Cloned trophoblast cells constitute the main cause for the low success rate of nuclear transfer

It is well known that cloning by somatic nuclear transfer is generally associated with a very low success rate as judged by the birth rate of live pups. The underlying mechanism for this low success rate of cloning remains to be defined. A prevailing hypothesis in the field is that defects in the extraembryonic lineage are probably the major cause of the low success rate of reproductive cloning. However, this hypothesis has not yet been directly tested experimentally. For instance, one piece of the evidence supporting this hypothesis is that nuclear transfer embryonic stem (ntES) cells could be efficiently derived from cloned blastocysts and are equivalent to normal ES cells. However, recently two groups reported that trophoblast stem (TS) cells could also be easily generated from cloned blastocysts and these ntTS cells show a normal phenotype in vitro and in vivo. Thus, it is puzzling that both ntTS and ntES cells appear normal while the cloned embryos could have many developmental defects. Recently, a team of researchers, led by LI Jinsong, at the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, CAS, provided direct evidence that defects in trophoblast cell lineage underlie the low success rate of somatic nuclear transfer.

 

To directly test this hypothesis, LIN Jiangwei and his colleagues, under the supervision of Dr. Jinsong LI, used a modified tetraploid cell aggregation system. They isolated cloned inner cell mass (ICM) by immunosurgery and aggregated one cloned ICM with two fertilization-derived tetraploid embryos, and found that such aggregation dramatically improved the live birth rate of cloned pups. In a reciprocal experiment, they isolated ICM from normal fertilized embryos and aggregated it with two cloned tetraploid embryos, and found that embryonic development was dramatically impaired, and the resulting live birth rate is reduced to that of regular nuclear transfer procedure. These results provide the most direct evidence to date in support of the “trophoblast lineage defect” hypothesis.

 

This work entitled “Defects in trophoblast cell lineage account for the impaired in vivo development of cloned embryos generated by somatic nuclear transfer” was published in Cell Stem Cell on Apr 8th, 2011.

 

This study was supported by the grants from the Chinese Academy of Sciences, the Ministry of Science and Technology, National Natural Science Foundation of China and Shanghai Municipal Commission for Science and Technology.

 

AUTHOR CONTACT:

LI Jinsong

Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China

Phone:86-21-54921422; E-mail: jsli@sibs.ac.cn

 

 

(A) Schema of clonal mice generated after aggregation of one cloned ICM with two FD tetraploid embryos. (ZP, zona pellucida; BL, blastocyst)

(B) Cloned blastocysts exposed to guinea pig complement following incubated with rabbit anti-mouse serum. Only the outer trophectoderm cells are lysed.

(C) Isolated cloned ICMs.

(D) An aggregated blastocyst in a depression well.

(E) Aggregated embryos developed to blastocyst stage in vitro.

(F) Newborn clonal mice generated from aggregated embryos.

(G) Three-week-old mice derived from aggregated embryos.

(Image provided by Dr. LI Jinsong)