Paul F. A. Maderson

Ultrastructural contributions to an understanding of the cellular mechanisms involved in lizard skin shedding with comments on the function and evolution of a unique Lepidosaurian phenomenon

Previous reports on the fine structure of lizard epidermis are confirmed and extended by SEM and TEM observations of cell differentiation and the form of shed material from the American anole Anolis carolinensis. Attention is drawn to two issues: 1) the tips of the spinules arising from the mature oberhautchen are markedly curved; this morphology can be seen during differentiation; 2) the median keels of scales from all parts of the body show “naked” oberhautchen cells that lack characteristic spinules, but have a membrane morphology comprising a complex system of serpentine microridges.

Ultrastructural organization of avian stratum corneum lipids as the basis for facultative cutaneous waterproofing

The ultrastructure of naked neck epidermis from the ostrich (Struthio camelus) and ventral apterium from watered, and water‐deprived, Zebra finches (Taeniopygia [Poephila] guttata castanotis) is presented. The form and distribution of the fully differentiated products of the lipid‐enriched multigranular bodies are compared in biopsies post‐fixed with osmium tetroxide or ruthenium tetroxide. The fine structure of ostrich epidermis suggests it is a relatively poor barrier to cutaneous water loss (CWL). The fine structure from watered, and 16‐hr water‐deprived Zebra finches, considered in conjunction with measurements of CWL, confirms previous reports of “facultative waterproofing,” and emphasizes the rapidity of tissue response to dehydration. The seemingly counterintuitive facts that one xerophilic avian species, the ostrich, lacks a “good barrier” to CWL, whereas another, the Zebra finch, is capable of forming a good barrier, but does not always express this capability, are discussed. An explanation of these data in comparison to mammals centers on the dual roles of the integument of homeotherms in thermoregulation and conserving body water. It is concluded that birds, whose homeothermic control depends so much on CWL, cannot possess a permanent “good barrier,” as such would compromise the heat loss mechanism. Facultative waterproofing (also documented in lizards) protects the organism against sudden reductions in water availability. In birds, and probably in snakes and lizards, facultative waterproofing involves qualititative changes in epidermal cell differentiation. Possible control mechanisms are discussed.

'Fish matters': the relevance of fish skin biology to investigative dermatology.

Please cite this paper as:‘Fish matters’: the relevance of fish skin biology to investigative dermatology. Experimental Dermatology 2010.

Mammalian skin evolution: a reevaluation

Abstract:  A 1972 model for the evolutionary origin of hair suggested a primary mechanoreceptor role improving behavioral thermoregulation contributed to the success of late Paleozoic mammal‐like reptiles. An insulatory role appeared secondarily subsequent to protohair multiplication. That model is updated in light of new data on (a) palaeoecology of mammalian ancestors; (b) involvement of HRPs in keratinization; (c) lipogenic lamellar bodies that form the barrier to cutaneous water loss; and (d) growth factors involved in hair follicle embryogenesis and turnover. It is now proposed that multiplication of sensory protohairs caused by mutations in patterning genes initially protected the delicate barrier tissues and eventually produced the minimal morphology necessary for an insulatory pelage. The latter permitted Mesozoic mammals to occupy the nocturnal niche ‘in the shadow of dinosaurs’. When the giant reptiles became extinct, mammals underwent rapid radiation and reemerged as the dominant terrestrial vertebrates.

Ultrastructural observations on the embryonic development of the integument of Lacerta muralis (Lacertilia, Reptilia)

Integumentary development on the dorsal and ventral aspects of the body of 14, 21, 26, 33, and 40‐day incubated embryos of the European Wall Lizard (Lacerta muralis) is described. While the earliest stages of epidermal differentiation resemble those reported for other tetrapods, precocious differentiation of dermal collagen more resembles that of anamniotes than that of birds and mammals. Anchoring complexes comprising cellular components, anchor filaments, and collagen are described, and their possible relationship to the formation of scale anlagen is discussed. The first embryonic epidermal generation differentiates beneath the periderm; most features of its histogenesis resemble those that have been described for the epidermis of adult squamates, but certain previously ignored organelles, including possible earlier β‐keratin precursors, are reported. Different strategies regarding in ovo peridermal loss and posthatching shedding behavior are described and discussed in light of presently available data concerning control of cell differentiation in the squamate epidermis.

A histological study of the long‐term response to trauma of squamate integument

Scale neogenesis following excision of pieces of skin of various sizes and shapes has been studied in several squamate species. In small wounds, neogenesis does not occur, the wound region contracts, and increased areas of hinge differentiation are seen. In large wounds, the time taken for neogenesis to occur, and the size, shape, distribution, and number of the reformed units, are variable. We confirm previous reports that neogenesis accompanies a renewal phase of the shedding cycle, and suggests that this is because both types of morphogenesis require germinal stability.

Towards a comprehensive model of feather regeneration

Understanding of the regeneration of feathers, despite a 140 year tradition of study, has remained substantially incomplete. Moreover, accumulated errors and mis‐statements in the literature have confounded the intrinsic difficulties in describing feather regeneration. Lack of allusion to Rudalls (Rudall [ 1947 ] Biochem Biophys Acta 1:549–562) seminal X‐ray diffraction study that revealed two distinct keratins, β‐ and α‐, in a mature feather, is one of the several examples where lack of citation long inhibited progress in understanding. This article reviews and reevaluates the available literature and provides a synthetic, comprehensive, morphological model for the regeneration of a generalized, adult contour feather. Particular attention is paid to several features that have previously been largely ignored. Some of these, such as the β‐keratogenic sheath and the α‐keratogenic, supra‐umbilical, pulp caps, are missing from mature, functional feathers sensu stricto because they are lost through preening, but these structures nevertheless play a critical role in development. A new developmental role for a tissue unique to feathers, the medullary pith of the rachis and barb rami, and especially its importance in the genesis of the superior umbilical region (SUR) that forms the transition from the spathe (rachis and vanes) to the calamus, is described. It is postulated that feathers form through an intricate interplay between cyto‐ and histodifferentiative processes, determined by patterning signals that emanate from the dermal core, and a suite of interacting biomechanical forces. Precisely regulated patterns of loss of intercellular adhesivity appear to be the most fundamental aspect of feather morphogenesis and regeneration: rather than a hierarchically branched structure, it appears more appropriate to conceive of feathers as a sheet of mature keratinocytes that is “full of holes. J. Morphol. 2009.

From frog integument to human skin: dermatological perspectives from frog skin biology

For over a century, frogs have been studied across various scientific fields, including physiology, embryology, neuroscience, (neuro)endocrinology, ecology, genetics, behavioural science, evolution, drug development, and conservation biology. In some cases, frog skin has proven very successful as a research model, for example aiding in the study of ion transport through tight epithelia, where it has served as a model for the vertebrate distal renal tubule and mammalian epithelia. However, it has rarely been considered in comparative studies involving human skin. Yet, despite certain notable adaptations that have enabled frogs to survive in both aquatic and terrestrial environments, frog skin has many features in common with human skin. Here we present a comprehensive overview of frog (and toad) skin ontogeny, anatomy, cytology, neuroendocrinology and immunology, with special attention to its unique adaptations as well as to its similarities with the mammalian integument, including human skin. We hope to provide a valuable reference point and a source of inspiration for both amphibian investigators and mammalian researchers studying the structural and functional properties of the largest organ of the vertebrate body.

The Tetrapod Epidermis: A System Protoadapted as a Semiochemical Source

It is one thing to emphasize to an undergraduate class the importance of “communication” between organisms; it is quite another to comprehend how the organisms perceive and use the signal(s). Of cetacean vocalization it has been written: “This system is something we terrestrial mammals cannot imagine and for which we have no empathy,” (Bateson, 1966). Researchers who pursue mechanisms of communication which involve vibrational or electromagnetic energy have long had access to technologies which could record and measure the signal(s) objectively. Until relatively recently no such tools were available for studies of chemical communication, and experiments relied largely on observation and bioassays. However, advances are being made at the molecular level (Lancet, 1984), and these have arrived at a most opportune time. The relative lack of objective measurement produced some extraordinary examples of circular reasoning. General texts often give the implicit or explicit impression that among vertebrates only mammals really use olfaction. However, the relatively poor performance of Homo sapiens in this context distorts our conceptualization of other classes. A brief review of available data on chemoreception in birds was summarized: “The best conclusion from all this is probably that the sense of smell in birds is comparable to that of man. It is present, but in most species is little used.” (Yapp, 1970; cf. Wenzel, this symposium).

The effects of androgens on the β-glands of the tokay (Gekko gecko): Modification of an hypothesis

Study of the posterior abdominal epidermis in hypophysectomized/thyroidectomized male and female tokays following surgery, and subsequent androgen therapy, indicates that, contrary to a previous model, all aspects of β‐gland differentiation are under direct androgenic control. On the other hand, another epidermal specialization, the digital foot‐pad, shows a pattern of histogenesis directly comparable to that of β‐glands, but is unaffected by androgens. These data are discussed with respect to the evolution of glandular epidermal specializations in gekkonid lizards and the possible role of androgens in modifying the control of cell differentiation in lizard epidermis.