The species-specific egg receptor for sea urchin sperm adhesion is EBR1,a novel ADAMTS protein

Abstract

Species-specific adhesion of sperm to the egg during sea urchin fertilization involves the interaction of the sperm adhesive protein, bindin, and a complementary receptor on the egg surface, and serves to restrict the gene pool to individuals of the same species. We used PCR representation difference analysis to clone the species-specific egg receptor for bindin, EBR1, from Strongylocentrotus franciscanus (Sf) and S. purpuratus (Sp). Sf-EBR1 contains a novel ADAMTS-like N-terminal domain followed by ∼19 tandem EBR repeats consisting of alternating CUB and thrombospondin type 1 (TSP-1) domains where the last 10 EBR repeats are species-specific and highly conserved. Recombinant protein corresponding to the species-specific EBR repeat displays species-specific sperm adhesion and bindin-binding activity. The Sp-EBR1 ortholog has the same ADAMTS (a disintegrin and metalloprotease with thrombospondin type-1 modules) core region followed by eight and one-half tandem egg bindin receptor (EBR) repeats that share 88% identity with the Sf-EBR1 repeats, but has an entirely different species-specific domain consisting of hyalin-like (HYR) repeats. Thus, the species-specific domains of egg bindin receptor 1 (EBR1) from both species function as the egg surface receptor to mediate species-specific sperm adhesion. Received July 14, 2003; revised version accepted August 25, 2003. Sperm-egg interaction typically exhibits species specificity in most animals. Several molecules from both sperm and eggs that are thought to mediate gamete interaction have been identified in many animals. In abalone, the acrosomal protein of sperm, lysin, interacts with the egg vitelline envelope receptor for lysin (VERL) and creates a hole on the extracellular matrix (ECM) of the egg with species selectivity (Swanson and Vacquier 1997). In mammals, numerous molecules, such as galactosyltransferase, ADAM (a disintegrin and metalloprotease), and Sp56, have been identified from sperm and are proposed to interact with such as egg zona pellucida proteins Zp2, Zp3, or Integrins on the egg. However, a clear understanding of the specificity of these interactions and the regulation of species specificity is not yet known (Primakoff and Myles 2002;He et al. 2003).Acrosome-reacted sea urchin sperm adhere to glycoprotein receptors that are components of the vitelline envelope (VE) known as the ECM of the egg. It has been known for several decades that the protein bindin on the acrosome-reacted sea urchin sperm head mediates the species-specific adhesion of sperm to the VE during fertilization (Summers and Hylander 1975;Glabe and Vacquier 1977b;Vacquier and Moy 1977;Glabe et al. 1982). The egg ECM also serves as a major barrier for interspecific fertilization in mammalian systems (Yanagimachi 1981(Yanagimachi , 1994. In sea urchins, the complementary receptor for bindin was shown to be an ∼350-kD protein on the VE of the egg (Glabe and Vacquier 1978;Carroll et al. 1986;Ohlendieck et al. 1993). However, the identity of this receptor has remained elusive, and att...

Speciation and the evolution of gamete recognition genes: pattern and process

“…We found 13 and 14 different repeats in these two individuals (allowing for 1 or 2 base substitutions due to possible Taq and cloning error) in 26 and 27 clones, respectively (SR Palumbi and J Alipaz, in preparation). This suggests an average of 6-7 different repeats in the 11 repeat array in an individual allele, similar to the number of different repeats in the single cloned allele presented by Kamei and Glabe (2003). Other sea urchin species show similar patterns.…”

“…The Van Doorn model depends on the egg receptor reaching a critical threshold of egg surface diversity. Though early data from abalone suggested this might be minimal because of the homogenizing effects of concerted evolution (Swanson and Vacquier, 1998), data from sea urchins shows profligate variation (Figure 4; Kamei and Glabe, 2003). The Van Doorn model also presupposes some ecological diversification, a common feature of sympatric sea urchin and abalone species (Lessios, 2007).…”

“…Sequences were obtained by amplifying genomic DNA with primers that recognize intron-exon junctions present in each repeat, cloning PCR products into plasmid vectors and sequencing individual clones. (Data from Kamei and Glabe, 2003;SR Palumbi and J Alipaz, unpublished. ) urchins, bindin genes show a very different pattern, with a large amount of polymorphism within species as well as large differences between them.…”

“…However, in sea Figure 4 Amino-acid variation in the hyalin-like repeats motifs of the sea urchin sperm receptor within and between species. The top 11 sequences are from different repeats of the EBR1 gene sequenced from Strongylocentrotus purpuratus (Kamei and Glabe, 2003), showing variation at six amino-acid positions. Sequences from one individual Echinometra mathaei (Em16) and one E. oblonga (Eo27) show strong homology to S. purpuratus at about half of the amino-acid positions but are highly variable among repeats.…”

Postcopulatory sexual selection: Darwin's omission and its consequences

“…The section of the bindin molecule that is involved in attachment to the egg varies sharply among species in 3 genera, in each of which there is evidence that positive selection produced the changes; in 3 other genera, divergence in the attachment portion is low, and there is no evidence for positive selection (84). Egg molecules involved in both induction of the acrosome reaction and the docking process on the egg have diverged in 1 genus that has rapidly diverging bindin (87).…”