Fig. 7.

Hypothetical model of the menin-mediated effect on mammary epithelial cell numbers and the lactation curve pattern of mammary glands. The gradual decrease in menin expression after the initiation of lactation in mammary glands causes epithelial cell growth arrest in G1 stage through repression of Cyclin D1, also inducing cell apoptosis. Menin expression continues to decrease until reaching its lowest point at the peak lactation stage. However, in the late lactation stage and/or dry period (no lactation), menin expression levels are recovered, possibly related to differences in hormone secretion (Li et al. 2017; Karnik et al. 2007). The growth of epithelial cells becomes derepressed, and extracellular matrix degradation resulting from decreased menin ceases. Epithelial cells proliferate again, and the extracellular matrix undergoes remodeling, in preparation for the next lactation cycle. “+” indicates relative menin expression levels; grey-filled circles indicate G1-arrested mammary epithelial cells. Upward arrows indicate increased expression or activity, while downward arrows indicate decreased expression or activity