Development and characterization of the BALB/cNIV mouse strain.

The strain BALB/cNIV/Crgl was developed by infecting BALB/c/Crgl mice with mouse mammary tumor virus from C3Hf mice. A BALB/c normal mammary duct was transplanted into the gland-free fat pad of a hormone-stimulated female C3Hf X BALB/c F1 mouse. A hyperplastic alveolar nodule was found in the BALB/c ductal outgrowth and was transplanted into another hybrid gland-free fat pad.

Metastasis of murine mammary tumour lines from the mammary gland and ectopic sites.

A murine model of spontaneous metastasis of mammary adenocarcinomas in mice was developed by serial transplantation of spontaneous BALB/cfC3H/ Crgl tumours into the mammary gland. Through 8 transplant generations, 5 lines demonstrated maintenance of metastatic phenotype and consistent gross and histological morphology and growth properties. Tumour lines M12, M35 , and M51 metastasized from the mammary gland with overall frequencies of 53, 80, and 85%, respectively.

Mechanical tension induces lateral movement of intramembrane components of the tight junction: studies on mouse mammary cells in culture.

Occluding junctions of mammary epithelial cells in nonproliferating primary culture occasionally display an atypical pattern of intramembrane strands oriented predominantly perpendicular, instead of roughly parallel, to the apical border of the junction. To test whether the orienting influence was a centripetal cytoskeletal tension often observed in epithelial sheets on fixed substrates, we seeded cells at low density; this allows them to spread maximally while forming a barely confluent pavement. The result was a fourfold increase in the percentage of junctions with the strongly aligned, atypical pattern.

Effects of extracellular calcium depletion on membrane topography and occluding junctions of mammary epithelial cells in culture.

Ca2+ dependence of occluding junction structure and permeability, well documented in explanted or cultured epithelial sheets, presumably reflects inherent control mechanisms. As an approach to identification of these mechanisms, we induced disassembly of zonulae occludentes in confluent monolayers of mouse mammary epithelial cells by exposure to low concentrations of the chelators, EGTA or sodium citrate. Stages in disassembly were monitored during treatment by phase-contrast microscopy and prepared for transmission and scanning electron microscopy.