Abstract
All cells are covered by glycans, an individually unique layer of oligo- and polysaccharides that are critical moderators of self-recognition and other cellular-level interactions (e.g. fertilization). The functional similarity between these processes suggests that gamete surface glycans may also have an important, but currently overlooked, role in sexual selection. Here we develop a user-friendly methodological approach designed to facilitate future tests of this possibility. Our proposed method is based on flow cytometric quantification of female-induced sperm acrosome reaction and sperm surface glycan modifications in the Mediterranean mussel Mytilus galloprovincialis. In this species, as with many other taxa, eggs release water-soluble factors that attract conspecific sperm (chemoattraction) and promote potentially measurable changes in sperm behavior and physiology. We demonstrate that flow cytometry is able to identify sperm from other seawater particles as well as accurately measure both acrosome reaction and structural modifications in sperm glycans. This methodological approach can increase our understanding of chemically-moderated gamete-level interactions and individual-specific gamete recognition in Mytilus sp. and other taxa with similar, easily identifiable acrosome structure. Our approach is also likely to be applicable to several other species, since carbohydrate-mediated cellular-level interactions between gametes are universal among externally and internally fertilizing species.
Highlights
All cells are covered by glycans, an individually unique layer of oligo- and polysaccharides that are critical moderators of self-recognition and other cellular-level interactions
We found that forward scatter (FCS, particle size) and side scatter (SSC, granularity/complexity of the particle) characteristics of both pure seawater and egg water samples (n = 5, in both groups) were clearly different than that of sperm: both water samples contained only a small number of particles within the gated sperm population (SW: < 0.001%; EW < 1 .0%) (Fig. 1)
The present study demonstrates that flow cytometry is capable of separating M. galloprovincialis sperm from other seawater particles and highlights its utility in identifying and quantifying the egg water – induced acrosome reaction and sperm surface glycan modifications
Summary
All cells are covered by glycans, an individually unique layer of oligo- and polysaccharides that are critical moderators of self-recognition and other cellular-level interactions (e.g. fertilization). Our proposed method is based on flow cytometric quantification of female-induced sperm acrosome reaction and sperm surface glycan modifications in the Mediterranean mussel Mytilus galloprovincialis In this species, as with many other taxa, eggs release water-soluble factors that attract conspecific sperm (chemoattraction) and promote potentially measurable changes in sperm behavior and physiology. We demonstrate that flow cytometry is able to identify sperm from other seawater particles as well as accurately measure both acrosome reaction and structural modifications in sperm glycans This methodological approach can increase our understanding of chemically-moderated gamete-level interactions and individual-specific gamete recognition in Mytilus sp. The evidence that glycans exhibit striking structural complexity and play a key role both in cellular-level self-recognition and fertilization[37] (self-recognition in marine invertebrates: see e.g. Smith et al.38), suggests that glycans may mediate individual-specific gamete preferences during the fertilization process. Some current glycobiological tools, including lectins (carbohydrate-binding proteins), can offer powerful methodological approaches that can significantly increase our current understanding of the structure and function of the cell surface carbohydrates, especially in intact cells or tissues[39,41]
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