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Transcripts encoding the sperm surface protein tMDC II are non-functional in the human
J Frayne1, E A Dimsey, J A Jury
1Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, U.K.
Abstract:
Five members of the MDC (metalloproteinase-like,disintegrin-like cysteine-rich domain) family of proteins (fertilin alpha, fertilin beta, tMDC I, tMDC II and tMDC III) are expressed on the surface of macaque (Macaca fascicularis) sperm, where they have been proposed to play a role in sperm-egg binding via an interaction between their disintegrin-like domain and one or more integrins on the egg plasma membrane. Of these, two (fertilin alpha and tMDC I) have recently been shown to be non-functional in the human. Here we report the existence of multiple isoforms of human tMDC II transcripts in the human, all of which are also non-functional owing to the presence of deletions and in-frame termination codons, when compared with the macaque orthologue, a finding which is further supported by the lack of immunoreactivity on Western blots of human testis and sperm extracts probed with a macaque anti-tMDC II polyclonal antiserum. These results are discussed in the context of our proposed model for multiple proteins implicated in sperm-egg interactions.
Insights
Human tMDC II transcripts, unlike macaque orthologues, contain non-functional deletions and stop codons. This finding suggests human tMDC II is not involved in sperm-egg interactions, impacting reproductive biology research.
Area of Science:
- Reproductive Biology
- Molecular Biology
- Cell Biology
Background:
- Metalloproteinase-like, disintegrin-like, cysteine-rich domain (MDC) proteins are found on sperm surfaces.
- These proteins, including fertilin alpha, beta, tMDC I, II, and III, are hypothesized to mediate sperm-egg binding through interactions with egg integrins.
Purpose of the Study:
- To investigate the functionality of human tMDC II transcripts in sperm-egg interactions.
- To compare human tMDC II with its macaque orthologue.
Main Methods:
- Analysis of human tMDC II transcript isoforms.
- Comparison with macaque tMDC II sequences.
- Western blot analysis of human testis and sperm extracts using macaque anti-tMDC II antiserum.
Main Results:
- Multiple non-functional isoforms of human tMDC II transcripts were identified.
- These isoforms contain deletions and in-frame termination codons compared to the macaque orthologue.
- Western blot analysis showed a lack of immunoreactivity, confirming the absence of functional tMDC II in human sperm.
Conclusions:
- Human tMDC II is non-functional and unlikely to participate in sperm-egg binding.
- Previous findings of non-functional human fertilin alpha and tMDC I are consistent with these results.
- This research contributes to understanding the complex molecular mechanisms of human fertilization.