title: SPARC triggers a cell-autonomous program of synapse elimination.
abstract: Elimination of the excess synaptic contacts established in the early stages of neuronal development is required to refine the function of neuronal circuits. Here we investigate whether secreted protein acidic and rich in cysteine (SPARC), a molecule produced by glial cells, is involved in synapse removal. SPARC production peaks when innervation of the rat superior cervical ganglion and the tail of Xenopus tropicalis tadpoles are remodeled. The formation of new cholinergic synapses in autaptic single-cell microcultures is inhibited by SPARC. The effect resides in the C-terminal domain, which is also responsible for triggering a concentration- and time-dependent disassembly of stable cholinergic synapses. The loss of synaptic contacts is associated with the formation of retracted axon terminals containing multivesicular bodies and secondary lysosomes. The biological relevance of in vitro results was supported by injecting the tail of Xenopus tropicalis tadpoles with peptide 4.2, a 20-aa sequence derived from SPARC that mimics full-length protein effects. Swimming was severely impaired at ∼5 h after peptide application, caused by the massive elimination of neuromuscular junctions and pruning of axonal branches. Effects revert by 6 d after injection, as motor innervation reforms. In conclusion, SPARC triggers a cell-autonomous program of synapse elimination in cholinergic neurons that likely occurs when protein production peaks during normal development.
authors.affiliation: Laboratory of Neurobiology, Department of Pathology and Experimental Therapeutics, University of Barcelona, L'Hospitalet de Llobregat, Barcelona 08907, Spain; Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Barcelona 08907, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: López-Murcia
authors.affiliation: Laboratory of Neurobiology, Department of Pathology and Experimental Therapeutics, University of Barcelona, L'Hospitalet de Llobregat, Barcelona 08907, Spain; Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Barcelona 08907, Spain.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Terni
authors.affiliation: Laboratory of Neurobiology, Department of Pathology and Experimental Therapeutics, University of Barcelona, L'Hospitalet de Llobregat, Barcelona 08907, Spain; Bellvitge Biomedical Research Institute (IDIBELL), L'Hospitalet de Llobregat, Barcelona 08907, Spain allobet@ub.edu.
authors.forename: Artur
authors.identifier: http://orcid.org/0000-0001-5797-6782
authors.initials: A
authors.lastname: Llobet
mesh_terms: D000818:Animals; D007150:Immunohistochemistry; D007814:Larva; D008854:Microscopy, Electron; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009420:Nervous System / Q000254:growth & development*; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology*; D015676:Osteonectin / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D010455:Peptides / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D017783:Superior Cervical Ganglion / Q000166:cytology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology*; D014981:Xenopus
chemical_list: C498233:4.2 kDa peptide; D015676:Osteonectin; D010455:Peptides
keywords: SPARC; Xenopus tropicalis; cholinergic synapse; neuron–glia interaction; synapse elimination