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Topic: Cleavage (embryo)

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	Cleavage (embryo) - Wikipedia, the free encyclopedia
		In embryology, cleavage is the division of cells in the early embryo.
		Radial cleavage is characteristic of the deuterostomes, which inlude some vertebrates and echinoderms, in which the spindle axes are parallel or at right angles to the polar axis of the oocyte.
		In spiral cleavage, the cleavage planes are oriented obliquely to the polar axis of the oocyte.
	en.wikipedia.org /wiki/Cleavage_(embryo) (602 words)

	Cleavage and Blastulation
		Cleavage is the process after fertilization when early mitotic cell divisions occur that progressively reduce cell size.
		However, in zebrafish, meroblastic cleavage occurs and cell cleavage is initially confined to the animal (or top) half of the embryo.
		Also unique to mammalian cleavage is that the cells do not always divide at the same time producing the 2, 4, or 8 cell stages but sometimes divide at different times so that odd numbers of cells may be present such as a 5-cell embryo.
	main.uab.edu /show.asp?durki=19952 (1252 words)

	Cleavage and Blastocyst Formation
		Note that in all of the the early stages, the embryo is encased in its zona pellucida.
		Embryos from other mammals have a very similar appearance, and the general sequence of stages is seen in all mammals.
		There is, for instance, little transcription in the embryos of most species prior to the 8 cell stage, but as embryos develops into morulae, then blastocysts, a large number of genes become transcritionally active and the total level of transcription increases dramatically.
	arbl.cvmbs.colostate.edu /hbooks/pathphys/reprod/fert/cleavage.html (734 words)

	Cleavage 1
		The first is to have a feeding larval stage (as this embryo will have) to meet the nutritional requirements of the embryo, with the second being to have internal development such that the nutritional requirements of the embryo are met by the mother (what we will see later with mammals).
		The lighter area in the centre of the embryo is the beginning of the blastocoel.
		With continuing cleavage, the cells in centre begin to lose contact with one another, and a central fluid-filled cavity (the blastocoel) forms.
	www.uoguelph.ca /zoology/devobio/210labs/cleavage1.html (454 words)

	Cleavage
		There are two major consequences of cleavage: production of a multicellular organism from a single-celled zygote and acquisition by individual cells or groups of cells of differences that will facilitate their later development into different cell types.
		Thus, blastomere volume is decreased during cleavage to produce the small, individual cellular units that participate in the subsequent morphogenic events that mold the embryo.
		Cleavage also increases the number of nuclei, which amplifies the number of templates that will facilitate the later production of specialized proteins needed for formation of a functional organism.
	www.ucalgary.ca /UofC/eduweb/virtualembryo/cleavage.html (595 words)

	embryo - HighBeam Encyclopedia (Site not responding. Last check: 2007-11-07)
		EMBRYO [embryo], name for the developing young of an animal or plant.
		In its widest definition, the embryo is the young from the moment of fertilization until it has become structurally complete and able to survive as a separate organism.
		Embryology, the scientific study of embryonic development, deals with the period from fertilization until the hatching or birth of an animal or the germination of a plant.
	www.encyclopedia.com /doc/1E1-embryo.html (888 words)

	ScienceWeek
		The vertical axis of the embryo after transplantation in the uterus can be traced back to organization of the pre-implantation blastocyst, and this in turn reflects the organization of the cleavage stage embryo and the animal-vegetal axis of the zygote.
		During cleavage, almost no growth occurs between consecutive divisions, and the total volume of the embryo does not substantially change: the size of the cells is reduced by almost half at each division.
		Although the shape and volume of the embryo do not change during cleavage, an important change in gross organization occurs: as the blastomeres are produced, they move outward, leaving a centrally-located fluid-filled cavity, and the embryo at this stage approximates a hollow ball and is known as a "blastula".
	scienceweek.com /2004/sb040528-4.htm (1670 words)

	NURTURE (Nottingham University Research and Treatment Unit) - Embryo transfer (via CobWeb/3.1 planet03.csc.ncsu.edu) (Site not responding. Last check: 2007-11-07)
		The live birth success rate for a two embryo transfer is not significantly different to that of a three embryo transfer.
		Embryos may be frozen at any stage but only Grade 1 and 2 embryos are classed as suitable for freezing.
		Embryos are graded on a scale of 1-4 with 1 being the best.
	www.nurture.ac.uk.cob-web.org:8888 /pathway/embryo-transfer (167 words)

	Pacific Fertility Center
		The egg is a single large cell that divides or cleaves to become a 2-cell embryo about 18 hours after fertilization was confirmed.
		The best embryos will have 8 or more cells and the cells will be evenly shaped and similar in size.
		The information on embryo quality is then discussed with the couple and a decision is reached on how many embryos to transfer and how many to freeze for later use.
	www.infertilitydoctor.com /lab/lab_embryo_devel.htm (414 words)

	Cleavage - Wikipedia, the free encyclopedia
		Cleavage (embryo), in embryology, is the division of cells in the early embryo
		Cleavage (buttocks), partial exposure of buttock cheeks, particularly when visible because of low trousers, also known colloquially in the UK as builder's bum.
		Cleavage (toes), partial exposure of the top of a woman's toes, particularly when visble because of shoes with low cut vamps.
	en.wikipedia.org /wiki/Cleavage (204 words)

	Maternal Control of Early Development
		Fertilization acts as a trigger to initiate a program of events starting with cleavage, and continuing with gastrulation and neurulation, etc. Although fertilization results in union of maternal and paternal genomes, zygotic gene activity is not required until the blastula stage.
		Since cleavage could occur without transcription or a nucleus these observations suggested that some material other than DNA is directing early development.
		In the early 60's treatment of sea urchin embryos with puromycin demonstrated that, after fertilization, protein synthesis was required for early embryogenesis to proceed.
	www.ucalgary.ca /UofC/eduweb/virtualembryo/maternal_control.html (1200 words)

	Mammalian embryogenesis - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.cs.umd.edu) (Site not responding. Last check: 2007-11-07)
		After the 8-cell stage, mammalian embryos undergo what is called compactation, where the cells bind tightly to each other, forming a compact sphere.
		After compactation, the embryo is in the morula stage (16 cells).
		This stage in the developing embryo, reached after four to six days, is the blastocyst (akin to the blastula stage), and lasts approximately until the implantation in the uterus.
	en.wikipedia.org.cob-web.org:8888 /wiki/Mammalian_embryogenesis (813 words)

	Chapter 13B. Fertilization and Cleavage
		Cleavage is a series of rapid cell divisions without cell growth or gene expression which occurs in early embryogenesis.
		The pattern of cleavage is influenced by the amount of yolk in the egg.
		Cleavage in the zebrafish embryo is limited to a small region on "top" of the yolky mass.
	biology.kenyon.edu /courses/biol114/Chap13/Chapter_13B.html (1591 words)

	B&BRP Overview and Research Highlights FY 95-97 (Site not responding. Last check: 2007-11-07)
		This short moment in early embryo development presents a unique opportunity to characterize chromosomal defects transmitted to the embryo via the mother's oocytes or the father's sperm.
		Specific studies are underway to determine whether embryos are at increased risk of damage if they have been sired by a male (a) who carried constitutive chromosomal abnormalities, or (b) who were treated with a germinal mutagen before mating.
		An inability by the egg to repair damage transmitted by sperm would be expected to increase an embryo's chance of ending as a spontaneous abortion, or resulting with a birth defect, childhood cancer, or other disease.
	image.llnl.gov /bbrp/html/wyrobek.abst.html (249 words)

	Experimental taphonomy shows the feasibility of fossil embryos -- Raff et al. 103 (15): 5846 -- Proceedings of the ...
		Embryos have undergone autolysis: cytoplasmic lipid and pigment have coalesced (arrows); cleavage furrows have degraded (asterisks); and fertilization envelopes are disintegrating (arrowhead).
		Embryos in A, B, D, and F were killed by 12 min in seawater containing 1% ammonium, then treated as described.
		The embryo was slightly flattened under a coverslip to immobilize it; the beating cilia are visible, including the large apical tuft cilia at the animal pole (asterisk).
	www.pnas.org /cgi/content/full/103/15/5846 (4004 words)

	Lecture 15: Development, Coelom Formation (Site not responding. Last check: 2007-11-07)
		Radial cleavage – cleavage furrows are oriented parallel or perpendicular to animal-vegetal pole axis
		Following cleavage, the embryo is a mass of cells called a blastula
		The embryo now has 2 cell layers, the outside layer is called ectoderm and the cells lining the archenteron are called endoderm
	www.humboldt.edu /~zool110/Lectures/Lecture15.htm (822 words)

	Requirement for a Noncoding RNA in Drosophila Polar Granules for Germ Cell Establishment.
		The embryo in (I) was embedded, thin-sectioned, and hybridized with a double-stranded DIG-labeled Pgc DNA probe after sectioning (23); the embryo in (J) was hybridized before embedding.
		We examined embryos produced by mothers homozygous for various posterior-group mutations to determine the effects of such mutations on Pgc RNA localization.
		In embryos from either Bicaudal-C or Bicaudal-D females, Pgc RNA was mislocalized to the anterior in a diffuse manner (Fig.
	www.euchromatin.org /Nakamura1.htm (4108 words)

	Pharyngula: Spiral cleavage
		A quartet of micromeres is displaced anticlockwise in the levotropic cleavage (blue arrow, left) and clockwise in the dextrotropic cleavage (blue arrow, right) when viewed from the animal pole.
		The mutation in the sinistral form destroys the precise spiral asymmetry of the early embryo, but one unexplained phenomenon is that after the third division, the micromeres still migrate towards the furrows between the macromeres…but they consistently twist to the left instead of the right.
		Future micromeres at telophase and ones established in the 8-cell embryos are shaded in dark gray.
	scienceblogs.com /pharyngula/2006/04/spiral_cleavage.php (2378 words)

	embryo cleavage
		The Cambridge group, which has been studying the orientation of the very first cleavage in mouse embryos, recently reported that the "sperm entry point" (SEP) has a role to play in setting up embryonic axes that direct what will become the top and the tail of the developing embryo.
		Richard Gardner, head of the University of Oxford's Mammalian Development Laboratory, is concerned that the idea that the SEP specifies the plane of first cleavage has already entered the lore of early mammalian development.
		In the last few years, it has emerged that the pattern of cell division in the early mammalian embryo is not entirely random as had been assumed, but that something intrinsic to the egg helps specify the line along which the first cleavage occurs.
	www.vetscite.org /publish/items/001045 (536 words)

	Embryology (Site not responding. Last check: 2007-11-07)
		Cleavage and the formation of the blastula -- the cell during cleavage, distribution of the yolk and its effect on the cleavage, cleavage and formation of the blastula in amphioxus, organization of the embryo during cleavage and blastulation, properties of the embryo during cleavage and blastulation, molecular events during cleavage and blastulation.
		Neurulation of the neural crest and somite formation -- primary neural induction, formation of the neural tube, the neural crest, the mesoderm of the early embryo, secretion of extracellular materials, formation and differentiation of somites and somitomeres.
		Limb development -- initiation of the limb development, regulative properties of early limb primordium, axial determination of the limbs, outgrowth of the limb bud, apical ectodermal ridge, mesoderm of the early limb bud, limb regeneration.
	www.exammaster.com /Medical-Subject-Review/embryology.htm (701 words)

	Blastocyst versus early cleavage embryo transfer: a retrospective analysis of 4,165 transfers. (via CobWeb/3.1 ... (Site not responding. Last check: 2007-11-07)
		Blastocyst versus early cleavage embryo transfer: a retrospective analysis of 4,165 transfers.
		The purpose of this work is to address the relationship between transcriptional profile of embryos and the pregnancy success based on gene expression analysis of blastocyst biopsies taken prior to transfer to recipients.
		Biopsies (30-40% of the intact embryo) were taken from IVP day 7 blastocysts (n=118) and 60-70% part were transferred to recipients after re-expansion.
	lib.bioinfo.pl.cob-web.org:8888 /pmid:14998186 (1484 words)

	Cleavage stage versus blastocyst stage embryo transfer in assisted conception
		In the past decade, advances in the understanding of nutrient requirements of embryos, has led to the evolution of culture media designed to support extended culture of embryos in vitro from the standard procedure of 2 to 3 days (for early cleavage embryo transfer) to 5 to 6 days (blastocyst culture).
		Rates of embryo freezing per couple was significantly higher in Day 2 to 3 transfers (9 RCTs; OR 0.45, 95% CI 0.36 to 0.57).
		Failure to transfer any embryos per couple was significantly higher in the Day 5 to 6 group (10 RCTs: OR 3.21, 95% CI 2.15 to 4.81[Day 2/3 3.5% vs D 5/6 10.1%]), but was not significantly different for good prognosis patients (7RCTs, OR 1.58 95% CI 0.65 to 3.82).
	www.cochrane.org /reviews/en/ab002118.html (760 words)

	Ion Channels and Early Development of Neural Cells -- TAKAHASHI and OKAMURA 78 (2): 307 -- Physiological Reviews
		In the ascidian embryo, it is known that the two cells in the vegetal pole at the 64-cell stage are the pioneer cells to gastrulate
		To ascertain that this inductive phenomenon of Na spikes is equivalent to neural induction in the ascidian embryo, we examined
		Because the critical period of neural induction in the amphibian embryos occurs at the early to midgastrula stage (240),
	physrev.physiology.org /cgi/content/full/78/2/307 (10365 words)

	Temporal and Differential Effects of Amino Acids on Bovine Embryo Development in Culture -- Steeves and Gardner 61 (3): ...
		Effect of culture of the early bovine embryo with different groups of amino acids for the first 72 h and their effect on subsequent developmental competence.
		Effect of culture of the early bovine embryo for the first 72 h with nonessential amino acids in the presence and absence of glutamine and betaine, and the effect on subsequent developmental competence.
		Gardner DK, Lane M, Spitzer A, Batt PA. Enhanced rates of cleavage and development for sheep zygotes cultured to the blastocyst stage in vitro in the absence of serum and somatic cells: amino acids, vitamins, and culturing embryos in groups stimulate development.
	www.biolreprod.org /cgi/content/full/61/3/731 (7180 words)

	Embryogenesis - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.cs.umd.edu) (Site not responding. Last check: 2007-11-07)
		The zygote undergoes rapid mitotic divisions with no significant growth (a process known as cleavage) and cellular differentiation, leading to development of an embryo.
		Holoblastic cleavage occurs in animals with little yolk in their eggs, such as humans and other mammals who receive nourishment as embryos from the mother, via placenta or milk.
		The blastula is usually a spherical layer of cells (the blastoderm) surrounding a fluid-filled or yolk-filled cavity (the blastocoel).
	en.wikipedia.org.cob-web.org:8888 /wiki/Embryogenesis (740 words)

	Cleavage
		Cleavage is distinguished from division since no growth occurs- no increase in cytoplasm.
		Cleavage is initiated by calcium flux that causes degradation of cyclin.
		Frog Cleavage features (as one example that is well studied due to large egg size):
	mason.gmu.edu /~dcupo/Cleavage.htm (431 words)

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