Adaptive evolution of secretory cell lines in vertebrate skin

Abstract

The embryonic horny layer of vertebrates contains distinctive cell lines that account for the remarkable, diverse secretory performances of their cutaneous apparatuses. Aquatic classes (jawless, cartilaginous and bony fishes) possess single gland cells, scattered among ordinary epidermal cells, that manufacture proteinaceous or mucous substances. This dichotomy is retained in adult amphibians, although the secretory cells in anamnionic tetrapods begin to be arranged in complex glands located in the loose dermis. In the Amniota, intensive keratinisation involving the epidermis results in the loss of the ancestral secretory lines, accompanied by the onset of a novel, lipidproducing gland type, which in mammals is flanked by the exclusive sweat gland apparatus. In this concise up-to-date review, we attempt to phylogenetically narrow the large variety of secretory structures in vertebrate skin into a few basic schemes, in the light of the close relationships between environmental challenges and ecological, ethological as well as physiological roles of the cutaneous apparatus.

The evolution of milk secretion and its ancient origins

“…In mammals, mucous glands are restricted to oral and internal epithelial surfaces. Although Vorbach et al (2006) are certainly correct that mammary glands must derive, ultimately, from the simple glandular skin structures found in pre-amniotic tetrapods (Quagliata et al, 2006), there must have been intermediate stages that more closely resemble mammary glands.…”

Kugelzellen in larval anuran epidermis: an ultrastructural study on tadpoles of Pelobates cultripes (Pelobatidae) and Phyllobates bicolor (Dendrobatidae)

“…LC cytoplasm exhibits a central-peripheral polarization: the inner, perinuclear region (Hofcytoplasma) contains biosynthesis organelles, the outer region granules of various density. These granules may be discharged following LC rupture (Jarial, 1989) or released through merocrine processes (Quagliata et al, 2006). Similar epidermal cells have been described in tadpoles of the South African clawed frog Xenopus laevis and referred to as Kugelzellen (KZn or ball cells), on account of their spheroid shape (Fröhlich et al, 1977).…”

“…KZn have also been described as clear cells (Fox, 1988) or "vacuoles" (Seki et al, 1989) due to their remarkably transparent cytoplasm. KZn do not exhibit any ultrastructural patterns of secretory activity, but possess thick bundles of tonofi laments and a dense layer of peripheral cytoplasm (Fröhlich et al, 1977, Delfi no andQuagliata et al, 2006). KZn perform a mechanical function (Fröhlich et al, 1977) before undergoing degeneration during metamorphosis.…”

“…On account of the remarkable subcellular features outlined above, the present light and transmission electron microscope (LM and TEM) study investigates the larval epidermis of the western spadefoot frog Pelobates cultripes (Cuvier, 1829) (Frost et al, 2006). Although these frogs have been investigated in previous studies on epidermal specialized cell lines Quagliata et al, 2006), this is the fi rst comparative report which analyses KZn in their tadpoles.…”

Histology of the Suprapubic and Anogenital Cutaneous Glands in Male Cotton Top Tamarins (Saguinus oedipus)

“…Confirming the adaptive flexibility of secretory cell lines in the skin of vertebrates, scent glands are composed of constitutive cutaneous exocrine units that form conspicuous gland bodies in specific areas [Quagliata et al, 2006]. In mammals, scent glands are associated with hair follicles and include specialized sebaceous (holocrine and acinar) glands (SGs) and apocrine (tubular) glands (AGs).…”