The formation of the feather pattern in chick skin after a proportion of cells have been killed by X-irradiation

The formation of periodic patterns is of fundamental importance in embryonic development. One of the simplest and most frequently observed patterns is the maintenance of a minimum distance between neighbouring elements, for example between teeth, hair, feathers, digits etc. Theoretical models describing these phenomena have been proposed for feather patterning. However, there has been no detailed quantitative analysis of the relationship between cell population density and feather spacing. To define the relation between these quantities and specifically to test the prediction of a mathematical model, we have examined the formation of the feather pattern after varying proportions of the dermal cells have been killed by X-irradiation. It is known that the development of a feather primordium is normally associated with an increase in cell population density in the dermis. Using X-ray irradiation of the skin in vivo and in vitro, we show that the relation between cell population density and spacing of feather primordia indicates the importance of a threshold number of cells for feather patterning. Moreover, there is a prima facie case for supposing that X-rays act on feather spacing system, reducing the ability of dermal cells to prevent spreading of the pattern. Thus, X-irradiation may have a secondary effect on the spacing of primordia rather than, or as well as, affecting the mechanisms that determine their primary positions.

Phylogenetic re-evaluation of Trametes consors based on mitochondrial small subunit ribosomal DNA sequences

Mitochondrial small subunit ribosomal DNAs of Cerrena unicolor and Trametes consors were sequenced and compared with those of known mushroom taxa. Trametes consors is a species recently transferred from Irpex, and Cerrena is a genus closely related to Trametes. The present phylogenetic tree showed that Cerrena unicolor and Trametes consors clustered together and made an independent lineage from the Trametes group. A new combination, Cerrena consors (Berk.) Ko and Jung, comb nov., is proposed here by transferring Trametes consors into Cerrena based on molecular data along with taxonomic evidence.

Local inhibitory action of BMPs and their relationships with activators in feather formation: implications for periodic patterning

The formation of periodic patterns is fundamental in biology. Theoretical models describing these phenomena have been proposed for feather patterning; however, no molecular candidates have been identified. Here we show that the feather tract is initiated by a continuous stripe of Shh, Fgf-4, and Ptc expression in the epithelium, which then segregates into discrete feather primordia that are more strongly Shh and Fgf-4 positive. The primordia also become Bmp-2 and Bmp-4 positive. Bead-mediated delivery of BMPs inhibits local feather formation in contrast with the activators, SHH and FGF-4, which induce feather formation. Both FGF-4 and SHH induce local expression of Bmp-4, while BMP-4 suppresses local expression of both. FGF-4 also induces Shh. Based on these findings, we propose a model that involves (1) homogeneously distributed global activators that define the field, (2) a position-dependent activator of competence that propagates across the field, and (3) local activators and inhibitors triggered in sites of individual primordia that act in a reaction-diffusion mechanism. A computer simulation model for feather pattern formation is also presented.

Molecular histology in skin appendage morphogenesis

Classical histological studies have demonstrated the cellular organization of skin appendages and helped us appreciate the intricate structures and function of skin appendages. At this juncture, questions can be directed to determine how these cellular organizations are achieved. How do cells rearrange themselves to form the complex cyto-architecture of skin appendages? What are the molecular bases of the morphogenesis and histogenesis of skin appendages? Recently, many new molecules expressed in a spatial and temporal specific manner during the formation of skin appendages were identified by molecular biological approaches. In this review, novel molecular techniques that are useful in skin appendage research are discussed. The distribution of exemplary molecules from different categories including growth factors, intracellular signaling molecules, homeobox genes, adhesion molecules, and extracellular matrix molecules are summarized in a diagram using feather and hair as models. We hope that these results will serve as the ground work for completing the molecular mapping of skin appendages which will refine and re-define our understanding of the developmental process beyond relying on morphological criteria. We also hope that the listed protocols will help those who are interested in this venture. This new molecular histology of skin appendages is the foundation for forming new hypotheses on how molecules are mechanistically involved in skin appendage development and for designing experiments to test them. This may also lead to the modulation of healing and regeneration processes in future treatment modalities.

Asymmetric expression of Notch/Delta/Serrate is associated with the anterior-posterior axis of feather buds

We studied the roles of Notch, Delta, and Serrate in vertebrate epithelial appendage morphogenesis using feather as a model and found the following. (1) C-Notch-1, C-Delta-1, and C-Serrate-1 are not expressed at the early placode stage and are therefore not involved in the determination of bud versus interbud compartments. (2) From symmetric short buds to asymmetric long buds, C-Delta-1 and C-Serrate-1 are expressed in the posterior bud mesenchyme in a nested fashion, while C-Notch-1 is expressed as a stripe perpendicular to the anterior-posterior (A-P) axis and positioned posterior to the midpoint. (3) Epithelial-mesenchymal recombination with rotation led to the disappearance of these genes followed by their reappearance with new positions appearing to predict their new morphological orientation. (4) Conditions leading to branched buds (e.g., recombination of later buds) show polarized staining patterns before branching occurs. (5) Conditions leading to symmetrical round buds (e.g., treated with the protein kinase A agonist forskolin) suppress expression of all three genes. These results lead us to hypothesize that Notch, Delta, and Serrate are involved in establishing the A-P asymmetry of feather buds.