ABSTRACT
Samples .......................................................................................... 82 4.4.2 Comparison of DNA Methylation Profiles Between
Placentas from Diandric and Digynic Triploidies .......................... 84 4.4.3 Validation of DNA Methylation Patterns of Identified
Putative Imprinted DMRs .............................................................. 89 4.4.4 Confirmation of Parent-of-Origin Allelic Expression
for the Identified Putative Imprinted Genes .................................. 93 4.4.5 Tissue-Specific and Gestational Age-Specific Methylation of Imprinted DMRs ................................................... 96
4.5 Conclusion ................................................................................... 104 Keywords .............................................................................................. 104 Acknowledgment .................................................................................. 105 Competing Interests .............................................................................. 105 Authors’ Contributions .......................................................................... 105 References ............................................................................................. 105 Credits ................................................................................................... 109
4.1 INTRODUCTION
Genomic imprinting is a phenomenon in which one of the two alleles of a gene is expressed in a parent-of-origin manner [1]. Imprinted genes are thought to be particularly important to placental and fetal growth and development and may help regulate growth in response to maternal and fetal signals in utero [2]. To date, around 60 imprinted genes have been identified in humans (https://www.geneimprint.com website), largely after first being identified in mice or through characterization of specific imprinting disorders such as Prader-Willi syndrome and Angelman syndrome or Beckwith-Wiedemann syndrome. However, many genes are imprinted in mice but are not known to be in humans, for example, Impact [3]. Furthermore, many genes are imprinted only in specific tissues, for example, Ube3a, which is maternally expressed in the brain but biparentally expressed in other tissues [4], or may be polymorphically imprinted, for example, IGF2R [5]. These issues complicate the discovery and characterization of imprinted genes in humans.
