Keratinization of sheath and calamus cells in developing and regenerating feathers

Feather's Composition of South Polar Skua (Stercorarius maccormicki) Using WDXRF

This study investigated the feathers' composition of South polar skua (Stercorarius maccormicki) using WDXRF, evaluating the concentration of essential and non-essential elements in the feathers, and dividing it into rachis and barb parts. We collected South polar skuas feathers from Hennequin Point, King George Island, South Shetland, Antarctic Peninsula in January of 2013. Our results show that 18 elements were observed in the composition of the feathers, with a different concentration between the rachis and barbs, qualitatively and quantitatively. Only 3 elements observed were classified as non-essentials but still mostly elements do not have a function described in the literature to the feathers. According to our knowledge, this is the first study that uses this technique to evaluate the concentration of different elements in the feathers. The findings of this study highlight the use of alternative techniques to biomonitoring elements in the ecosystem and bring baseline information for future studies.

The Defeathering Effect by Scalding in Chickens Follows Their Intrinsic Dermal Histologies

This study aimed to delineate the fundamental skin histology and its association with feathers in broilers and native Red-Feather (RF) chickens and further elucidate their thermal alterations in respect to the defeathering effect by scalding. Comparisons of skin thickness between fresh samples and those after dehydration and fixation, as well as their collagen contents and histological differences, suggested that RF chickens had a thicker dermal layer with more collagen deposition and compact architecture, particularly in the neck and abdominal skin, but a thinner hypodermal layer in the back, chest, and abdomen skin. Despite an adolescent age, RF chickens showed a shorter calamus depth of tail feathers but a larger calamus diameter of wing feathers. Within the feather follicle punch, a very intense follicle sheath layer with compact collagenous matrixes to fulfill the space next to the inner feather root sheath was observed in RF chickens. Under both soft and hard scalding, RF chickens showed a lower degree of denaturation on hip skins and were more resistant to structural disintegration, primarily within the epidermal and dermal layer. Accordingly, a much narrower gap space between the feather sheath and surrounding follicle sheath was observed, and the gap expansion was also resistant to thermal changes. These results suggest that the defeathering effect by scalding follows the intrinsic skin histologies in chickens of various breeds and ages, primarily depending on the interaction of the feather calamus with the surrounding follicle sheath and neighboring cutaneous tissues, reflecting their resistance to thermal denaturation, but is irrelevant to the feathers per se.

Unique pattern of histogenesis of the parakeratinized epithelium on lingual prominence in the domestic goose embryos (Anser anser f. domestica)

A triangular lingual prominence (LP) is a characteristic part of the tongue in Anseriformes containing adipose tissue. The parakeratinized epithelium (PEp) covers the LP. Studies aimed to describe the histogenesis of PEp during the process of the intensive formation of the LP in domestic goose during embryonic period and to determine the structural readiness to perform a protective function. The study were conducted by using LM, SEM and TEM technique. The results revealed that on day 16th the undifferentiated epithelium of LP transformed into the typical avian multilayered epithelium. Contrary to pattern of histogenesis of parakeratinized epithelium on the lingual body, on the medial and lateral areas of the elongating and bulging LP were formed epithelial furrows. Which around 20th day, on lateral areas of LP deepened up to half of epithelium, whereas on the medial area began to fade. The ultrastructure of cells lying in furrows indicated progressive apoptosis-like degeneration. On the 25th day, shallow furrows were only present on lateral areas, where bulging of LP was continued. Whereas the epithelium on medial area started cornification by the accumulation of cytokeratin fibers. Lack of the periderm during the development of the PEp of the LP indicated its endodermal origin.

Vertebrate keratinization evolved into cornification mainly due to transglutaminase and sulfhydryl oxidase activities on epidermal proteins: An immunohistochemical survey

The epidermis of vertebrates forms an extended organ to protect and exchange gas, water, and organic molecules with aquatic and terrestrial environments. Herein, the processes of keratinization and cornification in aquatic and terrestrial vertebrates were compared using immunohistochemistry. Keratins with low cysteine and glycine contents form the main bulk of proteins in the anamniote epidermis, which undergoes keratinization. In contrast, specialized keratins rich in cysteine-glycine and keratin associated corneous proteins rich in cysteine, glycine, and tyrosine form the bulk of proteins of amniote soft cornification in the epidermis and hard cornification in scales, claws, beak, feathers, hairs, and horns. Transglutaminase (TGase) and sulfhydryl oxidase (SOXase) are the main enzymes involved in cornification. Their evolution was fundamental for the terrestrial adaptation of vertebrates. Immunohistochemistry results revealed that TGase and SOXase were low to absent in fish and amphibian epidermis, while they increased in the epidermis of amniotes with the evolution of the stratum corneum and skin appendages. TGase aids the formation of isopeptide bonds, while SOXase forms disulfide bonds that generate numerous cross-links between keratins and associated corneous proteins, likely increasing the mechanical resistance and durability of the amniote epidermis and its appendages. TGase is low to absent in the beta-corneous layers of sauropsids but is detected in the softer but pliable alpha-layers of sauropsids, mammalian epidermis, medulla, and inner root sheath of hairs. SOXase is present in hard and soft corneous appendages of reptiles, birds, and mammals, and determines cross-linking among corneous proteins of scales, claws, beaks, hairs, and feathers.

Morphogenesis of iridescent feathers in Anna's hummingbird Calypte anna

Color is a phenotypic trait of utmost importance, particularly in birds, which are known for their diverse color signals and color-producing mechanisms including pigment-based colors, light scattering from nanostructured feather tissues and combinations thereof. Bright iridescent plumage colors of hummingbirds are caused by light scattering by an organized array of flattened, pigment organelles, containing air-filled vesicles, called melanosomes. These hollow platelets are organized in multilayer arrays that contain numerous sharp air/melanin refractive index interfaces, producing brilliant iridescent colors. Despite their ecological significance and potential for inspiration of new optical materials, how platelets form and spatially arrange in nanostructures in growing feathers remains unknown. Here, we tested the hypothesis that melanosome formation and organization occurs mostly through passive self-assembly processes by assembling a developmental time series of growing hummingbird feathers using optical and electron microscopy. We show that hummingbird platelets contain air bubbles or vesicles upon their formation in pigment-producing cells, melanocytes. When melanosomes are transferred to neighboring keratinocytes (the cells shaping barbule structure) they drastically expand in size; and variation in this enlargement appears to be driven by physical constraints caused by the placement of the melanosomes within the barbule plate and their proximity to other melanosomes. As the barbule elongates and narrows, polymerizing feather corneous beta protein (CβP) orients melanosomes unilaterally, forcing them into a stacked configuration. These results reveal potentially novel forces driving the self-assembly of the nanostructures producing some of the brightest colors in nature.<.

Closing the Loop with Keratin-Rich Fibrous Materials

One of the agro-industry's side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.

Microbial enzymes catalyzing keratin degradation: Classification, structure, function

Keratin is an insoluble and protein-rich epidermal material found in e.g. feather, wool, hair. It is produced in substantial amounts as co-product from poultry processing plants and pig slaughterhouses. Keratin is packed by disulfide bonds and hydrogen bonds. Based on the secondary structure, keratin can be classified into α-keratin and β-keratin. Keratinases (EC 3.4.-.- peptide hydrolases) have major potential to degrade keratin for sustainable recycling of the protein and amino acids. Currently, the known keratinolytic enzymes belong to at least 14 different protease families: S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, M55 (MEROPS database). The various keratinolytic enzymes act via endo-attack (proteases in families S1, S8, S16, M4, M16, M36), exo-attack (proteases in families S9, S10, M14, M28, M38, M55) or by action only on oligopeptides (proteases in families M3, M32), respectively. Other enzymes, particularly disulfide reductases, also play a key role in keratin degradation as they catalyze the breakage of disulfide bonds for better keratinase catalysis. This review aims to contribute an overview of keratin biomass as an enzyme substrate and a systematic analysis of currently sequenced keratinolytic enzymes and their classification and reaction mechanisms. We also summarize and discuss keratinase assays, available keratinase structures and finally examine the available data on uses of keratinases in practical biorefinery protein upcycling applications.

Alpha-keratin and corneous beta protein in the parakeratinized epithelium of the tongue in the domestic goose (Anser anser f. domestica)

The parakeratinized epithelium is a common epithelium in the oral cavity in birds and is characterized by the presence of cell nuclei in the cells of the cornified layer. This epithelium covers almost the entire dorsal surface of the tongue in the domestic goose apart of the lingual nail and conical papillae. So far no study has identified the molecular proteins alpha-keratin (IF-keratin) and/or corneous beta protein (CBP), which are responsible for keratinization or cornification processes in the parakeratinized epithelium of domestic geese. The study was performed using immunohistochemical (IHC) methods to identify alpha-keratin. The innovative method of Raman microspectroscopy was used to determine the presence of CBP and specify their percentage in epithelial layers of the parakeratinized epithelium. The results revealed that alpha-keratin is present in the whole parakeratinized epithelium. A strong staining reaction was detected in the basal and intermediate layers and a less strong staining reaction in the cornified layer. Raman microspectroscopy analysis confirmed the presence of alpha-keratin and demonstrated that its percentage decreases from the basal layer to the cornified layer. The Raman microspectroscopy technique revealed the occurrence of CBP in the parakeratinized epithelium and demonstrated that the percentage of this protein increases from the basal layer to the cornified layer. Performed analysis determines that parakeratinized epithelium undergoes cornification. However, the lower percentage of CBP in the cornified layer of parakeratinized epithelium than in orthokeratinized epithelium points to the fact that parakeratinized epithelium has a weaker protective function.

Review: cornification, morphogenesis and evolution of feathers

Feathers are corneous microramifications of variable complexity derived from the morphogenesis of barb ridges. Histological and ultrastructural analyses on developing and regenerating feathers clarify the three-dimensional organization of cells in barb ridges. Feather cells derive from folds of the embryonic epithelium of feather germs from which barb/barbule cells and supportive cells organize in a branching structure. The following degeneration of supportive cells allows the separation of barbule cells which are made of corneous beta-proteins and of lower amounts of intermediate filament (IF)(alpha) keratins, histidine-rich proteins, and corneous proteins of the epidermal differentiation complex. The specific protein association gives rise to a corneous material with specific biomechanic properties in barbules, rami, rachis, or calamus. During the evolution of different feather types, a large expansion of the genome coding for corneous feather beta-proteins occurred and formed 3-4-nm-thick filaments through a different mechanism from that of 8-10 nm IF keratins. In the chick, over 130 genes mainly localized in chromosomes 27 and 25 encode feather corneous beta-proteins of 10-12 kDa containing 97-105 amino acids. About 35 genes localized in chromosome 25 code for scale proteins (14-16 kDa made of 122-146 amino acids), claws and beak proteins (14-17 kDa proteins of 134-164 amino acids). Feather morphogenesis is periodically re-activated to produce replacement feathers, and multiple feather types can result from the interactions of epidermal and dermal tissues. The review shows schematic models explaining the translation of the morphogenesis of barb ridges present in the follicle into the three-dimensional shape of the main types of branched or un-branched feathers such as plumulaceous, pennaceous, filoplumes, and bristles. The temporal pattern of formation of barb ridges in different feather types and the molecular control from the dermal papilla through signaling molecules are poorly known. The evolution and diversification of the process of morphogenesis of barb ridges and patterns of their formation within feathers follicle allowed the origin and diversification of numerous types of feathers, including the asymmetric planar feathers for flight.

Gap and tight junctions in the formation of feather branches: A descriptive ultrastructural study

The present study has focused on the distribution and ultrastructure of gap and tight junctions responsible for the formation of the barb/barbule branching in developing feathers using immunocytochemical detection. Apart from desmosomes, both tight and gap junctions are present between differentiating barb/barbule cells and during keratinization. While gap junctions are rare along the perimeter of these cells, tight junctions tend to remain localized in nodes joining barbule cells and between barb cells of the ramus. Occludin and connexin-26 but not connexin-43 have been detected between barb medullary, barb cortical and barbule cells during formation of barbs. Gap junctions are present in supportive cells located in the vicinity of barbule cells and destined to degenerate, but no close junctions are present between supportive and barb/barbule cells. Close junctions mature into penta-laminar junctions that are present between mature barb/barbule cells. Immunolabeling for occludin and Cx26 is rare along these cornified junctions. The junctions allow barb/barbule cells to remain connected until feather-keratin form the mature corneous syncytium that constitutes the barbs. A discussion of the role of gap and tight junctions during feather morphogenesis is presented.