Browsing by Author "McCoski, Sarah R."

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    Exposure to maternal obesity alters gene expression in the preimplantation ovine conceptus
    McCoski, Sarah R.; Vailes, McCauley T.; Owens, Connor E.; Cockrum, Rebecca R.; Ealy, Alan D. (2018-10-11)
    Background Embryonic and fetal exposure to maternal obesity causes several maladaptive morphological and epigenetic changes in exposed offspring. The timing of these events is unclear, but changes can be observed even after a short exposure to maternal obesity around the time of conception. The hypothesis of this work is that maternal obesity influences the ovine preimplantation conceptus early in pregnancy, and this exposure will affect gene expression in embryonic and extraembryonic tissues. Results Obese and lean ewe groups were established by overfeeding or normal feeding, respectively. Ewes were then bred to genetically similar rams. Conceptuses were collected at day 14 of gestation. Morphological assessments were made, conceptuses were sexed by genomic PCR analysis, and samples underwent RNA-sequencing analysis. While no obvious morphological differences existed between conceptuses, differentially expressed genes (≥ 2-fold; ≥ 0.2 RPKM; ≤ 0.05 FDR) were detected based on maternal obesity exposure (n = 21). Also, differential effects of maternal obesity were noted on each conceptus sex (n = 347). A large portion of differentially expressed genes were associated with embryogenesis and placental development. Conclusions Findings reveal that the preimplantation ovine conceptus genome responds to maternal obesity in a sex-dependent manner. The sexual dimorphism in response to the maternal environment coupled with changes in placental gene expression may explain aberrations in phenotype observed in offspring derived from obese females.
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    Manipulating Embryonic Development and Endometrial Function in Ruminants
    McCoski, Sarah R. (Virginia Tech, 2018-04-13)
    Early embryogenesis is highlighted by the emergence of several embryonic end extraembryonic lineages. One such lineage is the primitive endoderm, which will eventually give rise to the yolk sac. Once believed to be a vestigial structure, the yolk sac is now believed to play a more prominent role in embryogenesis as it provides nutrients to the preimplantation embryo. The endoderm may also interact with the trophectoderm lineage, as they develop in close contact within the embryo. The efficiency of developing primitive endoderm in vitro is considerably low, leading to a lapse in our understanding of its development and function in cattle and other ruminants. The goal of the first study was to establish a protocol for developing primitive endoderm cultures and characterizing these cells. Bovine embryos were produced in vitro, and primitive endoderm outgrowths were created with fibroblast growth factor 2 (FGF2) supplementation. These cells can be produced in culture with 80.3 5.6% efficiency. Furthermore, outgrowths can be maintained in culture for 6-8 weeks before reaching a quiescent state. A true bovine primitive endoderm cell line does not currently exist, however, these cells hold potential in improving the current understanding of early lineage specification in cattle. A second set of studies was performed to examine the effects of maternal obesity on the preimplantation conceptus and endometrium. Exposure to maternal obesity in utero affects offspring development at the postnatal, adolescent, and adult stages of development; however, its impacts on early embryogenesis are not well studied. This work utilized an obese ewe model. Once the obese phenotype was established, ewes were bred. Conceptus and endometrial tissue were collected at D 14 of pregnancy, and samples were processed for RNA-sequencing analysis. There were no differences in pregnancy rate, ovulation rate, or pregnancies/ovulation between obese and lean animals. At an RPKM threshold of 0.2, fold-change 2, and FDR 0.05, 669 and 21 differentially expressed genes (DEGs) were identified between obese- and lean-derived endometrial samples and conceptus samples, respectively. Likewise, 137 DEGs were identified between male and female conceptuses. The PANTHER GO-Slim Biological Process system identified several biological processes affected by obesity in both the endometrium and conceptus tissue. GO terms do not currently exist for "placenta" and "trophoblast", so a literature search was conducted to identify DEGs involved in implantation and placentation. This revealed 125 placentation DEGs in the endometrium, and 4 DEGs in conceptuses between obese and lean groups. A follow-up study was conducted to examine the abundance of transcripts with regulatory roles in embryogenesis. Conceptuses exhibited differential expression of DNA methyltransferase 1 (DNMT1) based on obesity exposure, fibroblast growth factor receptor 2 (FGFR2) in a sex*obesity interaction, and peroxisome proliferator-activated receptor gamma (PPARG) and prostaglandin-endoperoxide synthase 2 (PTGS2) in a sex-specific manner. Collectively these results identify the preimplantation period as a susceptible time to maternal obesity in both conceptus and endometrial tissue. Together, these studies aim to provide a better understanding of the events controlling early embryogenesis, and insight into the implication of insults during this time. These findings will prove to be beneficial in establishing the link between maternal health, endometrial function, and subsequent offspring outcomes, with the hope of promoting a more viable embryo and thus healthier offspring.