Avian Epidermal Lipids: Functional Considerations and Relationship to Feathering1

Drying eggs to inhibit bacteria: Incubation during laying in a cavity nesting passerine

Early incubation has been suggested as a defensive adaptation against potentially pathogenic bacteria colonizing avian eggshells in the wild. The inhibitory mechanisms underlying this adaptation are poorly understood and only recent experimental evidence demonstrates that keeping eggs dry is a proximate mechanism for the antimicrobial effects of avian incubation. We estimated partial incubation (the bouts of incubation that some birds perform during the egg-laying period, days of lay 3-5 in our population) intensity of female pied flycatchers breeding in nest-boxes using data loggers that allowed a precise measurement of temperature just between the eggs in the nest-cup. We also measured relative humidity within the nest-boxes and related it to incubation intensity, showing that more intense incubation during laying contributes to drying the air near the eggs. We analyzed separately the effects of incubation and of relative humidity on loads of three types of culturable bacteria known to be present on eggshells, heterotrophic bacteria, Gram-negative enterics and pseudomonads. Our results show an association of early incubation with an inhibition of bacterial proliferation through a drying effect on eggshells, as we found that incubation intensity was negatively and relative humidity positively associated with eggshell bacterial loads for heterotrophic bacteria, Gram-negative bacteria and pseudomonads, although the significance of these associations varied between bacterial groups. These results point to microclimatically driven effects of incubation on bacterial proliferation on eggshells during laying in a temperate cavity nesting passerine.

Potential semiochemical molecules from birds: a practical and comprehensive compilation of the last 20 years studies

During the past 2 decades, considerable progress has been made in the study of bird semiochemistry, and our goal was to review and evaluate this literature with particular emphasis on the volatile organic constituents. Indeed, since the importance of social chemosignaling in birds is becoming more and more apparent, the search for molecules involved in chemical communication is of critical interest. These molecules can be found in different sources that include uropygial gland secretions, feather-surface compounds, and molecules from feces and skin. Although many studies have examined the chemical substances secreted by birds, research on bird chemical communication is still at the start, so new strategies for collecting samples and development of new methods of analysis are urgently required. As a first step, we built a database that brings together potential semiochemicals, using a unique chemical nomenclature for comparing different bird species and also for referencing the different classes of substances that can be found in order to adapt future parameters of analysis. The most important patterns of the wax fraction of preen secretions are highlighted and organized in an ordered table. We also draw up a list of various combinations of sampling and analytical techniques, so that each method can be compared at a glance.

Development of skin structure and cutaneous water loss in nestling desert house sparrows from Saudi Arabia

The outer layer of the epidermis, the stratum corneum (SC), contains lipids and corneocytes, which together form layers that limit cutaneous water loss (CWL). We examined the development of structure of the SC and CWL in nestling House Sparrows (Passer domesticus) from Saudi Arabia. We measured CWL of nestlings, and characterized development of their epidermis using electron microscopy. We tested two antagonistic hypotheses, that CWL decreases as nestlings age, a response to increased thickness of SC, and an opposite idea that CWL increases as nestlings age even though the number of layers of the SC remains constant. CWL of nestling House Sparrows varied with developmental stages, in a non-linear fashion, but not significantly so. CWL of nestlings averaged 7.31+/-1.5 g H(2)O/(m(2) h), whereas for adults it was 4.95 g/(m(2) h); adult CWL was 67.7% that of nestlings. We found that morphology of the SC did not change linearly with age, but seemed to vary with developmental stage. CWL decreased as the SC thickness increased and as the total thickness of the corneocytes increased. Further, we found that CWL decreased as the thickness of the extracellular space increased, number of corneocytes increased, and proportion of the SC that is extracellular space increased.

Identification of complex mixtures of sphingolipids in the stratum corneum by reversed-phase high-performance liquid chromatography and atmospheric pressure photospray ionization mass spectrometry

Sphingolipids, such as ceramides and cerebrosides, are important molecules in the formation and maintenance of the epidermal barrier to water vapor diffusion. In this paper we explore a new method to identify the sphingolipids found in the stratum corneum (SC), the outer layer of the epidermis, of House sparrows living in Saudi Arabia using reversed-phase high-performance liquid chromatography (HPLC) coupled with atmospheric pressure photo-ionization mass spectrometry (APPI-MS). First, using thin layer chromatography (TLC) we found that the SC contains ceramides, cerebrosides, and free fatty acids along with smaller amounts of cholesterol. Knowing the classes of sphingolipids present in the SC markedly reduced the number of possible molecules present. Then, we identified each sphingolipid molecule in our sample by both negative and positive mode of APPI-MS. We confirmed our identifications by generation of accurate mass data, and by examination of MS/MS spectra for selected molecules. Using APPI-MS, we identified 7 families of cerebrosides, for a total of 97 molecular species, and 4 families of ceramides, for a total of 79 molecules, in the SC of House sparrows, a wider array than would be found in mammals. Carbon chain lengths of fatty acids in the sphingolipids were longer than those that have been reported for mammalian SC; chain lengths of over 40 carbons were common. We also compared our estimates of the quantity of lipids in the SC obtained by HPLC/MS with those from TLC. Estimates of the amount of total ceramides and cerebrosides using TLC differed from those obtained by HPLC/MS by +0.95% and -2.5%, respectively. We conclude that our protocol using reversed-phase HPLC and APPI-MS is an useful method of analyzing complex mixtures of sphingolipids in the SC.

Fine structure of the organ of attachment of the teleost, Garra gotyla gotyla (Ham)

We describe the morphology of the attachment organ (AO) of the teleost, Garra gotyla gotyla (Cyprinidae). It is located ventrally around the mouth opening and used by the species for attachment to submerged rocks in sub-Himalayan streams and rivers where it lives. The AO consists of three crescentic parts and a central callus part. Scanning electron microscopy (SEM) shows the former to possess numerous tubercles, each of which bears about 23-27 curved spines. Light microscopy shows the epidermis of the tuberculated parts to possess one type of cell arranged into 7-8 rows. Transmission electron microscopy (TEM) reveals these cells to contain abundant tonofilaments (hence called the filament cells). The epidermis of the callus part possesses the filament cells and additionally mucous cells, which are absent in the tuberculated parts. The superficial epidermis is apparently keratinized (thickness: 5-8 microm), and a part of the cells of the outer row is modified into spines. These cells show a thick plasma membrane envelope and possess mucous granules (diameter: 0.1-0.3 microm) and bundles of tonofilaments. The cells of the inner two to four rows possess similar organelles and additionally, prominent Golgi bodies and rough endoplasmic reticulum. Immunohistochemically, the cells of the outer row and the spines stain positively for cytokeratin. The cells of the innermost rows (five to eight) possess few tonofilaments and no mucous granules. It is evident that the filament cells of the mid- to upper epidermis are specialized for the production of mucous granules and tonofilaments, which is unique for the teleost epidermis concerned. It appears that the tuberculated parts with spines assist in anchorage and interlocking with the substratum, while the central callus part probably utilizes both suction and frictional mechanisms, and mucous secretion protects the spines from damage during anchorage and abrasion.

Ultrastructural and immunohistochemical observations on the process of horny growth in chelonian shells

The process of growth of horny scutes of the carapace and plastron in chelonians is poorly understood. In order to address this problem, the shell of the terrestrial tortoise Testudo hermanni, the freshwater turtle Chrysemys picta, and the soft shelled turtle Trionix spiniferus were studied. The study was carried out using immunohistochemistry, electron microscopy and autoradiography following injection of tritiated histidine. The species used in the present study illustrate three different types of shell growth that occur in chelonians. In scutes of Testudo and Chrysemys, growth mainly occurs in the hinge regions by the production of cells that accumulate beta-keratin and incorporate tritiated histidine. Newly produced bundles of alpha- and beta-keratin incorporate most of the histidine. No keratohyalin is observed in the epidermis of any of the species studied here. In Testudo, newly generated corneocytes containing beta-keratin form a corneous layer to form the growing rings of scutes. In Chrysemys, newly generated corneocytes containing beta-keratin form the new, expanded corneous layer. In the latter species, at the end of the growing season (autumn/fall), thin corneocytes containing little beta-keratin are produced underneath the corneous layer, and gradually form a scission layer. In the following growing season (spring-summer) the shedding layer matures and determines the loss of the outer corneous layer. In this way, scutes expand their surface at any new molt. In Trionix, no distinct scutes and hinge regions are present and during the growing season, new corneocytes are mainly produced along the perimeter of the shell. Corneocytes of Trionix contain little beta-keratin and form a thick corneous layer in which cells resemble the alpha-layer of the softer epidermis of the limbs, tail and neck. Neither keratohyalin nor specific histidine incorporation was observed in these cells. Corneocytes are gradually lost from the epidermal surface. Dermal scutes are absent in Trionix, but the dermis is organized in 6-10 layers of plywood-patterned collagen bundles. The stratified layers gradually disappear toward the growing border of the shell. The mode of growth of horny scutes in these different species of chelonians is discussed.

Structural and Immunocytochemical Characterization of Keratinization in Vertebrate Epidermis and Epidermal Derivatives

This review presents comparative aspects of epidermal keratinization in vertebrates, with emphasis on the evolution of the stratum corneum in land vertebrates. The epidermis of fish does not contain proteins connected with interkeratin matrix and corneous cell envelope formation. Mucus-like material glues loose keratin filaments. In amphibians a cell corneous envelope forms but matrix proteins, aside from mucus/glycoproteins, are scarce or absent. In reptiles, birds, and mammals specific proteins associated with keratin become relevant for the production of a resistant corneous layer. In reptiles some matrix, histidine-rich and sulfur-rich corneous cell envelope proteins are produced in the soft epidermis. In avian soft epidermis low levels of matrix and cornified proteins are present while lipids become abundant. In mammalian keratinocytes, interkeratin proteins, cornified cell envelope proteins, and transglutaminase are present. Topographically localized areas of dermal-epidermal interactions in amniote skin determine the formation of skin derivatives such as scales, feathers, and hairs. New types of keratin and associated proteins are produced in these derivatives. In reptiles and birds beta-keratins form the hard corneous material of scales, claws, beaks, and feathers. In mammals, small sulfur-rich and glycine-tyrosine-rich proteins form the corneous material of hairs, horns, hooves, and claws. Molecular studies on reptilian beta-keratins show they are glycine-rich proteins. They have C- and N-terminal amino acid regions homologous to those of mammalian proteins and a central core with homology to avian scale/feather keratins. These findings suggest that ancient reptiles already possessed some common genes that later diversified to produce some keratin-associated protein in extant reptiles and birds, and others in mammals. The evolution of these small proteins represents the more recent variation of the process of cornification in vertebrates.

Carotenoid pigments and the selectivity of psittacofulvin-based coloration systems in parrots

Carotenoid pigments are commonly used as colorants of feathers and bare parts by birds. However, parrots (Aves: Psittaciformes) use a novel class of plumage pigments (called psittacofulvins) that, like carotenoids, are lipid-soluble and red, orange, or yellow in color. To begin to understand how and why parrots use these pigments and not carotenoids in their feathers, we must first describe the distribution of these two types of pigments in the diet, tissues, and fluids of these birds. Here, we studied the carotenoid content of blood in five species of parrots with red in their plumage to see if they show the physiological ability to accumulate carotenoids in the body. Although Scarlet (Ara macao) and Greenwing Macaws (Ara chloroptera) and Eclectus (Eclectus roratus), African Gray (Psittacus erithacus) and Blue-fronted Amazon (Amazona aestiva) Parrots all use psittacofulvins to color their feathers red, we found that they also circulated high concentrations of both dietary (lutein, zeaxanthin, beta-cryptoxanthin) and metabolically derived (anhydrolutein, dehydrolutein) carotenoids through blood at the time of feather growth, at levels comparable to those found in many other carotenoid-colored birds. These results suggest that parrots have the potential to use carotenoids for plumage pigmentation, but preferentially avoid depositing them in feathers, which is likely under the control of the maturing feather follicle. As there is no evidence of psittacofulvins in parrot blood at the tune of feather growth, we presume that these pigments are locally synthesized by growing feathers within the follicular tissue.

Differentiation of the epidermis in turtle: an immunocytochemical, autoradiographic and electrophoretic analysis

Proteins involved in the process of cornification of turtle epidermis are not well known. The present immunocytochemical, electrophoretic and autoradiographic study reports on the localization patterns and molecular weights of keratins, which are cornification proteins, and of tritiated histidine in turtle epidermis. Alpha-keratins with a molecular weight of 40-62 kDa are present in the epidermis. Beta-keratin is mainly detectable in the stratum corneum of the carapace and plastron, but is rarely present or even absent in the corneous layer of limb, tail and neck epidermis. After electrophoresis and immunoblotting with an antibody against chicken scale beta-keratin, bands at 15-17, 22-24, and 36-38 kDa appeared. This antibody recognized weaker bands at 38-40 and 58-60 kDa in the soft epidermis. After reduction and carboxymethylation of proteins extracted from carapace and plastron, but not of proteins from the soft epidermis, protein bands at 15-17 and 35-37 kDa were found when using the anti-beta 1-keratin antibody. Loricrin-, filaggrin-, sciellin-, and transglutaminase-like immunostaining was detectable only in the transitional and lowermost corneous layers of the soft epidermis. Vesicular bodies in the transitional layer were immunolabeled by the anti-loricrin antibody, and weakly by the anti-filaggrin and anti-transglutaminase antibodies. In immunoblots, the anti-loricrin antibody reacted with a major band at 50-54 kDa in both carapace-plastron and soft epidermis. The anti-sciellin antibody detected major bands at 38-40 and 50 kDa in hard epidermis, and at 50 and 54-56 kDa in soft epidermis. Filaggrin-like immunostained bands were observed at 50-55 and 62-64 kDa. This immunostaining was probably due to a common epitope in filaggrin and some keratins. Histidine was evenly incorporated in the epidermis, and the ultrastructural study showed random labeling, often associated with keratin bundles of alpha and beta-keratinocytes. Histidine-labeled protein bands were not found in the carapace-plastron. In the soft epidermis, weakly labeled bands at 15-20, 25, and 45-60 kDa were found occasionally. The latter bands probably represented neo-synthesized keratins as was also indicated by the ultrastructural autoradiographic analysis. In conclusion, our study suggests that proteins with epitopes that they have in common with cornification proteins of mammalian epidermis are also present in the epidermis of turtle.

Lutein-based plumage coloration in songbirds is a consequence of selective pigment incorporation into feathers

Many birds obtain colorful carotenoid pigments from the diet and deposit them into growing tissues to develop extravagant red, orange or yellow sexual ornaments. In these instances, it is often unclear whether all dietary pigments are used as integumentary colorants or whether certain carotenoids are preferentially excluded or incorporated into tissues. We examined the carotenoid profiles of three New World passerines that display yellow plumage coloration-the yellow warbler (Dendroica petechia), common yellowthroat (Geothlypis trichas) and evening grosbeak (Coccothraustes vespertinus). Using high-performance liquid chromatography, we found that all species used only one carotenoid-lutein-to color their plumage yellow. Analyses of blood carotenoids (which document those pigments taken up from the diet) in two of the species, however, revealed the presence of two dietary xanthophylls-lutein and zeaxanthin-that commonly co-occur in plants and animals. These findings demonstrate post-absorptive selectivity of carotenoid deposition in bird feathers. To learn more about the site of pigment discrimination, we also analyzed the carotenoid composition of lipid fractions from the follicles of immature yellow-pigmented feathers in G. trichas and D. petechia and again detected both lutein and zeaxanthin. This suggests that selective lutein incorporation in feathers is under local control at the maturing feather follicle.