Inconspicuous breeding coloration to conceal eggs during mouthbrooding in male cardinalfish

Animals exhibit colorations optimal for their niche, which hides their existence from other organisms. In Apogoninae fishes, the father broods their egg inside their mouth. Since the color of eggs is different from parental fish, it can disrupt the optimal camouflage coloration of parental fish if the lower jaw is transparent. Here, we identified male- and breeding season-specific whitish coloration consisting of iridophores in the lower jaw. Artificial implantation of eggs inside the mouth of females and males showed that iridophores in the lower jaws concealed the conspicuous coloration of eggs only in males. In addition, it was revealed that iridophore development in the lower jaw is induced by androgen through the Alkal-Ltk pathway. These results suggest that androgen-dependent breeding colorations in males, which have been considered to attract females, may serve the opposite function, "inconspicuous breeding coloration" in these species.

Recent advances in the color of aquatic products: Evaluation methods, discoloration mechanism, and protection technologies

Color plays a pivotal role in guiding and assessing the industrial production of aquatic products due to the swift sensory perception of information through vision. This review provides a comprehensive overview of the following four aspects: (a) mechanisms governing natural color formation in aquatic products, (b) factors and mechanisms contributing to the discoloration of aquatic products, (c) cutting-edge methods for color analysis and detection, and (d) current valuable techniques for preserving color quality. The natural color of aquatic products is derived from skin chromatophores, endogenous pigment proteins, and astaxanthin. Discoloration of aquatic products can occur due to lipid oxidation, as well as enzymatic and non-enzymatic browning. Furthermore, this review examines frontier color protective technologies, encompassing physical methods like ultra-high pressure, irradiation, and low-temperature plasma, as well as chemical methods involving natural preservatives. The findings of this study offer significant insights into the development of high-quality aquatic products.

Multifaceted Roles of ALK Family Receptors and Augmentor Ligands in Health and Disease: A Comprehensive Review

This review commemorates the 10-year anniversary of the discovery of physiological ligands Augα (Augmentor α; ALKAL2; Fam150b) and Augβ (Augmentor β; ALKAL1; Fam150a) for anaplastic lymphoma kinase (ALK) and leukocyte tyrosine kinase (LTK), previously considered orphan receptors. This manuscript provides an in-depth review of the biophysical and cellular properties of ALK family receptors and their roles in cancer, metabolism, pain, ophthalmology, pigmentation, central nervous system (CNS) function, and reproduction. ALK and LTK receptors are implicated in the development of numerous cancers, and targeted inhibition of their signaling pathways can offer therapeutic benefits. Additionally, ALK family receptors are involved in regulating body weight and metabolism, modulating pain signaling, and contributing to eye development and pigmentation. In the CNS, these receptors play a role in synapse modulation, neurogenesis, and various psychiatric pathologies. Lastly, ALK expression is linked to reproductive functions, with potential implications for patients undergoing ALK inhibitor therapy. Further research is needed to better understand the complex interactions of ALK family receptors and Aug ligands and to repurpose targeted therapy for a wide range of human diseases.

Leukocyte Tyrosine Kinase (Ltk) Is the Mendelian Determinant of the Axolotl Melanoid Color Variant

The great diversity of color patterns observed among amphibians is largely explained by the differentiation of relatively few pigment cell types during development. Mexican axolotls present a variety of color phenotypes that span the continuum from leucistic to highly melanistic. The melanoid axolotl is a Mendelian variant characterized by large numbers of melanophores, proportionally fewer xanthophores, and no iridophores. Early studies of melanoid were influential in developing the single-origin hypothesis of pigment cell development, wherein it has been proposed that all three pigment cell types derive from a common progenitor cell, with pigment metabolites playing potential roles in directing the development of organelles that define different pigment cell types. Specifically, these studies identified xanthine dehydrogenase (XDH) activity as a mechanism for the permissive differentiation of melanophores at the expense of xanthophores and iridophores. We used bulked segregant RNA-Seq to screen the axolotl genome for melanoid candidate genes and identify the associated locus. Dissimilar frequencies of single-nucleotide polymorphisms were identified between pooled RNA samples of wild-type and melanoid siblings for a region on chromosome 14q. This region contains gephyrin (Gphn), an enzyme that catalyzes the synthesis of the molybdenum cofactor that is required for XDH activity, and leukocyte tyrosine kinase (Ltk), a cell surface signaling receptor that is required for iridophore differentiation in zebrafish. Wild-type Ltk crispants present similar pigment phenotypes to melanoid, strongly implicating Ltk as the melanoid locus. In concert with recent findings in zebrafish, our results support the idea of direct fate specification of pigment cells and, more generally, the single-origin hypothesis of pigment cell development.

Zebrafish pigment cells develop directly from persistent highly multipotent progenitors

Neural crest cells are highly multipotent stem cells, but it remains unclear how their fate restriction to specific fates occurs. The direct fate restriction model hypothesises that migrating cells maintain full multipotency, whilst progressive fate restriction envisages fully multipotent cells transitioning to partially-restricted intermediates before committing to individual fates. Using zebrafish pigment cell development as a model, we show applying NanoString hybridization single cell transcriptional profiling and RNAscope in situ hybridization that neural crest cells retain broad multipotency throughout migration and even in post-migratory cells in vivo, with no evidence for partially-restricted intermediates. We find that leukocyte tyrosine kinase early expression marks a multipotent stage, with signalling driving iridophore differentiation through repression of fate-specific transcription factors for other fates. We reconcile the direct and progressive fate restriction models by proposing that pigment cell development occurs directly, but dynamically, from a highly multipotent state, consistent with our recently-proposed Cyclical Fate Restriction model.

Patient-associated mutations in Drosophila Alk perturb neuronal differentiation and promote survival

Activating anaplastic lymphoma kinase (ALK) receptor tyrosine kinase (RTK) mutations occur in pediatric neuroblastoma and are associated with poor prognosis. To study ALK-activating mutations in a genetically controllable system, we employed CRIPSR/Cas9, incorporating orthologs of the human oncogenic mutations ALKF1174L and ALKY1278S in the Drosophila Alk locus. AlkF1251L and AlkY1355S mutant Drosophila exhibited enhanced Alk signaling phenotypes, but unexpectedly depended on the Jelly belly (Jeb) ligand for activation. Both AlkF1251L and AlkY1355S mutant larval brains displayed hyperplasia, represented by increased numbers of Alk-positive neurons. Despite this hyperplasic phenotype, no brain tumors were observed in mutant animals. We showed that hyperplasia in Alk mutants was not caused by significantly increased rates of proliferation, but rather by decreased levels of apoptosis in the larval brain. Using single-cell RNA sequencing, we identified perturbations during temporal fate specification in AlkY1355S mutant mushroom body lineages. These findings shed light on the role of Alk in neurodevelopmental processes and highlight the potential of Alk-activating mutations to perturb specification and promote survival in neuronal lineages. This article has an associated First Person interview with the first author of the paper.

Skin patterning and internal anatomy in a fossil moonfish from the Eocene Bolca Lagerstätte illuminate the ecology of ancient reef fish communities

Colour patterning in extant animals can be used as a reliable indicator of their biology and, in extant fish, can inform on feeding strategy. Fossil fish with preserved colour patterns may thus illuminate the evolution of fish behaviour and community structure, but are understudied. Here we report preserved melanin-based integumentary colour patterning and internal anatomy of the fossil moonfish Mene rhombea (Menidae) from the Bolca Lagerstätte (Eocene (Ypresian), north-east Italy). The melanosome-based longitudinal stripes of M. rhombea differ from the dorsal rows of black spots in its extant relative M. maculata, suggesting that the ecology of moonfish has changed during the Cenozoic. Extant moonfish are coastal schooling fish that feed on benthic invertebrates, but the longitudinal stripes and stomach contents with fish remains in M. rhombea suggest unstructured open marine ecologies and a piscivorous diet. The localized distribution of extant moonfish species in the Indo-Pacific Ocean may reflect, at least in part, tectonically-driven reorganization of global oceanographic patterns during the Cenozoic. It is likely that shifts in habitat and colour patterning genes promoted colour pattern evolution in the menid lineage.

Cell Fate Decisions in the Neural Crest, from Pigment Cell to Neural Development

The neural crest shows an astonishing multipotency, generating multiple neural derivatives, but also pigment cells, skeletogenic and other cell types. The question of how this process is controlled has been the subject of an ongoing debate for more than 35 years. Based upon new observations of zebrafish pigment cell development, we have recently proposed a novel, dynamic model that we believe goes some way to resolving the controversy. Here, we will firstly summarize the traditional models and the conflicts between them, before outlining our novel model. We will also examine our recent dynamic modelling studies, looking at how these reveal behaviors compatible with the biology proposed. We will then outline some of the implications of our model, looking at how it might modify our views of the processes of fate specification, differentiation, and commitment.

Chromosome Imbalances in Neuroblastoma-Recent Molecular Insight into Chromosome 1p-deletion, 2p-gain, and 11q-deletion Identifies New Friends and Foes for the Future

Simple Summary

Neuroblastoma is a pediatric cancer that arises in the sympathetic nervous system. High-risk neuroblastoma is clinically challenging and identification of novel therapies, particularly those that offer a reduction in morbidity for these patients, is a high priority. Combining genetic analyses with investigation of molecular mechanisms, while considering recent advances in our understanding of key developmental events, provides avenues for future treatment. Here we review and highlight several recently published articles that address novel molecular mechanisms arising from chromosome 1p, 2p, and 11q aberrations, which likely contribute to high-risk neuroblastoma, and discusses their potential impact on treatment options.

Abstract

Neuroblastoma is the most common extracranial solid pediatric tumor, with around 15% childhood cancer-related mortality. High-risk neuroblastomas exhibit a range of genetic, morphological, and clinical heterogeneities, which add complexity to diagnosis and treatment with existing modalities. Identification of novel therapies is a high priority in high-risk neuroblastoma, and the combination of genetic analysis with increased mechanistic understanding—including identification of key signaling and developmental events—provides optimism for the future. This focused review highlights several recent findings concerning chromosomes 1p, 2p, and 11q, which link genetic aberrations with aberrant molecular signaling output. These novel molecular insights contribute important knowledge towards more effective treatment strategies for neuroblastoma.

Defining Pathological Activities of ALK in Neuroblastoma, a Neural Crest-Derived Cancer

Neuroblastoma is a common extracranial solid tumour of childhood, responsible for 15% of cancer-related deaths in children. Prognoses vary from spontaneous remission to aggressive disease with extensive metastases, where treatment is challenging. Tumours are thought to arise from sympathoadrenal progenitor cells, which derive from an embryonic cell population called neural crest cells that give rise to diverse cell types, such as facial bone and cartilage, pigmented cells, and neurons. Tumours are found associated with mature derivatives of neural crest, such as the adrenal medulla or paraspinal ganglia. Sympathoadrenal progenitor cells express anaplastic lymphoma kinase (ALK), which encodes a tyrosine kinase receptor that is the most frequently mutated gene in neuroblastoma. Activating mutations in the kinase domain are common in both sporadic and familial cases. The oncogenic role of ALK has been extensively studied, but little is known about its physiological role. Recent studies have implicated ALK in neural crest migration and sympathetic neurogenesis. However, very few downstream targets of ALK have been identified. Here, we describe pathological activation of ALK in the neural crest, which promotes proliferation and migration, while preventing differentiation, thus inducing the onset of neuroblastoma. Understanding the effects of ALK activity on neural crest cells will help find new targets for neuroblastoma treatment.

Transcriptomic Analysis of Skin Color in Anole Lizards

Color and color pattern are critical for animal camouflage, reproduction, and defense. Few studies, however, have attempted to identify candidate genes for color and color pattern in squamate reptiles, a colorful group with over 10,000 species. We used comparative transcriptomic analyses between white, orange, and yellow skin in a color-polymorphic species of anole lizard to 1) identify candidate color and color-pattern genes in squamates and 2) assess if squamates share an underlying genetic basis for color and color pattern variation with other vertebrates. Squamates have three types of chromatophores that determine color pattern: guanine-filled iridophores, carotenoid- or pteridine-filled xanthophores/erythrophores, and melanin-filled melanophores. We identified 13 best candidate squamate color and color-pattern genes shared with other vertebrates: six genes linked to pigment synthesis pathways, and seven genes linked to chromatophore development and maintenance. In comparisons of expression profiles between pigment-rich and white skin, pigment-rich skin upregulated the pteridine pathway as well as xanthophore/erythrophore development and maintenance genes; in comparisons between orange and yellow skin, orange skin upregulated the pteridine and carotenoid pathways as well as melanophore maintenance genes. Our results corroborate the predictions that squamates can produce similar colors using distinct color-reflecting molecules, and that both color and color-pattern genes are likely conserved across vertebrates. Furthermore, this study provides a concise list of candidate genes for future functional verification, representing a first step in determining the genetic basis of color and color pattern in anoles.

Genetics of white color and iridophoroma in "Lemon Frost" leopard geckos

The squamates (lizards and snakes) are close relatives of birds and mammals, with more than 10,000 described species that display extensive variation in a number of important biological traits, including coloration, venom production, and regeneration. Due to a lack of genomic tools, few genetic studies in squamates have been carried out. The leopard gecko, Eublepharis macularius, is a popular companion animal, and displays a variety of coloration patterns. We took advantage of a large breeding colony and used linkage analysis, synteny, and homozygosity mapping to investigate a spontaneous semi-dominant mutation, “Lemon Frost”, that produces white coloration and causes skin tumors (iridophoroma). We localized the mutation to a single locus which contains a strong candidate gene, SPINT1, a tumor suppressor implicated in human skin cutaneous melanoma (SKCM) and over-proliferation of epithelial cells in mice and zebrafish. Our work establishes the leopard gecko as a tractable genetic system and suggests that a tumor suppressor in melanocytes in humans can also suppress tumor development in iridophores in lizards.

The squamates (lizards and snakes) comprise a diverse group of reptiles, with more than 10,000 described species that display extensive variation in a number of important biological traits, including coloration. In this manuscript, we used quantitative genetics and genomics to map the mutation underlying white coloration in the Lemon Frost morph of the common leopard gecko, Eublepharis macularius. Lemon Frost geckos have increased white body coloration with brightened yellow and orange areas. This morph also displays a high incidence of iridophoroma, a tumor of white-colored cells. We obtained phenotype information and DNA samples from geckos in a large breeding colony and used genome sequencing and genetic linkage analysis to localize the Lemon Frost mutation to a single locus. This locus contains a strong candidate gene, SPINT1, a tumor suppressor implicated in human skin cutaneous melanoma. Together with other recent advances, our work brings reptiles into the modern genetics era.

Variation on a theme: pigmentation variants and mutants of anemonefish

Pigmentation patterning systems are of great interest to understand how changes in developmental mechanisms can lead to a wide variety of patterns. These patterns are often conspicuous, but their origins remain elusive for many marine fish species. Dismantling a biological system allows a better understanding of the required components and the deciphering of how such complex systems are established and function. Valuable information can be obtained from detailed analyses and comparisons of pigmentation patterns of mutants and/or variants from normal patterns. Anemonefishes have been popular marine fish in aquaculture for many years, which has led to the isolation of several mutant lines, and in particular color alterations, that have become very popular in the pet trade. Additionally, scattered information about naturally occurring aberrant anemonefish is available on various websites and image platforms. In this review, the available information on anemonefish color pattern alterations has been gathered and compiled in order to characterize and compare different mutations. With the global picture of anemonefish mutants and variants emerging from this, such as presence or absence of certain phenotypes, information on the patterning system itself can be gained.

Transcriptome Regulation by Oncogenic ALK Pathway in Mammalian Cortical Development Revealed by Single-Cell RNA Sequencing

Precise regulation of embryonic neurodevelopment is crucial for proper structural organization and functioning of the adult brain. The key molecular machinery orchestrating this process remains unclear. Anaplastic lymphoma kinase (ALK) is an oncogenic receptor-type protein tyrosine kinase that is specifically and transiently expressed in developing nervous system. However, its role in the mammalian brain development is unknown. We found that transient embryonic ALK inactivation caused long-lasting abnormalities in the adult mouse brain, including impaired neuronal connectivity and cognition, along with delayed neuronal migration and decreased neuronal proliferation during neurodevelopment. scRNA-seq on human cerebral organoids revealed a delayed transition of cell-type composition. Molecular characterization identified a group of differentially expressed genes (DEGs) that were temporally regulated by ALK at distinct developmental stages. In addition to oncogenes, many DEGs found by scRNA-seq are associated with neurological or neuropsychiatric disorders. Our study demonstrates a pivotal role of oncogenic ALK pathway in neurodevelopment and characterized cell-type-specific transcriptome regulated by ALK for better understanding mammalian cortical development.

The MITF paralog tfec is required in neural crest development for fate specification of the iridophore lineage from a multipotent pigment cell progenitor

Understanding how fate specification of distinct cell-types from multipotent progenitors occurs is a fundamental question in embryology. Neural crest stem cells (NCSCs) generate extraordinarily diverse derivatives, including multiple neural, skeletogenic and pigment cell fates. Key transcription factors and extracellular signals specifying NCSC lineages remain to be identified, and we have only a little idea of how and when they function together to control fate. Zebrafish have three neural crest-derived pigment cell types, black melanocytes, light-reflecting iridophores and yellow xanthophores, which offer a powerful model for studying the molecular and cellular mechanisms of fate segregation. Mitfa has been identified as the master regulator of melanocyte fate. Here, we show that an Mitf-related transcription factor, Tfec, functions as master regulator of the iridophore fate. Surprisingly, our phenotypic analysis of tfec mutants demonstrates that Tfec also functions in the initial specification of all three pigment cell-types, although the melanocyte and xanthophore lineages recover later. We show that Mitfa represses tfec expression, revealing a likely mechanism contributing to the decision between melanocyte and iridophore fate. Our data are consistent with the long-standing proposal of a tripotent progenitor restricted to pigment cell fates. Moreover, we investigate activation, maintenance and function of tfec in multipotent NCSCs, demonstrating for the first time its role in the gene regulatory network forming and maintaining early neural crest cells. In summary, we build on our previous work to characterise the gene regulatory network governing iridophore development, establishing Tfec as the master regulator driving iridophore specification from multipotent progenitors, while shedding light on possible cellular mechanisms of progressive fate restriction.

Anemonefish, a model for Eco-Evo-Devo

Anemonefish, are a group of about 30 species of damselfish (Pomacentridae) that have long aroused the interest of coral reef fish ecologists. Combining a series of original biological traits and practical features in their breeding that are described in this paper, anemonefish are now emerging as an experimental system of interest for developmental biology, ecology and evolutionary sciences. They are small sized and relatively easy to breed in specific husbandries, unlike the large-sized marine fish used for aquaculture. Because they live in highly structured social groups in sea anemones, anemonefish allow addressing a series of relevant scientific questions such as the social control of growth and sex change, the mechanisms controlling symbiosis, the establishment and variation of complex color patterns, and the regulation of aging. Combined with the use of behavioral experiments, that can be performed in the lab or directly in the wild, as well as functional genetics and genomics, anemonefish provide an attractive experimental system for Eco-Evo-Devo.

Insights Into the Albinism Mechanism for Two Distinct Color Morphs of Northern Snakehead, Channa argus Through Histological and Transcriptome Analyses

The great northern snakehead (Channa argus) is one of the most important economic and conservational fish in China. In this study, the melanocytes in the skin of two distinct color morphs C. argus were investigated and compared through employment of the microscopic analysis, hematoxylin and eosin (H&E) and Masson Fontana staining. Our results demonstrated the uneven distribution of melanocytes with extremely low density and most of them were in the state of aging or death. Meanwhile, there was no obvious pigment layer and melanocytes distribution pattern found in the albino-type (AT), while the melanocytes were evenly distributed with abundance in the bicolor-type (BT). The transcriptome analysis through Illumina HiSeq sequencing showed that a total of 34.93 Gb Clean Data was obtained, and Q30 base percentage reached 92.66%. The BT and AT northern snakeheads transcriptome data included a total of 56,039,701 and 60,410,063 clean reads (n = 3), respectively. In gene expression analyses, the sample correlation coefficients (r) were ranged between 0.92 and 1.00; the contribution of PC1 and PC2 were 50.25 and 13.73% by using PCA cluster analysis, the total number of DEGs were 1024 (559 up-regulated and 465 down-regulated), and the number of annotated DEGs was 767 (COG 172, KEGG 262, GO 288, SwissProt 548, Pfam 579 and NR 765). Additionally, 46,363 ± 873 and 44,947 ± 392 single nucleotide polymorphisms (SNPs) were compiled via genetic structure analysis, respectively. Ten key pigment-related genes were screened using qRT-PCR. And all of them revealed extremely higher expression levels in the skin of BT than those of AT. This is the first study to analyze the mechanism of albino characteristics of Channa via histology and transcriptomics, and also provide the oretical and practical support for the protection and development of germplasm resources for C. argus.

Topological data analysis of zebrafish patterns

Self-organized pattern behavior is ubiquitous throughout nature, from fish schooling to collective cell dynamics during organism development. Qualitatively these patterns display impressive consistency, yet variability inevitably exists within pattern-forming systems on both microscopic and macroscopic scales. Quantifying variability and measuring pattern features can inform the underlying agent interactions and allow for predictive analyses. Nevertheless, current methods for analyzing patterns that arise from collective behavior capture only macroscopic features or rely on either manual inspection or smoothing algorithms that lose the underlying agent-based nature of the data. Here we introduce methods based on topological data analysis and interpretable machine learning for quantifying both agent-level features and global pattern attributes on a large scale. Because the zebrafish is a model organism for skin pattern formation, we focus specifically on analyzing its skin patterns as a means of illustrating our approach. Using a recent agent-based model, we simulate thousands of wild-type and mutant zebrafish patterns and apply our methodology to better understand pattern variability in zebrafish. Our methodology is able to quantify the differential impact of stochasticity in cell interactions on wild-type and mutant patterns, and we use our methods to predict stripe and spot statistics as a function of varying cellular communication. Our work provides an approach to automatically quantifying biological patterns and analyzing agent-based dynamics so that we can now answer critical questions in pattern formation at a much larger scale.

Regulation of zebrafish melanocyte development by ligand-dependent BMP signaling

Preventing terminal differentiation is important in the development and progression of many cancers including melanoma. Recent identification of the BMP ligand GDF6 as a novel melanoma oncogene showed GDF6-activated BMP signaling suppresses differentiation of melanoma cells. Previous studies have identified roles for GDF6 orthologs during early embryonic and neural crest development, but have not identified direct regulation of melanocyte development by GDF6. Here, we investigate the BMP ligand gdf6a, a zebrafish ortholog of human GDF6, during the development of melanocytes from the neural crest. We establish that the loss of gdf6a or inhibition of BMP signaling during neural crest development disrupts normal pigment cell development, leading to an increase in the number of melanocytes and a corresponding decrease in iridophores, another neural crest-derived pigment cell type in zebrafish. This shift occurs as pigment cells arise from the neural crest and depends on mitfa, an ortholog of MITF, a key regulator of melanocyte development that is also targeted by oncogenic BMP signaling. Together, these results indicate that the oncogenic role ligand-dependent BMP signaling plays in suppressing differentiation in melanoma is a reiteration of its physiological roles during melanocyte development.

Zebrafish Pigment Pattern Formation: Insights into the Development and Evolution of Adult Form

Vertebrate pigment patterns are diverse and fascinating adult traits that allow animals to recognize conspecifics, attract mates, and avoid predators. Pigment patterns in fish are among the most amenable traits for studying the cellular basis of adult form, as the cells that produce diverse patterns are readily visible in the skin during development. The genetic basis of pigment pattern development has been most studied in the zebrafish, Danio rerio. Zebrafish adults have alternating dark and light horizontal stripes, resulting from the precise arrangement of three main classes of pigment cells: black melanophores, yellow xanthophores, and iridescent iridophores. The coordination of adult pigment cell lineage specification and differentiation with specific cellular interactions and morphogenetic behaviors is necessary for stripe development. Besides providing a nice example of pattern formation responsible for an adult trait of zebrafish, stripe-forming mechanisms also provide a conceptual framework for posing testable hypotheses about pattern diversification more broadly. Here, we summarize what is known about lineages and molecular interactions required for pattern formation in zebrafish, we review some of what is known about pattern diversification in Danio, and we speculate on how patterns in more distant teleosts may have evolved to produce a stunningly diverse array of patterns in nature.

The identification of genes involved in the evolution of color patterns in fish

The genetic basis of morphological variation, both within and between species, provides a major topic in evolutionary biology. Teleost fish produce most elaborate color patterns, and among the more than 20000 species a number have been chosen for more detailed analyses because they are suitable to study particular aspects of color pattern evolution. In several fish species, color variants and pattern variants have been collected, transcriptome analyses have been carried out, and the recent advent of gene editing tools, such as CRISPR/Cas9, has allowed the production of mutants. Covering mostly the literature from the last three years, we discuss the cellular basis of coloration and the identification of loci involved in color pattern differences between sister species in cichlids and Danio species, in which cis-regulatory changes seem to prevail.

Targeting anaplastic lymphoma kinase in neuroblastoma

Over the last decade, anaplastic lymphoma kinase (ALK), a receptor tyrosine kinase (RTK), has been identified as a fusion partner in a diverse variety of translocation events resulting in oncogenic signaling in many different cancer types. In tumors where the full‐length ALK RTK itself is mutated, such as neuroblastoma, the picture regarding the role of ALK as an oncogenic driver is less clear. Neuroblastoma is a complex and heterogeneous tumor that arises from the neural crest derived peripheral nervous system. Although high‐risk neuroblastoma is rare, it often relapses and becomes refractory to treatment. Thus, neuroblastoma accounts for 10–15% of all childhood cancer deaths. Since most cases are in children under the age of 2, understanding the role and regulation of ALK during neural crest development is an important goal in addressing neuroblastoma tumorigenesis. An impressive array of tyrosine kinase inhibitors (TKIs) that act to inhibit ALK have been FDA approved for use in ALK‐driven cancers. ALK TKIs bind differently within the ATP‐binding pocket of the ALK kinase domain and have been associated with different resistance mutations within ALK itself that arise in response to therapeutic use, particularly in ALK‐fusion positive non‐small cell lung cancer (NSCLC). This patient population has highlighted the importance of considering the relevant ALK TKI to be used for a given ALK mutant variant. In this review, we discuss ALK in neuroblastoma, as well as the use of ALK TKIs and other strategies to inhibit tumor growth. Current efforts combining novel approaches and increasing our understanding of the oncogenic role of ALK in neuroblastoma are aimed at improving the efficacy of ALK TKIs as precision medicine options in the clinic.

Developmental and comparative transcriptomic identification of iridophore contribution to white barring in clownfish

Actinopterygian fishes harbor at least eight distinct pigment cell types, leading to a fascinating diversity of colors. Among this diversity, the cellular origin of the white color appears to be linked to several pigment cell types such as iridophores or leucophores. We used the clownfish Amphiprion ocellaris, which has a color pattern consisting of white bars over a darker body, to characterize the pigment cells that underlie the white hue. We observe by electron microscopy that cells in white bars are similar to iridophores. In addition, the transcriptomic signature of clownfish white bars exhibits similarities with that of zebrafish iridophores. We further show by pharmacological treatments that these cells are necessary for the white color. Among the top differentially expressed genes in white skin, we identified several genes (fhl2a, fhl2b, saiyan, gpnmb, and apoD1a) and show that three of them are expressed in iridophores. Finally, we show by CRISPR/Cas9 mutagenesis that these genes are critical for iridophore development in zebrafish. Our analyses provide clues to the genomic underpinning of color diversity and allow identification of new iridophore genes in fish.

The minimal gap-junction network among melanophores and xanthophores required for stripe-pattern formation in zebrafish

Connexin39.4 (Cx39.4) and Connexin41.8 (Cx41.8), two gap-junction proteins expressed in both melanophores and xanthophores, are critical for the intercellular communication among pigment cells that is necessary for generating the stripe pigment pattern of zebrafish. We previously characterized the gap-junction properties of Cx39.4 and Cx41.8, but how these proteins contribute to stripe formation remains unclear; this is because distinct types of connexins potentially form heteromeric gap junctions, which precludes accurate elucidation of individual connexin functions in vivo. Here, by arranging Cx39.4 and Cx41.8 expression in pigment cells, we identified the simplest gap-junction network required for stripe generation: Cx39.4 expression in melanophores is required but expression in xanthophores is not necessary for stripe patterning, whereas Cx41.8 expression in xanthophores is sufficient for the patterning, and Cx41.8 expression in melanophores might stabilize the stripes. Moreover, patch-clamp recordings revealed that Cx39.4 gap junctions exhibit spermidine-dependent rectification property. Our results suggest that Cx39.4 facilitates the critical cell-cell interactions between melanophores and xanthophores that mediate a unidirectional activation-signal transfer from xanthophores to melanophores, which is essential for melanophore survival.

Leukocyte receptor tyrosine kinase interacts with secreted midkine to promote survival of migrating neural crest cells

Neural crest cells migrate long distances throughout the embryo and rely on extracellular signals that attract, repel and/or stimulate survival to ensure proper contribution to target derivatives. Here, we show that leukocyte receptor tyrosine kinase (LTK), an ALK-type receptor tyrosine kinase, is expressed by neural crest cells during early migratory stages in chicken embryos. Loss of LTK in the cranial neural crest impairs migration and results in increased levels of apoptosis. Conversely, midkine, previously proposed as a ligand for ALK, is secreted by the non-neural ectoderm during early neural crest migratory stages and internalized by neural crest cells in vivo Similar to loss of LTK, loss of midkine reduces survival of the migratory neural crest. Moreover, we show by proximity ligation and co-immunoprecipitation assays that midkine binds to LTK. Taken together, these results suggest that LTK in neural crest cells interacts with midkine emanating from the non-neural ectoderm to promote cell survival, revealing a new signaling pathway that is essential for neural crest development.

A systems biology approach uncovers the core gene regulatory network governing iridophore fate choice from the neural crest

Multipotent neural crest (NC) progenitors generate an astonishing array of derivatives, including neuronal, skeletal components and pigment cells (chromatophores), but the molecular mechanisms allowing balanced selection of each fate remain unknown. In zebrafish, melanocytes, iridophores and xanthophores, the three chromatophore lineages, are thought to share progenitors and so lend themselves to investigating the complex gene regulatory networks (GRNs) underlying fate segregation of NC progenitors. Although the core GRN governing melanocyte specification has been previously established, those guiding iridophore and xanthophore development remain elusive. Here we focus on the iridophore GRN, where mutant phenotypes identify the transcription factors Sox10, Tfec and Mitfa and the receptor tyrosine kinase, Ltk, as key players. Here we present expression data, as well as loss and gain of function results, guiding the derivation of an initial iridophore specification GRN. Moreover, we use an iterative process of mathematical modelling, supplemented with a Monte Carlo screening algorithm suited to the qualitative nature of the experimental data, to allow for rigorous predictive exploration of the GRN dynamics. Predictions were experimentally evaluated and testable hypotheses were derived to construct an improved version of the GRN, which we showed produced outputs consistent with experimentally observed gene expression dynamics. Our study reveals multiple important regulatory features, notably a sox10-dependent positive feedback loop between tfec and ltk driving iridophore specification; the molecular basis of sox10 maintenance throughout iridophore development; and the cooperation between sox10 and tfec in driving expression of pnp4a, a key differentiation gene. We also assess a candidate repressor of mitfa, a melanocyte-specific target of sox10. Surprisingly, our data challenge the reported role of Foxd3, an established mitfa repressor, in iridophore regulation. Our study builds upon our previous systems biology approach, by incorporating physiologically-relevant parameter values and rigorous evaluation of parameter values within a qualitative data framework, to establish for the first time the core GRN guiding specification of the iridophore lineage.

Ontogenetic and phylogenetic simplification during white stripe evolution in clownfishes

Background

Biologists have long been fascinated by the striking diversity of complex color patterns in tropical reef fishes. However, the origins and evolution of this diversity are still poorly understood. Disentangling the evolution of simple color patterns offers the opportunity to dissect both ultimate and proximate causes underlying color diversity.

Results

Here, we study clownfishes, a tribe of 30 species within the Pomacentridae that displays a relatively simple color pattern made of zero to three vertical white stripes on a dark body background. Mapping the number of white stripes on the evolutionary tree of clownfishes reveals that their color pattern diversification results from successive caudal to rostral losses of stripes. Moreover, we demonstrate that stripes always appear with a rostral to caudal stereotyped sequence during larval to juvenile transition. Drug treatments (TAE 684) during this period leads to a dose-dependent loss of stripes, demonstrating that white stripes are made of iridophores and that these cells initiate the stripe formation. Surprisingly, juveniles of several species (e.g., Amphiprion frenatus) have supplementary stripes when compared to their respective adults. These stripes disappear caudo-rostrally during the juvenile phase leading to the definitive color pattern. Remarkably, the reduction of stripe number over ontogeny matches the sequences of stripe losses during evolution, showing that color pattern diversification among clownfish lineages results from changes in developmental processes. Finally, we reveal that the diversity of striped patterns plays a key role for species recognition.

Conclusions

Overall, our findings illustrate how developmental, ecological, and social processes have shaped the diversification of color patterns during the radiation of an emblematic coral reef fish lineage.

Electronic supplementary material

The online version of this article (10.1186/s12915-018-0559-7) contains supplementary material, which is available to authorized users.

Iridophores as a source of robustness in zebrafish stripes and variability in Danio patterns

Zebrafish (Danio rerio) feature black and yellow stripes, while related Danios display different patterns. All these patterns form due to the interactions of pigment cells, which self-organize on the fish skin. Until recently, research focused on two cell types (melanophores and xanthophores), but newer work has uncovered the leading role of a third type, iridophores: by carefully orchestrated transitions in form, iridophores instruct the other cells, but little is known about what drives their form changes. Here we address this question from a mathematical perspective: we develop a model (based on known interactions between the original two cell types) that allows us to assess potential iridophore behavior. We identify a set of mechanisms governing iridophore form that is consistent across a range of empirical data. Our model also suggests that the complex cues iridophores receive may act as a key source of redundancy, enabling both robust patterning and variability within Danio.

Transcription and Signaling Regulators in Developing Neuronal Subtypes of Mouse and Human Enteric Nervous System

BACKGROUND & AIMS

The enteric nervous system (ENS) regulates gastrointestinal function via different subtypes of neurons, organized into fine-tuned neural circuits. It is not clear how cell diversity is created within the embryonic ENS; information required for development of cell-based therapies and models of enteric neuropathies. We aimed to identify proteins that regulate ENS differentiation and network formation.

METHODS

We generated and compared RNA expression profiles of the entire ENS, ENS progenitor cells, and non-ENS gut cells of mice, collected at embryonic days 11.5 and 15.5, when different subtypes of neurons are formed. Gastrointestinal tissues from R26ReYFP reporter mice crossed to Sox10-CreER^T2 or Wnt1-Cre mice were dissected and the 6 populations of cells were isolated by flow cytometry. We used histochemistry to map differentially expressed proteins in mouse and human gut tissues at different stages of development, in different regions. We examined enteric neuronal diversity and gastric function in Wnt1-Cre x Sox6^fl/fl mice, which do not express the Sox6 gene in the ENS.

RESULTS

We identified 147 transcription and signaling factors that varied in spatial and temporal expression during development of the mouse ENS. Of the factors also analyzed in human ENS, most were conserved. We uncovered 16 signaling pathways (such as fibroblast growth factor and Eph/ephrin pathways). Transcription factors were grouped according to their specific expression in enteric progenitor cells (such as MEF2C), enteric neurons (such as SOX4), or neuron subpopulations (such as SATB1 and SOX6). Lack of SOX6 in the ENS reduced the numbers of gastric dopamine neurons and delayed gastric emptying.

CONCLUSIONS

Using transcriptome and histochemical analyses of the developing mouse and human ENS, we mapped expression patterns of transcription and signaling factors. Further studies of these candidate determinants might elucidate the mechanisms by which enteric stem cells differentiate into neuronal subtypes and form distinct connectivity patterns during ENS development. We found expression of SOX6 to be required for development of gastric dopamine neurons.

ALKALs are in vivo ligands for ALK family receptor tyrosine kinases in the neural crest and derived cells

Neuroblastoma is a pediatric tumor arising from the neural crest. Dysregulation of the receptor tyrosine kinase ALK has been linked to neuroblastoma, making it important to understand its function in native conditions. In zebrafish, a related receptor—Ltk—is also expressed in neural crest and regulates development of specific pigment cells—iridophores. Ligands activating human ALK were recently identified as the ALKAL proteins (FAM150, AUG) by biochemical means. Our data show that this ligand–receptor pair functions in vivo in the neural crest of zebrafish to drive development of iridophores. Removal of Ltk or all three zebrafish ALKALs results in larvae completely lacking these cells. Using Drosophila and human cell lines, we show evolutionary conservation of this important interaction.

Mutations in anaplastic lymphoma kinase (ALK) are implicated in somatic and familial neuroblastoma, a pediatric tumor of neural crest-derived tissues. Recently, biochemical analyses have identified secreted small ALKAL proteins (FAM150, AUG) as potential ligands for human ALK and the related leukocyte tyrosine kinase (LTK). In the zebrafish Danio rerio, DrLtk, which is similar to human ALK in sequence and domain structure, controls the development of iridophores, neural crest-derived pigment cells. Hence, the zebrafish system allows studying Alk/Ltk and Alkals involvement in neural crest regulation in vivo. Using zebrafish pigment pattern formation, Drosophila eye patterning, and cell culture-based assays, we show that zebrafish Alkals potently activate zebrafish Ltk and human ALK driving downstream signaling events. Overexpression of the three DrAlkals cause ectopic iridophore development, whereas loss-of-function alleles lead to spatially distinct patterns of iridophore loss in zebrafish larvae and adults. alkal loss-of-function triple mutants completely lack iridophores and are larval lethal as is the case for ltk null mutants. Our results provide in vivo evidence of (i) activation of ALK/LTK family receptors by ALKALs and (ii) an involvement of these ligand–receptor complexes in neural crest development.

Anterior-posterior gene expression differences in three Lake Malawi cichlid fishes with variation in body stripe orientation

Morphological differentiation among closely related species provides opportunities to study mechanisms shaping natural phenotypic variation. Here, we address variation in the orientation of melanin-colored body stripes in three cichlid species of the tribe Haplochromini. Melanochromis auratus displays a common pattern of dark, straight horizontal body stripes, whereas in Aristochromis christyi and Buccochromis rhoadesii, oblique stripes extend from the anterior dorsal to the posterior mid-lateral trunk. We first validated a stably reference gene, and then, investigated the chromatophore distribution in the skin by assessing the expression levels of the iridophore and melanophore marker genes, ltk and slc24a5, respectively, as well as pmel, a melanophore pigmentation marker gene. We found anterior-posterior differences in the expression levels of the three genes in the oblique-striped species. The higher anterior expression of ltk, indicates increased iridophore density in the anterior region, i.e., uneven horizontal distribution of iridophores, which coincides with the anterior dorsalization of melanophore stripe in these species. The obliqueness of the horizontal body stripes might be a result of distinct migratory or patterning abilities of melanophores in anterior and posterior stripe regions which could be reflected by variation in the expression of genes involved in melanophore patterning. To address this, we investigated anterior-posterior expression levels of a primary set of candidate target genes with known functions in melanophore migration and stripe patterning in the adult zebrafish, and their related gene regulatory network. Among these genes, those with differences in anterior-posterior expression showed only species-specific differential expression, e.g., sdf1a, col14a1a, ifitm5, and agpat3, with the exception of fbxw4/hagoromo (differentially expressed in an oblique-and the straight-striped species). In summary, distinct anterior-posterior gradients in iridophore density found to be more similar characteristic between the two oblique-striped species. Furthermore, the species-specific differential expression of genes involved in stripe patterning might also implicate distinct molecular processes underlying the obliqueness of body stripe in two closely related cichlid species.

The role of the ALK receptor in cancer biology

A vast array of oncogenic variants has been identified for anaplastic lymphoma kinase (ALK). Therefore, there is a need to better understand the role of ALK in cancer biology in order to optimise treatment strategies. This review summarises the latest research on the receptor tyrosine kinase ALK, and how this information can guide the management of patients with cancer that is ALK-positive. A variety of ALK gene alterations have been described across a range of tumour types, including point mutations, deletions and rearrangements. A wide variety of ALK fusions, in which the kinase domain of ALK and the amino-terminal portion of various protein partners are fused, occur in cancer, with echinoderm microtubule-associated protein-like 4 (EML4)-ALK being the most prevalent in non-small-cell lung cancer (NSCLC). Different ALK fusion proteins can mediate different signalling outputs, depending on properties such as subcellular localisation and protein stability. The ALK fusions found in tumours lack spatial and temporal regulation, which can also affect dimerisation and substrate specificity. Two ALK tyrosine kinase inhibitors (TKIs), crizotinib and ceritinib, are currently approved in Europe for use in ALK-positive NSCLC and several others are in development. These ALK TKIs bind slightly differently within the ATP-binding pocket of the ALK kinase domain and are associated with the emergence of different resistance mutation patterns during therapy. This emphasises the need to tailor the sequence of ALK TKIs according to the ALK signature of each patient. Research into the oncogenic functions of ALK, and fast paced development of ALK inhibitors, has substantially improved outcomes for patients with ALK-positive NSCLC. Limited data are available surrounding the physiological ligand-stimulated activation of ALK signalling and further research is needed. Understanding the role of ALK in tumour biology is key to further optimising therapeutic strategies for ALK-positive disease.

Alk and Ltk ligands are essential for iridophore development in zebrafish mediated by the receptor tyrosine kinase Ltk

Anaplastic lymphoma kinase (Alk) and leucocyte tyrosine kinase (Ltk) were identified as "orphan" receptor tyrosine kinases (RTKs) with oncogenic potential. Recently ALKAL1 and ALKAL2 (also named "augmentor-β" and "augmentor-α" or "FAM150A" and "FAM150B," respectively) were discovered as physiological ligands of Alk and Ltk. Here, we employ zebrafish as a model system to explore the physiological function and to characterize in vivo links between Alk and Ltk with their ligands. Unlike the two ligands encoded by mammalian genomes, the zebrafish genome contains three genes: aug-α1, aug-α2, and aug-β Our experiments demonstrate that these ligands play an important role in zebrafish pigment development. Deficiency in aug-α1, aug-α2, and aug-β results in strong impairment in iridophore patterning of embryonic and adult zebrafish that is phenocopied in zebrafish deficient in Ltk. We show that aug-α1 and aug-α2 are essential for embryonic iridophore development and adult body coloration. In contrast, aug-α2 and aug-β are essential for iridophore formation in the adult eye. Importantly, these processes are entirely mediated by Ltk and not by Alk. These experiments establish a physiological link between augmentor ligands and Ltk and demonstrate that particular augmentors activate Ltk in a tissue-specific context to induce iridophore differentiation from neural crest-derived cells and pigment progenitor cells.

How fish color their skin: A paradigm for development and evolution of adult patterns: Multipotency, plasticity, and cell competition regulate proliferation and spreading of pigment cells in Zebrafish coloration

Pigment cells in zebrafish - melanophores, iridophores, and xanthophores - originate from neural crest-derived stem cells associated with the dorsal root ganglia of the peripheral nervous system. Clonal analysis indicates that these progenitors remain multipotent and plastic beyond embryogenesis well into metamorphosis, when the adult color pattern develops. Pigment cells share a lineage with neuronal cells of the peripheral nervous system; progenitors propagate along the spinal nerves. The proliferation of pigment cells is regulated by competitive interactions among cells of the same type. An even spacing involves collective migration and contact inhibition of locomotion of the three cell types distributed in superimposed monolayers in the skin. This mode of coloring the skin is probably common to fish, whereas different patterns emerge by species specific cell interactions among the different pigment cell types. These interactions are mediated by channels involved in direct cell contact between the pigment cells, as well as unknown cues provided by the tissue environment.

Heterotypic interactions regulate cell shape and density during color pattern formation in zebrafish

The conspicuous striped coloration of zebrafish is produced by cell-cell interactions among three different types of chromatophores: black melanophores, orange/yellow xanthophores and silvery/blue iridophores. During color pattern formation xanthophores undergo dramatic cell shape transitions and acquire different densities, leading to compact and orange xanthophores at high density in the light stripes, and stellate, faintly pigmented xanthophores at low density in the dark stripes. Here, we investigate the mechanistic basis of these cell behaviors in vivo, and show that local, heterotypic interactions with dense iridophores regulate xanthophore cell shape transition and density. Genetic analysis reveals a cell-autonomous requirement of gap junctions composed of Cx41.8 and Cx39.4 in xanthophores for their iridophore-dependent cell shape transition and increase in density in light-stripe regions. Initial melanophore-xanthophore interactions are independent of these gap junctions; however, subsequently they are also required to induce the acquisition of stellate shapes in xanthophores of the dark stripes. In summary, we conclude that, whereas homotypic interactions regulate xanthophore coverage in the skin, their cell shape transitions and density is regulated by gap junction-mediated, heterotypic interactions with iridophores and melanophores.

Summary: The conspicuous pigmentation pattern of zebrafish is produced by three kinds of interacting pigment cells. Here we address the cellular consequences of these interactions in wild-type fish and mutants with altered pigment patterns.

Homotypic cell competition regulates proliferation and tiling of zebrafish pigment cells during colour pattern formation

The adult striped pattern of zebrafish is composed of melanophores, iridophores and xanthophores arranged in superimposed layers in the skin. Previous studies have revealed that the assembly of pigment cells into stripes involves heterotypic interactions between all three chromatophore types. Here we investigate the role of homotypic interactions between cells of the same chromatophore type. Introduction of labelled progenitors into mutants lacking the corresponding cell type allowed us to define the impact of competitive interactions via long-term in vivo imaging. In the absence of endogenous cells, transplanted iridophores and xanthophores show an increased rate of proliferation and spread as a coherent net into vacant space. By contrast, melanophores have a limited capacity to spread in the skin even in the absence of competing endogenous cells. Our study reveals a key role for homotypic competitive interactions in determining number, direction of migration and individual spacing of cells within chromatophore populations.