In 2012, a research group led by Jinsong Li and Guoliang Xu published a Cell paper reporting the creation of sperm-originated haploid embryonic stem cells (AG-haESCs) that can support full-term embryonic development upon injection into MII oocytes, leading to the generation of semi-cloned (SC) mice (Cell, 2012, 149, 605). One major drawback of this technology is the frequently observed aberrant development of AG-haESC-derived embryos and the very low birth rate of healthy SC mice (around 2% of total SC embryos). Recently, Jinsong Li’s group has shown that AG-haESCs carrying deletions in the DMRs (differentially DNA methylated regions) controlling two paternally repressed imprinted genes, H19 and Gtl2, designated as DKO-AG-haESCs, can efficiently support the generation of SC pups at a rate of 20% (Cell Stem Cell, 2015, 17, 221). Nevertheless, the feasibility of using oocyte-originated haESCs (PG-haESCs) for generation of SC mice via oocyte injection has not yet been demonstrated.
On Nov 17th, a team of researchers from Shanghai Institutes for Biological Sciences, led by LI Jinsong of the Institute of Biochemistry and Cell Biology, has reported that oocyte-originated haESCs carrying deletions in the DMRs controlling H19 and Gtl2, (referred to as DKO-PG-haESCs) can also efficiently support the generation of SC pups at a rate of 15.5%.
To test whether oocyte-originated haESCs can be used as a sperm replacement, Zhong Cuiqing, Xie Zhengfei, Yin Qi, and their colleagues generated 6 PG-haESC lines from parthenogenetic embryos derived by chemical activation of mature oocytes. By injection of these cells into mature oocytes, they found that PG-ahESCs failed to produce SC mice. They then attempted to distinguish the differences between PG-haESCs and AG-haESCs by performing RNA-seq analysis. Surprisingly, the results showed that PG-haESCs and AG-haESCs exhibited highly similar expression profiles based on all genes and all imprinted genes. Bisulfite-sequencing analysis of several typical paternal and maternal imprinted genes indicated that DMRs of paternal genes were free of methylation as expected. Interestingly, DMRs of two maternal imprinted genes, Snrpn and Peg1, which should largely retain methylation, quickly lost methylation imprint during the process of haESC derivation, thus exhibiting a similar imprinting pattern to that of AG-haESCs. Because they recently demonstrated that H19 and IG DMRs are two barriers to the high-efficiency generation of SC mice in AG-haESCs, they next tested whether removal of both DMRs would also induce high-efficiency generation of SC mice in PG-haESCs. A total of 44 DKO-PG-haESC lines were derived. Surprisingly, after injection of these cells into mature oocytes, the researchers found that over 15% of SC embryos developed to healthy pups.
This study shows that removal of H19 and IG DMRs can functionally convert the imprinting status of parthenogenetic haploid cells such that they can provide the equivalent of a paternally inherited genome. This study advances on the previous study that has already shown that the same deletion also dramatically enhances mouse generation from AG-haESCs via semicloning. In addition to the technical achievement this study is also of interest for researchers in genomic imprinting and epigenetic regulation.
This work entitled “Parthenogenetic haploid embryonic stem cells efficiently support mouse generation by oocyte injection” has been published online in Cell Research on Nov 17th.
This study was supported by the grants from the Chinese Academy of Sciences (the Strategic Priority Research Program), the Ministry of Science and Technology, National Natural Science Foundation of China and Shanghai Municipal Commission for Science and Technology.
AUTHOR CONTACT:
LI Jinsong, Principal Investigator
Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences,
Shanghai 200031, China
E-mail: jsli@sibcb.ac.cn
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