‘Formation of the trophectoderm lineage. The first cell fate decision in mammalian development’.
The crucial outcome of the early mammalian development is the attachment of the embryo to the uterine lining. The cell population that will support this attachment, the trophectoderm (TE), is distinguished from the inner cell mass (ICM) at the blastocyst stage and this separation represents the earliest lineage restriction. Up to the 8-cell stage, the embryo is characterized by a loose structure, but then compaction follows, a phenomenon mediated by increased cell-cell adhesion (tight junctions, increased E-cadherin expression). Acquisition of a microvillus apical membrane domain, polarization of the cytoplasm and reorganization of cytoskeleton elements establish apicobasal polarity while blastomeres become flattened. (Gilbert, Fleming et al., 2001). Still at this stage, all cells maintain communication with their environment, but after sequential divisions they either take an inner or outer position in the late morula. By 32-cell stage, the blastocoel cavity is formed surrounded by the TE that will give rise to extraembryonic tissues (extraembryonic ectoderm and the trophoblast). Attached to one side of the TE epithelium, the ICM will form the embryo proper and nontrophoblast extraembryonic tissues. The molecular mechanisms behind this first differentiation event remain elusive. Clarification of these mechanisms will contribute to our understanding of early mammalian development and will support the field of stem cell biology and induced pluripotency.
Conservative versus differantiative cell divisions.
After the compacted morula, the embryo undergoes two rounds of cleavage, during which the two cell populations become gr...
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...(Cdx2, Eomes, Fgfr2) were re-expressed after the introduction of exogenous Sox2. Therefore, Sox2 was suggested as an early player in the introduction of the TE lineage, but interactions with the other transcriptional regulators as well as actual contribution or not of maternal Sox2 mRNA still need to be illuminated.
From all the above, it is understood that the transcriptional network regulating the first cell fate decision is complicated and yet not clearly defined. Recent evidence supports a dual role of Klf5 in lineage specification (Fig 4). Upregulation of Klf5 is critical for TE development (upstream of Cdx2 and in parallel to Fgf signal), whereas low levels of Klf5 are needed to maintain the expression of Oct4 and Nanog in the ICM. Still, the exact mechanism and the interactions with other members of the network need to be examined (Lin., et al., 2010).
Takahashi, Y., et al. “Analysis of Promoter binding by the E2F and pRB Families In Vivo: Distinct E2F Proteins Mediate Activation and Repression.” Genes 14 (2000): 804-816.
During interphase, the cells in both animals and bacteria carry out their division general functions according to the type of their cells. Unlike in plants, a preprophase group of cytoskeletal proteins emerge at a future location of the cell plate. At prophase stage, duplicated chromosomes compress in a way that can be seen with the help of a microscope. On the other hand, the mitotic spindle is formed at one side of nucleus, whereas in plants, spindle is formed around the nucleus. During prometaphase in animals and bacteria, the nuclear membrane disappears, the chromosomes attach themselves to mictotubules and start to move. In plants, however, the preprophase group dissolves while at metaphase stage, the chromosomes get aligned at the core of the cell. At anaphase, there are fewer differences between animals and plants. The chromosomes shift apart towards the both par...
After seeing this, they tested out if DII is responsible for the down regulation of Ubx/Abd-A. They used double-label experiments using antibodies against butterfly DII and Ubx/Abd-A antibodies and performed them. The activation of DII in the proleg trails repression for Ubx and Abd-A expression, which showed that repression of BX-C gene, is the initial event. When DII expression abdominal segments of drosophila embryo expression is repressed due Ubx and Abd-A, the abdominal limb formation in but...
They seemed to have had a touch of success when the nucleus of a fibroblast had appeared to divide but it never completed. It took 71 eggs from seven volunteers before they could create their first cloned embryo. Out of the eight eggs with cumulus cells, two of them divided to form early embryos of four cells and another went to at least six cells before it stopped growing.
Stem cells are pluripotent cells of the body which are “undifferentiated.” This means that stem cells can ultimately give rise to any type of body tissue. Thus stem cells have the potential to cure a vast number of diseases and physical ailments including Parkinson’s, diabetes, spinal cord injury, and heart disease. Consequently, stem cell research and the development of associated medical applications are of great interest to the scientific and medical community. The area of stem cell research involving human embryonic stem cells is of particular interest in that embryonic stem cells are derived from week-old blastocysts developed from in vitro fertilized eggs. As opposed to adult stem cells, which must undergo a complicated process of de-differen...
Transcription factors allow cells to perform logic operations and combine different sources of information to "decide" whether to express a gene.
The importance of embryonic stem cells rests in their lack of specialization. These basic cells are present in the earliest stages of developing embryos and are able to develop into virtually any type of cell and tissue in the body. Being self-renewing, they offer a potentially limitless source of cells and tissue. (Tucker)
...39-0512-6_10.Use of Genome-Wide RNAi Screens to Identify Regulators of Embryonic Stem Cell Pluripotency and Self-Renewal. Zheng X1, Hu G.
The debate of whether dinosaurs were cold blooded or warm blooded has been ongoing since the beginning of the century. At the turn of the century scientists believed that dinosaurs had long limbs and were fairly slim, supporting the idea of a cold blooded reptile. Recently, however, the bone structure, number or predators to prey, and limb position have suggested a warm blooded species. In addition, the recent discovery of a fossilized dinosaur heart has supported the idea that dinosaurs were a warm blooded species. In this essay, I am going to give supporting evidence of dinosaurs being both warm and cold blooded. I will provide background information on the dinosaur that was discovered and what information it provides scientists.
The first neural induction in amphibian embryos has given the Nobel Prize in Medicine award to Hans Spemann in 1935 for his “Spemann-Mangold organizer” paper. The discovery with her student Hilde Mangold leads to establishment of a neuroectodermal primordium from where the nervous system arise involving induction of chemicals such as the fibroblast growth factor (FGF) and WNT signalling, together with inhibition of bone morphogenetic protein-4 (BMP) signalling activity to promotes neuron development. Spemann’s study has successfully identified a morphologically distinct cluster of mesodermal cell located in dorsal lip of blastophore known as ‘organizer’ which has the potential in neural induction. BMP will trigger neural induction and are formed during the gastrulation in vertebrate embryo which is secreted by ventral gastrula signalling centre (Spermann H, Mangold H, 1924). In a normal mechanism BMP binds with receptor on ectoderm cell to form epidermis. However, by inhibiting BMP, ectoderm cells will differentiate to form the neurons cells without the presence of neural inducers t...
Sadler, T. W., and Jan Langman. Langman's Medical Embryology. Philadelphia: Lippincott Williams & Wilkins, 2006. Print.
The merger of two germinal cells, one being a sperm cell and the other being an egg cell, is complete within twelve hours, at which time the egg is fertilized and becomes a zygote containing forty six chromosomes required to create a new human life. It is during this remarkable process when conception occurs. Conception confirms life and makes that undeveloped human one of a kind (Rorvik & Shettles, 1983, p. 16). Many researchers, as well as scientists, identify the first moments of life as the instant when a sperm cell unites with an ovum, o...
Distinct characteristics are not only an end result of the DNA sequence but also of the cell’s internal system of expression orchestrated by different proteins and RNAs present at a given time. DNA encodes for many possible characteristics, but different types of RNA aided by specialized proteins sometimes with external signals express the needed genes. Control of gene expression is of vital importance for an eukaryote’s survival such as the ability of switching genes on/off in accordance with the changes in the environment (Campbell and Reece, 2008). Of a cell’s entire genome, only 15% will be expressed, and in multicellular organisms the genes active will vary according to their specialization. (Fletcher, Ivor & Winter, 2007).
Once the sperm fuses with the ovum both chromosomes will pair up and begin the first stages of cell division.
There are certain things that must happen first before the cell can actually split. There is a six step process required during Mitosis. The first five steps of mitosis are called prophase, prometaphase, metaphase, anaphase, and telophase. This is where all the training and preparation is done for cell division. The sixth step is Cytokinesis, and that is when the cell literally splits into two. Like I said, there are certain things in order to happen before it can enter the M phase. first, it must meet the requirements of the certain size and environment. Since in the S phase the cell duplicated it’s amount of chromosomes it be represented as 2N, where N equals the number of chromosomes in the cell. Cells about to enter M phase, which have passed through S phase and replicated their DNA, have 4N chromosomes. Because of this they are now allowed to enter within the M phase to prophase. Here is where the cell thickens up its chromosomes and begin to sprout microtubules from clone centrosomes. Microtubules tub-like are protein filaments and where the chromosomes migrate but are still within the nuclear envelope in the nucleus. There are centromeres, that are inside the chromosomes and during the later process of this phase, specialized microtubules called kinetochores, assemble on the centromere then later attach to these sites. They act like magnets and go