Talk:Week 1

Dynamic changes in gene expression during human early embryo development: from fundamental aspects to clinical applications

Assou S, Boumela I, Haouzi D, Anahory T, Dechaud H, De Vos J, Hamamah S. Hum Reprod Update. 2010 Aug 17. [Epub ahead of print] PMID: 20716614 http://www.ncbi.nlm.nih.gov/pubmed/20716614

The first week of human embryonic development comprises a series of events that change highly specialized germ cells into undifferentiated human embryonic stem cells (hESCs) that display an extraordinarily broad developmental potential. The understanding of these events is crucial to the improvement of the success rate of in vitro fertilization. With the emergence of new technologies such as Omics, the gene expression profiling of human oocytes, embryos and hESCs has been performed and generated a flood of data related to the molecular signature of early embryo development. METHODS In order to understand the complex genetic network that controls the first week of embryo development, we performed a systematic review and study of this issue. We performed a literature search using PubMed and EMBASE to identify all relevant studies published as original articles in English up to March 2010 (n = 165). We also analyzed the transcriptome of human oocytes, embryos and hESCs. RESULTS Distinct sets of genes were revealed by comparing the expression profiles of oocytes, embryos on Day 3 and hESCs, which are associated with totipotency, pluripotency and reprogramming properties, respectively. Known components of two signaling pathways (WNT and transforming growth factor-beta) were linked to oocyte maturation and early embryonic development. CONCLUSIONS Omics analysis provides tools for understanding the molecular mechanisms and signaling pathways controlling early embryonic development. Furthermore, we discuss the clinical relevance of using a non-invasive molecular approach to embryo selection for the single-embryo transfer program.

Life-giving caspases: revealing new roles during mouse embryo preimplantation development

Int J Dev Biol. 2010;54(5):857-65.

Busso D, Dominguez C, Perez-Acle T, Moreno RD.

Department of Physiology, Facultad de Ciencias Biologicas, Pontificia Universidad Catolica de Chile, Santiago, Chile. dbusso@bio.puc.cl Abstract Caspases, cystein proteases traditionally related to programmed cell death, have recently been found to be involved in vital processes such as cell proliferation, adhesion and differentiation. Although caspases are expressed in mouse embryos before the blastocyst stage, their role is unclear, since apoptosis does not occur significantly before implantation. In this work, we have used mouse preimplantation development as a model to evaluate the existence of non-lethal caspase activities. The use of specific caspase inhibitors during in vitro embryo culture showed that caspase 8 activity, but not caspase 2 or 9, was relevant for development. The inhibition of caspase 8 affected the compaction of morulae and the progression to the blastocyst stage. In agreement with these results, caspase 8 was expressed in mouse embryos, as shown by indirect immunofluorescence and RT-PCR. An in silico approach was used to find putative caspase targets expressed in mouse preimplantation embryos. Large-scale management of sequence data from mouse embryos was used to predict caspase substrates by tools matrix-based on known cleavage sites. A total of 510 potential caspase targets expressed in mouse embryos were identified by this procedure. The functional characterization of these proteins by Gene Onthology associations showed that many of these putative caspase targets were previously related to non-apoptotic functions and only 63 had been previously reported to be actually cleaved by caspases. Interestingly, eleven knockout mice models for caspase substrates identified in our work, i.e. catenin alpha and beta, geminin, pescadillo, calpain-2, have preimplantation lethal phenotypes. This work supports the involvement of caspases in vital functions during mouse preimplantation development and proposes a model in which the regulated cleavage of caspase substrates could account for this role.

PMID: 20336607 http://www.ncbi.nlm.nih.gov/pubmed/20336607

http://www.intjdevbiol.com/paper.php?doi=10.1387/ijdb.092921db

Human embryonic stem cell lines derived from single blastomeres of two 4-cell stage embryos

Geens M, Mateizel I, Sermon K, De Rycke M, Spits C, Cauffman G, Devroey P, Tournaye H, Liebaers I, Van de Velde H. Hum Reprod. 2009 Nov;24(11):2709-17. Epub 2009 Jul 24.

BACKGROUND: Recently, we demonstrated that single blastomeres of a 4-cell stage human embryo are able to develop into blastocysts with inner cell mass and trophectoderm. To further investigate potency at the 4-cell stage, we aimed to derive pluripotent human embryonic stem cells (hESC) from single blastomeres.

METHODS: Four 4-cell stage embryos were split on Day 2 of preimplantation development and the 16 blastomeres were individually cultured in sequential medium. On Day 3 or 4, the blastomere-derived embryos were plated on inactivated mouse embryonic fibroblasts (MEFs).

RESULTS: Ten out of sixteen blastomere-derived morulae attached to the MEFs, and two produced an outgrowth. They were mechanically passaged onto fresh MEFs as described for blastocyst ICM-derived hESC, and shown to express the typical stemness markers by immunocytochemistry and/or RT-PCR. In vivo pluripotency was confirmed by the presence of all three germ layers in the teratoma obtained after injection in immunodeficient mice. The first hESC line displays a mosaic normal/abnormal 46, XX, dup(7)(q33qter), del(18)(q23qter) karyotype. The second hESC line displays a normal 46, XY karyotype.

CONCLUSION: We report the successful derivation and characterization of two hESC lines from single blastomeres of four split 4-cell stage human embryos. These two hESC lines were derived from distinct embryos, proving that at least one of the 4-cell stage blastomeres is pluripotent.

PMID: 19633307 http://www.ncbi.nlm.nih.gov/pubmed/19633307

http://humrep.oxfordjournals.org/content/24/11/2709.long

© The Author 2009. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org The online version of this article has been published under an open access model. Users are entitled to use, reproduce, disseminate, or display the open access version of this article for non-commercial purposes provided that: the original authorship is properly and fully attributed: the Journal and Oxford University Press are attributed as the original place of publication with the correct citation details given: if an article is subsequently reproduced or disseminated not in its entirety but only in part or as a derivative word this must be clearly indicated.

Genomic RNA profiling and the programme controlling preimplantation mammalian development

Bell CE, Calder MD, Watson AJ. Mol Hum Reprod. 2008 Dec;14(12):691-701. Epub 2008 Nov 29. PMID: 19043080