Topographical mapping of α- and β-keratins on developing chicken skin integuments: Functional interaction and evolutionary perspectives (original) (raw)
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Topographical mapping of α and β keratins on developing chicken skin integuments
Avian integumentary organs include feathers, scales, claws, and beaks. They cover the body surface and play various functions to help adapt birds to diverse environments. These keratinized structures are mainly composed of corneous materials made of α-keratins, which exist in all vertebrates, and β-keratins, which only exist in birds and reptiles. Here, members of the keratin gene families were used to study how gene family evolution contributes to novelty and adaptation, focusing on tissue morphogenesis. Using chicken as a model, we applied RNA-seq and in situ hybridization to map αand β-keratin genes in various skin appendages at embryonic developmental stages. The data demonstrate that temporal and spatial αand β-keratin expression is involved in establishing the diversity of skin appendage phenotypes. Embryonic feathers express a higher proportion of β-keratin genes than other skin regions. In feather filament morphogenesis, β-keratins show intricate complexity in diverse substructures of feather branches. To explore functional interactions, we used a retrovirus transgenic system to ectopically express mutant αor antisense β-keratin forms. αand β-keratins show mutual dependence and mutations in either keratin type results in disrupted keratin networks and failure to form proper feather branches. Our data suggest that combinations of αand β-keratin genes contribute to the morphological and structural diversity of different avian skin appendages, with feather-β-keratins conferring more possible composites in building intrafeather architecture complexity, setting up a platform of morphological evolution of functional forms in feathers.
BMC evolutionary biology, 2014
Vertebrate skin appendages are constructed of keratins produced by multigene families. Alpha (α) keratins are found in all vertebrates, while beta (β) keratins are found exclusively in reptiles and birds. We have studied the molecular evolution of these gene families in the genomes of 48 phylogenetically diverse birds and their expression in the scales and feathers of the chicken. We found that the total number of α-keratins is lower in birds than mammals and non-avian reptiles, yet two α-keratin genes (KRT42 and KRT75) have expanded in birds. The β-keratins, however, demonstrate a dynamic evolution associated with avian lifestyle. The avian specific feather β-keratins comprise a large majority of the total number of β-keratins, but independently derived lineages of aquatic and predatory birds have smaller proportions of feather β-keratin genes and larger proportions of keratinocyte β-keratin genes. Additionally, birds of prey have a larger proportion of claw β-keratins. Analysis of...
Regulatory Divergence among Beta-Keratin Genes during Bird Evolution
Molecular biology and evolution, 2016
Feathers, which are mainly composed of α- and β-keratins, are highly diversified, largely owing to duplication and diversification of β-keratin genes during bird evolution. However, little is known about the regulatory changes that contributed to the expressional diversification of β-keratin genes. To address this issue, we studied transcriptomes from five different parts of chicken contour and flight feathers. From these transcriptomes we inferred β-keratin enriched co-expression modules of genes and predicted transcription factors (TFs) of β-keratin genes. In total, we predicted 262 TF-target gene relationships in which 56 TFs regulate 91 β-keratin genes; we validated 14 of them by in vitro tests. A dual criterion of TF enrichment and 'TF-target gene' expression correlation identified 26 TFs as the major regulators of β-keratin genes. According to our predictions, the ancestral scale and claw β-keratin genes have common and unique regulators, whereas most feather β-keratin...
The Expression of Beta (β) Keratins in the Epidermal Appendages of Reptiles and Birds1
American Zoologist, 2000
SYNOPSIS. The integuments of extant vertebrates display a variety of epidermal appendages whose patterns, morphology and terminal differentiation (epidermal keratins) depend upon interactions between ectodermal (epidermis) and mesodermal (dermis) tissues. In reptiles and birds, appendage morphogenesis precedes terminal differentiation. Studies have demonstrated that appendage morphogenesis influences the expression of the appendage specific keratin genes. However, little is known about the nature of the structural genes expressed by the epidermal appendages of reptiles. How pattern formation and/or appendage morphogenesis influence terminal differentiation of reptilian appendages is not known. The epidermal appendages of reptiles and birds are characterized by the presence of both alpha (␣) and beta () type keratin proteins. Studies have focused on the genes of avian  keratins because they are the major structural proteins of feathers. The occurrence of  keratin proteins in the scales and claws of both birds and reptiles and their immunological cross-reactivity suggest that the genes for reptilian  keratins may be homologous with those of birds. In bird appendages, the  keratins are the products of a large family of homologous genes. Specific members of this gene family are expressed during the development of each appendage. Recent sequence analyses of feather  keratins, from different orders of birds, demonstrate that there is more diversity at the DNA level than was implied by earlier protein sequencing studies. Immunological techniques show that the same antibodies that react with the epidermal  keratins of the chicken (Gallus domesticus) react with the epidermal  keratins of American alligators (Alligator mississippiensis). Furthermore, a peptide sequence (20 amino acids) from an alligator claw  keratin is similar to a highly conserved region of avian claw, scale, feather, and feather-like  keratins. These observations suggest that the  keratin genes of avian epidermal appendages have homologues in the American alligator. Understanding the origin and evolution of the  keratin gene families in reptiles and birds will undoubtedly add to our understanding of the evolution of skin appendages such as scales and feathers.
Evolutionary relationships among copies of feather beta ( ) keratin genes from several avian orders
Integrative and Comparative Biology, 2008
The feather beta (b) keratins of the white leghorn chicken (order Galliformes, Gallus gallus domesticus) are the products of a multigene family that includes claw, feather, feather-like, and scale genes ). Here we characterize the feather b-keratin genes in additional bird species. We designed primers for polymerase chain reactions (PCR) using sequences available from chicken, cloned the resulting amplicons to isolate individual copies, and sequenced multiple clones from each PCR reaction for which we obtained amplicons of the expected size. Feather b-keratins of 18 species from eight avian orders demonstrate DNA sequence variation within and among taxa, even in the protein-coding regions of the genes. Phylogenies of these data suggest that Galliformes (fowl-like birds), Psittaciformes (parrots), and possibly Falconiformes (birds of prey) existed as separate lineages before duplication of the feather b-keratin gene began in Ciconiiformes (herons, storks, and allies), Gruiformes (cranes, rails, and allies), and Piciformes (woodpeckers and allies). Sequences from single species of Coraciiformes (kingfishers) and Columbiformes (pigeons) are monophyletic and strikingly divergent, suggesting feather b-keratin genes in these birds also diverged after these species last shared a common ancestor with the other taxa investigated. Overall, these data demonstrate considerable variation in this structural protein in the relatively recent history of birds, and raise questions concerning the origin and homology of claw, feather-like, and scale b-keratins of birds and the reptilian b-keratins.
Linking the molecular evolution of avian beta (β) keratins to the evolution of feathers
Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 2011
Feathers of today's birds are constructed of beta (b)-keratins, structural proteins of the epidermis that are found solely in reptiles and birds. Discoveries of ''feathered dinosaurs'' continue to stimulate interest in the evolutionary origin of feathers, but few studies have attempted to link the molecular evolution of their major structural proteins (b-keratins) to the appearance of feathers in the fossil record. Using molecular dating methods, we show that before the appearance of Anchiornis ($155 Million years ago (Ma)) the basal b-keratins of birds began diverging from their archosaurian ancestor 216Ma.However,thesubfamilyoffeatherb−keratins,asfoundinlivingbirds,didnotbegindiverginguntil216 Ma. However, the subfamily of feather b-keratins, as found in living birds, did not begin diverging until 216Ma.However,thesubfamilyoffeatherb−keratins,asfoundinlivingbirds,didnotbegindiverginguntil143 Ma. Thus, the pennaceous feathers on Anchiornis, while being constructed of avian b-keratins, most likely did not contain the feather b-keratins found in the feathers of modern birds. Our results demonstrate that the evolutionary origin of feathers does not coincide with the molecular evolution of the feather b-keratins found in modern birds. More likely, during the Late Jurassic, the epidermal structures that appeared on organisms in the lineage leading to birds, including early forms of feathers, were constructed of avian b-keratins other than those found in the feathers of modern birds. Recent biophysical studies of the b-keratins in feathers support the view that the appearance of the subfamily of feather b-keratins altered the biophysical nature of the feather establishing its role in powered flight. How to cite this article: Greenwold MJ, Sawyer RH. 2011. Linking the molecular evolution of avian beta (b) keratins to the evolution of feathers. J. Exp. Zool. (Mol. Dev. Evol.) 316:609-616.