Animal Sciences electronic theses and dissertations (MU)
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The items in this collection are the theses and dissertations written by students of the Division of Animal Sciences. Some items may be viewed only by members of the University of Missouri System and/or University of Missouri-Columbia. Click on one of the browse buttons above for a complete listing of the works.
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Item CRISPR/Cas9-mediated gene targeting for robust transgene expression in chickens(University of Missouri--Columbia, 2025) Klein, Rachel; Lee, Hong JoThis thesis explores the development and implementation of a targeted gene integration strategy using CRISPR/Cas9 to achieve robust and consistent transgene expression in chickens. Stable transgene expression remains a critical challenge in avian genetic engineering due to the limitations of random integration approaches, such as piggyBac transposition and viral transduction, which are prone to epigenetic silencing and positional effects. To address this, we investigated the use of two ubiquitously expressed housekeeping genes—GAPDH and ACTB—as potential genomic safe harbor loci for precise transgene insertion in chicken fibroblast (DF-1) cells and primordial germ cells (PGCs). Guide RNAs were designed to target the 3′ coding and intronic regions of these genes, enabling Cas9-mediated double-strand breaks followed by non-homologous end joining (NHEJ)-driven knock-in of reporter constructs. Editing efficiency and indel formation were evaluated via T7E1 assays and Sanger sequencing, with GAPDH demonstrating superior integration rates and consistent GFP expression. Knock-in cell lines were further validated by functional Cas9 activity, and successful targeted integration in PGCs suggests potential for germline transmission. In addition to presenting experimental results, this thesis includes a comprehensive literature review on the evolution of genome editing technologies in chickens, challenges in transgene silencing, and the rationale for targeting housekeeping genes. Collectively, this work establishes a foundation for the development of reliable, site-specific transgene expression systems in poultry, with implications for agricultural biotechnology, pharmaceutical protein production, and basic research.Item Progesterone receptor in uterine glands is required for pregnancy establishment in mice(University of Missouri--Columbia, 2025) Bayammagari, Greeshma Sai; Kelleher, Andrew M.||Spencer, Thomas E.Pregnancy establishment relies on complex interactions between the maternal environment and the early embryo, which are essential for maintaining pregnancy to term. Disruptions in these processes can lead to pregnancy loss, a major concern in human reproduction. Communication between the endometrium and the embryo is primarily regulated by estrogen and progesterone (P4) signaling. In addition, uterine glands secrete histotrophs and bioactive factors under the control of estrogen, progesterone, and the transcription factor FOXA2, all of which are critical for embryo implantation and decidualization. Studies over the past several decades have demonstrated that P4, acting through the progesterone receptor (PGR), plays a vital role in regulating the normal physiology of the female reproductive system. In the uterine endometrium, P4-PGR signaling induces downstream target genes and initiates epithelial-stromal crosstalk, facilitating the development of a receptive endometrium for blastocyst implantation. P4-PGR also induces critical genes involved in stromal cell decidualization to support the implanted embryo. However, a significant gap in understanding remains as the role of PGR signaling in the uterine glands during pregnancy continues to be a "black box" in reproductive biology. Thus, aims of this thesis were to: (1) decipher the impact of loss of PGR in the glandular epithelium (GE); and (2) determine the role of PGR in regulating endometrial receptivity. These objectives were addressed by using the Prss29-Cre mouse model to conditionally ablate PGR in the adult uterine glands. The results of this study demonstrated that: (1) PGR loss in glands of the uterus impact fertility; (2) embryo implantation is defective in Prss29Cre/CrePgrflox/flox (Pgr gecKO) mice; (3) PGR in GE influences the uterine transcriptome; (4) intraperitoneal LIF rescues embryo implantation and pregnancy in Pgr gecKO mice. Collectively, these findings provide strong evidence that PGR signaling in the uterine glands is essential for endometrial receptivity and embryo implantation, primarily through the regulation of nidatory Lif expression, a pivotal factor for successful implantation.Item Local regulation of milk secretion : mechanisms altering milk production in the dairy cow(University of Missouri--Columbia, 2025) Shangraw, Erin M.; McFadden, Thomas B.Milk removal is a well-recognized factor regulating lactation in most mammals, including the dairy cow. Increasing the number of milkings per day increases milk yields, whereas reducing milkings to once a day reduces milk yields. This dissertation investigated multiple mechanisms associated with both increased and reduced milking frequency to better understand how milk removal regulates lactation. The first two experiments focused on mechanisms related to increased milk secretion. The first experiment examined the effects of increased milking frequency during secretory activation. Ipsilateral mammary glands milked every 6 h postpartum produced more milk than contralateral glands milked every 12 h but this effect was not controlled by transcriptional regulation of the lactose synthesis pathway. Changes in mammary gene expression were instead controlled by time after parturition. The second experiment further investigated whether milk production increases because the mammary gland is exposed to lower concentrations of a milk-derived feedback inhibitor of lactation. Isosmotic sucrose solution infused into mammary glands increased milk secretion rates by 23 percent compared to water-infused or untreated mammary glands. However, changes in milk composition appeared to be driven by infusion of the sucrose solution rather than by dilution of feedback inhibitors. In contrast, the remaining chapters focused on intramammary pressure (IMP) as a primary factor regulating milk production when milk secretion is reduced. Mammary glands were inflated with air to assess IMP independent of milk-derived inhibitors. Air inflation induced subclinical mastitis, yet a high initial IMP (40 mm Hg) was required to reduce milk yields. Leakage of lactose across the blood-milk barrier (BMB) and direct effects on mammary secretory epithelial cells, but not changes in total mammary blood flow or mammary uptake of nutrients, contributed to the changes in milk yield and composition. Collectively, these studies identified potential and critical roles of the BMB when implementing increased and reduced milking frequency, respectively, though lactational responses were controlled by different mechanisms.Item Morphology of the female reproductive organs of sea otters (Enhydra lutris L.)(University of Missouri--Columbia, 1965) Sinha, Akhouri Achyutanand; Conaway, Clinton H."The purpose of this study was to investigate the gross and microscopic anatomy of the reproductive organs of the female sea otter (Enhydra lutris L.) and relate them to the reproductive cycle. Emphasis has been given to ovarian histology. Although the value of the sea otter has been known to fur hunters for over two centuries, very little is known about this animal. Barabash-Nikiforov (1947) noted that sea otters have lentioulate shaped ovaries. Pearson (1952) studied a single pregnant sea otter and noted that the ovaries have irregular surface and subsurface fissures, besides the small Graafian follicles and a corpus luteun. The uterus was bipartite. Lensink (1962) briefly described reproduction in sea otters, based upon field observations."--Introduction.Item The influence of the bursa on Fabricius, spleen and thymus on the course of Plasmodium lophurae infections in chickens(University of Missouri--Columbia, 1968) Longenecker, Bryan M.; Breitenbach, Robert P."Splenectomized chicks were severely deficient in their ability to combat an infection or reinfection with Plasmodium lophurae. Infection of splenectomized chicks usually caused death while sham-operated controls recovered. Birds splenectomized on the 5th day of an infection, when parasitemias had dropped to a low level, showed an immediate and usually fatal recrudescence. Chicks which were hormonally or surgically bursectomized on the 1st day after hatching demonstrated higher parasitemias then their sham-operated controls. However, parasitemias of birds bursectomized at 18 days of age did not differ from their control group. Thymectomy had no significant effect on the resultant parasitemias. It is thus concluded that the spleen is of primary importance in the development of immunity to this strain of Plasmodium lophurae. The bursa is of secondary importance and contributes something to the development of the immune mechanism before 18 days of age. Bursaless birds demonstrated higher initial gamma-1, beta-1, beta-2, alpha-1 and alpha-2 values than sham operated control groups. These high mean values in the bursaless birds decreased during the malarial infection to a low level on about day four of the infection. The infected control group showed no decrease; in fact, an increase was often observed in this group. On the other hand, low albumin and gamma-2 titers were obtained in the bursaless groups. These altered protein changes were most apparent in the hormonally bursectomized groups, and especially in the thymectomized-hormonally bursectomized group. The plasma protein values of the thymectomized group were similiar to those of the sham operated infected birds. The major plasma protein response to the injected malarial parasites in the sham operated infected group was an increase in gamma-1 globulin. An early peak was noted on day two of the infection as well as an increase from day ten to fifteen. This response did not appear in any of the bursaless groups or in the non-infected group. The possible significance of a relationship between the high alpha and low gamma-2 globulin levels of bursaless birds is discussed. Antimalarial antibodies were detected in the plasma of normal birds which recovered from infection with P. lophurae. These antibodies were detected as specific antiparasitic agglutinins in normal birds. These agglutinins were not detected in the plasma of bursaless birds which had been infected and reinfected. The administration of hyperimmune plasma to bursaless and normal birds resulted in highly depressed parasitemias. Interestingly, infected bursaless birds which were given normal plasma from mature cockerels demonstrated parasitemias which were depressed to the level of parasitemias of intact infected birds. This indicated that bursaless birds lack a natural antibody which birds normally develop. Splenectomized-infected birds which received hyperimmune plasma eventually recovered from an infection. Splenectomized—controls, however, succumbed to the infection. The surviving splenectomized birds subsequently demonstrated an ability to control the parasites, as attempts to reinfect these birds failed. It was postulated that in the absence of the spleen and during intense antigenic stimulation, other lymphoid centers develop which are able to participate in normal anamnestic reactions."--Summary.