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Limited predictive value of blastomere angle of division in trophectoderm and inner cell mass specification.

ABSTRACT: The formation of trophectoderm (TE) and pluripotent inner cell mass (ICM) is one of the earliest events during mammalian embryogenesis. It is believed that the orientation of division of polarised blastomeres in the 8- and 16-cell stage embryo determines the fate of daughter cells, based on how asymmetrically distributed lineage determinants are segregated. To investigate the relationship between angle of division and subsequent fate in unperturbed embryos, we constructed cellular resolution digital representations of the development of mouse embryos from the morula to early blastocyst stage, based on 4D confocal image volumes. We find that at the 16-cell stage, very few inside cells are initially produced as a result of cell division, but that the number increases due to cell movement. Contrary to expectations, outside cells at the 16-cell stage represent a heterogeneous population, with some fated to contributing exclusively to the TE and others capable of contributing to both the TE and ICM. Our data support the view that factors other than the angle of division, such as the position of a blastomere, play a major role in the specification of TE and ICM.

SUBMITTER: Watanabe T

PROVIDER: S-EPMC4034423 | biostudies-literature | 2014 Jun

REPOSITORIES: biostudies-literature

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Limited predictive value of blastomere angle of division in trophectoderm and inner cell mass specification.

Watanabe Tomoko T Biggins John S JS Tannan Neeta Bala NB Srinivas Shankar S

Development (Cambridge, England) 20140601 11

The formation of trophectoderm (TE) and pluripotent inner cell mass (ICM) is one of the earliest events during mammalian embryogenesis. It is believed that the orientation of division of polarised blastomeres in the 8- and 16-cell stage embryo determines the fate of daughter cells, based on how asymmetrically distributed lineage determinants are segregated. To investigate the relationship between angle of division and subsequent fate in unperturbed embryos, we constructed cellular resolution dig ...[more]

PMID: 24866117

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Project description:Aneuploidy has been well documented in blastocyst embryos, but prior studies have been limited in scale and/or lack mechanistic data. We previously reported preclinical validation of microarray 24-chromosome preimplantation genetic screening (PGS) in a 24-hour protocol. The method diagnoses chromosome copy number, structural chromosome aberrations, parental source of aneuploidy, and distinguishes certain meiotic from mitotic errors. In this study our objective was to examine aneuploidy in human blastocysts and determine correspondence of karyotypes between trophectoderm (TE) and inner cell mass (ICM). We disaggregated 51 blastocysts from seventeen couples into ICM and one or two TE fractions. The average maternal age was 31. Next, we ran 24-chromosome microarray molecular karyotyping on all of the samples, and then performed a retrospective analysis of the data. The average per-chromosome confidence was 99.95%. Approximately 80% of blastocysts were euploid. The majority of aneuploid embryos were simple aneuploid, i.e., one or two whole-chromosome imbalances. Structural chromosome aberrations, which are common in cleavage stage embryos, occurred in only three blastocysts (5.8%). All TE biopsies derived from the same embryos were concordant. Forty-nine of fifty-one (96.1%) inner cell mass (ICM) samples were concordant with TE biopsies derived from the same embryos. Discordance between TE and ICM occurred only in the two embryos with structural chromosome aberration. We conclude that trophectoderm karyotype is an excellent predictor of inner cell mass karyotype. Discordance between TE and ICM occurred only in embryos with structural chromosome aberrations. We thawed all fractions at 22°C, and then added Arcturus PicoPure Lysis Buffer (Molecular Devices, Sunnyvale, CA) to each of the biopsies. The tubes were incubated at 56°C for one hour, and then heat inactivated at 95°C for 10 minutes. DNA from the lysed biospsies was amplified using a commercial kit (GE Healthcare, Waukesha, WI) for multiple displacement amplification (MDA). MDA reactions were incubated at 30°C for 2.5 hours and then heat-inactivated at 65°C for five minutes. The amplified samples were genotyped using Illumina (San Diego, CA, USA) Infinium II genotyping microarrays (CytoSNP-12 chips) using a modified 24-hour protocol, as described previously*. Previously, we developed a genotyping microarray molecular karyotyping technology that uses parental genetic data to increase accuracy and determine mechanism and source of aneuploidy*. The algorithm uses parental genotypes and the observed distribution of unprocessed single cell microarray channel intensities to diagnose whole-chromosome imbalances and structural chromosome aberrations*. Because parental genotypes are available, the algorithm readily identifies parental source of whole-chromosome imbalances and structural chromosome aberrations. Additionally, the algorithm uses parental information, high confidence disomic single cell measurements on children, and recombination probabilities (genome.ucsc.edu) to determine the phase of the parental chromosomes. The phased data is then used to determine whether certain trisomies and uniparental disomies were mitotic or meiotic in origin*. *Johnson DS, Gemelos G, Baner J, Ryan A, Cinnioglu C, Banjevic M, Ross R, Alper M, Barrett B, Frederick J, Potter D, Behr B, Rabinowitz M. (2010). Preclinical validation of a microarray method for full molecular karyotyping of blastomeres in a 24-hour protocol. Human Reproduction January 24 [Epub ahead of print].

Project description:We report the cloning and characterization of MOEP19, a novel 19 kDa RNA binding protein that marks a defined cortical cytoplasmic domain in oocytes and provides evidence of mammalian oocyte polarity and a form of pre-patterning that persists in zygotes and early embryos through the morula stage. MOEP19 contains a eukaryotic type KH-domain, typical of the KH-domain type I superfamily of RNA binding proteins, and both recombinant and native MOEP19 bind polynucleotides. By immunofluorescence, MOEP19 protein was first detected in primary follicles throughout the ooplasm. As oocytes expanded in size during oogenesis, MOEP19 increased in concentration. MOEP19 localized in the ovulated egg and early zygote as a symmetrical spherical cortical domain underlying the oolemma, deep to the zone of cortical granules. MOEP19 remained restricted to a cortical cytoplasmic crescent in blastomeres of 2-, 4- and 8-cell embryos. The MOEP19 domain was absent in regions underlying cell contacts. In morulae, the MOEP19 domain was found at the apex of outer, polarized blastomeres but was undetectable in blastomeres of the inner cell mass. In early blastocysts, MOEP19 localized in both mural and polar trophectoderm and a subset of embryos showed inner cell mass localization. MOEP19 concentration dramatically declined in late blastocysts. When blastomeres of 4- to 8-cell stages were dissociated, the polarized MOEP19 domain assumed a symmetrically spherical localization, while overnight culture of dissociated blastomeres resulted in formation of re-aggregated embryos in which polarity of the MOEP19 domain was re-established at the blastomere apices. MOEP19 showed no evidence of translation in ovulated eggs, indicating that MOEP19 is a maternal effect gene. The persistence during early development of the MOEP19 cortical oocyte domain as a cortical crescent in blastomers suggests an intrinsic pre-patterning in the egg that is related to the apical-basolateral polarity of the embryo. Although the RNAs bound to MOEP19 are presently unknown, we predict that the MOEP19 domain directs RNAs essential for normal embryonic development to specific locations in the oocyte and early embryo.

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Limited predictive value of blastomere angle of division in trophectoderm and inner cell mass specification.

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Limited predictive value of blastomere angle of division in trophectoderm and inner cell mass specification.

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