Totipotent cells

After about 5 days and several cycles of cell division, the totipotent cells form a hollow sphere of cells called a blastocyst. The blastocyst has an outer layer of cells surrounding clusters of cells. Those cells on the outside continue... 

Well, it s only human nature to ask, If sea anemones can clone themselves without hardly trying, and the natural cloning powers of plants are so easily exploited, why can t we begin learning how to clone ourselves The answer to that question is hidden in the secrets of the cell. All plants have one kind of cell that remains forever in the embryonic condition. These cell layers of embryonic tissue are totipotent and can give rise to new differentiated cells. Cut the stem of a plant and these cells will produce root, stem, and leaf tissues. In some animals, totipotent cells—as in the foot of a sea anemone—when cut, will dedifferentiate, and return to an embryonic condition. Then they... 

After about five days and several cycles of cell division, the totipotent cells form a hollow sphere of cells called a blastocyst. The blastocyst has an outer layer of cells surrounding clusters of cells. Those cells on the outside continue to divide and grow into the placenta and supporting tissues. The clusters of cells on the inside divide and form virtually all the cell types, except the placenta and supporting tissues, which give rise to a human being. These are the pluripotent stem cells, and they give rise to many different types of cells, but not a new individual. 

The fertilized egg, or zygote, is the ultimate totipotent cell because it has the capability to generate all the cell types of the body. Although not technically a stem cell because it is not self-renewing, the zygote does give rise to... 

It should be emphasized that further progress in research of the molecular genetics of farm animals will provide the information necessary not only to introduce new genes into the genome but also to contra-select for certain genes which interfere with healthy performance. This could even be done 1 vitro if totipotent cell lines of livestock were available, thus transferring... 

Metchnikoff (1883) recognized the role of cell types (phagocytes) which were responsible for the engulfinent and digestion of microorganisms. They are a major line of defence against microbes that breach the initial barriers described above. Two types of phagocytic cells are found in the blood, both of which are derived from the totipotent bone marrow stem cell. 

All secondary cell walls develop from primary cell walls. Cells no longer grow once lignin is added to their wails. Lignification, which is a key step in the conversion of a primary cell wall into a secondary cell wall, results in terminal differentiation of the encased cell. Indeed, many cells with lignified walls die. The totipotency of plant cells is limited to cells enveloped in primary walls. 

Instructions for the behaviour of every cell in the bodies of worms, flies and humans will soon reside in public databases for all to read. A complete set of these instructions, packaged as chromosomes, is inherited by most cells in our body. Because of this, many if not most somatic nuclei in mammals are totipotent that is, they are capable of programming all of mammalian development when injected into enucleated eggs (Wilmut et al 1997). Dolly s creation had dramatic practical consequences but its feasibility was never improbable on theoretical grounds. How cells inherit two complete packages of the genome at each cell division is one of the most fundamental questions in biology (Fig. la). 

Stem cells are divided into three different categories totipotent, pluripotent, and multipotent. A description of the genesis of stem cells is shown in Fig. 4.11. 

Totipotent stem cells are obtained from embryos that are less than 5 days old. These cells have the full potential to develop into another individual and every cell type. 

Karin M, Mintz B. Receptor-mediated endocytosis of transferrin in developmen-tally totipotent mouse teratocarcinoma stem cells. J Biol Chem 1981 256(7) ... 

Stem cells—Unspecialized cells able to develop into specialized cells may have limited capacity (multipotent or pluripotent) or may be able to turn into any cell of the body (totipotent). 

Totipotent— Able to turn into any cell in the body, under the appropriate conditions. 

Stem cells of totipotent, pluripotent, or multipotent nature supply new germ cells and other cells for multicellular organisms when needed... 

In order to produce secondary metabolic products from a plant, exogenous plant tissue instead of a whole plant, may be cultivated as a suspension culture in an aseptic condition. The technical rationale for using plant tissue is based on the unique biochemical totipotency of plant cells.8... 

A population of desired cell types that have the potential to produce new tissues should be generated. The potential of embryonic totipotent stem cells could be exploited in the transplantation of retinal pigment epithelium, myocardial progenitor cells capable of restoring cardiac function and contractility, dopaminergic neurons for the treatment of Parkinson s disease, pancreatic cells for the treatment of diabetes, and others.55... 

As an alternative to adult stem cells, embryonic stem cells can be used. These are totipotent and can be obtained from the internal blastocyst cell mass. Because of the capacity of these cells to generate any type of functional cell, their manipulation and differentiation have gained in significance. In spite of recent advances (Daley, 2003 Hwang et al., 2004), knowledge on the control of their differentiation and proliferation is still lacking, but will be necessary to make the exploitation of all their therapeutic potential turn into reality. Further discussion on cell therapy can be found in Chapter 20. 

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