Tandem Repetitive D Domains of the Sperm Ligand Zonadhesin Evolve Faster in the Paralogue Than in the Orthologue Comparison |
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Authors: | Holger Herlyn Hans Zischler |
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Institution: | (1) Institute of Anthropology, University of Mainz, Colonel-Kleinmann-Weg 2 (SB II), D-55099, Germany |
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Abstract: | Gene duplication is regarded as an important evolutionary mechanism creating genetic and phenotypic novelty. At the same time,
the evolutionary mechanisms following gene duplication have been a subject of much debate. Here we analyze the sequence evolution
of zonadhesin, a mammalian sperm ligand that binds to the oocyte zona pellucida in a species-specific manner. In pig, rabbit,
and primates, precursor zonadhesin comprises, among others, one partial and four complete tandem repetitive D domains. The
mouse precursor is distinguished by 20 additional partial D3 domains consisting of 120 amino acids each. This gene structure
allows sequence comparison in both paralogues and orthologues. Detailed sequence analysis reveals that D domains evolve faster
across paralogues than orthologues. Moreover, at the codon level, partial D3 paralogues of mouse show evidence of positive
selection, whereas the corresponding orthologues do not. Individual posttranslational motif patterns and positive selection
point to neofunctionalization of partial D3 paralogues of mouse, rather than subfunctionalization. However, as we found additional
evidence for homogenization by partial gene conversion, sequence evolution of partial D3 paralogues of mouse might be better
described as a combination of divergent and convergent evolution. So far, the divergence at the codon level has outbalanced
the convergence at the level of smaller fragments. The probable driving force behind the evolutionary patterns observed is
sexual selection. We finally discuss whether the functional determination influences the evolutionary regime acting on sperm
ligands and egg receptors, respectively.
Reviewing Editor: Dr. Yves Van de Peer] |
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Keywords: | Sperm-egg interaction Neofunctionalization Subfunctionalization Positive selection Motif prediction Sexual selection |
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