Mouse Prolactin (PRL) is a peptide hormone belonging to the prolactin/growth hormone family, which also includes growth hormone (GH) and placental lactogen–related hormones that regulate growth, metabolism, and reproductive physiology. In mice (Mus musculus), prolactin is produced primarily by lactotroph cells in the anterior pituitary gland and signals through the prolactin receptor (PRLR), activating intracellular pathways such as JAK2/STAT5, MAPK, and PI3K, which regulate gene expression and cellular responses. PRL plays a critical role in mammary gland development, lactation, and maternal behavior, supporting milk production and nurturing activities after parturition. In mice, prolactin is also involved in reproductive regulation, immune function, and metabolic processes, and can influence ovarian function and corpus luteum maintenance. Because mice are widely used as genetic models, PRL and PRLR knockout or transgenic mouse strains have been extensively used to study hormonal control of lactation, reproductive endocrinology, immune modulation, and mammary gland biology. These murine models have been essential for understanding prolactin signaling pathways and their roles in development, fertility, and endocrine regulation, providing insights relevant to human reproductive and hormonal disorders.