Loss of H3K27me3 imprinting in the Sfmbt2 miRNA cluster causes enlargement of cloned mouse placentas

Kimiko Inoue,Michiko Hirose,Narumi Ogonuki,Masashi Hada,Atsuo Ogura,Ayumi Hasegawa,Satoshi Kamimura,Yukiko Dodo,Arata Honda,Hiroki Inoue,Naomi Watanabe,Keiji Mochida,Kento Miura,Shogo Matoba

doi:10.1038/s41467-020-16044-8

Abstract

Somatic cell nuclear transfer (SCNT) in mammals is an inefficient process that is frequently associated with abnormal phenotypes, especially in placentas. Recent studies demonstrated that mouse SCNT placentas completely lack histone methylation (H3K27me3)-dependent imprinting, but how it affects placental development remains unclear. Here, we provide evidence that the loss of H3K27me3 imprinting is responsible for abnormal placental enlargement and low birth rates following SCNT, through upregulation of imprinted miRNAs. When we restore the normal paternal expression of H3K27me3-dependent imprinted genes (Sfmbt2, Gab1, and Slc38a4) in SCNT placentas by maternal knockout, the placentas remain enlarged. Intriguingly, correcting the expression of clustered miRNAs within the Sfmbt2 gene ameliorates the placental phenotype. Importantly, their target genes, which are confirmed to cause SCNT-like placental histology, recover their expression level. The birth rates increase about twofold. Thus, we identify loss of H3K27me3 imprinting as an epigenetic error that compromises embryo development following SCNT.

Highlights

Somatic cell nuclear transfer (SCNT) in mammals is an inefficient process that is frequently associated with abnormal phenotypes, especially in placentas
Experiments showed that at least two of these imprinted genes (Sfmbt[2] and Gab1) are essential for normal placental development, and their biallelic expression mediated by loss of imprinting (LOI) may cause SCNT-associated placental hyperplasia[17,18]
The SCNT placentas that carried the maternal KO for Sfmbt[2], Gab[1], and Slc38a4 weighed 0.280 ± 0.025, 0.322 ± 0.036, and 0.280 ± 0.010 g, respectively, which were significantly different from the weights of the in vitro fertilization (IVF)-derived placentas (Fig. 1a)

Summary

Introduction

Somatic cell nuclear transfer (SCNT) in mammals is an inefficient process that is frequently associated with abnormal phenotypes, especially in placentas. We provide evidence that the loss of H3K27me[3] imprinting is responsible for abnormal placental enlargement and low birth rates following SCNT, through upregulation of imprinted miRNAs. When we restore the normal paternal expression of H3K27me3-dependent imprinted genes (Sfmbt[2], Gab[1], and Slc38a4) in SCNT placentas by maternal knockout, the placentas remain enlarged. None of the recent technical breakthroughs, such as histone deacetylase treatment, correction of Xist expression, removal of repressive histone H3K9me[3], or their combination, can ameliorate SCNT-specific placental abnormalities, even though the birth rates are currently as high as 18.7% Experiments showed that at least two of these imprinted genes (Sfmbt[2] and Gab1) are essential for normal placental development, and their biallelic expression mediated by LOI may cause SCNT-associated placental hyperplasia[17,18]. Many miRNAs are known to be critically involved in the placental development via these processes[19], and some are under the control of imprinted genes[20]

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Conclusion