubules in vivo (Smith et al, 1977; Hirokawa, 1982; Benshalom and Reese, 1985; Pannese et al, 1986; Price et al, 1991). These cross-bridges may represent both dynamic (motor proteins) and static links (docking or anchoring proteins) between axonal mitochondria and the microtubule-based cytoskeleton.…”

Docking of Axonal Mitochondria by Syntaphilin Controls Their Mobility and Affects Short-Term Facilitation

“…Given that the sequence of SNPH is not homologous to any known microtubule-binding protein in the database, SNPH likely acts as a docking receptor specific for axonal mitochondria through a unique interaction with the microtubule-based cytoskeleton. These findings provide a molecular explanation for the biochemical interactions between neuronal mitochondria and microtubules (Linden et al, 1989;Jung et al, 1993;Leterrier et al, 1994), and morphological observations of axonal ultra-structures, which revealed cross-bridges between mitochondria and microtubule in vivo (Smith et al, 1977;Hirokawa, 1982;Benshalom and Reese, 1985;Pannese et al, 1986;Price et al, 1991). These cross-bridges may represent both dynamic (motor proteins) and static (docking or adaptor proteins) links between axonal mitochondria and the microtubule-based cytoskeleton.…”

The axonal transport of mitochondria

“…This indicates that there might be an apparatus for specific mitochondrial docking. Although most of the cross-bridges observed between mitochondria and the axonal cytoskeleton in vivo (Smith et al, 1977;Hirokawa, 1982;Benshalom and Reese, 1985;Pannese et al, 1986;Hirokawa and Yorifuji, 1986;Price et al, 1991) now seem to be dynamic (perhaps motor proteins themselves), others are likely to represent more static links. Indeed, the specialized presynaptic region of the calyx of Held contains a mitochondrion-associated adherens complex, a clearly observable physical substrate for holding and organizing the mitochondria (Rowland et al, 2000).…”