Mammary gland development and early tumor development is not influenced by MMP13.

<p>(A) Morphometric analysis of ductal epithelial penetration during normal mammary gland development. Representative whole mount-stained #4 mammary glands from <i>Mmp13^+/+</i> (n = 4 and n = 4 at 4 and 6 weeks of age, respectively), and <i>Mmp13^−/−</i> mice (n = 3 and n = 7 at 4 and 6 weeks of age, respectively. The distances from the nipple to the three most far-reaching ducts and to the edge of the fat pad were measured. The mean ductal epithelial penetration as percentage of the whole fat pad is shown with the SEM. (B) Morphometric analysis of early MMTV-PyMT tumor growth. Representative whole mount-stained #4 gland tumors from <i>MMTV-PyMT;Mmp13^+/+</i> and <i>MMTV-PyMT;Mmp13^−/−</i> mice at 6-weeks-of-age. The tumor area was measured in 4- and 6-week-old <i>MMTV-PyMT;Mmp13^+/+</i> (n = 5 and n = 7, respectively) and <i>MMTV-PyMT;Mmp13^−/−</i> mice (n = 3 and n = 10, respectively) and are presented as mean with the SEM.