Involvement of cAMP-dependent unique signaling cascades in the decrease of serine/threonine-phosphorylated proteins in boar sperm head

Calmodulin is involved in the occurrence of extracellular Ca2+ -dependent full-type hyperactivation in boar ejaculated spermatozoa incubated with cyclic AMP analogs

In mammals, hyperactivation is essential for sperm fertilization with oocytes in vivo. Two types of hyperactivation "full-type and nonfull-type patterns" can be observed in the spermatozoa from boars, bulls, and mice. We have a hypothesis that the full-type hyperactivation is a physiological (in vivo) pattern and are elucidating its molecular bases. The aims of this study were to detect calmodulin in boar sperm flagella by Western blotting and indirect immunofluorescence and to investigate effects of extracellular Ca²⁺ and calmodulin antagonists "W-7 and W-5 (W-5; a less potent antagonist)" on the occurrence of full-type hyperactivation in boar spermatozoa. Calmodulin was specifically detected as the 17-kDa antigen in the flagella and postacrosomal region of the heads. Full-type hyperactivation could be induced effectively in the samples incubated with 3.42 mM CaCl₂ for 120-180 min, and it was significantly reduced in the concentration-dependent manners of W-7 and W-5. Suppressing effects of W-7 on the full-type hyperactivation were stronger than those of W-5. These observations indicate that flagellar calmodulin is involved in the occurrence of extracellular Ca²⁺ -dependent full-type hyperactivation in boar spermatozoa. This is the first indication of the intracellular Ca²⁺ -sensing molecule which can function in the full-type hyperactivation.

Identification of isoforms of calyculin A-sensitive protein phosphatases which suppress full-type hyperactivation in bull ejaculated spermatozoa

In bull spermatozoa, extracellular Ca²⁺-dependent full-type hyperactivation, which is characterized by the asymmetrical beating in whole parts of the middle/principal pieces, is suppressed by calyculin A-sensitive protein phosphatases. The aim of this study was to identify isoforms of these protein phosphatases. Ejaculated spermatozoa were used for the investigation on effects of protein phosphatase inhibitors (calyculin A with high specificity for both of protein phosphatases 1 and 2A, and okadaic acid with relatively higher specificity for protein phosphatase 2A than protein phosphatase 1) on the induction of extracellular Ca²⁺-dependent full-type hyperactivation by incubation with CaCl₂ and cAMP analog (cBiMPS). They were also used for the immunodetection of protein phosphatases 1α, 1β, 1γ, 2Aα and 2Aβ. Percentages of full-type hyperactivated spermatozoa significantly increased after incubation with calyculin A (10 nM) in a concentration-dependent manner of CaCl₂ (0-3.42 mM), though only minor increases in the percentages of full-type hyperactivated spermatozoa were observed after incubation with okadaic acid (10 nM). Moreover, the immunodetection of protein phosphatase isoforms showed sperm connecting piece and flagellum included protein phosphatases 1α and 1γ, but did not do the other isoforms. These results suggest that calyculin A-sensitive and okadaic acid-less sensitive protein phosphatases (1α and 1γ) are suppressors for the extracellular Ca²⁺-dependent full-type hyperactivation in bull ejaculated spermatozoa.

Reconsideration of the evaluation criteria for bull ejaculated sperm motility in the context of rotation

Progressive movement of spermatozoa has conventionally been regarded as a good indicator of motility. However, bull spermatozoa exhibit two types of progressive movement: progressive/planar movement without rotation and progressive/helical movement with rotation. The aim of this study was to reconsider the evaluation criteria of bull ejaculated sperm motility in the context of rotation. Here, we compared the movement patterns of ejaculated spermatozoa with relatively high and low protein kinase A (PKA)-mediated signaling activities, because sperm motility is positively regulated by PKA-mediated signaling activities. We prepared sperm samples with high and low PKA-mediated signaling activities by suspending spermatozoa in media containing either the stimulator (NaHCO₃) or inhibitor (KH-7) of adenylyl cyclase 10, and we then investigated movement patterns and relative velocities using a microscopic high-speed camera and recording system. In the control medium without NaHCO₃ and KH-7, most spermatozoa exhibited round/planar movement without rotation and asymmetrical bends in the principal pieces. NaHCO₃ significantly promoted changes in movement patterns from round/planar movement to progressive/planar movement (without rotation) as well as symmetrization of flagellar bends and increased relative velocities. KH-7 significantly increased spermatozoa exhibiting progressive/helical movement (with rotation), decreased relative velocities, and symmetrized flagellar bends with a reduction in their size. These indicate that progressive/planar movement (without rotation) and fast movement characterize the movement patterns of bull ejaculated spermatozoa with high PKA-mediated signaling activities. A sign of reduced PKA-mediated signaling activity is not only slow movement but also helical movement (with rotation). Thus, it is beneficial to add a new parameter of “rotation” to the evaluation criteria of bull ejaculated sperm motility.

Characterization of extracellular Ca2+ -dependent full-type hyperactivation in ejaculated boar spermatozoa preincubated with a cAMP analog

Ejaculated boar spermatozoa exhibit two types of hyperactivation: full and non-full. Full-type hyperactivation is characterized by the asymmetrical bending of the entire middle piece-principal piece and a twisting/figure-eight-like trajectory, and can be induced by simple incubation with CaCl₂ after preincubation with a cAMP analog (Sp-5,6-dichloro-1-β-D-ribofuranosyl-benzimidazole-3',5'-cyclic monophosphorothioate [cBiMPS]). Here, we compared the sperm flagellar motility after treatments with elevators of [Ca²⁺ ]_i (cBiMPS/CaCl₂ , thimerosal, procaine, and 4-aminopyridine) to characterize the regulatory mechanism of extracellular Ca²⁺ -dependent, full-type hyperactivation in ejaculated boar spermatozoa, and examined the possible involvement of Transient receptor potential cation channel subfamily C member 3 (TRPC3) in this event using the specific inhibitor Pyr3. Full-type hyperactivation was induced by a 60-min incubation with CaCl₂ following a 180-min preincubation with cBiMPS but without Ca²⁺ . Thimerosal-treated spermatozoa exhibited full-type hyperactivation in a manner independent of extracellular Ca²⁺ ; conversely, this was not observed in procaine- or 4-aminopyridine-treated spermatozoa. A 20-min treatment with Pyr3 between preincubation with cBiMPS and incubation with CaCl₂ , significantly suppressed the normal phenotype. These observations indicated that mechanisms underlying full-type hyperactivation in spermatozoa incubated with CaCl₂ after preincubation with cBiMPS are different from those in the thimerosal-treated spermatozoa. Furthermore, indirect immunofluorescence localized TRPC3 in the upper segment of the middle piece, which bends asymmetrically during full-type hyperactivation but not in non-full-type hyperactivation, suggesting that TRPC3 may be involved in the extracellular Ca²⁺ -dependent full-type hyperactivation in ejaculated boar spermatozoa.