Practice question

Hyperactivated motility characterized by high-amplitude asymmetrical flagellar whipping enables sperm to escape oviductal reservoir and penetrate viscous cumulus matrix. Activation depends on alkaline and progesterone-induced opening of CatSper, multimeric calcium channel complex comprising four alpha subunits and auxiliary proteins localized to flagellar principal piece. Progesterone from cumulus cells via ABHD2 receptor triggers CatSper-mediated calcium influx raising intracellular calcium, modifying axonemal sliding. Pharmacological blockade or genetic null of CatSper abolishes hyperactivation and leads to infertility despite normal counts. Zona proteins and sodium influx do not drive this motility conversion; CatSper represents master chemotactic and motility regulator in mammalian fertilization cascade.