Identification of non-parthenogenetic and euploid blastocysts from one pronuclear
zygote for embryo transfer by single nucleotide polymorphism (SNP) array
1Institute
Tan K1, Zhang SP1, Gong F2, Xiong B2, Lu CF2, Lu GX1, Lin G1
of Reproductive & Stem cell Engineering, Central South University;2Reproductive & Genetic Hospital of CITIC-XIANGYA. Changsha, 410078
STUDY QUESTION: One pronuclear (1PN) oocyte has high
developmental potential but is routinely excluded for embryo
transfer due to its possible parthenogenetic origin and increased
risk for aneuploidy. SNP array is now widely used for aneuploidy
screening. Could SNP array also help to distinguish
parthenogenetic origin of 1PN oocyte?
SUMMARY ANSWER: The blastocysts from parthenogenesis
(either with or without extrusion of second polar body) exhibit
low degree of heterozygosity (below 2%) when compared to
blastocysts from normal fertilized oocyte (range from 3.0%-9.35%)
after SNP analysis. This characteristic is efficient to select nonparthenogentic embryo for transfer and resulted in normal live
birth.
WHAT IS KNOWN ALREADY: Parthenogenetic stem cell (pSC)
lines have unique SNP signature (highly homozygous or pericentromeric homozygous) when compared to stem cell lines
derived from normal fertilized zygote (highly heterozygous). But
currently no data indicate whether this signature could be
translate into preimplantation genetic screen to distinguish
parthenogenetic origin for 1PN embryos.
STUDY DESIGN, SIZE AND DURATION: This was an experimental
study to compare the SNP signature and the degree of
heterozygosity of 4 pSC lines and 5 blastocysts from
parthenogenesis with 200 normal fertilized embryos, followed by
cases report.
PARTICIPANTS/MATERIALS, SETTING, METHODS: Small cell
samples from 4 pSC lines and 5 parthenogenetic blastocysts were
processed for whole genome amplification (WGA) and SNP array
analysis. The SNP signature and heterozygosity were analyzed by
CNAT 4.0 and compared to previously generated SNP data of 200
blastocysts. The established criteria were utilized for 8 1PN
blastocysts for selection.
MAIN RESULTS AND THE ROLE OF CHANCE: The typical homozygous distribution patterns were not observed in
pSC lines and parthenogenetic blastocysts under the detection of low density SNP array after WGA, but the
samples from parthenogenesis have reduced rate of heterozygosity, range from 0.5~1.5%, when compared to
3.0~9.35% of 200 normal fertilized blastocysts. Thereafter, 8 1PN-derived blastocysts were analyzed by SNP array
to determine the chromosomal constitution and the rate of heterozygosity for transfer. Two highly homozygous
and diploid blastocysts were identified and further validated by imprinted gene expression to be parthenogenesis,
which indicates that 1PN oocytes may originated from parthenogenetic activation with the extrusion of second
polar body and undergo diploidization in subsequent cleavages. To date, one blastocyst confirmed to be normal
were transferred and resulted in a healthy birth.
LIMITATIONS, REASONS FOR CAUTION: The clinical value for identification of 1PN-derived embryos resulted from
parthenogenesis by SNP array needs to be further validated by larger sample size.
WIDER IMPLICATIONS OF THE FINDINGS: Our result suggested a new application of SNP array for preimplantation
genetic screen.
STUDY FUNDING/COMPETING INTEREST(S): National Science foundation of China 81222007.The authors have no
competing interests to declare.
TRIAL REGISTRATION NUMBER: Not applicable.
KEYWORDS: one pronuclear zygote, single nucleotide polymorphism, Parthenogenesis, loss of heterozygosity,
preimplantation genetic screening
The CN state and the LOH result of 2 1PN blastocysts.
(a,c) CN states, (b,d) LOH probability. The left blastocyst originate from normal fertilization but has
lost of chr11(Arrow). Although the right blastocyst has normal CN state, the clear of the hetersplashes indicate of the homozygosity.