The Sall3 locus is an epigenetic hotspot of aberrant DNA methylation associated with placentomegaly of cloned mice

Abstract

DNA methylation controls various developmental processes by silencing, switching and stabilizing genes as well as remodeling chromatin. Among various symptoms in cloned animals, placental hypertrophy is commonly observed. We identified the Spalt-like gene3 ( Sall3 ) locus as a hypermethylated region in the placental genome of cloned mice. The Sall3 locus has a CpG island containing a tissue-dependent differentially methylated region (T-DMR) specific to the trophoblast cell lineage. The T-DMR sequence is also conserved in the human genome at the SALL3 locus of chromosome 18q23, which has been suggested to be involved in the 18q deletion syndrome. Intriguingly, larger placentas were more heavily methylated at the Sall3 locus in cloned mice. This epigenetic error was found in all cloned mice examined regardless of sex, mouse strain and the type of donor cells. In contrast, the placentas of in vitro fertilized (IVF) and intracytoplasmic sperm injected (ICSI) mice did not show such hypermethylation, suggesting that aberrant hypermethylation at the Sall3 locus is associated with abnormal placental development caused by nuclear transfer of somatic cells. We concluded that the Sall3 locus is the area with frequent epigenetic errors in cloned mice. These data suggest that there exists at least genetic locus that is highly susceptible to epigenetic error caused by nuclear transfer.

Blastocyst elongation, trophoblastic differentiation, and embryonic pattern formation

“…Epigenetic regulation of transcription factors by DNA methylation and histone acetylation have recently been found to regulate imprinted genes, in mouse and humans, and some trophoblast related genes may also be involved in epigenetic regulation: reports suggest NANOG, POU5F1, sal-like protein 3 (SALL3), and serpin inhibitor clade B member 5 (SERPINB5) are involved in epigenetic regulation that influence trophoblast cell proliferation, differentiation, and invasion (Ohgane et al 2004, Dokras et al 2006, Ferguson-Smith et al 2006, Tomikawa et al 2006. However, in the bovine embryo, there is again only limited evidence regarding epigenetic modification of trophoblastspecific genes (Kremenskoy et al 2006a(Kremenskoy et al , 2006b.…”

Review Paper: A Review of the Pathology of Abnormal Placentae of Somatic Cell Nuclear Transfer Clone Pregnancies in Cattle, Sheep, and Mice

“…28 The underlying cases of SCNT placental pathology are uncertain but usually appear to involve inefficient epigenetic reprogramming of the somatic cell genome by the oocyte cytoplasm. 53,73 Such reprogramming is necessary for a somatic cell nucleus to reacquire totipotency and become functionally equivalent to that of a zygote, which requires reestablishment of the coordinated pattern of gene expression necessary for embryonic and fetal development. 99 Acquisition of this state by a somatic cell nucleus and subsequent development Vet Pathol 45:6, 2008 of the fetus and placenta require global epigenetic changes, including erasure of the somatic pattern of DNA methylation and its progressive reestablishment throughout development.…”

“…73 The Sal-like 3 locus has a CpG island containing a tissue-dependent differentially methylated region specific to the trophoblast cell lineage. 93 This locus represents the area in which frequent epigenetic errors occur that are believed to be responsible for alterations of placental gene expression resulting in placental overgrowth in SCNT mice.…”

Epigenetic characterization of the PBEF and TIMP-2 genes in the developing placentae of normal mice

“…Previous studies have shown that epigenetic reprogramming defects often occur in cloned embryos, as reflected by aberrant gene expression (6) and abnormal DNA methylation patterns (4-6). Furthermore, tissue-dependent differentially methylated regions (T-DMRs) within Spalt-like gene 3 (Sall3) locus at the telomeric E3 subregion of mouse chromosome 18 was reported to be an epigenetic hotspot for aberrant DNA methylation associated with placentomegaly among cloned mice (25). Together, these previous findings indicate that aberrant gene expression in placentae may be due in part to DNA methylation abnormalities.…”