DNA methylation contributes to the tissue-specific expression of the rPL-Iv gene.
To understand the tissue-specific expression of the rat placental lactogen-I variant (rPL-Iv) gene, we investigated the methylation pattern of the 5'-flanking region of this gene in various rat tissues. We report that the 5'-flanking region of the rPL-Iv gene was hypomethylated in placenta that expressed the gene and hypermethylated in those tissues that did not express the gene. Moreover, the intron region of the rPL-Iv gene was hypomethylated in the placenta, but hypermethylated in the liver, kidney and pituitary. Although there are 5 CpG sites and the density of CpG dinucleotide is lower within 2 kb of the rPL-Iv 5'-flanking region, the methylated promoter reporter gene produced strong repression in the transcriptional activity of the gene. In addition, the 5'-flanking and intron regions of the rPL-Iv gene were hypomethylated on day 12 of gestation, and the methylation pattern in the placenta remained unchanged from mid-pregnancy until term. The entire genomic region of the rPL-Iv gene might be hypermethylated in tissues other than the placenta, within which its methylated status repress expression of the placenta-specific rPL-Iv gene. Interestingly, the methylation status of the intron region of the rPL-Iv in proliferating Rcho-1 cells was changed to the unmethylated status on day 8 and 12 of differentiation of Rcho-1 cells. These results demonstrate that demethylation in the rPL-Iv upstream region was induced at an early stage of placental development, and once the 5'-flanking region of the rPL-Iv had been demethylated, its status on the rPL-Iv genomic region was continued during pregnancy. Taken together, these results suggest that DNA methylation is responsible for the silencing of tissue-specific genes in non-expressing cells, while defined combinations of trophoblast factors dictate the expression of unmethylated rPL-Iv gene in placenta trophoblast cells.
Ko
Y-G
YG
Animal Genetic Resources Station, National Institute of Animal Science, RDA, Namwon, Republic of Korea.
Park
H J
HJ
Yun
J
J
Koh
P-O
PO
Min
W
W
Cho
K-W
KW
Won
C-K
CK
Seong
H-H
HH
Kim
G-S
GS
Cho
J-H
JH
D024506:5' Flanking Region; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D019175:DNA Methylation; D005260:Female; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D017930:Genes, Reporter; D007438:Introns; D009928:Organ Specificity; D010920:Placenta / Q000378:metabolism*; D010928:Placental Lactogen / Q000235:genetics / Q000378:metabolism*; D010929:Placentation; D011247:Pregnancy; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014327:Trophoblasts / Q000166:cytology / Q000378:metabolism
D012333:RNA, Messenger; C066927:placental lactogen I-variant; D010928:Placental Lactogen