Milk yield is dependent on both the number and secretory activity of mammary alveolar cells. The number of cells is controlled by their proliferation and death. In the first study, the effect of eukaryotic translation initiation factor 4E (eIF-4E) on the growth of a bovine mammary epithelial cell line, MAC-T, was investigated. Compared to the parental controls, overexpression of mouse wild-type (wt) eIF-4E in 11A, a subclone of MAC-T cells, increased the growth rate and saturation density (number of cells per well at confluence), whereas overexpression of a mutant eIF-4E (W56A) decreased growth rates and saturation densities. Furthermore, cyclin D1 expression among the 4E-overexpressing and parental cells was compared. Compared to the controls, the amounts of cyclin D1 mRNA and proteins were higher in the cells overexpressing wt eIF-4E but lower in the cells with mutant eIF-4E expression. Our results suggest that altered expression of eIF-4E leads to changes in cyclin D1 expression, which consequently modulate the growth properties of MAC-T 11A cells. / Because of its unknown sequence, bovine eIF-4E cDNA was then cloned in the second study. Its coding region consists of 651 nucleotides which encode 217 amino acids (AAs). Bovine eIF-4E cDNA shares 94%, 89% and 94% homology with those of human, mouse and rabbit, respectively. Differences in protein sequences between bovine and human, mouse and rabbit eIF-4E are 2, 4, and 3 AAs, respectively. Furthermore, expression of eIF-4E in bovine mammary tissues at different physiological periods was investigated by Northern blot analysis, using the cloned cDNA as the probe. eIF-4E was not detectable at prepubertal period and expressed at a very low level at the third estrous cycle. In the lactating mammary tissues, eIF-4E was highly expressed. Differential expression of eIF-4E in bovine mammary gland at distinct physiological stages indicates its potential involvement in mammary development. / Cell proliferation and apoptosis were also studied in the Escherichia coli (E. coli)-infected bovine mammary glands in the last study. Both proliferation and apoptosis increased in the mastitic tissue, as determined by immunohistological assays. Compared to the controls, expression of the pro-apoptotic proteins, Bax and interleukin-1beta converting enzyme (ICE), increased at 24 h and 72 h post-infection, whereas expression of the anti-apoptotic protein Bcl-2 decreased only at 24 h post-infusion. Induction of extracellular matrix (ECM)-degrading enzymes, including matrix metal loproteinase-9 (MMP-9), stromelysin-1 (SL-1) and urokinase-type plasminogen activator (uPA), was also observed in the mastitic tissue. Therefore, apoptosis may be mediated through pathways involving the actions of Bcl-2, Bax and ICE, and may partially be accounted by ECM breakdown. / Taken together, our study has demonstrated the effect of eIF-4E on bovine mammary cell proliferation. In addition, its involvement in bovine mammary gland development has been suggested. Finally, increased mammary cell apoptosis and proliferation during E. coli-induced mastitis has been revealed, in association with altered expression of apoptosis-related genes and ECM-degrading enzymes. Understanding the regulation of mammary cell proliferation and death may eventually lead to improvement of milk production.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.37766 |
| Date | January 2001 |
| Creators | Long, Ezhou. |
| Contributors | Zhao, Xin (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Animal Science.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001808814, proquestno: NQ70082, Theses scanned by UMI/ProQuest. |
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