Talk:Morula

Regulation of compaction initiation in mouse embryo

Yi Chuan. 2009 Dec;31(12):1177-84. (Article in Chinese)

Li CB, Hu LL, Wang ZD, Zhong SQ, Lei L.

Department of Histology and Embryology, Harbin Medical University, Harbin 150081, Chin. zl2007cb@yahoo.com.cn Abstract Developmental events in preimplantation mouse embryos include the first cleavage, the activation of the embryonic genome, the compaction of the blastomeres to form morula (MO), and the formation of the blastocyst (BL). Compaction, the first cell differentiation event in mammalian development, occurs at the late eight-cell stage in the mouse and may be described in terms of some types of morphological change, which involve reorganization within a cell and intercellular reorganization. Surface microvilli became restricted to a few basal sites and to an externally facing (apical) pole. Prior to compaction, the blastomeres are spherical and lack specialized intercellular junctions. During compaction, the cells were flattened against one another, thus maximizing intercellular contact and obscuring intercellular boundaries. It is believed that the events of compaction have an important influence on the processes involved in blastocyst formation, namely the initiation of inner cell mass and trophectoderm differentiation. The inner cell mass will form the future embryo proper, whereas the trophectoderm cells will form only extraembryonic tissues. Compaction is initiated by E-cadherin mediated cell adhesion, which is regulated post-translationally via protein kinase C. With E-cadherin knock-out, maternal E-cadherin is able to mediate the compaction process at the morula stage. Initial adhesion is mediated by homophilic interactions between E-cadherin extracellular domains.In this review, we attempted to describe this process in detail.

PMID: 20042384 http://www.ncbi.nlm.nih.gov/pubmed/20042384

The four blastomeres of a 4-cell stage human embryo are able to develop individually into blastocysts with inner cell mass and trophectoderm

Hum Reprod. 2008 Aug;23(8):1742-7. Epub 2008 May 24.

Van de Velde H, Cauffman G, Tournaye H, Devroey P, Liebaers I.

Research Centre Reproduction and Genetics, Universitair Ziekenhuis Brussel (UZ Brussel), Laarbeeklaan 101, 1090 Brussels, Belgium. hilde.vandevelde@uzbrussel.be Abstract BACKGROUND: Early mammalian blastomeres are thought to be flexible and totipotent allowing the embryo to overcome perturbations in its organization during preimplantation development. In the past, experiments using single blastomeres from 2-, 4- and 8-cell stage mammalian embryos have provided evidence that at least some of the isolated cells can develop into healthy fertile animals and therefore are totipotent. We investigated whether isolated blastomeres of human 4-cell stage embryos could develop in vitro into blastocysts with trophectoderm (TE) and inner cell mass (ICM).

METHODS: Six 4-cell stage human embryos were split and the four blastomeres were cultured individually. The expression of NANOG, a marker for ICM cells, was analysed by immunocytochemistry.

RESULTS: The majority of the blastomere-derived embryos followed the normal pattern of development with compaction on Day 4 and cavitation on Day 5 and developed into small blastocysts with TE and ICM on Day 6 (n = 12). The four cells of one embryo were individually capable of developing into blastocysts with TE and ICM, and NANOG was expressed in the ICM.

CONCLUSIONS: Although based on a small number of embryos, we conclude that the blastomeres of a 4-cell stage human embryo are flexible and able to develop into blastocysts with ICM and TE.

http://www.ncbi.nlm.nih.gov/pubmed/18503052

http://humrep.oxfordjournals.org/content/23/8/1742.long

Zonula occludens-1 (ZO-1) is involved in morula to blastocyst transformation in the mouse

Wang H, Ding T, Brown N, Yamamoto Y, Prince LS, Reese J, Paria BC. Dev Biol. 2008 Jun 1;318(1):112-25. Epub 2008 Mar 20.

It is unknown whether or not tight junction formation plays any role in morula to blastocyst transformation that is associated with development of polarized trophoblast cells and fluid accumulation. Tight junctions are a hallmark of polarized epithelial cells and zonula occludens-1 (ZO-1) is a known key regulator of tight junction formation. Here we show that ZO-1 protein is first expressed during compaction of 8-cell embryos. This stage-specific appearance of ZO-1 suggests its participation in morula to blastocyst transition. Consistent with this idea, we demonstrate that ZO-1 siRNA delivery inside the blastomeres of zona-weakened embryos using electroporation not only knocks down ZO-1 gene and protein expressions, but also inhibits morula to blastocyst transformation in a concentration-dependent manner. In addition, ZO-1 inactivation reduced the expression of Cdx2 and Oct-4, but not ZO-2 and F-actin. These results provide the first evidence that ZO-1 is involved in blastocyst formation from the morula by regulating accumulation of fluid and differentiation of nonpolar blastomeres to polar trophoblast cells.

PMID: 18423437 http://www.ncbi.nlm.nih.gov/pubmed/18423437

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2442465/?tool=pubmed

Ras-MAPK signaling promotes trophectoderm formation from embryonic stem cells and mouse embryos

Nat Genet. 2008 Jul;40(7):921-6. Epub 2008 Jun 8.

Lu CW, Yabuuchi A, Chen L, Viswanathan S, Kim K, Daley GQ.

Division of Pediatric Hematology and Oncology, Children's Hospital Boston and Dana Faber Cancer Institute, Boston, Massachusetts 02115, USA. Abstract In blastocyst chimeras, embryonic stem (ES) cells contribute to embryonic tissues but not extraembryonic trophectoderm. Conditional activation of HRas1(Q61L) in ES cells in vitro induces the trophectoderm marker Cdx2 and enables derivation of trophoblast stem (TS) cell lines that, when injected into blastocysts, chimerize placental tissues. Erk2, the downstream effector of Ras-mitogen-activated protein kinase (MAPK) signaling, is asymmetrically expressed in the apical membranes of the 8-cell-stage embryo just before morula compaction. Inhibition of MAPK signaling in cultured mouse embryos compromises Cdx2 expression, delays blastocyst development and reduces trophectoderm outgrowth from embryo explants. These data show that ectopic Ras activation can divert ES cells toward extraembryonic trophoblastic fates and implicate Ras-MAPK signaling in promoting trophectoderm formation from mouse embryos.

PMID: 18536715 http://www.ncbi.nlm.nih.gov/pubmed/18536715

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2690707/?tool=pubmed

===Tight junction protein ZO-2 expression and relative function of ZO-1 and ZO-2 during mouse blastocyst formation. Sheth B, Nowak RL, Anderson R, Kwong WY, Papenbrock T, Fleming TP.

School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO167PX, UK. Abstract Apicolateral tight junctions (TJs) between epithelial cells are multiprotein complexes regulating membrane polarity and paracellular transport and also contribute to signalling pathways affecting cell proliferation and gene expression. ZO-2 and other ZO family members form a sub-membranous scaffold for binding TJ constituents. We investigated ZO-2 contribution to TJ biogenesis and function during trophectoderm epithelium differentiation in mouse preimplantation embryos. Our data indicate that ZO-2 is expressed from maternal and embryonic genomes with maternal ZO-2 protein associated with nuclei in zygotes and particularly early cleavage stages. Embryonic ZO-2 assembled at outer blastomere apicolateral junctional sites from the late 16-cell stage. Junctional ZO-2 first co-localised with E-cadherin in a transient complex comprising adherens junction and TJ constituents before segregating to TJs after their separation from the blastocyst stage (32-cell onwards). ZO-2 siRNA microinjection into zygotes or 2-cell embryos resulted in specific knockdown of ZO-2 mRNA and protein within blastocysts. Embryos lacking ZO-2 protein at trophectoderm TJs exhibited delayed blastocoel cavity formation but underwent normal cell proliferation and outgrowth morphogenesis. Quantitative analysis of trophectoderm TJs in ZO-2-deficient embryos revealed increased assembly of ZO-1 but not occludin, indicating ZO protein redundancy as a compensatory mechanism contributing to the mild phenotype observed. In contrast, ZO-1 knockdown, or combined ZO-1 and ZO-2 knockdown, generated a more severe inhibition of blastocoel formation indicating distinct roles for ZO proteins in blastocyst morphogenesis.

PMID: 18817772

Gene replacement reveals a specific role for E-cadherin in the formation of a functional trophectoderm

Kan NG, Stemmler MP, Junghans D, Kanzler B, de Vries WN, Dominis M, Kemler R. Development. 2007 Jan;134(1):31-41. Epub 2006 Nov 30. PMID: 17138661

Maternal beta-catenin and E-cadherin in mouse development

De Vries WN, Evsikov AV, Haac BE, Fancher KS, Holbrook AE, Kemler R, Solter D, Knowles BB. Development. 2004 Sep;131(18):4435-45. Epub 2004 Aug 11. PMID: 15306566