Instructive role of melanocytes during pigment pattern formation of the avian skin

Structure, function and formation of the amniote skin pattern

From feather and hair dotted arrays to pigmented stripes and spots, the spatial distribution of skin appendages and colouration often forms visible ornaments crucial for fitness in the coat of birds and mammals. These geometrical motifs are extremely diverse in nature. Yet, phenotypic surveys evidenced common themes in variation: the orientation, appendage-specificity or pigmentation of a given region may be conserved across groups or species. Here, we review naturalist observations of natural variation in the anatomy and ecological function of the skin pattern in amniotes. We then describe several decades of genetics, mathematical modelling and experimental embryology work aiming at understanding the molecular and morphogenetic mechanisms responsible for pattern formation. We discuss how these studies provided evidence that the morphological trends and differences representative of the phenotypic landscape of skin patterns in wild amniote species is rooted in the mechanisms controlling the production of distinct compartments in the embryonic skin.

Adaptive patterning of vascular network during avian skin development: Mesenchymal plasticity and dermal vasculogenesis

A vasculature network supplies blood to feather buds in the developing skin. Does the vasculature network during early skin development form by sequential sprouting from the central vasculature or does local vasculogenesis occur first that then connect with the central vascular tree? Using transgenic Japanese quail Tg(TIE1p.H2B-eYFP), we observe that vascular progenitor cells appear after feather primordia formation. The vasculature then radiates out from each bud and connects with primordial vessels from neighboring buds. Later they connect with the central vasculature. Epithelial-mesenchymal recombination shows local vasculature is patterned by the epithelium, which expresses FGF2 and VEGF. Perturbing noggin expression leads to abnormal vascularization. To study endothelial origin, we compare transcriptomes of TIE1p.H2B-eYFP+ cells collected from the skin and aorta. Endothelial cells from the skin more closely resemble skin dermal cells than those from the aorta. The results show developing chicken skin vasculature is assembled by (1) physiological vasculogenesis from the peripheral tissue, and (2) subsequently connects with the central vasculature. The work implies mesenchymal plasticity and convergent differentiation play significant roles in development, and such processes may be re-activated during adult regeneration. SUMMARY STATEMENT: We show the vasculature network in the chicken skin is assembled using existing feather buds as the template, and endothelia are derived from local bud dermis and central vasculature.

A sequence of SVA retrotransposon insertions in ASIP shaped human pigmentation

Retrotransposons comprise about 45% of the human genome1, but their contributions to human trait variation and evolution are only beginning to be explored2,3. Here, we find that a sequence of SVA retrotransposon insertions in an early intron of the ASIP (agouti signaling protein) gene has probably shaped human pigmentation several times. In the UK Biobank (n = 169,641), a recent 3.3-kb SVA insertion polymorphism associated strongly with lighter skin pigmentation (0.22 [0.21-0.23] s.d.; P = 2.8 × 10-351) and increased skin cancer risk (odds ratio = 1.23 [1.18-1.27]; P = 1.3 × 10-28), appearing to underlie one of the strongest common genetic influences on these phenotypes within European populations4-6. ASIP expression in skin displayed the same association pattern, with the SVA insertion allele exhibiting 2.2-fold (1.9-2.6) increased expression. This effect had an unusual apparent mechanism: an earlier, nonpolymorphic, human-specific SVA retrotransposon 3.9 kb upstream appeared to have caused ASIP hypofunction by nonproductive splicing, which the new (polymorphic) SVA insertion largely eliminated. Extended haplotype homozygosity indicated that the insertion allele has risen to allele frequencies up to 11% in European populations over the past several thousand years. These results indicate that a sequence of retrotransposon insertions contributed to a species-wide increase, then a local decrease, of human pigmentation.

Exploring the Maintaining Period and the Differentially Expressed Genes between the Yellow and Black Stripes of the Juvenile Stripe in the Offspring of Wild Boar and Duroc

Coloration is a crucial trait that allows species to adapt and survive in different environments. Wild boars exhibit alternating black (dark) and yellow (light) longitudinal stripes on their back during their infancy (juvenile stripes), and as adults, they transform into uniform wild-type coat color. Aiming to record the procedure of juvenile stripes disappearing, piglets (WD) with juvenile stripes were produced by crossing a wild boar with Duroc sows, and photos of their coat color were taken from 20 d to 220 d. The pigments in the hairs from the black and yellow stripes were determined. Furthermore, the differentially expressed genes between the black and yellow stripes were investigated in 5 WD with the age of 30 d using whole-transcriptome sequencing to explore the genetic mechanism of the juvenile stripes. The juvenile stripes started to disappear at about 70 d, and stripes were not distinguished with the naked eye at about 160 d; that is, the juvenile stripe completely disappeared. A hotspot of a differentially expressing (DE) region was found on chromosome 13, containing/covering 2 of 13 DE genes and 8 of 10 DE lncRNAs in this region. A network among ZIC4, ssc-miR-532-3p, and ENSSSCG00000056225 might regulate the formation of juvenile stripes. Altogether, this study provides new insights into spatiotemporal coat color pattern.

Integrating genomics and transcriptomics to identify candidate genes for high-altitude adaptation and egg production in Nixi chicken

1. This study combined genome-wide selection signal analysis with RNA-sequencing to identify candidate genes associated with high altitude adaptation and egg production performance in Nixi chickens (NXC).2. Based on the whole-genome data from 20 NXC (♂:10; ♀:10), the population selection signal was analysed by sliding window analysis. The selected genes were screened by combination with the population differentiation statistic (FST). The sequence diversity statistic (θπ). RNA-seq was performed on the ovarian tissues of NXC (n = 6) and Lohmann laying hens (n = 6) to analyse the differentially expressed genes (DEGs) between the two groups. The functional enrichment analysis of the selected genes and differentially expressed genes was performed.3. There were 742 genes under strong positive selection and 509 differentially expressed genes screened in NXC. Integrated analysis of the genome and transcriptome revealing 26 overlapping genes. The candidate genes for adaptation to a high-altitude environment, as well as for egg production, disease resistance, vision and pigmentation in NXC were preliminarily screened.4. The results provided theoretical guidance for further research on the genetic resource protection and utilisation of NXC.

Gap junctions in Turing-type periodic feather pattern formation

Periodic patterning requires coordinated cell-cell interactions at the tissue level. Turing showed, using mathematical modeling, how spatial patterns could arise from the reactions of a diffusive activator-inhibitor pair in an initially homogeneous 2D field. Most activators and inhibitors studied in biological systems are proteins, and the roles of cell-cell interaction, ions, bioelectricity, etc. are only now being identified. Gap junctions (GJs) mediate direct exchanges of ions or small molecules between cells, enabling rapid long-distance communications in a cell collective. They are therefore good candidates for propagating nonprotein-based patterning signals that may act according to the Turing principles. Here, we explore the possible roles of GJs in Turing-type patterning using feather pattern formation as a model. We found 7 of the 12 investigated GJ isoforms are highly dynamically expressed in the developing chicken skin. In ovo functional perturbations of the GJ isoform, connexin 30, by siRNA and the dominant-negative mutant applied before placode development led to disrupted primary feather bud formation. Interestingly, inhibition of gap junctional intercellular communication (GJIC) in the ex vivo skin explant culture allowed the sequential emergence of new feather buds at specific spatial locations relative to the existing primary buds. The results suggest that GJIC may facilitate the propagation of long-distance inhibitory signals. Thus, inhibition of GJs may stimulate Turing-type periodic feather pattern formation during chick skin development, and the removal of GJ activity would enable the emergence of new feather buds if the local environment were competent and the threshold to form buds was reached. We further propose Turing-based computational simulations that can predict the sequential appearance of these ectopic buds. Our models demonstrate how a Turing activator-inhibitor system can continue to generate patterns in the competent morphogenetic field when the level of intercellular communication at the tissue scale is modulated.

Bioelectricity in dental medicine: a narrative review

BACKGROUND

Bioelectric signals, whether exogenous or endogenous, play crucial roles in the life processes of organisms. Recently, the significance of bioelectricity in the field of dentistry is steadily gaining greater attention.

OBJECTIVE

This narrative review aims to comprehensively outline the theory, physiological effects, and practical applications of bioelectricity in dental medicine and to offer insights into its potential future direction. It attempts to provide dental clinicians and researchers with an electrophysiological perspective to enhance their clinical practice or fundamental research endeavors.

METHODS

An online computer search for relevant literature was performed in PubMed, Web of Science and Cochrane Library, with the keywords "bioelectricity, endogenous electric signal, electric stimulation, dental medicine."

RESULTS

Eventually, 288 documents were included for review. The variance in ion concentration between the interior and exterior of the cell membrane, referred to as transmembrane potential, forms the fundamental basis of bioelectricity. Transmembrane potential has been established as an essential regulator of intercellular communication, mechanotransduction, migration, proliferation, and immune responses. Thus, exogenous electric stimulation can significantly alter cellular action by affecting transmembrane potential. In the field of dental medicine, electric stimulation has proven useful for assessing pulp condition, locating root apices, improving the properties of dental biomaterials, expediting orthodontic tooth movement, facilitating implant osteointegration, addressing maxillofacial malignancies, and managing neuromuscular dysfunction. Furthermore, the reprogramming of bioelectric signals holds promise as a means to guide organism development and intervene in disease processes. Besides, the development of high-throughput electrophysiological tools will be imperative for identifying ion channel targets and precisely modulating bioelectricity in the future.

CONCLUSIONS

Bioelectricity has found application in various concepts of dental medicine but large-scale, standardized, randomized controlled clinical trials are still necessary in the future. In addition, the precise, repeatable and predictable measurement and modulation methods of bioelectric signal patterns are essential research direction.

Mechanisms Underlying the Formation and Evolution of Vertebrate Color Patterns

Vertebrates exhibit a wide range of color patterns, which play critical roles in mediating intra- and interspecific communication. Because of their diversity and visual accessibility, color patterns offer a unique and fascinating window into the processes underlying biological organization. In this review, we focus on describing many of the general principles governing the formation and evolution of color patterns in different vertebrate groups. We characterize the types of patterns, review the molecular and developmental mechanisms by which they originate, and discuss their role in constraining or facilitating evolutionary change. Lastly, we outline outstanding questions in the field and discuss different approaches that can be used to address them. Overall, we provide a unifying conceptual framework among vertebrate systems that may guide research into naturally evolved mechanisms underlying color pattern formation and evolution.

Electrochemical Devices in Cutaneous Wound Healing

In healthy skin, vectorial ion transport gives rise to a transepithelial potential which directly impacts many physiological aspects of skin function. A wound is a physical defect that breaches the epithelial barrier and changes the electrochemical environment of skin. Electroceutical dressings are devices that manipulate the electrochemical environment, host as well as microbial, of a wound. In this review, electroceuticals are organized into three mechanistic classes: ionic, wireless, and battery powered. All three classes of electroceutical dressing show encouraging effects on infection management and wound healing with evidence of favorable impact on keratinocyte migration and disruption of wound biofilm infection. This foundation sets the stage for further mechanistic as well as interventional studies. Successful conduct of such studies will determine the best dosage, timing, and class of stimulus necessary to maximize therapeutic efficacy.

Optogenetic control of gut movements reveals peristaltic wave-mediated induction of cloacal contractions and reactivation of impaired gut motility

Gut peristalsis, recognized as a wave-like progression along the anterior-posterior gut axis, plays a pivotal role in the transportation, digestion, and absorption of ingested materials. The embryonic gut, which has not experienced ingested materials, undergoes peristalsis offering a powerful model for studying the intrinsic mechanisms underlying the gut motility. It has previously been shown in chicken embryos that acute contractions of the cloaca (an anus-like structure) located at the posterior end of the hindgut are tightly coupled with the arrival of hindgut-derived waves. To further scrutinize the interactions between hindgut and cloaca, we here developed an optogenetic method that produced artificial waves in the hindgut. A variant form of channelrhodopsin-2 (ChR2(D156C)), permitting extremely large photocurrents, was expressed in the muscle component of the hindgut of chicken embryos using Tol2-mediated gene transfer and in ovo electroporation techniques. The D156C-expressing hindgut responded efficiently to local pulses of blue light: local contractions emerge at an ectopic site in the hindgut, which were followed by peristaltic waves that reached to the endpoint of the hindgut. Markedly, the arrival of the optogenetically induced waves caused concomitant contractions of the cloaca, revealing that the hindgut-cloaca coordination is mediated by signals triggered by peristaltic waves. Moreover, a cloaca undergoing pharmacologically provoked aberrant contractions could respond to pulsed blue light irradiation. Together, the optogenetic technology developed in this study for inducing gut peristalsis paves the way to study the gut movement and also to explore therapeutic methodology for peristaltic disorders.

Gap junctions in Turing-type periodic feather pattern formation

Periodic patterning requires coordinated cell-cell interactions at the tissue level. Turing showed, using mathematical modeling, how spatial patterns could arise from the reactions of a diffusive activator-inhibitor pair in an initially homogenous two-dimensional field. Most activators and inhibitors studied in biological systems are proteins, and the roles of cell-cell interaction, ions, bioelectricity, etc. are only now being identified. Gap junctions (GJs) mediate direct exchanges of ions or small molecules between cells, enabling rapid long-distance communications in a cell collective. They are therefore good candidates for propagating non-protein-based patterning signals that may act according to the Turing principles. Here, we explore the possible roles of GJs in Turing-type patterning using feather pattern formation as a model. We found seven of the twelve investigated GJ isoforms are highly dynamically expressed in the developing chicken skin. In ovo functional perturbations of the GJ isoform, connexin 30, by siRNA and the dominant-negative mutant applied before placode development led to disrupted primary feather bud formation, including patches of smooth skin and buds of irregular sizes. Later, after the primary feather arrays were laid out, inhibition of gap junctional intercellular communication in the ex vivo skin explant culture allowed the emergence of new feather buds in temporal waves at specific spatial locations relative to the existing primary buds. The results suggest that gap junctional communication may facilitate the propagation of long-distance inhibitory signals. Thus, the removal of GJ activity would enable the emergence of new feather buds if the local environment is competent and the threshold to form buds is reached. We propose Turing-based computational simulations that can predict the appearance of these ectopic bud waves. Our models demonstrate how a Turing activator-inhibitor system can continue to generate patterns in the competent morphogenetic field when the level of intercellular communication at the tissue scale is modulated.

Identification of differential methylome signatures of white pigmented skin patches in Nili Ravi buffalo of India

The DNA methylation events mark a major epigenetic change in the genome, reflecting non-genetic disease developments and varied phenotypes. The water buffalo is a dairy production animal with wide agro-climatic distribution in India. Breed-wise the coat color of water buffalo varies from ash-gray to jet black. A typical pigmentation pattern is found in one of the breeds of North India, Nili Ravi, with variedly distributed white patches. The DNA methylation pattern could potentially reveal the epigenetic factors responsible for the pigmentation patterns. To address this question, the DNA isolated from the skin tissues of Nili Ravi with varied white pigmentation and black Murrah buffaloes was subjected to reduced representation bisulfite sequencing. DNA methylation analysis revealed, 68.44%, 63.39%, and 47.94% of the promoter regions were hypermethylated in Nili Ravi over-white versus Murrah, Nili Ravi under-white versus Murrah, and Nili Ravi under-white versus Nili Ravi over-white, respectively. Major genes identified to be differentially methylated among over-white and under-white skin tissues in Nili Ravi included TBX2, SNAI2, HERC2, and CITED1. Overall the results have indicated differential methylation patterns to be potentially involved in hyper or hypopigmentation in Nili Ravi and Murrah buffaloes.

Newly raised anti-c-Kit antibody visualizes morphology of interstitial cells of Cajal in the developing gut of chicken embryos

The gut peristaltic movement, a wave-like propagation of a local contraction, is important for the transportation and digestion of ingested materials. Among three types of cells, the enteric nervous system (ENS), smooth muscle cells, and interstitial cells of Cajal (ICCs), the ICCs have been thought to act as a pacemaker, and therefore it is important to decipher the cellular functions of ICCs for the understanding of gut peristalsis. c-Kit, a tyrosine kinase receptor, has widely been used as a marker for ICCs. Most studies with ICCs have been conducted in mammals using commercially available anti-c-Kit antibody. Recently, the chicken embryonic gut has emerged as a powerful model to study the gut peristalsis. However, since the anti-c-Kit antibody for mammals does not work for chickens, cellular mechanisms by which ICCs are regulated have largely been unexplored. Here, we report a newly raised polyclonal antibody against the chicken c-Kit protein. The specificity of the antibody was validated by both Western blotting analyses and immunocytochemistry. Co-immunostaining with the new antibody and anti-α smooth muscle actin (αSMA) antibody successfully visualized ICCs in the chicken developing hindgut in the circular muscle- and longitudinal muscle layers: as previously shown in mice, common progenitors of ICCs and smooth muscle cells at early stages were double positive for αSMA and c-Kit, and at later stages, differentiated ICCs and smooth muscle cells exhibited only c-Kit and αSMA, respectively. A novel ICC population was also found that radially extended from the submucosal layer to circular muscle layer. Furthermore, the new antibody delineated individual ICCs in a cleared hindgut. The antibody newly developed in this study will facilitate the study of peristaltic movement in chicken embryos.

A conserved molecular template underlies color pattern diversity in estrildid finches

The color patterns that adorn animals' coats not only exhibit extensive diversity linked to various ecological functions but also display recurrences in geometry, orientation, or body location. How processes of pattern formation shape such phenotypic trends remains a mystery. Here, we surveyed plumage color patterns in passerine finches displaying extreme apparent variation and identified a conserved set of color domains. We linked these domains to putative embryonic skin regions instructed by early developmental tissues and outlined by the combinatory expression of few genetic markers. We found that this embryonic prepattern is largely conserved in birds displaying drastic color differences in the adult, interspecies variation resulting from the masking or display of each domain depending on their coloration. This work showed that a simple molecular landscape serves as common spatial template to extensive color pattern variation in finches, revealing that early conserved landmarks and molecular pathways are a major cause of phenotypic trends.

The feather pattern autosomal barring in chicken is strongly associated with segregation at the MC1R locus

Color patterns within individual feathers are common in birds but little is known about the genetic mechanisms causing such patterns. Here, we investigate the genetic basis for autosomal barring in chicken, a horizontal striping pattern on individual feathers. Using an informative backcross, we demonstrate that the MC1R locus is strongly associated with this phenotype. A deletion at SOX10, underlying the dark brown phenotype on its own, affects the manifestation of the barring pattern. The coding variant L133Q in MC1R is the most likely causal mutation for autosomal barring in this pedigree. Furthermore, a genetic screen across six different breeds showing different patterning phenotypes revealed that the most striking shared characteristics among these breeds were that they all carried the MC1R alleles Birchen or brown. Our data suggest that the presence of activating MC1R mutations enhancing pigment synthesis is an important mechanism underlying pigmentation patterns on individual feathers in chicken. We propose that MC1R and its antagonist ASIP play a critical role for determining within-feather pigmentation patterns in birds by acting as activator and inhibitor possibly in a Turing reaction-diffusion model.

Cis-acting mutation affecting GJA5 transcription is underlying the Melanotic within-feather pigmentation pattern in chickens

Melanotic (Ml) is a mutation in chickens that extends black (eumelanin) pigmentation in normally brown or red (pheomelanin) areas, thus affecting multiple within-feather patterns [J. W. Moore, J. R. Smyth Jr, J. Hered. 62, 215-219 (1971)]. In the present study, linkage mapping using a back-cross between Dark Cornish (Ml/Ml) and Partridge Plymouth Rock (ml+/ml+ ) chickens assigned Ml to an 820-kb region on chromosome 1. Identity-by-descent mapping, via whole-genome sequencing and diagnostic tests using a diverse set of chickens, refined the localization to the genomic region harboring GJA5 encoding gap-junction protein 5 (alias connexin 40) previously associated with pigmentation patterns in zebrafish. An insertion/deletion polymorphism located in the vicinity of the GJA5 promoter region was identified as the candidate causal mutation. Four different GJA5 transcripts were found to be expressed in feather follicles and at least two showed differential expression between genotypes. The results showed that Melanotic constitutes a cis-acting regulatory mutation affecting GJA5 expression. A recent study established the melanocortin-1 receptor (MC1R) locus and the interaction between the MC1R receptor and its antagonist agouti-signaling protein as the primary mechanism underlying variation in within-feather pigmentation patterns in chickens. The present study advances understanding the mechanisms underlying variation in plumage color in birds because it demonstrates that the activity of connexin 40/GJA5 can modulate the periodic pigmentation patterns within individual feathers.

Connexins in melanoma: Potential role of Cx46 in its aggressiveness

Melanoma is the most aggressive skin cancer, and in metastatic advanced states, it is completely refractory to chemotherapy. Therefore, it is relevant to understand the molecular bases that rule their aggressiveness. Connexins (Cxs) are proteins that under normal physiological conditions participate in intercellular communication, via the exchange of signaling molecules between the cytoplasm and extracellular milieu and the exchange of ions/second messengers between the cytoplasm of contacting cells. These proteins have shown important roles in cancer progression, chemo- and radiotherapy resistance, and metastasis. Accordingly, Cx26 and Cx43 seem to play important roles in melanoma progression and metastasis. On the other hand, Cx46 is typically expressed in the eye lens, where it seems to be associated with oxidative stress protection in fiber lens cells. However, in the last decade, Cx46 expression has been associated with breast and brain cancers, due to its role in potentiation of both extracellular vesicle release and cancer stem cell-like properties. In this review, we analyzed a potential role of Cx46 as a new biomarker and therapeutic target in melanoma.

Bioelectric signaling: Reprogrammable circuits underlying embryogenesis, regeneration, and cancer

How are individual cell behaviors coordinated toward invariant large-scale anatomical outcomes in development and regeneration despite unpredictable perturbations? Endogenous distributions of membrane potentials, produced by ion channels and gap junctions, are present across all tissues. These bioelectrical networks process morphogenetic information that controls gene expression, enabling cell collectives to make decisions about large-scale growth and form. Recent progress in the analysis and computational modeling of developmental bioelectric circuits and channelopathies reveals how cellular collectives cooperate toward organ-level structural order. These advances suggest a roadmap for exploiting bioelectric signaling for interventions addressing developmental disorders, regenerative medicine, cancer reprogramming, and synthetic bioengineering.

Making region-specific integumentary organs in birds: evolution and modifications

Birds are the most diversified terrestrial vertebrates due to highly diverse integumentary organs that enable robust adaptability to various eco-spaces. Here we show that this complexity is built upon multi-level regional specifications. Across-the-body (macro-) specification includes the evolution of beaks and feathers as new integumentary organs that are formed with regional specificity. Within-an-organ (micro-) specification involves further modifications of organ shapes. We review recent progress in elucidating the molecular mechanisms underlying feather diversification as an example. (1) β-Keratin gene clusters are regulated by typical enhancers or high order chromatin looping to achieve macro- and micro-level regional specification, respectively. (2) Multi-level symmetry-breaking of feather branches confers new functional forms. (3) Complex color patterns are produced by combinations of macro-patterning and micro-patterning processes. The integration of these findings provides new insights toward the principle of making a robustly adaptive bio-interface.

Evolution of pigment cells and patterns: recent insights from teleost fishes

Skin pigment patterns of vertebrates are stunningly diverse, and nowhere more so than in teleost fishes. Several species, including relatives of zebrafish, recently evolved cichlid fishes of East Africa, clownfishes, deep sea fishes, and others are providing insights into pigment pattern evolution. This overview describes recent advances in understanding periodic patterns, like stripes and spots, the loss of patterns, and the role of cell-type diversification in generating pigmentation phenotypes. Advances in this area are being facilitated by the application of modern methods of gene editing, genomics, computational analysis, and other approaches to non-traditional model organisms having interesting pigmentary phenotypes. Several topics worthy of future attention are outlined as well.

Genomic Analysis Revealed a Convergent Evolution of LINE-1 in Coat Color: A Case Study in Water Buffaloes (Bubalus bubalis)

Visible pigmentation phenotypes can be used to explore the regulation of gene expression and the evolution of coat color patterns in animals. Here, we performed whole-genome and RNA sequencing and applied genome-wide association study, comparative population genomics and biological experiments to show that the 2,809-bp-long LINE-1 insertion in the ASIP (agouti signaling protein) gene is the causative mutation for the white coat phenotype in swamp buffalo (Bubalus bubalis). This LINE-1 insertion (3' truncated and containing only 5' UTR) functions as a strong proximal promoter that leads to a 10-fold increase in the transcription of ASIP in white buffalo skin. The 165 bp of 5' UTR transcribed from the LINE-1 is spliced into the first coding exon of ASIP, resulting in a chimeric transcript. The increased expression of ASIP prevents melanocyte maturation, leading to the absence of pigment in white buffalo skin and hairs. Phylogenetic analyses indicate that the white buffalo-specific ASIP allele originated from a recent genetic transposition event in swamp buffalo. Interestingly, as a similar LINE-1 insertion has been identified in the cattle ASIP gene, we discuss the convergent mechanism of coat color evolution in the Bovini tribe.

Mechanisms of melanocyte polarity and differentiation: What can we learn from other neuroectoderm-derived lineages?

Melanocytes are neuroectoderm-derived pigment-producing cells with highly polarized dendritic morphology. They protect the skin against ultraviolet radiation by providing melanin to neighbouring keratinocytes. However, the mechanisms underlying melanocyte polarization and its relevance for diseases remain mostly elusive. Numerous studies have instead revealed roles for polarity regulators in other neuroectoderm-derived lineages including different neuronal cell types. Considering the shared ontogeny and morphological similarities, these lineages may be used as reference models for the exploration of melanocyte polarity, for example, regarding dendrite formation, spine morphogenesis and polarized organelle transport. In this review, we summarize and compare the latest progress in understanding polarity regulation in neuronal cells and melanocytes and project key open questions for future work.

Transcriptome Reveals Multi Pigmentation Genes Affecting Dorsoventral Pattern in Avian Body

Certain animals exhibit a special dorsoventral pattern with a lighter ventral side compared to the dorsal one and this phenomenon was preserved in the long-term evolution process. Birds also retain this trait. Recently, Inaba et al. (2019) found that ASIP (agouti signal protein) regulated interconversion between different melanocyte types leads to dorsal stripe pattern, which may partly explain the birds' dorsoventral plumage color difference. In this study, we used the embryo samples of LBM (light brown mottling) ducks (Anas platyrhynchos) with white ventral and dark dorsal body parts to investigate the mechanism of dorsoventral color variation. Firstly, melanin deposition process of duck embryos was investigated. The result indicated that E13 and E16 were the active stages of melanin synthesis. Moreover, the melanin deposition on the dorsum of LBM ducks was higher than that on the ventral side throughout. Then, RNA-seq was conducted for the dorsal and ventral skin tissues from E7 (early), E13 (middle) and E19 (late) of LBM ducks. Expression pattern analysis showed that the mRNA expression of most melanin synthesis related genes were at the highest level at E13, which was consistent with the section analysis. A correlation was found between melanogenesis pathway and dorsoventral color difference by co-expression analysis. In the DEG (differentially expressed gene) analysis, we added the dorsal skin transcriptome of embryonic white and black duck of same subspecies (Anas platyrhynchos domestica) for horizontal comparison. The results showed that 8 melanogenesis related genes (TYR, TYRP1, MLANA, RAB38, OCA2, TSPAN10, MC1R, and MSLN) were the common DEGs (Differential expressed genes) in the comparisons of body parts and breeds suggesting that the underlying molecular regulatory mechanism of dorsoventral plumage color difference may be similar to that of albino and melanic duck, which were caused by the different expression of multiple genes in melanin synthesis pathway. In addition, the molecular regulation of melanin synthesis pathway in the dorsal and ventral side of LBM ducks was analyzed. In this pathway, ASIP, MC1R, TYR, and TYRP1 have differential mRNA expression. ASIP, as an upstream gene in this pathway, was likely to play a decisive role in determining the dorsoventral plumage pattern.

Integrating Bioelectrical Currents and Ca2+ Signaling with Biochemical Signaling in Development and Pathogenesis

Roles of bioelectrical signals are increasingly recognized in excitable and nonexcitable non-neural tissues. Diverse ion-selective channels, pumps, and gap junctions participate in bioelectrical signaling, including those transporting calcium ions (Ca2+). Ca2+ is the most versatile transported ion, because it serves as an electrical charge carrier and a biochemical regulator for multiple molecular binding, enzyme, and transcription activities. We aspire to learn how bioelectrical signals crosstalk to biochemical/biomechanical signals. In this study, we review four recent studies showing how bioelectrical currents and Ca2+ signaling affect collective dermal cell migration during feather bud elongation, affect chondrogenic differentiation in limb development, couple with mechanical tension in aligning gut smooth muscle, and affect mitochondrial function and skeletal muscle atrophy. We observe bioelectrical signals involved in several developmental and pathological conditions in chickens and mice at multiple spatial scales: cellular, cellular collective, and subcellular. These examples inspire novel concept and approaches for future basic and translational studies.

Avian Pigment Pattern Formation: Developmental Control of Macro- (Across the Body) and Micro- (Within a Feather) Level of Pigment Patterns

Animal color patterns are of interest to many fields, such as developmental biology, evolutionary biology, ethology, mathematical biology, bio-mimetics, etc. The skin provides easy access to experimentation and analysis enabling the developmental pigment patterning process to be analyzed at the cellular and molecular level. Studies in animals with distinct pigment patterns (such as zebrafish, horse, feline, etc.) have revealed some genetic information underlying color pattern formation. Yet, how the complex pigment patterns in diverse avian species are established remains an open question. Here we summarize recent progress. Avian plumage shows color patterns occurring at different spatial levels. The two main levels are macro- (across the body) and micro- (within a feather) pigment patterns. At the cellular level, colors are mainly produced by melanocytes generating eumelanin (black) and pheomelanin (yellow, orange). These melanin-based patterns are regulated by melanocyte migration, differentiation, cell death, and/or interaction with neighboring skin cells. In addition, non-melanin chemical pigments and structural colors add more colors to the available palette in different cell types or skin regions. We discuss classic and recent tissue transplantation experiments that explore the avian pigment patterning process and some potential molecular mechanisms. We find color patterns can be controlled autonomously by melanocytes but also non-autonomously by dermal cells. Complex plumage color patterns are generated by the combination of these multi-scale patterning mechanisms. These interactions can be further modulated by environmental factors such as sex hormones, which generate striking sexual dimorphic colors in avian integuments and can also be influenced by seasons and aging.

A quantitative trait locus on chromosome 2 was identified that accounts for a substantial proportion of phenotypic variance of the yellow plumage color in chicken

Chicken plumage color is an important economical trait in poultry breeding, as triple-yellow indigenous broilers are preferred over western commercial broilers in the Chinese market. However, the studies on the pigmentation of plumage coloration are relatively rare at present. Here, we performed a genome-wide mapping study on an F₂ intercross, whose 2 founders were one hybrid commercial line “High Quality chicken Line A” that originated from the Anak red chicken and one indigenous line “Huiyang Beard” chicken that is a classical “triple-yellow” Chinese indigenous breed. Moreover, we used an automatic colorimeter that can quantitatively assess the colorations in L∗, a∗, and b∗ values. One major quantitative trait locus (QTL) on chromosome 2 was thus identified by both genome-wide association and linkage analyses, which could explain 10 to 20% of the total phenotypic variance of the b∗ measurements of the back plumage color. Using linkage analysis, 2 additional QTL on chromosome 1 and 20 were also found to be significantly associated with the plumage coloration in this cross. With additional samples from Anak red and Huiyang Beard chickens as well as pooled resequencing data from the 2 founders of this cross, we then further narrowed down the QTL regions and identified several candidate genes, such as CABLES1, CHST11, BCL2L1, and CHD22. As the effects of QTL found in this study were substantial, quantitatively measuring the coloration rather than the descriptive measurements provides stronger statistical power for the analyses. In addition, this major QTL on chromosome 2 that was associated with feather pigmentation at the genome-wide level will facilitate the future chicken breeding for yellow plumage color. In conclusions, we mapped 3 associated QTL on chromosome 1, 2, and 20. The candidate genes identified in this study shed light in the genetic basis of yellow plumage color in chicken.