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Evidence for an increased sensitivity to Ca2+ in the flagella of sperm from tw32/+mice
C B Lindemann1, J S Goltz, K S Kanous
1Department of Biological Sciences, Oakland University, Rochester, Michigan 48309-4401.
Abstract:
The majority of sperm from mice carrying the tw32 haplotype undergo hyperactivation sooner than sperm from +/+ mice of the same strains (Olds-Clarke, Dev Biol 131:475-482, 1989). To investigate the mechanism underlying this abnormal motility, the Ca2+ sensitivity of their flagellar apparatus was compared to that of age- and strain-matched controls using Triton X-100-extracted sperm. Under these conditions, the curvature of the sperm flagellum is controlled by the free calcium concentration. Sperm from mice carrying the tw32 haplotype consistently exhibited a change in flagellar curvature at lower free calcium concentrations than controls. In addition, intact sperm from tw32/+ mice were much more likely than congenic control sperm to have a hook-like bend in the midpiece, which persisted throughout most of the beat cycle. Sperm exhibiting the hooked middle piece could be converted to a more normal appearance by 2 mM procaine, which immobilizes cytoplasmic calcium. Thus an increased sensitivity of the sperm motor apparatus to calcium could be the cause of the precocious hyperactivation of sperm from mice carrying the tw32 haplotype.
Insights
Sperm from mice with the tw32 haplotype show precocious hyperactivation due to increased calcium sensitivity in their flagellar apparatus. This heightened sensitivity causes abnormal motility and flagellar curvature.
Area of Science:
- Reproductive Biology
- Sperm Motility
- Calcium Signaling
Background:
- Sperm from mice with the tw32 haplotype exhibit premature hyperactivation compared to controls.
- The underlying mechanism for this abnormal sperm motility is not fully understood.
Purpose of the Study:
- To investigate the calcium (Ca2+) sensitivity of the sperm flagellar apparatus in mice carrying the tw32 haplotype.
- To determine if altered Ca2+ sensitivity contributes to the precocious hyperactivation observed in tw32/+ mice.
Main Methods:
- Comparison of Ca2+ sensitivity in Triton X-100-extracted sperm from tw32/+ mice and age-/strain-matched controls.
- Analysis of sperm flagellar curvature in response to varying free calcium concentrations.
- Assessment of intact sperm morphology, including midpiece bending, and the effect of procaine.
Main Results:
- Sperm from tw32/+ mice showed altered flagellar curvature at lower free calcium concentrations than controls.
- A significant proportion of intact tw32/+ sperm displayed a persistent hook-like midpiece bend.
- Procaine, which immobilizes cytoplasmic calcium, normalized the hooked midpiece morphology.
Conclusions:
- The sperm motor apparatus in tw32/+ mice exhibits increased sensitivity to calcium.
- This heightened Ca2+ sensitivity is a likely cause of the precocious hyperactivation and abnormal motility observed in these mice.