Circumanal glands of the dog: a new classification and cell degeneration

Apocrine secretion in the salivary glands of Drosophilidae and other dipterans is evolutionarily conserved

Apocrine secretion is a transport and secretory mechanism that remains only partially characterized, even though it is evolutionarily conserved among all metazoans, including humans. The excellent genetic model organism Drosophila melanogaster holds promise for elucidating the molecular mechanisms regulating this fundamental metazoan process. Two prerequisites for such investigations are to clearly define an experimental system to investigate apocrine secretion and to understand the evolutionarily and functional contexts in which apocrine secretion arose in that system. To this end, we recently demonstrated that, in D. melanogaster, the prepupal salivary glands utilize apocrine secretion prior to pupation to deliver innate immune and defense components to the exuvial fluid that lies between the metamorphosing pupae and its chitinous case. This finding provided a unique opportunity to appraise how this novel non-canonical and non-vesicular transport and secretory mechanism is employed in different developmental and evolutionary contexts. Here we demonstrate that this apocrine secretion, which is mechanistically and temporarily separated from the exocytotic mechanism used to produce the massive salivary glue secretion (Sgs), is shared across Drosophilidae and two unrelated dipteran species. Screening more than 30 species of Drosophila from divergent habitats across the globe revealed that apocrine secretion is a widespread and evolutionarily conserved cellular mechanism used to produce exuvial fluid. Species with longer larval and prepupal development than D. melanogaster activate apocrine secretion later, while smaller and more rapidly developing species activate it earlier. In some species, apocrine secretion occurs after the secretory material is first concentrated in cytoplasmic structures of unknown origin that we name "collectors." Strikingly, in contrast to the widespread use of apocrine secretion to provide exuvial fluid, not all species use exocytosis to produce the viscid salivary glue secretion that is seen in D. melanogaster. Thus, apocrine secretion is the conserved mechanism used to realize the major function of the salivary gland in fruitflies and related species: it produces the pupal exuvial fluid that provides an active defense against microbial invasion during pupal metamorphosis.

Apocrine secretion: New insights into an old phenomenon

BACKGROUND

While apocrine secretion was among the earliest secretory mechanisms to be identified, its underlying basis remains poorly understood.

SCOPE OF REVIEW

This review reappraises our understanding of apocrine secretion using insights about apocrine secretion from the salivary glands of Drosophila, in which molecular genetic analyses have provided a glimmer of hope for elucidating the mechanistic aspects of this fundamental process.

MAJOR CONCLUSIONS

In contrast to the well-defined process of exocytosis, apocrine secretion is non-vesicular transport and secretory pathway that entails the loss of part of the cytoplasm. It often involves apical protrusions and generates cytoplasmic fragments inside a secretory lumen. In its most intense phase this process is accompanied by the release of large fragments of cellular structures and entire organelles that include mitochondria, Golgi, and portions of the endoplasmic reticulum, among others. Proteomic analyses revealed that the secretion is composed of hundreds to thousands of membranous, cytoskeletal, microsomal, mitochondrial, ribosomal, and even nuclear as well as nucleolar proteins. Strikingly, although many nuclear proteins are released, the nuclear deoxyribonucleic acid itself remains intact. In spite of this complexity, it appears that several protein components of apocrine secretion are identical, regardless of the location of the apocrine gland.

GENERAL SIGNIFICANCE

This type of secretion appears to be common to many, if not all, barrier epithelial tissues including skin derivatives and the epididymis, and is implicated also in lung/bronchi and intestinal epithelium. Apocrine secretion is a mechanism that provides the en masse delivery of a very complex proteinaceous mixture from polarized epithelial tissues to allow for communication at exterior interfaces.

Histochemical analyses of anti-microbial substances in canine perianal skin with special reference to glandular structures

Circumanal glands are prominent features of the canine perianal skin, which are often located near to the sebaceous glands and apocrine glands. As the functional relevance of circumanal glands is yet unknown, we studied the localisation of sialic acids and anti-microbial substances (lysozyme, immunoglobulin A, lactoferrin, β-defensin) in these glandular structures by lectin histochemistry and immunohistochemistry. The glands exhibited a number of sialic acids that were linked to α2-6Gal/GalNAc and α2-3Galβ1-4GlcNAc. Additionally, lysozyme, lactoferrin and β-defensin could be demonstrated in the three types of skin glands, whereas IgA was only detectable in the apocrine glands. The results of the study suggest the specific significance of the circumanal glands. Independent of a certain endocrine role, their products may mainly function as protective agents to preserve the integrity of the anal region, considering that sialic acids and anti-microbial substances are important in defence mechanisms.

Aspectos histológicos da pele de cães e gatos como ferramenta para dermatopatologia

A pele não é histologicamente igual nas diferentes espécies animais. Muito do que se sabe sobre a morfologia da pele humana não pode ser aplicado para cães e gatos. Dessa forma, o conhecimento dos aspectos histológicos básicos da pele nas diferentes espécies se faz necessário para todo profissional da área da patologia veterinária. Além disso, o reconhecimento das principais semelhanças e diferenças estruturais da pele em diferentes regiões do corpo desses animais é fundamental para o exercício da dermatopatologia. Este artigo revisa os principais aspectos da anatomia microscópica da pele de cães e gatos, a fim de auxiliar aqueles patologistas veterinários que estão iniciando no campo da dermatopatologia, pois somente com o reconhecimento das características peculiares desse órgão será possível compreender o método de diagnóstico através de padrões de lesão.

Immunohistochemical study of 3 beta-hydroxysteroid dehydrogenase in dog's perianal sinus

In this study, the localization of 3 beta-hydroxysteroid dehydrogenase (3beta-HSD) activity in the wall of canine perianal sinus (PS) was determined. The 3 beta-HSD activity was found out both in the cytoplasm of cells, situated in the propria and forming clusters adjacently to apocrine glands and in the cytoplasm of some epithelial cells in apocrine cells' glands. The results obtained about the 3 beta-HSD activity allowed us to propose a role of this enzyme in PS development and possibly, in tumourogenesis.

Apocrine sweat glands in the circumanal glands of the dog

Apocrine sweat glands in the circumanal glands of the dog are not connected morphologically with the lobules of the circumanal glands. However, an apparent functional association has been demonstrated and it is possible that the apocrine sweat glands might serve as excretory ducts for degenerated polyhedral cells of the circumanal glands. In this study, we examined the ultrastructure of the apocrine sweat glands in the circumanal glands of the dog in an effort to define more precisely the relationship between the apocrine sweat glands and the circumanal glands. Paraffin sections stained with azan and sections after immunohistochemical staining with antibodies against actin were examined by light microscopy. Samples fixed by aldehyde perfusion were examined with the electron microscope. Diameters of apocrine sweat glands and height of cells in the secretory epithelium varied considerably. Immunohistochemical staining for actin was weakly positive in the supranuclear regions of secretory cells and very intense in myoepithelial cells. In secretory cells, the endoplasmic reticulum was well-developed. Multivesicular bodies were abundant and were discharged into lumens. Apocrine secretion and exocytosis were observed at luminal surfaces of secretory cells. There were three types of large granule in the cytoplasm: giant mitochondria without cristae; membrane-enclosed globules with or without myelin-like contents; and electron-dense, homogeneous, globular structures. Luminal surfaces were always covered with microvilli, and extensive folding of the cell membrane was found in basal regions. Bundles of actin filaments were dispersed throughout the cytoplasm. In the lumens of apocrine tubules, we observed shed secretory cells with well-preserved normal fine structures. We also noted the differentiation of secretory cells that was due to cell renewal. Apocrine sweat glands in the circumanal glands of the dog appear to be more active than those on the general body surface in terms of apocrine secretion, exocytosis, and the release of multivesicular bodies. Shed secretory cells containing large granules, as well as degenerated polyhedral cells from the circumanal glands, might contribute, to some extent, to the subtle composition of sweat from these apocrine sweat glands.