Application of a uniaxial force by pulling the skin around the mammary gland may affect the orientation of the ducts and the length of the mammary ductal network: Findings from computational modeling and laboratory experiments

The orientation of the epithelial ducts determines the overall shape of the ductal network in the mammary gland. However, how the orientation of the duct is specified is not well understood. This study examined if an externally applied tensional force alters the orientation of the epithelial ducts during puberty, in vivo. In the first experiment, uniaxial forces were applied continuously to mouse mammary glands from 5-7 weeks of age, that is, during pubertal formation of the epithelial ductal network. The uniaxial forces were applied by pulling and adhering the skin around the nipple of the right abdominal number four mammary glands (n = 10; TENSION). For experiment two, the uniaxial force was applied from 5-6 weeks of age, and glands from half the mice (n = 10/group; TENSION and control (CTL)) were collected. In the remaining mice, the application of force was removed at 6 weeks from the TENSION group, and then the glands were collected at 7 weeks of age (n = 10/group; TENSION and CTL). This pulling force on the right gland made the left abdominal number four gland also experience a contralateral (CONTRA) force. Following dissection, whole mounts were prepared, and panoramic images were captured. The ductal network in the images was skeletonized and straightened along the longitudinal midline to capture the length of the ductal network without bias from its curvature. Findings indicated that there was no difference in ductal area in either experiment, but the length of the ductal network was increased in the TENSION and CONTRA mammary glands compared to CTL (p