Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Genomic imprinting is characterized by the restrictive expression of a gene from one of the two inherited parental alleles. Many of these genes have been implicated in neonatal growth and mammalian reproduction. The two studies discussed in this dissertation focus on the tissue-specific contributions of Paternally Expressed Gene 3 (Peg3) on lactation and maternal care as well as the regulation of this gene through an antisense RNA (APeg3). In the first study, a conditional knockout allele has been developed to further characterize these known functions of Peg3 in a tissue-specific manner. The mutant line was first crossed with germline Cre, producing a progeny that displayed growth retardation phenotypes consistent with previous reports. The mutant line was then crossed individually with MMTV- and Nkx2.1-Cre lines to test Peg3’s roles in the mammary gland and hypothalamus, respectively. The results indicate that the milk letdown process was impaired in the nursing females with the Peg3 mutation in the mammary gland, but not in the hypothalamus. In contrast, one of the maternal-caring behaviors, nest-building, was interrupted in the females with the mutation in both MMTV- and Nkx2.1-driven lines. Overall, this is the first study to introduce a conditional knockout allele of Peg3 and to further dissect its contribution to mammalian reproduction in a tissue-specific manner. In the second study, we investigate the functions of APeg3, a gene that lies antisense of the Peg3 3’-untranslated region, with comparative genomics and cell line-based approaches. APeg3 transcript displays a high degree of sequence conservation among placental mammals, but without any obvious open reading frame, suggesting APeg3 may have been selected as a ncRNA gene during eutherian evolution. RNA secondary structure analyses also support a ncRNA function. The results from cell line-based transfection experiments demonstrate APeg3 has the potential to down-regulate the mRNA and protein levels of Peg3. Overall, these results suggest that APeg3 has evolved as a ncRNA gene and controls the function of its sense gene Peg3. When combined, the two studies in this dissertation offer new insight into the regulation and function of the imprinted transcription factor Peg3.



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Committee Chair

Kim, Joomyeong