ABSTRACT
The imprinted delta like 1 homolog (DLK1) - thyroxine deiodinase type III (DIO3) locus regulates development and growth. Its imprinting regulation involves two differentially methylated regions (DMRs), intergenic-DMR (IG-DMR) and maternally expressed gene 3-DMR (Meg3-DMR). In mice, a maternal deletion of the IG-DMR leads to LOI in the locus, proving that the IG-DMR is a cis-acting imprinting control region of the locus. However, the Meg3-DMR overlaps with the promoter, exon 1 and intron 1 of the Meg3 gene. Because deletion of the Meg3-DMR inactivates the Meg3 gene, their roles in imprinting regulation of Meg3-DMR mice is unknown. Therefore, we generated two mouse models: Meg3Δ(1-4) and Meg3Δ(2-4), respectively targeting exons 1-4 and exons 2-4 of the Meg3 gene. A maternal deletion of Meg3Δ(1-4) caused embryonic death and LOI in both embryos and placentas, but did not affect methylation status of the IG-DMR. In contrast, mice carrying a maternal deletion of Meg3Δ(2-4) were born normally and did not have LOI. These data indicate that it is the Meg3-DMR, not the Meg3 gene, which regulates imprinting of the Dlk1-Dio3 locus.
Subject(s)
DNA Methylation , Genetic Loci , Genomic Imprinting , RNA, Long Noncoding/genetics , Animals , Calcium-Binding Proteins/genetics , Embryonic Development/genetics , Exons/genetics , Female , Gene Expression Regulation, Developmental , Iodide Peroxidase/genetics , Male , Mice, Inbred BALB C , Mice, Inbred C57BL , Mice, Inbred DBA , Mice, Knockout , Mice, Transgenic , Placenta/metabolism , Pregnancy , Sequence DeletionABSTRACT
Human clinically non-functioning pituitary adenomas (NFAs) account for approximately 40% of diagnosed pituitary tumors. Epigenetic mutations in tumor suppressive genes play an important role in NFA development. Maternally expressed gene 3 (MEG3) is a long non-coding RNA (lncRNA) and we hypothesized that it is a candidate tumor suppressor whose epigenetic silencing is specifically linked to NFA development. In this study, we introduced MEG3 expression into PDFS cells, derived from a human NFA, using both inducible and constitutively active expression systems. MEG3 expression significantly suppressed xenograft tumor growth in vivo in nude mice. When induced in culture, MEG3 caused cell cycle arrest at the G1 phase. In addition, inactivation of p53 completely abolished tumor suppression by MEG3, indicating that MEG3 tumor suppression is mediated by p53. In conclusion, our data support the hypothesis that MEG3 is a lncRNA tumor suppressor in the pituitary and its inactivation contributes to NFA development.
