Comparative transcriptomics of the skin in the white and black olm (Proteus anguinus)Valenčič, Meta (Avtor) Kostanjšek, Rok (Mentor) Recknagel, Hans (Komentor) comparative transcriptomicsmelanogenesisProteus anguinustroglomorphyReduced pigmentation is a hallmark of cave-modified organisms; however, the underlying evolutionary mechanisms are not completely understood yet. The white and the black olm (Proteus anguinus anguinus/parkelj) are ideal subjects to study this phenomenon, as they are closely related and the former displays reduced skin pigmentation, whereas the latter exhibits darkly pigmented, melanized skin. Since anatomical and biochemical studies conducted thus far have not been able to fully explain the mechanisms behind the difference in their pigmentation, we decided to explore the genetic, evolutionary, and histological aspects of this phenomenon using comparative transcriptomics and RNA fluorescence in situ hybridization (RNA-FISH). Differential gene expression analysis showed that genes involved in pigment synthesis were less expressed in the skin of the white olm compared to the black olm. Furthermore, alternative splicing and isoform switch analysis identified increased expression of a nonfunctional isoform in the white olm relative to the black olm in the bloc1s6 gene, which might potentially block melanosome biogenesis in melanophores of the white olm. Through variant calling analysis of the transcriptomic data, nucleotide sequences of both lineages were compared, and potential relaxed purifying selection was detected among core melanogenesis genes. Among the differentially expressed genes, the tyrosinaserelated protein 1 (tyrp1) was chosen as a target for RNA-FISH for visual localisation of the melanogenesis in the olm’s skin. The presence of tyrp1 mRNA was confirmed inside pigment cells of the black olm, but not in the white olm, suggesting downregulation of melanogenesis in the skin of the white olm. Despite identified opportunities for methodological improvement, we successfully elucidated the genetic background and evolutionary mechanisms underlying reduced pigmentation in the skin of the white olm, which, in combination with the localisation of melanogenesis in the olm’s skin, provide an important step toward understanding the processes driving this universal trait of cave animals.M. Valenčič20262026-10-14 07:15:26Magistrsko delo/naloga189725sl