Fig. 1

Medaka Bncra, but not Bncrb, is required on the medaka egg for fertilization.

A Genomic regions and resulting transcripts and proteins of the bncr locus in zebrafish (blue; GRCz11/danRer11) and medaka (yellow; Ensembl 93: Jul 2018 (GRCh38.p12)). Zebrafish Bncr is encoded by a single-exon gene (NM_001365726.1). The medaka bncr locus (ENSORLG00000004579) comprises three exons that are alternatively spliced to generate Bncra (exons 1 and 3; ENSORLT00000005754) and Bncrb (exons 1 and 2; ENSORLT00000005758). The location of the CRISPR-induced genomic deletions for medaka bncra (5-nt deletion in exon 3) and bncrb (38-nt deletion in exon 2) are indicated by asterisks. The gene structures are depicted with untranslated regions (thin rectangles) and coding sequences (thick rectangles). B Protein sequence alignment of the LU domains of Bncra and Bncrb from selected fish species (Supplementary Data File 2). Note that seahorse Bncrb is a predicted translation product from a genomic region. Purple shading indicates amino acids with at least 30% conservation. The percent amino acid sequence identity (% ID) within the mature domains is indicated. Disulfide bonds are indicated by orange brackets. C Expression values of bncra and bncrb transcripts in medaka ovary and testis based on RNA-seq³⁶ from three biological replicates for each tissue. The Y-axis is plotted in log₁₀ scale. TPM transcripts per million. D Quantification of in vivo fertilization rates from wild type and medaka bncra and bncrb mutants; tg[res], transgenic rescue. (Kruskal–Wallis test with Dunn’s multiple comparisons test; ns not significant). Means ± SD are indicated in (C) and (D).