Histo- and cytophysiology of the lactating mammary gland of the African elephant ( Loxodonta africana)

Abstract

The lactating mammary gland of the African elephant (Loxodonta africana) has been studied with a panel of morphological techniques focusing on (1) the functional changes during the secretory process, (2) proliferative process [by application of proliferating cell nuclear antigen (PCNA) immunohistochemistry] and apoptotic phenomena [by use of the TUNEL technique] in the individual lobules, and (3) components of milk and milk-fat-globule membrane. In the lactating gland, the lobules are variably differentiated; within a lobule, however, the alveoli are usually similarly differentiated. The morphology of their alveoli suggests a classification of the lobules into types 1-3. Lobules of type 1 are composed of immature tubular alveoli with mitotic figures and numerous PCNA-positive nuclei; advanced type 1 alveoli contain abundant glycogen and specific secretory granules. Lobules of type 2 are further subdivided. In type 2a lobules, the epithelial cells of the alveoli form tall apical protrusions, which in part are occupied by small lipid droplets and which are pinched off in an apocrine fashion. The number of lysosomes varies considerably. Type 2b is the most common type, with striking basal membrane foldings, abundant rough endoplasmic reticulum cisterns, large Golgi apparatus, numerous mitochondria, lipid droplets, and protein vesicles with 30- to 90-nm-wide casein micelles. The lipid droplets are pinched off with minimal amounts of cytoplasm. Type 2c is composed of alveoli with a cuboidal epithelium and few signs of secretory activity. Increasing expression of peanut-agglutinin-binding sites parallels the maturation and differentiation of the glandular cells. Type 3 lobules are marked by numerous TUNEL-positive nuclei and large lipid droplets and are apparently degenerating structures. Cytokeratin (CK) 14 is usually present in the myoepithelial cells; CK 19 and CK 7 mark ductal and immature alveolar epithelia. Milk protein content varies between 2.6% and 6.3%, and casein micelles range from 35 to 90 nm in diameter. The diameter of intra-alveolar milk fat globules ranges from 5 to 25 micrometer and the membranes bear a filamentous surface coat composed of membrane-anchored mucins; gel-electrophoretic analysis of these mucins from different individuals demonstrates the presence of mucin MUC 1, which is expressed with considerable genetic heterogeneity.

BRIEF COMMUNICATION: Histology of the pouch epithelium and the mammary glands during chemically induced oestrus in the brushtail possum (Trichosurus vulpecula)

“…The observations clearly indicate that some changes occur in mammary glands associated with treatment regimes that induce ovulation, with the formation of structures similar to those reported in mammary glands from a range of eutherian mammals (reviewed by Wooding, 1977) including dogs (Nelson & Kelly, 1974), pigs (Kensinger et al. 1982), African elephants (Welsch et al. 1998) and rats (Masso‐Welch et al.…”

The number and activity of mammary epithelial cells, determining factors for milk production

“…Indeed, the elephant is known for its extremely lengthy period of lactation, so that mammary tissue regeneration in this species raises several questions. Histological analysis of the mammary gland from this animal demonstrated the presence of different types of lobules containing alveoli at different stages of differentiation within lactating tissue [28]. A first type of lobule contained weakly differentiated alveoli containing cells with mitotic configurations, and a second type of lobule containing fully differentiated, milk-secreting alveoli.…”

Cutaneous Eccrine Glands of the Foot Pads of the Rock Hyrax (<i>Procavia capensis</i>, Hyracoidea, Mammalia)

“…For in situ detection of cell death the terminal transferase (TdT)-mediated d-UTP nick-end-labeling (TUNEL) procedure was performed on dewaxed paraffin sections according to Gavrieli et al [1992] with the modifications described by Welsch et al [1998b].…”