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The interaction of sperm cells with exogenous DNA: a role of CD4 and major histocompatibility complex class II
M Lavitrano1, B Maione, E Forte
1Department of Experimental Medicine, University La Sapienza, Rome, Italy.
Abstract:
Mouse epidydimal sperm cells have the spontaneous ability to take up exogenous DNA, a part of which is further internalized into nuclei. We report here that sperm cells from MHC class II knockout mice have a reduced ability to bind DNA compared to sperm cells from wild-type animals. Spermatozoa from CD4 knockout mice are instead fully capable of binding exogenous DNA, yet lose the ability to further internalize it. MHC class II expression was not detected on sperm heads using monoclonal antibodies. In contrast, CD4 molecules were found on sperm heads by both immunofluorescence and Western blot analysis. Moreover, we show that nuclear internalization of exogenous DNA was prevented in wild-type sperm cells preincubated with anti-CD4 mAbs. These results support the conclusion that CD4 and MHC class II molecules play distinct roles in the process of sperm/DNA interaction: though not present in mature sperm cells, MHC class II expression appears to be required during spermatogenesis to produce sperm cells capable of taking up foreign DNA, while CD4 molecules present on sperm cells mediate the nuclear internalization of sperm-bound DNA.
Insights
MHC class II is needed for sperm to take up foreign DNA, while CD4 molecules on sperm help internalize it. This reveals distinct roles for these molecules in sperm-DNA interactions.
Area of Science:
- Reproductive biology
- Immunogenetics
Background:
- Sperm cells can naturally bind and internalize exogenous DNA.
- The molecular mechanisms governing sperm-DNA interaction are not fully understood.
Purpose of the Study:
- To investigate the roles of MHC class II and CD4 molecules in sperm's ability to interact with exogenous DNA.
- To elucidate the distinct functions of MHC class II and CD4 in DNA uptake and nuclear internalization by sperm.
Main Methods:
- Comparison of DNA binding and internalization in sperm from wild-type, MHC class II knockout, and CD4 knockout mice.
- Immunofluorescence and Western blot analysis to detect MHC class II and CD4 expression on sperm.
- Inhibition assays using anti-CD4 monoclonal antibodies (mAbs) to assess CD4's role in DNA internalization.
Main Results:
- Sperm from MHC class II knockout mice showed reduced DNA binding capacity.
- Sperm from CD4 knockout mice could bind DNA but failed to internalize it.
- MHC class II was not detected on mature sperm heads, while CD4 was present.
- Anti-CD4 mAbs blocked the nuclear internalization of DNA by wild-type sperm.
Conclusions:
- MHC class II, though absent on mature sperm, is crucial during spermatogenesis for developing sperm's DNA uptake capability.
- CD4 molecules on sperm heads actively mediate the nuclear internalization of bound exogenous DNA.
- MHC class II and CD4 play distinct, sequential roles in the process of sperm-mediated exogenous DNA internalization.