Super-resolution imaging of live sperm reveals dynamic changes of the actin cytoskeleton during acrosomal exocytosis

Ana Romarowski, Ángel G. Velasco Félix, Paulina Torres Rodríguez, María G. Gervasi, Xinran Xu, Guillermina M. Luque, Gastón Contreras-Jiménez, Claudia Sánchez-Cárdenas, Héctor V. Ramírez-Gómez, Diego Krapf, Pablo E. Visconti, Dario Krapf, Adán Guerrero, Alberto Darszon, Mariano G. Buffone

Instituto de Biología y Medicina Experimental (IBYME), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Buenos Aires C1428ADN, Argentina; Laboratorio Nacional de Microscopía Avanzada, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos 62210, México; Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México (UNAM), Cuernavaca, Morelos 62210, México; Department of Veterinary and Animal Science, Paige Labs, University of Massachusetts, Amherst, MA 01003, USA; Department of Electrical and Computer Engineering, School of Biomedical Engineering, 1301 Campus Delivery, Fort Collins, CO 80523, USA; Instituto de Biología Molecular y Celular de Rosario (CONICET-UNR), Rosario, Santa Fe S2000EZP, Argentina

Abstract: Filamentous actin (F-actin) is a key factor in exocytosis in many cell types. In mammalian sperm, acrosomal exocytosis (denoted the acrosome reaction or AR), a special type of controlled secretion, is regulated by multiple signaling pathways and the actin cytoskeleton. However, the dynamic changes of the actin cytoskeleton in live sperm are largely not understood. Here, we used the powerful properties of SiR-actin to examine actin dynamics in live mouse sperm at the onset of the AR. By using a combination of super-resolution microscopy techniques to image sperm loaded with SiR-actin or sperm from transgenic mice containing Lifeact-EGFP, six regions containing F-actin within the sperm head were revealed. The proportion of sperm possessing these structures changed upon capacitation. By performing live-cell imaging experiments, we report that dynamic changes of F-actin during the AR occur in specific regions of the sperm head. While certain F-actin regions undergo depolymerization prior to the initiation of the AR, others remain unaltered or are lost after exocytosis occurs. Our work emphasizes the utility of live-cell nanoscopy, which will undoubtedly impact the search for mechanisms that underlie basic sperm functions

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Journal of Cell Science – doi:10.1242/jcs.218958
Received 12 April 2018; Accepted 25 September 2018; Published 8 November 2018