Most mammary development is postnatal. Mammary growth that occurs before puberty is diminutive in amount but consequential for future milk production, especially in dairy heifers. With advanced knowledge on fundamental aspects that govern prepubertal mammary development, scientists and farmers alike can ensure that heifers perform their best once they become cows. The Hippo pathway has been identified as an evolutionarily conserved pathway that regulates organ size in many animal species; it might contribute to mammary growth in dairy heifers. This pathway is mediated by yes-associated protein (YAP) and through downstream gene transcription activation, results in cell proliferation. Because YAP has never been identified in bovine mammary tissue, questions examined in this body of work mainly focused on the abundance and localization of YAP in mammary tissue of prepubertal heifers. The first trial investigated effects of in vivo estradiol administration on YAP abundance and localization in prepubertal bovine mammary epithelial and myoepithelial cells. While YAP was present in nuclei and cytoplasm of both cell types, it was also discovered that estrogen did not influence YAP abundance or location. The second research trial focused on determining the effects of in vivo estradiol blockade on YAP abundance and localization in prepubertal bovine mammary epithelial and myoepithelial cells. Similar to the first experiment, results indicate that YAP abundance and localization was not influenced by estrogen blockade. Despite not being responsive to in vivo estradiol administration (experiment 1) or estradiol blockade (experiment 2) under the conditions of our experiments, YAP was present in nearly all mammary epithelial cells and myoepithelial cells of the 21 total prepubertal heifers examined. Its presence hints at an underlying biological function but that function was not ascertained here. It will be up to the next researcher to deduce what YAP contributes to mammary growth in prepubertal dairy heifers. / MSLFS / Replacement dairy heifers are the future of any dairy herd and the successful growth and development of their mammary glands, during early stages of life, can have long term impacts on future milk production. Today, many aspects of mammary growth remain unclear. The studies described herein investigated the effects of the hormone estradiol on a biologically conserved pathway, the Hippo Pathway, which is implicated in organ size across many animal species. The first study investigated the effects of administering estradiol to heifers on Hippo pathway activity, which was thought to be implicated with mammary growth. It was discovered that estradiol administration did not affect pathway activity and therefore may not be the hormone implicated in causing growth and development through Hippo pathway signaling. The second experiment investigated the effect of blocking estradiol’s mammogenic actions on the mammary gland and whether the Hippo pathway was impacted. Results indicated that estradiol blockade did not affect pathway activity. It is possible that another hormone may be linked to mammary growth and development through Hippo pathway signaling. Overall this work contributes to the understanding of biological mechanisms involved in mammary growth and development in dairy heifers.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/96240 |
| Date | 09 July 2018 |
| Creators | Granger, Paulnisha Davida |
| Contributors | Dairy Science, Daniels, Kristy M., Corl, Benjamin A., Akers, Robert Michael |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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