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Progress in studies concerning the process of mammogenesis have been stimulated by the development of the three-dimensional (3D) culture systems, which enable mammary epithelial cells to form structures mimicking the alveoli of mammary gland in vivo. Mammary epithelial cells (MECs) supported on a laminin-rich extracellular matrix (ECM) form 3D acinar structures - mammospheres - which mature to form polarized and functional monolayers surrounding a lumen and have the ability to produce milk proteins. These structures develop an axis of apico-basal polarity, subsequently become unresponsive to proliferative signals, and finally a bona fide lumen is formed by cavitation, involving the removal of centrally localized cells via multiple cell death processes. Lumen formation is associated with the selective apoptosis of centrally located cells. Autophagy, which is a process responsible for maintaining cell homeostasis, also seems to be crucial in mammary gland development and remodeling. This review describes the role of autophagy in the formation of acinar structures by mammary epithelial cells. Studies on MECs from different species (human, mouse, cow) cultured on Matrigel™ have shown the protective role of autophagy in centrally located cells of differentiating mammospheres. Autophagy seems to be the cells’ first response to the lack of contact with ECM, which in consequence leads to apoptotic cell death, anoikis, and lumen formation in developing alveoli.
The article briefly discusses specific phases of lactation cycle in the sow by taking into account the results of research in this field presented by various authors. Special attention was placed on the influence of temperature and litter size and time of milk flow on the milk production in the sow. The above-mentioned factors may be evolutionary positive for larger litters but may also limit milk production in the sow.
Autophagy is an important cellular process responsible for the maintenance of homeostasis in the mammary gland during its development and remodeling. The main function of autophagy is to degrade long-lived proteins and damaged organelles in double-membrane autophagic vacuoles containing hydrolytic enzymes. This process is also involved in the regulation of cell development and death. Three-dimensional (3D) cell cultures made it possible to recreate in vitro the process of alveoli formation by mammary epithelial cells (MECs). When cultured on extracellular matrix (ECM) components, MECs form 3D acini structures called mammospheres, composed of a single layer of polarized cells and a hollow lumen in the center of the acini. It has been shown that during the process of mammosphere formation, autophagy is induced in the centrally located cells in response to the stress related to their loss of contact with the ECM. Studies have shown that the induction of autophagy is augmented in the presence of sex steroids, which regulate cell survival during starvation conditions. Additionally, these hormones control the process of lumen formation, regulating the rate of apoptotic death in mammospheres. TGF-â1 also induces autophagy in 3D cultures, but the presence of this cytokine inhibits the development of acinar structures. On the other hand, IGF-I stimulates the growth of mammospheres, inducing autophagy in the numerous cells located in the centre of acinar structures, where the availability of nutrition is insufficient. The present review article describes some latest studies that point to the role of the close regulation of autophagy by endocrine and intramammary signals during mammogenesis.
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