Two Distinct Ca2+ Signaling Pathways Modulate Sperm Flagellar Beating Patterns in Mice1

Abstract

Hyperactivation, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization. It is characterized by asymmetrical flagellar beating and an increase of cytoplasmic Ca(2+). We observed that some mouse sperm swimming in the oviduct produce high-amplitude pro-hook bends (bends in the direction of the hook on the head), whereas other sperm produce high-amplitude anti-hook bends. Switching direction of the major bends could serve to redirect sperm toward oocytes. We hypothesized that different Ca(2+) signaling pathways produce high-amplitude pro-hook and anti-hook bends. In vitro, sperm that hyperactivated during capacitation (because of activation of CATSPER plasma membrane Ca(2+) channels) developed high-amplitude pro-hook bends. The CATSPER activators procaine and 4-aminopyridine (4-AP) also induced high-amplitude pro-hook bends. Thimerosal, which triggers a Ca(2+) release from internal stores, induced high-amplitude anti-hook bends. Activation of CATSPER channels is facilitated by a pH rise, so both Ca(2+) and pH responses to treatments with 4-AP and thimerosal were monitored. Thimerosal triggered a Ca(2+) increase that initiated at the base of the flagellum, whereas 4-AP initiated a rise in the proximal principal piece. Only 4-AP triggered a flagellar pH rise. Proteins were extracted from sperm for examination of phosphorylation patterns induced by Ca(2+) signaling. Procaine and 4-AP induced phosphorylation of proteins on threonine and serine, whereas thimerosal primarily induced dephosphorylation of proteins. Tyrosine phosphorylation was unaffected. We concluded that hyperactivation, which is associated with capacitation, can be modulated by release of Ca(2+) from intracellular stores to reverse the direction of the dominant flagellar bend and, thus, redirect sperm.

Bimodal rheotactic behavior reflects flagellar beat asymmetry in human sperm cells

“…Possible explanations for a curved midpiece are intrinsic curvature or symmetry breaking caused by a dynamic buckling instability. Intrinsic midpiece curvature is a known feature of rodent sperm (56) and has been linked to strongly asymmetric beat patterns (57). A less pronounced intrinsic curvature has been reported for human sperm, requiring artificial elevation of the intracellular calcium levels (58) absent in our experiments.…”

Functional anatomy of the mammalian sperm flagellum

“…Entry of Ca 21 from these two reservoirs cause disparate effects on the sperm motility pattern Suarez et al, 2007). This has lead them to the conclusion that there are two separate regulatory pathways acting in the midpiece and principal piece (Chang and Suarez, 2011). This may be a function of spatial distribution of the entrant Ca 21 , but it is also possible that there is difference in the responsiveness to Ca 21 in the principal and midpiece regions.…”

“…Consequently, the progressive changes in the motility pattern that depend on the flexibility of the midpiece, in addition to the large torques generated by the unique functional anatomy of the flagellum, are crucial to the physiology of mammalian reproduction. Although it is still uncertain to state to what extent chemotaxis plays in the fertilization process in mammals, the ability to convert between dominant bending in the two beat directions as demonstrated by Chang and Suarez (2011) may be a key factor in chemotactic orientation.…”

An alkaline follicular fluid fraction induces capacitation and limited release of oviduct epithelium-bound stallion sperm

“…As a result of Ca 2C influx, a small subpopulation of spermatozoa resumes motility, which rapidly progresses to hyperactivated motility (Hunter et al 1999) and generates sufficient force to detach the sperm from the oviduct epithelium such that they can escape from the mucosal pockets (Demott & Suarez 1992, Lishko & Kirichok 2010, Chang & Suarez 2011. Supported by this newly generated power, the released and hyperactivated sperm are able to progress through the viscous fluid of the oviduct and up to the site of fertilization at the ampullary-isthmic junction (Suarez & Pacey 2006, Suarez 2008a, Lishko & Kirichok 2010, Chang & Suarez 2011. Hyperactivation also assists the spermatozoa in penetrating the cumulus matrix and is essential for penetration of the zona pellucida to allow the fertilization of the oocyte (Publicover et al 2007.…”

“…Possible contributors, however, are likely to be present in oviduct epithelial secretions or around the cumulus-oocyte-complex (Suarez & Pacey 2006, Suarez 2008a, Lishko & Kirichok 2010, Chang & Suarez 2011. The molecular basis of hyperactivation is also incompletely understood.…”