Melanin Deficiency Is Associated with Immune Homeostasis in the Critically Endangered Yangtze Sturgeon (Acipenser dabryanus).

The Yangtze sturgeon (Acipenser dabryanus), a critically endangered living fossil whose wild populations are now extinct, faces new challenges to survival in captive breeding. Among these, the emergence of albino and gray color morphs raise fundamental questions about the molecular basis and physiological consequences of pigmentation loss. Here, we integrated histological, transcriptomic, and quantitative PCR to investigate pigmentation variation and associated immune alterations in this species. Histology revealed a complete absence of melanin in albino individuals and marked reduction in gray morphs. Transcriptomic profiling across the three color morphs uncovered a broad downregulation of core melanogenic genes, including PMEL, TYR, TYRP1, DCT, SLC45A2, OCA2, MREG, and MLPH, indicating impaired melanosome formation, melanin synthesis, and intracellular transport. Notably, pigmentation loss coincided with systematic changes in the expression of immune-related genes: phagosome pathway genes (e.g., C3, MHC I/II, TAP2) were downregulated, while pro-inflammatory mediators (e.g., IL-8, IL-17, CXCL10) were upregulated, suggesting a transcriptional pattern correlated with reduced expression of pathogen defense-related genes and increased genes associated with inflammation mediators. These findings reveal a mechanistic correlation between melanin deficiency and immune dysfunction in a basal vertebrate lineage, offering the first molecular evidence of an association between albinism and altered immune-related gene expression in sturgeons and highlighting its implications for conservation and captive management.