THE DEVELOPMENT OF THE TERMINAL END BUD IN THE PREPUBERTAL-PUBERTAL MOUSE MAMMARY-GLAND

Background: The mammary gland is one of the few organ systems in mamma ls that completes its morphologic development postnatally, Due to this unique developmental property, it serves as an excellent model for st udying ductal morphogenesis beyond embryonic life, The primary objecti ve of this study was to investigate the development of terminal end bu d (TEE) structure in the prepubertal-pubertal mouse mammary gland. Met hods: Seventy-five mice, weaned at 21 days of age, were fed a high fat , nonrestricted intake diet for optimum mammary gland growth, Wholemou nt preparations and a computer-assisted image analyzer were used to re cord the size and number of TEE structures in the thoracic and inguina l mammary glands. A light microscope was used to determine the number of cap cells present in select TEE structures. Results: In the prepube rtal age group, the size and number (No.) of TEBs in the No, 2 and No, 3 thoracic glands were significantly greater than those in the No, 4 inguinal gland, In the pubertal age group, the size and number of TEBs in the No, 2 gland significantly decreased, indicating that for this particular gland the largest size and greatest number of TEBs are pres ent during the prepubertal growth period, In contrast, the size and nu mber of TEBs in the No, 3 and No, 4 glands remained relatively constan t throughout the prepubertal-pubertal growth period. Conclusions: The results of this study show: (1) like the rat mammary gland, there is a synchronous growth among the mouse mammary glands, (2) the maximum siz e and number of TEBs in the prepubertal-pubertal mouse mammary glands are a function of the gland of origin and the age of the mouse, and (3 ) the number of cap cells per TEE structure is directly correlated wit h the size of the TEE structure. (C) 1998 Wiley-Liss, Inc.