Although recent experimental studies have suggested that the interactions among the pigment cells play a key role in the skin pattern formation, details of the mechanism remain largely unknown. By using an in vitro cell culture system, we have detected interactions between the two pigment cell types, melanophores and xanthophores, in the zebrafish skin. During primary culture, the melanophore membrane transiently depolarizes when contacted with the dendrites of a xanthophore. This depolarization triggers melanophore migration to avoid further contact with the xanthophores. Cell depolarization and repulsive movement were not observed in pigment cells with the jaguar mutant, which shows defective segregation of melanophores and xanthophores. The depolarization-repulsion of wild-type pigment cells may explain the pigment cell behaviors generating the stripe pattern of zebrafish.

Animal skin pigment patterns are excellent models to study the mechanism of biological self-organization. Theoretical approaches developed mathematical models of pigment patterning and molecular genetics have brought progress; however, the responsible cellular mechanism is not fully understood. One long unsolved controversy is whether the patterning information is autonomously determined by melanocytes or nonautonomously determined from the environment. Here, we transplanted purified melanocytes and demonstrated that melanocytes could form periodic pigment patterns cell autonomously. Results of heterospecific transplantation among quail strains are consistent with this finding. Further, we observe that developing melanocytes directly connect with each other via filopodia to form a network in culture and in vivo. This melanocyte network is reminiscent of zebrafish pigment cell networks, where connexin is implicated in stripe formation via genetic studies. Indeed, we found connexin40 (cx40) present on developing melanocytes in birds. Stripe patterns can form in quail skin explant cultures. Several calcium channel modulators can enhance or suppress pigmentation globally, but a gap junction inhibitor can change stripe patterning. Most interestingly, in ovo, misexpression of dominant negative cx40 expands the black region, while overexpression of cx40 expands the yellow region. Subsequently, melanocytes instruct adjacent dermal cells to express agouti signaling protein (ASIP), the regulatory factor for pigment switching, which promotes pheomelanin production. Thus, we demonstrate Japanese quail melanocytes have an autonomous periodic patterning role during body pigment stripe formation. We also show dermal agouti stripes and how the coupling of melanocytes with dermal cells may confer stable and distinct pigment stripe patterns.Japanese quail | stripe pattern | melanocytes | ASIP | gap junction A nimal skin pigment patterns, such as periodic leopard spots and zebra stripes, represent some of the most amazing phenomena observed in nature, which have fascinated biologists and nonbiologists. The mechanisms of pigment patterning have been studied by mathematical and empirical approaches. Studies on zebrafish stripe patterning have led investigators to propose that the pattern is formed by pigment cell interactions that satisfy a Turing-type model (1,2). Mammalian genetic studies performed on horses, zebras, cheetahs, and chipmunks have identified some of the molecules involved in this process (3-5). Although theoretical models and the genetic backgrounds in the pigment patterning are well studied, how the pigment-related genes control the cell-cell interactions that generate the pigment pattern is largely unknown. Avian species present an excellent model system to answer these questions because of their extraordinarily diverse micropigment patterns within feathers (6) and embryonic manipulability that allows analyses of cell-cell interactions leading to macropigment patterning throughout the body. Japanese quail (JQ), a m...

Gut peristaltic movements recognized as the wave-like propagation of a local contraction are crucial for effective transportation and digestion/absorption of ingested materials. Although the physiology of gut peristalsis has been well studied in adults, it remains largely unexplored how the cellular functions underlying these coordinated tissue movements are established along the rostral-caudal gut axis during development. The chicken embryonic gut serves as an excellent experimental model for elucidating the endogenous potential and regulation of these cells since peristalsis occurs even though no ingested material is present in the moving gut. By combining video-recordings and kymography, we provide a spatial map of peristaltic movements along the entire gut posterior to the duodenum: midgut (jejunum and ileum), hindgut, caecum, and cloaca. Since the majority of waves propagate bidirectionally at least until embryonic day 12 (E12), the sites of origin of peristaltic waves (OPWs) can unambiguously be detected in the kymograph. The spatial distribution map of OPWs has revealed that OPWs become progressively confined to specific regions/zones along the gut axis during development by E12. Ablating the enteric nervous system (ENS) or blocking its activity by tetrodotoxin perturb the distribution patterns of OPWs along the gut tract. These manipulations have also resulted in a failure of transportation of inter-luminally injected ink. Finally, we have discovered a functional coupling of the endpoint of hindgut with the cloaca. When surgically separated, the cloaca ceases its acute contractions that would normally occur concomitantly with the peristaltic rhythm of the hindgut. Our findings shed light on the intrinsic regulations of gut peristalsis, including unprecedented ENS contribution and inter-region cross talk along the gut axis.

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.

No abstract