ABSTRACT: White fin ornamentation in teleosts provides a striking model to study pigment cell diversity, differentiation, and patterning. In zebrafish (Danio rerio), white melanoleucophores (ML) and xantholeucophores (XL) produce white and yellowish-white fin patterns, respectively, arising from melanophore and xanthophore lineages. Here, we investigated white fin-pattern cells in zebrafish and a closely related cyprinid, the white cloud minnow (Tanichthys albonubes), which diverged 32–52 million years ago. We identified three distinct leucophore phenotypes in cyprinids: ML, XL, and Tanichthys leucophores, the latter containing white material but lacking substantial carotenoid pigmentation. Transmission electron microscopy revealed that XL and Tanichthys leucophores contain large pterinosome-like organelles, distinct from melanoleucophores and iridophores, suggesting different physicochemical bases for these white phenotypes. Fate-mapping in zebrafish demonstrated that XL arise directly from xanthophore-like progenitors, a process dependent on gap-junction-mediated communication via Gja5b and Cx39.4. Bulk mRNA sequencing of XL versus progenitor cells revealed upregulation of pteridine biosynthesis genes, notably sepiapterin reductase (spra), whose disruption via CRISPR/Cas9 abrogated white pigment formation in both zebrafish XL and Tanichthys leucophores. Chemical analyses confirmed enrichment of colorless pteridines, including biopterin and pterin, in tissues containing these cells. Together, our findings demonstrate that convergent white fin patterns in zebrafish and white cloud minnow rely on pteridine-based leucophores, arising via lineage-specific differentiation programs, and underscore the diversity of cellular and molecular strategies underlying white pigmentation in cyprinids.
