Development of the pteridine pathway in the zebrafish, Danio rerio

Comprehensive bioinformatics analysis of structural and functional consequences of deleterious missense mutations in the human QDPR gene

Quinonoid dihydropteridine reductase (QDPR) is an enzyme that regulates tetrahydrobiopterin (BH4), a cofactor for enzymes involved in neurotransmitter synthesis and blood pressure regulation. Reduced QDPR activity can cause dihydrobiopterin (BH2) accumulation and BH4 depletion, leading to impaired neurotransmitter synthesis, oxidative stress, and increased risk of Parkinson's disease. A total of 10,236 SNPs were identified in the QDPR gene, with 217 being missense SNPs. Over 18 different sequence-based and structure-based tools were employed to assess the protein's biological activity, with several computational tools identifying deleterious SNPs. Additionally, the article provides detailed information about the QDPR gene and protein structure and conservation analysis. The results showed that 10 mutations were harmful and linked to brain and central nervous system disorders, and were predicted to be oncogenic by Dr. Cancer and CScape. Following conservation analysis, the HOPE server was used to analyse the effect of six selected mutations (L14P, V15G, G23S, V54G, M107K, G151S) on the protein structure. Overall, the study provides insights into the biological and functional impact of nsSNPs on QDPR activity and the potential induced pathogenicity and oncogenicity. In the future, research can be conducted to systematically evaluate QDPR gene variation through clinical studies, investigate mutation prevalence across different geographical regions, and validate computational results with conclusive experiments.Communicated by Ramaswamy H. Sarma.

Triphenyltin induced darker body coloration by disrupting melanocortin system and pteridine metabolic pathway in a reef fish, Amphiprion ocellaris

Triphenyltin (TPT) is a typical persistent organic pollutant whose occurrence in coral reef ecosystems may threaten the survival of reef fishes. In this study, a brightly colored representative reef fish, Amphiprion ocellaris was used to explore the effects of TPT at environmental levels (1, 10, and 100 ng/L) on skin pigment synthesis. After the fish were exposed to TPT for 60 days, the skin became darker, owing to an increase in the relative area of black stripes, a decrease in orange color values while an increase in brown color values, and an increase in the number of melanocytes in the orange part of the skin tissues. To explore the mechanisms by which TPT induces darker body coloration, the enzymatic activity and gene expression levels of the members of melanocortin system that affect melanin synthesis were evaluated. Leptin levels and lepr expression were found to be increased after TPT exposure, which likely contributed to the increase found in pomc expression and α-melanocyte-stimulating hormone (α-MSH) levels. Then Tyr activity and mc1r, tyr, tyrp1, mitf, and dct were upregulated, ultimately increasing melanin levels. Importantly, RT-qPCR results were consistent with the transcriptome analysis of trends in lepr and pomc expression. Because the orange color values decreased, pterin levels and the pteridine metabolic pathway were also evaluated. The results showed that TPT induced BH4 levels and spr, xdh, and gch1 expression associated with pteridine synthesis decreased, ultimately decreasing the colored pterin content (sepiapterin). We conclude that TPT exposure interferes with the melanocortin system and pteridine metabolic pathway to increase melanin and decrease colored pterin levels, leading to darker body coloration in A. ocellaris. Given the importance of body coloration for the survival and reproduction of reef fishes, studies on the effects of pollutants (others alongside TPT) on body coloration are of high priority.

Pigment Identification and Gene Expression Analysis during Erythrophore Development in Spotted Scat (Scatophagus argus) Larvae

Red coloration is considered an economically important trait in some fish species, including spotted scat, a marine aquaculture fish. Erythrophores are gradually covered by melanophores from the embryonic stage. Despite studies of black spot formation and melanophore coloration in the species, little is known about erythrophore development, which is responsible for red coloration. 1-phenyl 2-thiourea (PTU) is a tyrosinase inhibitor commonly used to inhibit melanogenesis and contribute to the visualization of embryonic development. In this study, spotted scat embryos were treated with 0.003% PTU from 0 to 72 h post fertilization (hpf) to inhibit melanin. Erythrophores were clearly observed during the embryonic stage from 14 to 72 hpf, showing an initial increase (14 to 36 hpf), followed by a gradual decrease (36 to 72 hpf). The number and size of erythrophores at 36 hpf were larger than those at 24 and 72 hpf. At 36 hpf, LC-MS and absorbance spectrophotometry revealed that the carotenoid content was eight times higher than the pteridine content, and β-carotene and lutein were the main pigments related to red coloration in spotted scat larvae. Compared with their expression in the normal hatching group, rlbp1b, rbp1.1, and rpe65a related to retinol metabolism and soat2 and apoa1 related to steroid hormone biosynthesis and steroid biosynthesis were significantly up-regulated in the PTU group, and rh2 associated with phototransduction was significantly down-regulated. By qRT-PCR, the expression levels of genes involved in carotenoid metabolism (scarb1, plin6, plin2, apoda, bco1, and rep65a), pteridine synthesis (gch2), and chromatophore differentiation (slc2a15b and csf1ra) were significantly higher at 36 hpf than at 24 hpf and 72 hpf, except for bco1. These gene expression profiles were consistent with the developmental changes of erythrophores. These findings provide insights into pigment cell differentiation and gene function in the regulation of red coloration and contribute to selective breeding programs for ornamental aquatic animals.

The genetic basis of conspicuous coloration in the Guadeloupean anole: Evolution by sexual and ecological selection

Understanding how natural selection acts on the genome and contributes to the process of speciation is a primary aim of the study of evolution. Here we used natural variation in two subspecies of the Guadeloupean anole (Anolis marmoratus ssp.), from the island of Guadeloupe in the Lesser Antilles, to explore the genomic basis of adaptation and speciation in Anolis lizards. These subspecies inhabit distinct ecological environments and display marked differences in adult male color and pattern. We sequenced the complete genomes of 20 anoles, 10 from each subspecies, at 1.4× coverage. We used genome-wide scans of population differentiation, allele frequency spectrum, and linkage disequilibrium to characterize the genomic architecture within and between the subspecies. While most of the genome was undifferentiated, we observed five large divergent regions. Within these regions we identified blocks, 5 kb pairs in length, enriched for fixed single nucleotide polymorphisms. These blocks encompass 97 genes, two of which are candidate pigmentation genes. One is melanophilin (mlph), which helps transport melanosomes within melanocytes. The other is a cluster of differentiation 36 (cd36), which regulates carotenoid pigment sequestration. We used high-pressure liquid chromatography to confirm that carotenoid pigments are significantly more abundant in the conspicuous orange-pigmented skin of male A. m. marmoratus suggesting that cd36 may be regulating pigment deposition in this tissue. We identified for the first time a carotenoid gene that is a potential target of divergent sexual selection and may be contributing to the early stages of speciation in Anolis lizards.

Transcriptome analyses of betta fish (Betta splendens) provide novel insights into fin regeneration and color-related genes

The betta fish (Betta splendens), an important ornamental fish, haswell-developed and colorful fins.After fin amputation, betta fish can easily regenerate finssimilar to the originalsin terms of structureand color. The powerful fin regeneration ability and a variety of colors in the betta fish are fascinating. However, the underlying molecular mechanisms are still not fully understood. In this study, tail fin amputation and regeneration experiments were performed on two kinds of betta fish: red and white color betta fish. Then, transcriptome analyseswere conducted to screen out fin regeneration and color-relatedgenes in betta fish. Through enrichment analyses of differentially expressed genes (DEGs), we founda series of enrichment pathways and genes related to finregeneration, including cell cycle (i.e. plcg2), TGF-beta signaling pathway (i.e. bmp6), PI3K-Akt signaling pathway (i.e. loxl2aand loxl2b), Wnt signaling pathway(i.e. lef1), gap junctions (i.e. cx43), angiogenesis (i.e. foxp1), and interferon regulatory factor (i.e. irf8). Meanwhile, some fin color-related pathways and genes were identified in betta fish, especially melanogenesis (i.e. tyr, tyrp1a, tyrp1b, and mc1r) and carotenoid color genes (i.e. pax3, pax7, sox10, and ednrba). In conclusion, this studycan not only enrich the research onfish tissue regeneration, but also has a potential significance for the aquaculture and breeding of the betta fish.

Effects of Natural and Synthetic Astaxanthin on Growth, Body Color, and Transcriptome and Metabolome Profiles in the Leopard Coral Grouper (Plectropomus leopardus)

Natural and synthetic astaxanthin can promote pigmentation in fish. In this study, the effects of dietary astaxanthin on growth and pigmentation were evaluated in leopard coral grouper (Plectropomus leopardus). Fish were assigned to three groups: 0% astaxanthin (C), 0.02% natural astaxanthin (HP), and 0.02% synthetic astaxanthin (AS). Brightness (L*) was not influenced by astaxanthin. However, redness (a*) and yellowness (b*) were significantly higher for fish fed astaxanthin-containing diets than fish fed control diets and were significantly higher in the HP group than in the AS group. In a transcriptome analysis, 466, 33, and 32 differentially expressed genes (DEGs) were identified between C and HP, C and AS, and AS and HP, including various pigmentation-related genes. DEGs were enriched for carotenoid deposition and other pathways related to skin color. A metabolome analysis revealed 377, 249, and 179 differential metabolites (DMs) between C and HP, C and AS, and AS and HP, respectively. In conclusion, natural astaxanthin has a better coloration effect on P. leopardus, which is more suitable as a red colorant in aquaculture. These results improve our understanding of the effects of natural and synthetic astaxanthin on red color formation in fish.

Differential gene expression patterns between the head and thorax of Gynaephora aureata are associated with high-altitude adaptation

Grassland caterpillars (Lepidoptera: Erebidae: Gynaephora) are important pests in alpine meadows of the Qinghai-Tibetan Plateau (QTP). These pests have morphological, behavioral, and genetic adaptations for survival in high-altitude environments. However, mechanisms underlying high-altitude adaptation in QTP Gynaephora species remain largely unknown. Here, we performed a comparative analysis of the head and thorax transcriptomes of G. aureata to explore the genetic basis of high-altitude adaptation. We detected 8,736 significantly differentially expressed genes (sDEGs) between the head and thorax, including genes related to carbohydrate metabolism, lipid metabolism, epidermal proteins, and detoxification. These sDEGs were significantly enriched in 312 Gene Ontology terms and 16 KEGG pathways. We identified 73 pigment-associated genes, including 8 rhodopsin-associated genes, 19 ommochrome-associated genes, 1 pteridine-associated gene, 37 melanin-associated genes, and 12 heme-associated genes. These pigment-associated genes were related to the formation of the red head and black thorax of G. aureata. A key gene, yellow-h, in the melanin pathway was significantly upregulated in the thorax, suggesting that it is related to the formation of the black body and contributed to the adaptation of G. aureata to low temperatures and high ultraviolet radiation in the QTP. Another key gene, cardinal, in the ommochrome pathway was significantly upregulated in the head and may be related to red warning color formation. We also identified 107 olfactory-related genes in G. aureata, including genes encoding 29 odorant-binding proteins, 16 chemosensory proteins, 22 odorant receptor proteins, 14 ionotropic receptors, 12 gustatory receptors, 12 odorant degrading enzymes, and 2 sensory neuron membrane proteins. Diversification of olfactory-related genes may be associated with the feeding habits of G. aureata, including larvae dispersal and searching for plant resources available in the QTP. These results provide new insights into high-altitude adaptation of Gynaephora in the QTP and may contribute to the development of new control strategies for these pests.

Triphenyltin exposure induced abnormal morphological colouration in adult male guppies (Poecilia reticulata)

Fish morphological colouration is essential for their survival and reproduction success; however, it is vulnerable to environmental factors, such as pollutants. Triphenyltin (TPT) is widespread in aquatic ecosystems, and its impacts on fish have been problematic. Therefore, the purpose of this study was to investigate the effects of TPT at environment-related concentrations (0, 1, 10 and 100 ng Sn/L) on morphological colouration in male guppies (Poecilia reticulata). The results showed that TPT exposure affected both orange/red and dark morphological colouration in guppies. The faded orange/red colouration might be related to the decrease of coloured pteridine and Pts (6-Pyruvoyltetrahydropterin Synthase) expression. In addition, TPT exposure induced melanogenesis, however, much melanin was distributed diffusely in the skin and did not seem to form a spot pattern, giving the fish a dull appearance. According to the skin transcriptional profiles, the changes of dark morphological colouration might be related to the changes in genes related to the functions of melanosome components (Gpnmb, Slc45a2 and Tyr), construction (Ap3d1, Fig4, Hps3, Hps5, Lyst, Rabggta, Txndc5 and Vps33a), and transport (Rab27a). Additionally, genes related to the regulation of melanogenesis (Atrn and Pomc) and system effects (Atox1, Atp6ap2, Atp6v1f, Atp6v1h, Rpl24, Rps19 and Rps20) might also be involved in the molecular mechanisms of abnormal morphological colouration induced by TPT. The present study provides crucial data on the molecular basis of abnormal morphological colouration in fish exposed to TPT and underscores the importance of toxicological studies of the effects of pollutants in aquatic environments on fish morphological colouration.

Pterin-based pigmentation in animals

Pterins are one of the major sources of bright coloration in animals. They are produced endogenously, participate in vital physiological processes and serve a variety of signalling functions. Despite their ubiquity in nature, pterin-based pigmentation has received little attention when compared to other major pigment classes. Here, we summarize major aspects relating to pterin pigmentation in animals, from its long history of research to recent genomic studies on the molecular mechanisms underlying its evolution. We argue that pterins have intermediate characteristics (endogenously produced, typically bright) between two well-studied pigment types, melanins (endogenously produced, typically cryptic) and carotenoids (dietary uptake, typically bright), providing unique opportunities to address general questions about the biology of coloration, from the mechanisms that determine how different types of pigmentation evolve to discussions on honest signalling hypotheses. Crucial gaps persist in our knowledge on the molecular basis underlying the production and deposition of pterins. We thus highlight the need for functional studies on systems amenable for laboratory manipulation, but also on systems that exhibit natural variation in pterin pigmentation. The wealth of potential model species, coupled with recent technological and analytical advances, make this a promising time to advance research on pterin-based pigmentation in animals.

Xenobiotics Targeting Cardiolipin Metabolism to Promote Thrombosis in Zebrafish

Exposure to environmental pollutants is an important factor contributing to the development and severity of thrombosis. However, the important physiological molecules in the thrombotic processes affected by environmental exposures remain unknown. In this study, we show that exposure to environmental chemicals disrupts the equilibrium of cardiolipins (CLs), and directing CL synthesis promotes thrombosis. Using an untargeted metabolomics approach, approximately 3030 molecules were detected in zebrafish embryos exposed to 11 environmental chemicals and automatically clustered into a network. Interconnectivity among CLs and linoleates or isoxanthopterin was discovered through the highly consistent variations in the coregulated metabolites in the network. The chemical exposure resulted in significant upregulation of CLs through influencing the enzymatic activities of phospholipase A₂, cardiolipin synthase, and lysocardiolipin acyltransferase. Consequently, metabolic disorders of CLs affected the levels of anticardiolipin antibodies, disrupted the homeostasis between platelet thromboxane A₂ and endothelial prostacyclin, and promoted thrombotic events including heart ischemia and tachycardia. Our study thus reveals the common molecular mechanisms underlying the CL-induced thrombosis targeted by environmental exposures.

Tissue Transparency In Vivo

In vivo tissue transparency in the visible light spectrum is beneficial for many research applications that use optical methods, whether it involves in vivo optical imaging of cells or their activity, or optical intervention to affect cells or their activity deep inside tissues, such as brain tissue. The classical view is that a tissue is transparent if it neither absorbs nor scatters light, and thus absorption and scattering are the key elements to be controlled to reach the necessary transparency. This review focuses on the latest genetic and chemical approaches for the decoloration of tissue pigments to reduce visible light absorption and the methods to reduce scattering in live tissues. We also discuss the possible molecules involved in transparency.

Microbial (Enzymatic) Degradation of Cyanide to Produce Pterins as Cofactors

Cyanide is one of the most poisonous substances in the environment, which may have originated from natural and anthropogenic sources. There are many enzymes produced by microorganisms which can degrade and utilize cyanide. The major byproducts of cyanide degradation are alanine, glutamic acid, alpha-amino-butyric acid, beta-cyanoalanine, pterin etc. These products have many pharmaceutical and medicinal applications. For the degradation of cyanide, microbes produce necessary cofactors which catalyze the degradation pathways. Pterin is one of the cofactors for cyanide degradation. There are many pathways involved for the degradation of cyanide, cyanate, and thiocyanate. Some of the microorganisms possess resistance to cyanide, since they have developed adaptive alternative pathways for the production of ATP by utilization of cyanide as carbon and nitrogen sources. In this review, we summarized different enzymes, their mechanisms, and corresponding pathways for the degradation of cyanide and production of pterins during cyanide degradation. We aim to enlighten different types of pterin, its classification, and biological significance through this literature review.

QDPR homologues in Danio rerio regulate melanin synthesis, early gliogenesis, and glutamine homeostasis

Dihydropteridine reductase (QDPR) catalyzes the recycling of tetrahydrobiopterin (BH₄), a cofactor in dopamine, serotonin, and phenylalanine metabolism. QDPR-deficient patients develop neurological symptoms including hypokinesia, truncal hypotonia, intellectual disability and seizures. The underlying pathomechanisms are poorly understood. We established a zebrafish model for QDPR deficiency and analyzed the expression as well as function of all zebrafish QDPR homologues during embryonic development. The homologues qdpra is essential for pigmentation and phenylalanine metabolism. Qdprb1 is expressed in the proliferative zones of the optic tectum and eye. Knockdown of qdprb1 leads to up-regulation of pro-proliferative genes and increased number of phospho-histone3 positive mitotic cells. Expression of neuronal and astroglial marker genes is concomitantly decreased. Qdprb1 hypomorphic embryos develop microcephaly and reduced eye size indicating a role for qdprb1 in the transition from cell proliferation to differentiation. Glutamine accumulation biochemically accompanies the developmental changes. Our findings provide novel insights into the neuropathogenesis of QDPR deficiency.

Ultraspecific live imaging of the dynamics of zebrafish neutrophil granules by a histopermeable fluorogenic benzochalcone probe

Neutrophil granules (NGs) are key components of the innate immune response and mark the development of neutrophilic granulocytes in mammals. However, there has been no specific fluorescent vital stain up to now to monitor their dynamics within a whole live organism. We rationally designed a benzochalcone fluorescent probe (HAB) featuring high tissue permeability and optimal photophysics such as elevated quantum yield, pronounced solvatochromism and target-induced fluorogenesis. Phenotypic screening identified HAB as the first cell- and organelle-specific small-molecule fluorescent tracer of NGs in live zebrafish larvae, with no labeling of other cell types or organelles. HAB staining was independent of the state of neutrophil activation, labeling NGs of both resting and phagocytically active neutrophils with equal specificity. By high-resolution live imaging, we documented the dynamics of HAB-stained NGs during phagocytosis. Upon zymosan injection, labeled NGs were rapidly recruited to the forming phagosomes. Despite being a reversible ligand, HAB could not be displaced by high concentrations of pharmacologically relevant competing chalcones, indicating that this specific labeling was the result of the HAB's precise physicochemical signature rather than a general feature of chalcones. However, one of the competitors was discovered as a promising interstitial fluorescent tracer illuminating zebrafish histology, similarly to BODIPY-ceramide. As a yellow-emitting histopermeable vital stain, HAB functionally and spectrally complements most genetically incorporated fluorescent tags commonly used in live zebrafish biology, holding promise for the study of neutrophil-dependent responses relevant to human physiopathology such as developmental defects, inflammation and infection. Furthermore, HAB intensely labeled isolated live human neutrophils at the level of granulated subcellular structures consistent with human NGs, suggesting that the labeling of NGs by HAB is not restricted to the zebrafish model but also relevant to mammalian systems.

Unravelling paralogous gene expression dynamics during three-spined stickleback embryogenesis

Development requires the implementation of a plethora of molecular mechanisms, involving a large set of genes to ensure proper cell differentiation, morphogenesis of tissues and organs as well as the growth of the organism. Genome duplication and resulting paralogs are considered to provide the raw genetic materials important for new adaptation opportunities and boosting evolutionary innovation. The present study investigated paralogous genes, involved in three-spined stickleback (Gasterosteus aculeatus) development. Therefore, the transcriptomes of five early stages comprising developmental leaps were explored. Obtained expression profiles reflected the embryo's needs at different stages. Early stages, such as the morula stage comprised transcripts mainly involved in energy requirements while later stages were mostly associated with GO terms relevant to organ development and morphogenesis. The generated transcriptome profiles were further explored for differential expression of known and new paralogous genes. Special attention was given to hox genes, with hoxa13a being of particular interest and to pigmentation genes where itgb1, involved in the melanophore development, displayed a complementary expression pattern throughout studied stages. Knowledge obtained by untangling specific paralogous gene functions during development might not only significantly contribute to the understanding of teleost ontogenesis but might also shed light on paralogous gene evolution.

Comparative transcriptomes and reciprocal best hit analysis revealed potential pigment genes in two color forms of Tetranychus urticae

Tetranychus urticae Koch is a worldwide agricultural pest. There are two color forms: red and green. The molecular mechanism underlying this color variation is unknown. To elucidate the mechanism, we characterized differentially expressed pigment pathway genes shared in the transcriptomes of these two forms using RNA sequencing and reciprocal best hit analysis. Differentially expressed pigment pathway genes were determined by qRT-PCR to confirm the accuracy of RNA-Seq. The transcriptomes revealed 963 differentially expressed genes (DEGs), of which 687 DEGs were higher in the green form. KEGG enrichment analysis revealed carotenoid biosynthesis genes in T. urticae. Reciprocal best hit analysis revealed 817 putative pigment pathway genes, 38 of which were differentially expressed and mainly classified into four categories: heme, melanin, ommochrome and rhodopsin. Phylogenetic analysis of homologous ommochrome genes showed that tetur09g01950 is closely related to Ok. This study revealed putative pigment pathway genes in the two forms of T. urticae, and might provide a new resource for understanding the mechanism of color variation.

Comparative transcriptome analysis of molecular mechanism underlying gray-to-red body color formation in red crucian carp (Carassius auratus, red var.)

Red crucian carp (Carassius auratus red var.) is an ornamental fish with vivid red/orange color. It has been found that the adult body color of this strain forms a gray-to-red change. In this study, skin transcriptomes of red crucian carp are first obtained for three different stages of body color development, named by gray-color (GC), color-variation (CV), and red-color (RC) stages, respectively. From the skins of GC, CV, and RC, 103,229; 108,208; and 120,184 transcripts have been identified, respectively. Bioinformatics analysis reveals that 2483, 2967, and 4473 unigenes are differentially expressed between CV and GC, RC and CV, and RC and GC, respectively. A part of the differentially expressed genes (DEGs) are involved in the signaling pathway of pigment synthesis, such as the melanogenesis genes (Mitfa, Pax3a, Foxd3, Mc1r, Asip); tyrosine metabolism genes (Tyr, Dct, Tyrp1, Silva, Tat, Hpda); and pteridine metabolism genes (Gch, Xdh, Ptps, Tc). According to the data of transcriptome and quantitative PCR, the expression of Mitfa and its regulated genes which include the genes of Tyr, Tyrp1, Dct, Tfe3a, and Baxα, decreases with gray-to-red change. It is suggested that Mitfa and some genes, being related to melanin synthesis or melanophore development, are closely related to the gray-to-red body color transformation in the red crucian carp. Furthermore, the DEGs of cell apoptosis and autophagy pathway, such as Tfe3a, Baxα, Hsp70, Beclin1, Lc3, Atg9a, and Atg4a, might be involved in the melanocytes fade away of juvenile fish. These results shed light on the regulation mechanism of gray-to-red body color transformation in red crucian carp, and are helpful to the selective breeding of ornamental fish strains.

Characterization of unexplored amidohydrolase enzyme-pterin deaminase

Pterin deaminase is an amidohydrolase enzyme hydrolyzing pteridines to form lumazine derivatives and ammonia. The enzyme captured the attention of scientists as early as 1959 and had been patented for its application as an anticancer agent. It is ubiquitously present in prokaryotes and has been reported in some eukaryotes such as honey bee, silkworm and rats. The enzyme has been observed to have a spectrum of substrates with the formation of respective lumazines. The role of the substrates of the enzyme in various metabolic pathways warrants a significant role in the biological activity of both prokaryotes and eukaryotes. Even though the functions of the enzyme have been explored in prokaryotes, their niche in the eukaryotic system is not clear. There is very few information on the structural and functional properties of the enzyme. This review has been congregated to emphasize the significance of pterin deaminase and analyzes the lacunae in understanding the biological characters of the enzyme.

Origins of adult pigmentation: diversity in pigment stem cell lineages and implications for pattern evolution

Teleosts comprise about half of all vertebrate species and exhibit an extraordinary diversity of adult pigment patterns that function in shoaling, camouflage, and mate choice and have played important roles in speciation. Here, we review studies that have identified several distinct neural crest lineages, with distinct genetic requirements, that give rise to adult pigment cells in fishes. These lineages include post-embryonic, peripheral nerve-associated stem cells that generate black melanophores and iridescent iridophores, cells derived directly from embryonic neural crest cells that generate yellow-orange xanthophores, and bipotent stem cells that generate both melanophores and xanthophores. This complexity in adult chromatophore lineages has implications for our understanding of adult traits, melanoma, and the evolutionary diversification of pigment cell lineages and patterns.

Carotenoid-based coloration in cichlid fishes

Animal colors play important roles in communication, ecological interactions and speciation. Carotenoid pigments are responsible for many yellow, orange and red hues in animals. Whereas extensive knowledge on the proximate mechanisms underlying carotenoid coloration in birds has led to testable hypotheses on avian color evolution and signaling, much less is known about the expression of carotenoid coloration in fishes. Here, we promote cichlid fishes (Perciformes: Cichlidae) as a system in which to study the physiological and evolutionary significance of carotenoids. Cichlids include some of the best examples of adaptive radiation and color pattern diversification in vertebrates. In this paper, we examine fitness correlates of carotenoid pigmentation in cichlids and review hypotheses regarding the signal content of carotenoid-based ornaments. Carotenoid-based coloration is influenced by diet and body condition and is positively related to mating success and social dominance. Gaps in our knowledge are discussed in the last part of this review, particularly in the understanding of carotenoid metabolism pathways and the genetics of carotenoid coloration. We suggest that carotenoid metabolism and transport are important proximate mechanisms responsible for individual and population-differences in cichlid coloration that may ultimately contribute to diversification and speciation.

WHICH IS THE PROTON-SHUTTLE IN ISOXANTHOPTERIN DEAMINASE? QM/MM MD UNDERSTANDING

The deamination process of isoxanthopterin catalyzed by isoxanthopterin deaminase was determined using the combined QM(PM3)/MM molecular dynamics simulations. In this paper, the updated PM3 parameters were employed for zinc ions and the initial model was built up based on the crystal structure. Proton transfer and following steps have been investigated in two paths: Asp336 and His285 serve as the proton shuttle, respectively. Our simulations showed that His285 is more effective than Aap336 in proton transfer for deamination of isoxanthopterin. As hydrogen bonds between the substrate and surrounding residues play a key role in nucleophilic attack, we suggested mutating Thr195 to glutamic acid, which could enhance the hydrogen bonds and help isoxanthopterin get close to the active site. The simulations which change the substrate to pterin 6-carboxylate also performed for comparison. Our results provide reference for understanding of the mechanism of deaminase and for enhancing the deamination rate of isoxanthopterin deaminase.

De novo characterization of the gene-rich transcriptomes of two color-polymorphic spiders, Theridion grallator and T. californicum (Araneae: Theridiidae), with special reference to pigment genes

Background

A number of spider species within the family Theridiidae exhibit a dramatic abdominal (opisthosomal) color polymorphism. The polymorphism is inherited in a broadly Mendelian fashion and in some species consists of dozens of discrete morphs that are convergent across taxa and populations. Few genomic resources exist for spiders. Here, as a first necessary step towards identifying the genetic basis for this trait we present the near complete transcriptomes of two species: the Hawaiian happy-face spider Theridion grallator and Theridion californicum. We mined the gene complement for pigment-pathway genes and examined differential expression (DE) between morphs that are unpatterned (plain yellow) and patterned (yellow with superimposed patches of red, white or very dark brown).

Results

By deep sequencing both RNA-seq and normalized cDNA libraries from pooled specimens of each species we were able to assemble a comprehensive gene set for both species that we estimate to be 98-99% complete. It is likely that these species express more than 20,000 protein-coding genes, perhaps 4.5% (ca. 870) of which might be unique to spiders. Mining for pigment-associated Drosophila melanogaster genes indicated the presence of all ommochrome pathway genes and most pteridine pathway genes and DE analyses further indicate a possible role for the pteridine pathway in theridiid color patterning.

Conclusions

Based upon our estimates, T. grallator and T. californicum express a large inventory of protein-coding genes. Our comprehensive assembly illustrates the continuing value of sequencing normalized cDNA libraries in addition to RNA-seq in order to generate a reference transcriptome for non-model species. The identification of pteridine-related genes and their possible involvement in color patterning is a novel finding in spiders and one that suggests a biochemical link between guanine deposits and the pigments exhibited by these species.

Discovery and structure determination of the orphan enzyme isoxanthopterin deaminase

Two previously uncharacterized proteins have been identified that efficiently catalyze the deamination of isoxanthopterin and pterin 6-carboxylate. The genes encoding these two enzymes, NYSGXRC-9339a ( gi|44585104 ) and NYSGXRC-9236b ( gi|44611670 ), were first identified from DNA isolated from the Sargasso Sea as part of the Global Ocean Sampling Project. The genes were synthesized, and the proteins were subsequently expressed and purified. The X-ray structure of Sgx9339a was determined at 2.7 A resolution (Protein Data Bank entry 2PAJ ). This protein folds as a distorted (beta/alpha)(8) barrel and contains a single zinc ion in the active site. These enzymes are members of the amidohydrolase superfamily and belong to cog0402 within the clusters of orthologous groups (COG). Enzymes in cog0402 have previously been shown to catalyze the deamination of guanine, cytosine, S-adenosylhomocysteine, and 8-oxoguanine. A small compound library of pteridines, purines, and pyrimidines was used to probe catalytic activity. The only substrates identified in this search were isoxanthopterin and pterin 6-carboxylate. The kinetic constants for the deamination of isoxanthopterin with Sgx9339a were determined to be 1.0 s(-1), 8.0 muM, and 1.3 x 10(5) M(-1) s(-1) (k(cat), K(m), and k(cat)/K(m), respectively). The active site of Sgx9339a most closely resembles the active site for 8-oxoguanine deaminase (Protein Data Bank entry 2UZ9 ). A model for substrate recognition of isoxanthopterin by Sgx9339a was proposed on the basis of the binding of guanine and xanthine in the active site of guanine deaminase. Residues critical for substrate binding appear to be conserved glutamine and tyrosine residues that form hydrogen bonds with the carbonyl oxygen at C4, a conserved threonine residue that forms hydrogen bonds with N5, and another conserved threonine residue that forms hydrogen bonds with the carbonyl group at C7. These conserved active site residues were used to identify 24 other genes which are predicted to deaminate isoxanthopterin.

The zebrafish mutation m865 affects formation of dopaminergic neurons and neuronal survival, and maps to a genetic interval containing the sepiapterin reductase locus

The zebrafish mutation m865 was isolated during a large-scale mutagenesis screen aimed at identifying genes involved in the development and maintenance of subgroups of neurons in the zebrafish central nervous system. The phenotype of m865 mutant embryos shows defects in the development of dopaminergic neurons in the pretectum and of retinal amacrine cells, as well as abnormal caudal dopaminergic cluster in the diencephalon. The effects of the mutation appear not to be restricted to dopaminergic neurons, as development of other neurotransmitter systems (serotonergic and cholinergic) is impaired as well. Furthermore, increased apoptosis is localized to the m865 mutant retina and in the optic tectum starting at 24hpf, and may lead to the observed reduced size of the mutant head and eye. Early patterning is not affected in m865 mutant embryos, and expression of genes known to play a role in dopaminergic cell differentiation is normal except for reduced expression of nurr1 in the mutant retina. Thus the m865 mutation does not specifically affect dopaminergic neuron development. m865 was genetically mapped to linkage group 5, and the critical genomic interval could be narrowed down to a region of 110 kb, containing four candidate genes. For one of these candidate genes, sepiapterin reductase (spr), a requirement for neuronal survival has previously been implicated, including dopaminergic neurons. Identification of the mutated gene should lead to a more detailed understanding of the defects observed in m865 mutant embryos, and potentially could enhance the understanding of the development and maintenance of specific dopaminergic neuronal populations.

Pigment cell distributions in different tissues of the zebrafish, with special reference to the striped pigment pattern

The orderly pigment pattern of zebrafish (Danio rerio) is a good model system for studying how spatial patterns form in animals. Recent molecular genetic studies have shown that interactions between the pigment cells play major roles in pattern formation. In the present study, we performed comparative transmission electron microscopy of pigment cells, in order to clarify the structural interactions of pigment cells in tissues with and without a striped pattern. In patterned tissues, pigment cells were distributed as a one-cell-thick sheet. The layer order of the sheets is always kept strictly. In tissues without a striped pattern, the layer order was often disturbed or the cells were distributed in a scattered, double-sheeted, or an accumulated pile. Our observations suggest that the underlying mechanism that controls the vertical order of the pigment cells is related to that controlling the stripe pattern.

Expression of one isoform of GTP cyclohydrolase I coincides with the larval black markings of the swallowtail butterfly, Papilio xuthus

The larva of the swallowtail butterfly Papilio xuthus changes its body markings during the fourth ecdysis. We found that stage-specific cuticular black markings are mainly regulated by co-localization of two melanin synthesis enzymes; tyrosine hydroxylase (TH) and dopa decarboxylase (DDC). TH converts tyrosine to dihydroxyphenylalanine (dopa), and tyrosine itself is converted from phenylalanine by phenylalanine hydroxylase (PAH). Guanosine triphosphate cyclohydrolase I (GTPCHI) is essential for the synthesis of tetrahydrobiopterin (BH4) that is a cofactor of TH and PAH. In this report, we found that a GTPCHI inhibitor prevents pigmentation in cultured integuments, suggesting that the GTPCHI activity is also involved in cuticle pigmentation. We have cloned GTPCHI and PAH cDNAs from P. xuthus and investigated their spatial expression patterns in epidermis by whole-mount in situ hybridization. There are two isoforms of GTPCHI in larval epidermis (GTPCHIa and GTPCHIb). GTPCHIa is expressed at the black markings of the subsequent instar, similar to TH, whereas GTPCHIb is expressed uniformly, similar to PAH. This suggests that the region-specific expression of GTPCHIa supplies sufficient BH(4) reinforcing the TH activity in black marking area. Our results imply that larval markings are regulated by not only melanin synthesis enzymes but also the cofactor supplying enzyme.

Esrom, an ortholog of PAM (protein associated with c-myc), regulates pteridine synthesis in the zebrafish

Zebrafish esrom mutants have an unusual combination of phenotypes: in addition to a defect in the projection of retinal axons, they have reduced yellow pigmentation. Here, we investigate the pigment phenotype and, from this, provide evidence for an unexpected defect in retinal neurons. Esrom is not required for the differentiation of neural crest precursors into pigment cells, nor is it essential for cell migration, pigment granule biogenesis, or translocation. Instead, loss of yellow color is caused by a deficiency of sepiapterin, a yellow pteridine. The level of several other pteridines is also affected in mutants. Importantly, the cofactor tetrahydrobiopterin (BH4) is drastically reduced in esrom mutants. Mutant retinal neurons also appear deficient in this pteridine. BH4-synthesizing enzymes are active in mutants, indicating a defect in the regulation rather than production of enzymes. Esrom has recently been identified as an ortholog of PAM (protein associated with c-myc), a very large protein involved in synaptogenesis in Drosophila and C. elegans. These data thus introduce a new regulator of pteridine synthesis in a vertebrate and establish a function for the Esrom protein family outside synaptogenesis. They also raise the possibility that neuronal defects are due in part to an abnormality in pteridine synthesis.

Evolutionary diversification of pigment pattern in Danio fishes: differential fms dependence and stripe loss in D. albolineatus

The developmental bases for species differences in adult phenotypes remain largely unknown. An emerging system for studying such variation is the adult pigment pattern expressed by Danio fishes. These patterns result from several classes of pigment cells including black melanophores and yellow xanthophores, which differentiate during metamorphosis from latent stem cells of presumptive neural crest origin. In the zebrafish D. rerio, alternating light and dark horizontal stripes develop, in part, owing to interactions between melanophores and cells of the xanthophore lineage that depend on the fms receptor tyrosine kinase; zebrafish fms mutants lack xanthophores and have disrupted melanophore stripes. By contrast, the closely related species D. albolineatus exhibits a uniform pattern of melanophores, and previous interspecific complementation tests identified fms as a potential contributor to this difference between species. Here, we survey additional species and demonstrate marked variation in the fms-dependence of hybrid pigment patterns, suggesting interspecific variation in the fms pathway or fms requirements during pigment pattern formation. We next examine the cellular bases for the evolutionary loss of stripes in D. albolineatus and test the simplest model to explain this transformation, a loss of fms activity in D. albolineatus relative to D. rerio. Within D. albolineatus, we demonstrate increased rates of melanophore death and decreased melanophore migration, different from wild-type D. rerio but similar to fms mutant D. rerio. Yet, we also find persistent fms expression in D. albolineatus and enhanced xanthophore development compared with wild-type D. rerio, and in stark contrast to fms mutant D. rerio. These findings exclude the simplest model in which stripe loss in D. albolineatus results from a loss of fms-dependent xanthophores and their interactions with melanophores. Rather, our results suggest an alternative model in which evolutionary changes in pigment cell interactions themselves have contributed to stripe loss, and we test this model by manipulating melanophore numbers in interspecific hybrids. Together, these data suggest evolutionary changes in the fms pathway or fms requirements, and identify changes in cellular interactions as a likely mechanism of evolutionary change in Danio pigment patterns.

Localization of sepiapterin reductase in pigment cells of Oryzias latipes

Body colors of poikilothermal vertebrates are derived from three distinct types of pigment cells, melanophores, erythro/xanthophores and irido/leucophores. It is well known that melanin in melanophores is synthesized by tyrosinase within a specific organelle termed the melanosome. Although sepiapterin reductase (SPR) is an important enzyme involved in metabolizing biopterin and sepiapterin (a conspicuous pteridine as a coloring pigment in xanthophores) the distribution of SPR has not been shown in pigment cells. An antibody raised in rabbits against rat SPR was used to demonstrate the presence of SPR in pigment cells of Oryzias latipes. This study, which used immunohistochemistry with fluorescence or peroxidase/diaminobenzidine as markers, revealed that SPR could be detected readily in xanthophores, but only faintly in melanophores. These results suggest that sepiapterin is metabolized within xanthophores. Moreover, these experiments show that a protein sharing immunological cross-reactivity with rat SPR is located in teleost O. latipes xanthophores, which is significant considering the relationship of pteridine metabolism between poikilothermal vertebrates and mammals. Further progress in investigations of the roles of pteridines in vertebrates will be promoted by using these fish which can be bred in mass rather easily in the laboratory.

The pteridine pathway in zebrafish: regulation and specification during the determination of neural crest cell-fate

This review describes pteridine biosynthesis and its relation to the differentiation of neural crest derivatives in zebrafish. During the embryonic development of these fish, neural crest precursor cells segregate into neural elements, ectomesenchymal cells and pigment cells; the latter then diversifying into melanophores, iridophores and xanthophores. The differentiation of neural cells, melanophores, and xanthophores is coupled closely with the onset of pteridine synthesis which starts from GTP and is regulated through the control of GTP cyclohydrolase I activity. De novo pteridine synthesis in embryos of this species increases during the first 72-h postfertilization, producing H4biopterin, which serves as a cofactor for neurotransmitter synthesis in neural cells and for tyrosine production in melanophores. Thereafter, sepiapterin (6-lactoyl-7,8-dihydropterin) accumulates as yellow pigment in xanthophores, together with 7-oxobiopterin, isoxanthopterin and 2,4,7-trioxopteridine. Sepiapterin is the key intermediate in the formation of 7-oxopteridines, which depends on the availability of enzymes belonging to the xanthine oxidoreductase family. Expression of the GTP cyclohydrolase I gene (gch) is found in neural cells, in melanoblasts and in early xanthophores (xanthoblasts) of early zebrafish embryos but steeply declines in xanthophores by 42-h postfertilization. The mechanism(s) whereby sepiapterin branches off from the GTP-H4biopterin pathway is currently unknown and will require further study. The surge of interest in zebrafish as a model for vertebrate development and its amenability to genetic manipulation provide powerful tools for analysing the functional commitment of neural crest-derived cells and the regulation of pteridine synthesis in mammals.

Essential role for puma in development of postembryonic neural crest-derived cell lineages in zebrafish

Multipotent neural crest stem cells have been identified in late gestation amniote embryos. Yet, significant questions remain about the mechanisms by which these cells are generated, maintained, and recruited during postembryonic development. The zebrafish, Danio rerio, offers an opportunity to identify genes essential for these processes, by screening for mutants with defects in traits likely to depend on these cells during metamorphosis and adult life. One such trait is the pigment pattern formed by neural crest-derived pigment cells, or chromatophores, which include black melanophores, yellow xanthophores, and iridescent iridophores. Previous analyses have demonstrated that the adult zebrafish pigment pattern depends on the de novo differentiation of latent precursor cells during both early and late phases of pigment pattern metamorphosis. To better understand the development of these cells, in this study, we analyze the zebrafish puma mutant, which ablates most of the adult melanophores that differentiate during metamorphosis, but leaves intact early larval melanophores that differentiate during embryogenesis. We use epistasis analyses to show that puma promotes the development of both early-appearing metamorphic melanophores that depend on the kit receptor tyrosine kinase, as well as late-appearing metamorphic melanophores that depend on both the G-protein-coupled endothelin receptor b1 (ednrb1) and the kit-related fms receptor tyrosine kinase. We further demonstrate that, during pigment pattern metamorphosis, puma mutants have deficiencies in the numbers of cells expressing transcripts for kit, ednrb1, and fms, as well as the HMG domain transcription factor sox10. Because the puma mutant phenotype is temperature-sensitive, we use temperature-shift experiments to identify a critical period for puma activity during pigment pattern metamorphosis. Finally, we use cell transplantations to show that puma acts cell-autonomously to promote the expansion of pigment cell lineages during metamorphosis. These results suggest a model for the lineage diversification of neural crest stem cells during zebrafish postembryonic development.

Morphological and biochemical changes in carotenoid granules in the ventral skin during growth of the Japanese newt Cynops pyrrhogaster

The color of the ventral skin of the Japanese adult newt Cynops pyrrhogaster is red, whereas that of the small juvenile newts at metamorphosis is creamy. Xanthophores in the red skin have many ring carotenoid vesicles (rcv) and a few homogenous carotenoid granules (hcg), as reported earlier. To understand the reason for this change in coloration of the ventral skin of the newt, we carried out histological and biochemical studies to see whether the size and the number of carotenoid granules (hcg and rcv) in the xanthophores and also carotenoid content in the ventral skin change during the growth of this animal. By electron microscopic observation, only hcg were observed in the creamy skin of larvae at stage 59. The diameter of the hcg in the skin of the larvae was approximately 0.85 microm, but significantly decreased to 0.35 microm in the skin of the small juvenile newt. However, the number of the hcg/100 microm (2) of a xanthophore in the ventral skin was very low in the larva at stage 59, but increased in the small juvenile. The carotenoid content was very low in the creamy skin of small juveniles, but dramatically high in the red skin of the adult newts. In the red skin of the adult newt, many rcv (85%) and a few hcg (15%) were observed. However, the number of carotenoid granules (rcv and hcg)/100 microm(2) of a xanthophore in the red skin of adult newts was not different from that of hcg/100 microm (2) of a xanthophore in the creamy skin of small juveniles. The results, taken together, suggest that the increase in the size and the number of carotenoid granules and also carotenoid content in the ventral skin is very important for red body coloration during the growth of the Japanese newt Cynops pyrrhogaster.

Pigment pattern formation in zebrafish: a model for developmental genetics and the evolution of form

The zebrafish Danio rerio is an emerging model organism for understanding vertebrate development and genetics. One trait of both historical and recent interest is the pattern formed by neural crest-derived pigment cells, or chromatophores, which include black melanophores, yellow xanthophores, and iridescent iridophores. In zebrafish, an embryonic and early larval pigment pattern consists of several stripes of melanophores and iridophores, whereas xanthophores are scattered widely over the flank. During metamorphosis, however, this pattern is transformed into that of the adult, which comprises several dark stripes of melanophores and iridophores that alternate with light stripes of xanthophores and iridophores. In this review, we place zebrafish relative to other model and non-model species; we review what is known about the processes of chromatophore specification, differentiation, and morphogenesis during the development of embryonic and adult pigment patterns, and we address how future studies of zebrafish will likely aid our understanding of human disease and the evolution of form.

Hormonal control of GTP cyclohydrolase I gene expression and enzyme activity during color pattern development in wings of Precis coenia

Color patterns of butterfly wings are composed of single color points represented by each scale. In the case of Precis coenia, at the end of pupal development, different types of pigments are synthesized sequentially in the differently colored scales beginning with white (pterins) followed by red (ommatins) and then black (melanin). In order to explain how formation of these different colors is regulated, we examined the expression of an mRNA-encoding guanosine triphosphate-cyclohydrolase I (GTP-CH I; EC 3.5.4.16), the first key enzyme in the biosynthesis of pteridines, during pigment formation in the wings of P. coenia. The strongest positive signal was recognized around pigment formation one day before butterfly emergence. This GTP-CH I gene expression is paralleled by GTP-CH I enzyme activity measured in wing extracts. We also investigated the effect of 20-hydroxyecdysone on the expression of GTP-CH I mRNA and the enzyme activity during color formation. The results strongly suggest that the onset and duration of the expression of a GTP-CH I mRNA is triggered by a declining ecdysteroid hormone titer during late pupal development.

Cloning and developmental expression of zebrafish GTP cyclohydrolase I

GTP cyclohydrolase I (GCH) catalyses the conversion of GTP to dihydroneopterin triphosphate, initiating the pteridine pathway. The final product tetrahydrobiopterin (H4biopterin) is the cofactor for neurotransmitter synthesis and for tyrosine supply during melanogenesis. Sepiapterin accumulates as a pigment. We cloned the zebrafish gch cDNA, which encodes a protein highly homologous to other vertebrate sequences and characterised the recombinant enzyme. By in situ hybridisation, we found that gch is expressed in both the melanophore and xanthophore lineages during early development. gch-expression almost disappears after 3 days post-fertilisation (dpf), despite further sepiapterin synthesis. gch-transcripts are also located in catecholaminergic neurons, within the central nervous system and in the arch-associated neurons.

Pathways for urea production during early life of an air-breathing teleost, the African catfish Clarias gariepinus Burchell

Embryos and larvae of the African catfish Clarias gariepinus excrete significant quantities of urea. The present study focused on the potential urea-generating pathways during early development of this teleost; uricolysis, argininolysis and the ornithine–urea cycle (OUC). Uricase, allantoinase, allantoicase and ureidoglycollate lyase of the uricolytic pathway were expressed in all early life stages and in adult liver of C. gariepinus. Uricase activity increased in starved larvae compared with yolk-sac larvae. The key regulatory enzyme of the teleost OUC, carbamoyl phosphate synthetase III (CPSase III), was expressed predominantly in muscle of developing C. gariepinus larvae and showed negligible activity in the absence of its allosteric effector N-acetyl-l-glutamate. CPSase III and ornithine carbamoyl transferase activities increased in fed larvae compared with starved larvae. In contrast to the early developmental stages, adult C. gariepinus expressed only low and variable levels of CPSase III, suggesting that, under the experimental conditions employed, OUC expression is influenced by developmental stage in this species. The data indicate that early C. gariepinus life stages express the enzymes necessary for urea production by uricolysis, argininolysis and the OUC, and this may explain why urea tissue levels and urea excretion rates are substantial during the early development of this air-breathing teleost.

Mutational analysis of endothelin receptor b1 (rose) during neural crest and pigment pattern development in the zebrafish Danio rerio

Pigment patterns of fishes are a tractable system for studying the genetic and cellular bases for postembryonic phenotypes. In the zebrafish Danio rerio, neural crest-derived pigment cells generate different pigment patterns during different phases of the life cycle. Whereas early larvae exhibit simple stripes of melanocytes and silver iridophores in a background of yellow xanthophores, this pigment pattern is transformed at metamorphosis into that of the adult, comprising a series of dark melanocyte and iridophore stripes, alternating with light stripes of iridophores and xanthophores. Although several genes have been identified in D. rerio that contribute to the development of both early larval and adult pigment patterns, comparatively little is known about genes that are essential for pattern formation during just one or the other life cycle phase. In this study, we identify the gene responsible for the rose mutant phenotype in D. rerio. rose mutants have wild-type early larval pigment patterns, but fail to develop normal numbers of melanocytes and iridophores during pigment pattern metamorphosis and exhibit a disrupted pattern of these cells. We show that rose corresponds to endothelin receptor b1 (ednrb1), an orthologue of amniote Ednrb genes that have long been studied for their roles in neural crest and pigment cell development. Furthermore, we demonstrate that D. rerio ednrb1 is expressed both during pigment pattern metamorphosis and during embryogenesis, and cells of melanocyte, iridophore, and xanthophore lineages all express this gene. These analyses suggest a phylogenetic conservation of roles for Ednrb signaling in the development of amniote and teleost pigment cell precursors. As murine Ednrb is essential for the development of all neural crest derived melanocytes, and D. rerio ednrb1 is required only by a subset of adult melanocytes and iridophores, these analyses also reveal variation among vertebrates in the cellular requirements for Ednrb signaling, and suggest alternative models for the cellular and genetic bases of pigment pattern metamorphosis in D. rerio.