Very cool paper on species-specific fertilization in fish mediated by a single Ly6/uPAR protein, Bouncer. biorxiv.org/content/early/…
Bouncer expressed on oocytes is necessary for fertilization in zebrafish by mediating sperm-egg binding and entry. And, incredibly, oocytes expressing Bouncer from a distantly related fish (medaka) could be fertilized by medeka sperm, but not zebrafish sperm, and form chimeras!
This is super interesting, and the molecular mechanisms will be very interesting to follow up. In particular, what's the sperm receptor for Bouncer (since Bouncer is only required on the oocyte - it's not a homotypic interaction)? How did that pair of proteins co-evolve?
The other very interesting observation is that Bouncer is a GPI-linked protein - so it has no clear signaling capability (complicated mechanisms involving clustering / lipid rafts aside), consistent with the observations that the main action is to mediate sperm-egg binding.
What's super interesting is that this is a not-unique mechanism - GPI-linked proteins acting as regulators of adhesion for survival / mating in a species-specific manner. Self-(species)-recognition may be not through obvious signaling mechanisms, just binding!
Examples include the yeast mating proteins (both a- and alpha-agglutinin), Flo1 (also in yeast) acting as a greenbeard gene sufficient for species-specific flocculation (ncbi.nlm.nih.gov/pubmed/19013280), and csaA in slime mold fruiting body formation (ncbi.nlm.nih.gov/pubmed/12511650).
And the nearest human/mouse homolog of Bouncer, SPACA4, is also a GPI-linked protein (like most Ly6/uPAR family members).
So on top of the extremely exciting findings in this paper, there seems to be a general trend towards species-specific interactions across eukaryotes mediated by GPI-linked proteins - high affinity interactions where binding is the key, not signaling.
Awesome preprint, exciting read, and very cool implications! #ASAPBio #Evolution
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