PMEL is involved in snake color pattern transition from blotches to stripes [bulk RNA-seq]
Ontology highlight
ABSTRACT: Our genomic, bulk and single-cell transcriptomic, functional, and developmental characterization of the Terrazzo corn snake color morph and the extensive comparison with wild-type snakes puts forward the dual role of PMEL in snake skin coloration, both in the differentiation of chromatophores during embryogenesis and the melanogenesis in melanophores.
Project description:Our genomic, bulk and single-cell transcriptomic, functional, and developmental characterization of the Terrazzo corn snake color morph and the extensive comparison with wild-type snakes puts forward the dual role of PMEL in snake skin coloration, both in the differentiation of chromatophores during embryogenesis and the melanogenesis in melanophores.
Project description:<p><strong>BACKGROUND:</strong> Reptiles exhibit a wide variety of skin colors, which serve essential roles in survival and reproduction. However, the molecular basis of these conspicuous colors remains unresolved.</p><p><strong>RESULTS:</strong> We investigate color morph-enriched Asian vine snakes (<em>Ahaetulla prasina</em>), to explore the mechanism underpinning color variations. Transmission electron microscopy imaging and metabolomics analysis indicates that chromatophore morphology (mainly iridophores) is the main basis for differences in skin color. Additionally, we assemble a 1.77 Gb high-quality chromosome-anchored genome of the snake. Genome-wide association study and RNA sequencing reveal a conservative amino acid substitution (p.P20S) in <em>SMARCE1</em>, which may be involved in the regulation of chromatophore development initiated from neural crest cells. <em>SMARCE1</em> knockdown in zebrafish and immunofluorescence verify the interactions among <em>SMARCE1</em>, iridophores, and <em>tfec</em>, which may determine color variations in the Asian vine snake.</p><p><strong>CONCLUSIONS:</strong> This study reveals the genetic associations of color variation in Asian vine snakes, providing insights and important resources for a deeper understanding of the molecular and genetic mechanisms related to reptilian coloration.</p>
Project description:Reptilian skin coloration is spectacular and diverse, yet little is known about the ontogenetic processes that govern its establishment and the molecular signaling pathways that determine it. Here, we focus on the development of the banded pattern of leopard gecko hatchlings and the transition to black spots in the adult. With our histological analyses, we show that iridophores are present in the white and yellow bands of the hatchling and they gradually perish in the adult skin. Furthermore, we demonstrate that melanophores can autonomously form spots in the absence of the other chromatophores both on the regenerated skin of the tail and on the dorsal skin of the Mack Super Snow (MSS) leopard geckos. This color morph is characterized by uniform black coloration in hatchlings and black spots in adulthood; we establish that their skin is devoid of xanthophores and iridophores at both stages. Our genetic analyses identified a 13-nucleotide deletion in the PAX7 transcription factor of MSS geckos, affecting its protein coding sequence. With our single-cell transcriptomics analysis of embryonic skin, we confirm that PAX7 is expressed in iridophores and xanthophores, suggesting that it plays a key role in the differentiation of both chromatophores. Our in situ hybridizations on whole-mount embryos document the dynamics of the skin pattern formation and how it is impacted in the PAX7 mutants. We hypothesize that the melanophores–iridophores interactions give rise to the banded pattern of the hatchlings and black spot formation is an intrinsic capacity of melanophores in the postembryonic skin.
Project description:Background: Snakes exhibit a broad variety of adaptive colours and colour patterns, generated by the spatial arrangement of chromatophores, but little is known of the mechanisms responsible for these spectacular traits. Here, we investigate a monolocus trait with two recessive alleles that cause pattern aberrations in the corn snake: the motley and striped alleles. Results: We use mapping-by-sequencing to identify the genomic interval where the causal mutations reside. With our differential gene expression analyses, we find that CLCN2 (Chloride Voltage-Gated Channel 2), a gene within the genomic interval, is significantly downregulated in Motley embryonic skin. Furthermore, the insertion of a retrotransposon in CLCN2 results in a disruptive mutation in Stripe. We confirm the involvement of CLCN2 in colour pattern formation by producing knock-out snakes that present a phenotype similar to the Stripe one. In humans and mice, the disruption of CLCN2 results in leukoencephalopathy, as well as retinal and testes degeneration. Our single-cell transcriptomic analyses reveal that CLCN2 is indeed expressed in chromatophores during embryogenesis and in the adult brain. Although, we observe signs of vacuolation in the Stripe adult brain, the retina of Motley and Stripe animals is intact, and no fertility issues are reported for the carriers of both alleles. Conclusions: Our genomic, transcriptomic and functional analyses identify a plasma membrane anion channel to be involved in colour pattern development in Squamate reptiles and show that an active LTR-retrotransposon might be a key driver of trait diversification in corn snakes.
Project description:Background: Snakes exhibit a broad variety of adaptive colours and colour patterns, generated by the spatial arrangement of chromatophores, but little is known of the mechanisms responsible for these spectacular traits. Here, we investigate a monolocus trait with two recessive alleles that cause pattern aberrations in the corn snake: the motley and striped alleles. Results: We use mapping-by-sequencing to identify the genomic interval where the causal mutations reside. With our differential gene expression analyses, we find that CLCN2 (Chloride Voltage-Gated Channel 2), a gene within the genomic interval, is significantly downregulated in Motley embryonic skin. Furthermore, the insertion of a retrotransposon in CLCN2 results in a disruptive mutation in Stripe. We confirm the involvement of CLCN2 in colour pattern formation by producing knock-out snakes that present a phenotype similar to the Stripe one. In humans and mice, the disruption of CLCN2 results in leukoencephalopathy, as well as retinal and testes degeneration. Our single-cell transcriptomic analyses reveal that CLCN2 is indeed expressed in chromatophores during embryogenesis and in the adult brain. Although, we observe signs of vacuolation in the Stripe adult brain, the retina of Motley and Stripe animals is intact, and no fertility issues are reported for the carriers of both alleles. Conclusions: Our genomic, transcriptomic and functional analyses identify a plasma membrane anion channel to be involved in colour pattern development in Squamate reptiles and show that an active LTR-retrotransposon might be a key driver of trait diversification in corn snakes.
Project description:Corn snakes are emerging models for animal colouration studies. Here, we focus on the Terrazzo morph, whose skin pattern is characterized by stripes rather than blotches. Using genome mapping, we discover a disruptive mutation in the coding region of the Premelanosome protein (PMEL) gene. Our transcriptomic analyses reveal that PMEL expression is significantly downregulated in Terrazzo embryonic tissues. We produce corn snake PMEL knockouts, which present a comparable colouration phenotype to Terrazzo and the subcellular structure of their melanosomes and xanthosomes is also similarly impacted. Our single-cell expression analyses of wild-type embryonic dorsal skin demonstrate that all chromatophore progenitors express PMEL at varying levels. Finally, we show that in wild-type embryos PMEL-expressing cells are initially uniformly spread before forming aggregates and eventually blotches, as seen in the adults. In Terrazzo embryos, the aggregates fail to form. Our results provide insights into the mechanisms governing colouration patterning in reptiles.
Project description:While the vertebrate body plan is highly conserved amongst all species of this taxon, extreme variations thereof can be documented in snakes, which display both an absence of limbs and an unusually elongated trunk. As Hox genes are strong candidates both for the making and the evolution of this body plan, their comparative study in such a morphologically diverged group is informative regarding their potential causative importance in these processes. In this work we use an interspecies comparative approach where different aspects of regulation at the HoxD locus are investigated. We find that although spatial collinearity and associated epigenetic mark dynamics are conserved in the corn snake, other regulatory modalities have been largely restructured. A BAC transgenic approach indeed revealed that, while the majority of mesodermal enhancers in vertebrates appear to be mostly located outside of the cluster, the corn snake contains most mesodermal trunk enhancers within the HoxD cluster. We also find that, despite the absence of limbs and an altered Hoxd gene regulation in external genitalia, the bimodal chromatin structure at the corn snake HoxD locus is maintained. The analysis of particular enhancer sequences initially defined in the mouse and further isolated at the snake orthologous locus showed differences in their specificities for the limb and genital bud expression. Of particular interest, a snake counterpart of a mouse limb-only enhancer sequence evolved into a genital-only enhancer. Such a regulatory exaptation suggests that enhancer versatility may have been an important factor to accompany the transition towards the snake body plan. These results show that vertebrate morphological evolution is likely to have been associated with extensive reorganization at the HoxD regulatory landscapes while respecting a very conserved general regulatory framework.
Project description:While the vertebrate body plan is highly conserved amongst all species of this taxon, extreme variations thereof can be documented in snakes, which display both an absence of limbs and an unusually elongated trunk. As Hox genes are strong candidates both for the making and the evolution of this body plan, their comparative study in such a morphologically diverged group is informative regarding their potential causative importance in these processes. In this work we use an interspecies comparative approach where different aspects of regulation at the HoxD locus are investigated. We find that although spatial collinearity and associated epigenetic mark dynamics are conserved in the corn snake, other regulatory modalities have been largely restructured. A BAC transgenic approach indeed revealed that, while the majority of mesodermal enhancers in vertebrates appear to be mostly located outside of the cluster, the corn snake contains most mesodermal trunk enhancers within the HoxD cluster. We also find that, despite the absence of limbs and an altered Hoxd gene regulation in external genitalia, the bimodal chromatin structure at the corn snake HoxD locus is maintained. The analysis of particular enhancer sequences initially defined in the mouse and further isolated at the snake orthologous locus showed differences in their specificities for the limb and genital bud expression. Of particular interest, a snake counterpart of a mouse limb-only enhancer sequence evolved into a genital-only enhancer. Such a regulatory exaptation suggests that enhancer versatility may have been an important factor to accompany the transition towards the snake body plan. These results show that vertebrate morphological evolution is likely to have been associated with extensive reorganization at the HoxD regulatory landscapes while respecting a very conserved general regulatory framework.