CELL DIFFERENTIATION.pdf a ppt on cell differentiation
- 3. Cell Differentiation ❑A single cell, the fertilized egg, gives rise to hundreds of different cell types; muscle cells, epidermal cells, neurons, lens cells, lymphocytes, blood cells, fat cells etc. This generation of cellular diversity is called differentiation. ❖Do every cell of the body contains the same set of genes? ❖How can this identical set of genetic instructions produce different types of cells? ❖How can a single fertilized egg cell generate so many different cell types?
- 4. Undifferentiated cells Cell maturation Cell Differentiation Committed to a Specific cell lineage Gene expression Cell fate Determination Cell Fate Cell Specification Cell Commitment Cell Differentiation Cell Determination Cell Potency
- 6. It is the diversity of cell types that a single cell can become during Normal development in an organism Cell Fate Cell Commitment Process of Deciding the Fate of a cell Cell Specification Cell Determination Process by which a cell chooses any of the specific development pathway The first stage of commitment of cell or tissue fate Varying ability of stem cells to differentiate into specialized cell types Cell Potency
- 7. Cell differentiation is the process by which a cell acquires the structural and functional properties unique to a given cell type. Cell differentiation ❖ From an undifferentiated cell to a post-mitotic differentiated cell type, a cell goes through a process of maturation that experiences different levels of commitment toward its end fate. ❖ A cell is first specified toward a given fate, suggesting that it would develop into this cell type even in isolation. ❖ A cell is committed or determined to a given fate if it maintains its developmental maturation toward this cell type even when placed in a new environment.
- 8. ❑The process generation of specialized cell types during which ❖A cell ceases to divide, ❖ Develops specialized structural elements and ❖Distinct functional properties. Undifferentiated Cell ❖Fate determined ❖Committed ❖Specified ❖Differentiated Cell type Differentiation Commitment Stages Undifferentiated Differentiated Specification Determination
- 9. Commitment Specification The fate of a cell or tissue is said to be specified when it is capable of differentiating autonomously (i.e., by itself) when placed in an environment that is neutral with respect to the developmental pathway, such as in a petri dish or test tube. A cell or tissue is said to be determined when it is capable of differentiating autonomously even when placed into another region of the embryo or a cluster of differently specified cells in a petridish. Determination 1 2 ❖Capable of differentiating autonomously when placed in a neutral environment; ❖not when placed in non-neutral environment ❖Capable of differentiating autonomously even when placed into another embryonic regionor a cluster of differently specified cells in a petri dish
- 10. Levels of differentiation Undifferentiated cell ❖Fate determined ❖Committed ❖Differentiated cell type Differentiation Commitment Stages Undifferentiated Differentiated Specification Determination
- 11. Commitment Labile (fate reversible) Irreversible (fate irreversib Labile Irreversible Cell Fate deciding stage Specification Determination
- 12. Autonomous specification ❖Characteristic of most invertebrates (molluscs, annelids, and tunicates). ❖Specification by differential acquisition of certain cytoplasmic molecules present in the egg such as Morphogenetic determinants. ❖Invariant cleavages produce the same lineages in each embryo of the species. ❖Blastomere fates are generally invariant. ❖Cell type specification precedes any large-scale embryonic cell migration. ❖Produces “Mosaic”development: cells cannot change fate if a blastomere is lost. . In the absence of particular blastomeres, the larva lacked just those structures normally formed by those cells.
- 13. ❑if a particular blastomere is removed from an embryo early in its development, that isolated blastomere will produce the same types of cells that it would have made if it were still part of the embryo. ❑Moreover, the embryo from which that blastomere is taken will lack those cells (and only those cells) that would have been produced by the missing blastomere. Whittaker removed these two cells and placed them in isolation, they produced muscle tissue
- 14. Conditional specification ❖Characteristic of all vertebrates and few invertebrates. ❖Specification by interactions between cells. ❖ Relative positions of blastomeres are important. ❖Variable cleavages produce no invariant fate assignments to cells. ❖Massive cell rearrangements and migrations precede or accompany specification. ❖Capacity for “regulative” development: allows cells to acquire different functions.
- 15. ❖ If a blastomere is removed from an early embryo that uses conditional specification, the remaining embryonic cells alter their fates so that the roles of the missing cells can be taken over. ❖ The ability of embryonic cells to change their fates to compensate for the missing parts is called regulation ( Regulative development) ❖Critical in the development of identical twins. ❖In the formation of such twins the cleavage-stage cells of a single embryo divide into two groups, and each group of cells produces a fully developed individual
- 16. Conditional specification. (A)What a cell becomes depends upon its position in the embryo. Its fate is determined by interactions with neighboring cells. (B) If cells are removed from the embryo, the remaining cells can regulate and compensate for the missing part.
- 17. Syncytial specification ❖Characteristic of most insect classes. ❖Specification of body regions by interactions between cytoplasmic regions prior to cellularization of the blastoderm. ❖Variable cleavage produces no rigid cell fates for particular nuclei. ❖After cellularization, conditional specification is most often seen.
- 18. ❖Interactions occur not between cells, but between parts of one cell. ❖In early embryos of these insects, cell division is not complete. ❖The nuclei divide within the egg cytoplasm, creating many nuclei within one large egg cell. ❖A cytoplasm that contains many nuclei is called a syncytium.
- 19. ❖The first evidence for genomic equivalence came from embryologists studying the regeneration of excised tissues. removal of the neural retina promotes ❖regeneration from the pigmented retina, and if the lens is removed, a new lens can be formed from the cells of the dorsal iris. The regeneration of lens tissue from the iris (called Wolffian regeneration) ❖The formation of the lens by the differentiated cells of the iris is an example of metaplasia (or transdifferentiation), Genomic equivalence in cell and nuclei
- 20. Evidence that every cell in the body has the same genome originally came from the analysis of Drosophila chromosomes, in which the DNA of certain larval tissues undergoes numerous rounds of DNA replication without separation such that the structure of the chromosomes can be seen. In these Polytene chromosomes, no structural differences were seen between cells; however, different regions of the chromosomes were “puffed up” at different times and in different cell types, which suggested that these areas were actively making RNA Polytene chromosomes
- 21. Each cell's nucleus is identical to the zygote nucleus, then each Cell's nucleus should be totipotent (capable of directing the entire development of the organism) when transplanted into an activated enucleated egg. (1) A method for enucleating host eggs without destroying them; (2) a method for isolating intact Donor nuclei; (3) a method for transferring such nuclei into the host egg without damaging Either the nucleus or the oocyte. Amphibian cloning: The restriction of nuclear potency
- 22. ❖Cells from the mammary gland of an adult (6-year-old) pregnant ewe and put them into culture. ❖The culture medium was formulated to keep the nuclei in these cells at the resting stage of the cell cycle (g0). ❖They then obtained oocytes (the maturing egg cell) from a different strain of sheep and removed their nuclei. ❖The fusion of the donor cell and the enucleated oocyte was accomplished by bringing the two cells together and sending electrical pulses through them. ❖The electric pulses destabilized the cell membranes, allowing the cells to fuse together. ❖Moreover, the same pulses that fused the cells activated the egg to begin development. ❖The resulting embryos were eventually transferred into the uteri of pregnant sheep. Cloning mammals
- 24. Totipotency is the ability of a single cell to divide and produce all of the differentiated cells in an organism. Able to differentiate into any embryonic cell, as well as extraembryonic cells Eg. Spores and zygotes Totipotency Cell potency
- 25. Pluripotency refers to a stem cell that has the potential to differentiate into any of the three germ layers: Endoderm (interior stomach lining, gastrointestinal tract, the lungs), Mesoderm (muscle, bone, blood, urogenital), Ectoderm (epidermal tissues and nervous system), but not into extra-embryonic tissues like the placenta. Pluripotency
- 26. ❖Human development begins when a sperm fertilizes an egg and the resulting zygote. ❖After reaching a 16-cell stage, the totipotent cells of the morula differentiate into cells that will eventually become either the blastocyst's inner cell mass and the outer trophoblasts. ❖Four days after fertilization and after several cycles of cell division, these totipotent cells begin to specialize. ❖The inner cell mass, the source of embryonic stem cells, becomes pluripotent.
- 27. Multipotency describes progenitor cells which have the gene activation potential to differentiate into discrete cell types. Eg. a multipotent blood stem cell and this cell type can differentiate itself into several types of blood cell like lymphocytes, monocytes, neutrophils, etc. Multipotency
- 29. A unipotent cell is the concept that one stem cell has the capacity to differentiate into only one cell type. A close synonym for unipotent cell is precursor cell. It is currently unclear if true unipotent stem cells exist. Hepatoblasts, which differentiate into hepatocytes (which constitute most of the liver) or cholangiocytes (epithelial cells of the bile duct), are bipotent. Unipotent and Bipotent
- 31. Dedifferentiation Epimorphosis. In some species, adult structures can undergo dedifferentiation to form a relatively undifferentiated mass of cells (a blastema) that then redifferentiates to form the new structure. Such regeneration is characteristic of regenerating amphibian
- 33. Hormones and Differentiation sry gene present in the short arm of the Y chromosome produces SRY proteins SRY proteins responsible for the development of bipotential gonads into testes Testes produces two hormones 1. Testosterone 2. Antimullerian hormone