ZIA BC 010021 (ZIA) | |||
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Title | Biology of Mammary Gland Development and Tumorigenesis | ||
Institution | NCI, Bethesda, MD | ||
Principal Investigator | Smith, Gilbert | NCI Program Director | N/A |
Cancer Activity | N/A | Division | CCR |
Funded Amount | $690,828 | Project Dates | null - null |
Fiscal Year | 2018 | Project Type | Intramural |
Research Topics w/ Percent Relevance | Cancer Types w/ Percent Relevance | ||
Cancer (100.0%) | Breast (100.0%) | ||
Research Type | |||
Cancer Progression & Metastasis Technology Development and/or Marker Discovery |
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Abstract | |||
We have tested the hypothesis that non-cellular extracts from normal mammary tissue can reprogram non-mammary and cancer cell in the epithelium-divested mammary fat pad in vivo. We have published evidence that mammary extracellular matrix (mECM) can redirect testicular and embryonic stem cells from the mouse to mammary epithelial cell fates in vivo. Similar preparations from other organ systems were found negative for this activity. Mammary epithelial cell lineage analysis was performed via the Lyon's Hypothesis, which states that one of the two X chromosomes is silenced in each female cell during embryogenesis. Implants from a single mammary gland of an H253 transgenic female mouse heterozygous for a lacZ-labeled X chromosome were analyzed at various time points following transplantation into the epithelium-cleared mammary fat pads of immune-compromised mice. Our results show lacZ-marked X chromosome, demonstrated by X-gal staining, are confined to a single epithelial clone that gave rise to the cap cells of growing terminal end bud (TEB) in the expanding mammary outgrowths and also the basal myoepithelial cells of the mammary ducts. Luminal cells in these ducts were uniformly negative for lacZ expression indicating that they were derived from cellular precursors that contained a silenced lac-Z marked X chromosome. This observation confirms the earlier work of Williams and Daniel, who concluded that the terminal end bud-associated cap cells of growing mammary ducts were the precursors of the basal (myoepithelial cells) of mature mammary ducts. The results of our study indicates that a single clone (marked by an X chromosome carrying a lacZ gene) is responsible for the appearance of cap cells in the growing terminal end bud (TEB) and in turn give rise to the myoepithelial lineage of the mammary ductal system. This same clone is shown among the body cells of the marked TEBs as a group of closely associated cells also marked by lacZ. We conclude that this clone found in the body of the TEB gives rise to the specialized cap cells and subsequently to the myoepithelial lineage of the subtending mammary ducts. This is a slightly different interpretation presented by Williams and Daniel in 1983, who postulated that the cap cells themselves were multipotent and gave rise to both luminal and myoepithelial progeny in the growing ductal system. It is clear from our work that none of the luminal cells in the subtending ducts bear the un-silenced lacZ-marked X chromosome. We conclude that the luminal cells arise from a different set of progenitors. These conclusions mesh very well with our earlier discovery that lobule-only and duct-only progenitors are present amongst nulliparous mammary epithelium during transplantation of limiting dilutions of epithelial cells from primary cultures of post pubertal females. Confirmation of separate ductal and lobule-limited precursors was confirmed during serial passages of mammary tissue into subsequently impregnated hosts where ductal and lobular development were shown to be lost independently from one another. Telomeres are nucleoprotein structures comprised of simple repeat sequences located at the ends of chromosomes. They shorten upon cell division and are restored by a specialized ribonucleic-protein complex called telomerase (TER), which is made up of essential protein and RNA components. To determine if this activity was essential to mouse mammary gland growth in vivo, we serially transplanted mammary fragments from TER +/-, and TER -/- mammary tissues. Homozygous TER-/- and heterozygous TER+/-, where telomerase RNA template had been deleted, were examined over 6 transplant generations (12wk.) to determine if the rate of reaching growth senescence was adversely affected by the absence of telomerase template. Individual implants from both homozygous and heterozygous TER null outgrowth showed growth senescence beginning at the second transplant generation. This result suggests that either mammary |