Résumé :
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AChE is organized in tetramers by two associated proteins, the collagen Q (ColQ) and a transmembrane protein (PRiMA: Proline Rich Membrane Anchor). ColQ targets tetramers to the basal lamina (BL) and PRiMA to the plasma membrane. Biochemical analyses suggest that hetero-oligomers of AChE, AChE-ColQ and AChE-PRiMA, accumulates at the NMJ. The hydrolytic function of these hetero-oligomers, depends on the catalytic properties of AChE, but also probably on their cellular, subcellular and subsynaptic localization. Yet, the distribution of the two hetero-oligomers, at the NMJ is still largely unknown. We have generated KO mice for ColQ and PRiMA to differentiate AChE-ColQ and AChE-PRiMA localizations. We have studied the distribution of AChE at the NMJ, at photonic and electron microscopic (EM) levels, after detection of AChE with an antibody or a toxin (fasciculin). In normal mice, AChE is detected mostly post-synaptically at the level of muscle cells. EM observations after immunogold detection of AChE show a labeling in the primary synaptic cleft and in secondary folds at the surface of the BL. AChE is also detected in association with the membrane of terminal Schwann cells (SC), myelinating SC surrounding axons and vascular muscle cells. In KO-ColQ mice, only a pre-synaptic labeling is detected in association with the membrane of terminals or pre-terminals. No post-synaptic staining is seen. In KO-PRiMA mice, AChE is detected at post-synaptic level, in the primary synaptic cleft and in secondary folds at the surface of the BL. Some labelings are seen at the membrane of SC and vascular muscle cells. Our results suggest that there is a segregation of the compartmentalization of AChE hetero-oligomers at the NMJ: AChE-ColQ is mostly post-synaptically associated with the BL, whereas AChE-PRiMA is located at pre-synaptic sites. This suggests also, that pre- and post-synaptic control of acetylcholine levels by AChE at the NMJ involves specific hetero-oligomers.
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