Regulation of Mammalian Sperm Motility

Abstract

The physiological regulation of sperm motility has become more amenable to investigation since the demonstration that CAMP and calcium play a role in modulating the functioning of the flagellar axoneme. Although the external triggering mechanisms that initiate motility and capacitation are still unknown, evidence supports a modification of the calcium balance by gated Ca2+ channels, accompanied by shifts in the internal pH. Ca2' and pH may in turn act indirectly through CAMP and CAMPdependent kinase (kinase,) to control the phosphorylation state of functional proteins in the flagellar axoneme. The role of calcium is of central importance, but it is clear that several separate Ca2+-dependent mechanisms are involved. Ca2+ controls the curvature of the sperm flagellum and, so, can change the motility of the sperm from progressive swimming to tumbling. Under the appropriate conditions, calcium appears to have the capacity to deactivate motility by activating phosphodiesterase and phosphatase. The deactivating effect of Ca2+ may be offset under some circumstances by coactivation of adenyl cyclase, so phosphorylation of the axoneme and the motility are maintained. The specific factors determining the predominant calcium effect are not yet known, but internal pH of the sperm may play a major role.Key Words: Sperm motility; Mammalian sperm; Mammalian reproduction; Flagellum; Calcium; pH. INTRODUCTIONThis review explores the influences regulating motility in mammalian sperm. Sperm motility depends on a flagellum, the organelle that develops the propulsive force for swimming. The cellular signals that modulate the action of the flagellar motor apparatus are the primary focus of this survey. Evidence is also examined to define the role of the male and female reproductive tracts in controlling sperm motility. To facilitate this review, structure/function relationships in mammalian sperm flagellum are briefly discussed. For the most part, the information included in this review has been obtained from research studies on mammalian sperm to identify the regulatory mechanisms most likely to be of physiological importance in mammalian reproduction. Received and accepted January 24, 1989. MORPHOLOGICAL PARAMETERSMammalian sperm swim by the propulsive action of a single flagellum. The structural foundation of the mammalian sperm flagellum is the 9 + 2 arrangement of microtubules that extends centrally through its entire length. This microtubule arrangement, called the axoneme, is common to all eukaryotic flagella ( Fig. 1) and also to cilia. Surrounding the axoneme are larger fibers, called coarse fibers or outer dense fibers (ODF), that are paired with the 9 outer doublet tubules. These fibers are anchored to the base of the flagellum in a caplike structure known as the connecting piece (CP). From there they taper in diameter along the flagellar length, terminating one-half to three-quarters of the way down the flagellum. The sperm mitochondria are wrapped around the basal one-third of the flagellum and this section is referred ...

ADP‐ribosylation of Rho proteins inhibits sperm motility

“…It has been suggested that the microtubules play the major role in sperm motility [22]. Because Rho proteins are apparently not involved in the regulation of the microtubule system [3,7,23] our data extend the current concept of flagellar motility.…”

Regulation of acrosome reaction of fowl spermatozoa: evidence for the involvement of protein kinase C and protein phosphatase-type 1 and/or -type 2A

“…First, demembranated fowl spermatozoa can be motile even in the presence of millimolar concentrations of Ca 2C (Ashizawa et al 1989), whereas such high concentrations of Ca 2C inhibit the motility of demembranated mammalian spermatozoa (White & Voglmayer 1986, Feng et al 1988. Secondly, cAMP is indispensable for the initiation and stimulation of flagellar motility of mammalian spermatozoa (for a review, see Tash & Means 1983, Lindemann & Kanous 1989), but is not necessary for fowl spermatozoa, especially at 40 8C (Ashizawa et al 1992).…”

A soluble adenylyl cyclase from sea urchin spermatozoa

“…This alkalinization activates the dynein ATPase needed for sperm swimming. This pH change also activates SUsAC [23], increasing cAMP levels, which in turn activates PKA to phosphorylate axonemal proteins needed for initiation and maintenance of sperm motility [9,34,[58][59][60][61][62][63][64].…”