1a.Objectives (from AD-416)
Develop strategies that promote cell proliferation and replacement in the bovine mammary gland, in order to increase lactational productivity and efficiency.
1b.Approach (from AD-416)
We propose to accomplish the research objective by utilizing and extending current knowledge of mammary stem cell biology. Our specific aims are to manipulate mammary stem cell activity to enhance the growth of mammary epithelium and promote the replacement of senescent cells.
The project was initiated in February 2008. Two experiments were completed and one is in progress. An experiment designed to confirm and extend our previous finding that xanthosine infusion into the mammary gland of prepubertal Holstein heifers increased the number of mammary stem cells was completed. Infusion of the nucleosides, xanthosine or inosine, did not significantly increase the proportion of putative mammary stem cells at the time tested. A second experiment was initiated in 2008 to test the hypothesis that stimulated expansion of the mammary stem cell population via xanthosine treatment of prepubertal heifers will increase the number of mammary secretory cells and increase milk yield. Holstein heifers were reared at moderate or accelerated rates of gain prior to puberty and their mammary glands were treated with xanthosine. Milk production is currently being monitored. These two experiments address Specific Aim #1 of the grant. In addition to the stated objectives of the grant, a third experiment was performed to characterize gene expression in putative mammary stem cells and control cells from different regions of the mammary gland. The data provided evidence that bovine mammary stem cells are located in the basal layer of the mammary epithelium and more differentiated progenitor cells are located in suprabasal layers of the epithelium. Several potential markers for mammary stem cells have been identified and their utility is being evaluated. The approach used in this study is the first to isolate putative stem cells by a microscopic dissection procedure (laser microdissection) that permits isolation of cells from known positions within the mammary gland. Study of mammary stem cells and progenitor cells will provide insights into means to enhance production efficiency by altering their activity. Validation of markers for these cells will facilitate further studies. Monitoring activities associated with this project included annual updates presented to NIFA-AFRI-NRI NPS at the ADSA/ASAS National Meeting and submission to NIFA-NRI of an annual progress report.