SUMMARY Aging is closely associated with increased susceptibility to breast cancer, yet there have been limited systematic studies of aging-induced alterations in the mammary gland. Here, we leverage high-throughput single-cell RNA sequencing to generate a detailed transcriptomic atlas of young and aged murine mammary tissues. By analyzing epithelial, stromal, and immune cells, we identify age-dependent alterations in cell proportions and gene expression, providing evidence that suggests alveolar maturation and physiological decline. The analysis also uncovers potential pro-tumorigenic mechanisms coupled to the age-associated loss of tumor suppressor function and change in microenvironment. In addition, we identify a rare, age-dependent luminal population co-expressing hormone-sensing and secretory-alveolar lineage markers, as well as two macrophage populations expressing distinct gene signatures, underscoring the complex heterogeneity of the mammary epithelia and stroma. Collectively, this rich single-cell atlas reveals the effects of aging on mammary physiology and can serve as a useful resource for understanding aging-associated cancer risk.

Transmissible venereal tumours (TVT) are normally seen on the genitalia of both male and female dogs, and at times may be observed on extra-genital sites such as lips, oral mucosa, and peritoneum, or in organs such as the tonsils, eye, liver, spleen, kidney, lung, and musculature. The present communication deals with two rare cases of primary extragenital TVT involving the mammary glands of dogs and their pathology and immunohistochemistry. The study indicated that apart from routinely used markers such as vimentin, p53, PCNA, Ki-67 and c-myc, the oncogenes Rb and cyclin D1 proved to be novel markers of TVT in dogs. To the authors' knowledge, this is the first report of extra-genital mammary TVT in canines.

ABSTRACT:The retinoblastoma susceptibility gene RB-1 is a tumour suppressor gene that encodes a protein (Rb) that regulates the transition from the G1 phase to the S phase of the cell cycle. Inactivation of the Rb gene has been shown in a variety of human tumours, including breast, ovarian, hepatic, prostatic, and endometrial carcinomas. Although Rb protein is normally expressed in the nuclei of healthy cells, during carcinogenesis there is a partial or complete loss of nuclear expression. Recently, some reports have indicated aberrant cytoplasmic expression of Rb protein. However, little is known about its cytoplasmic expression and significance as a prognostic marker in canine mammary tumours (CMT). The present study was performed on 36 malignant CMT cases in order to assess the mutational status and prognostic significance of Rb in primary malignant CMT. We report an almost complete loss of nuclear expression of Rb protein with corresponding gain of aberrant cytoplasmic expression in basal/myoepithelial cells in CMT. Strikingly, our analysis reveals a significant positive correlation between survival time and cytoplasmic expression of Rb protein in basal cells. Moreover, cytoplasmic expression of Rb protein in basal cells was also correlated with tumour grade and stage.