Cell determination and differentiation

A brief of cell determination and differentiation

1. CELL DETERMINATION AND DIFFERENTIATION VISHNUPRIYA.C I MSc BIOCHEMISTRY

2. CELL DETERMINATION The process by which an undifferentiated embryonic cell becomes committed to develop into a specific type of cell . It can also be defined as the process by which portions of the genome are selected for different expression in embryonic cells Cell determination appears to involve the selective activation of certain sets of genes and the inactivation of others

3. There are 100 different types of cells that carry out a specific different functions and they have specific role in our body Eg : neuron – it propagates electrical signal between different types of cells. Once a zygote is formed, it begins mitotic divisions that produces most cells. These early cells are said to be totipotent which has ability to become all types of cell of an whole organism

4. As the cell divide and develop further the developmental potential decreases and the cell fate is determined.

5. Differential gene expression T he process of differential gene expression is how cells grow up and determine just what they are going to be . The neuron cell is separated from muscle cells by the components present in it, that gives it special characteristics These components are either made by proteins

6. Different proteins are expressed by different genes. Therefore specialized cell differ from one another in that genes that ultimately express. There are two different pathways in cell determination . The difference in the pathway 1 and pathway 2 lies in the types of genes that cells use

7. Pathway 1:

8. Pathway 2

9. MECHANISM OF CELL DETERMINATION In most cases cellular determination is due to inductive signaling between the cells In inductive signaling one produces a ligand that then goes onto a second cell and stimulates it to produce a particular pathway. T here are 3 different ways in cell determination

10. DIFFUSION: A nearby cell can produce a ligand that moves into a extracellular matrix and then attaches on to a protein receptor to target cells.

11. DIRECT CONTACT: In this second mechanism one cell can interact directly with another cell by using transmembrane protein this stimulates the formation of the signal molecule to the cell

12. GAP JUNCTIONS: Some cells are connected by gap junctions and the signaling molecules will move from one cell to another via gap junctions

13. CELL DIFFERENTIATION Cellular differentiation is the process where a cell changes from one cell type to another. Usually, the cell changes to a more specialized type Differentiation occurs numerous times during the development of a multicellular organism as it changes from a simple zygote to a complex system of tissues and cell types.

14. It is part of developmental biology. Different tissues have different kinds of organelles inside the cells . Differentiation dramatically changes a cell's size, shape, metabolic activity, and responsiveness to signals. These changes are largely due to changes in gene expression . With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself.

15. It does involve switching off many genes not needed in a particular tissue. Thus, cells in different tissues may have very different physical characteristics despite having the same genome PURPOSE OF CELL DIFFERENTIATION Humans have many different types of cells with different jobs, such as blood cells that carry oxygen and nerve cells that transmit signals to all parts of the body. Cell differentiation is the process by which cells become specialized in order to perform different function

16. PROCESS AND STEPS OF CELL DIFFERENTIATION A cell capable of differentiating into any type of cell is known as "totipotent". For mammals, totipotent includes the zygote and products of the first few cell divisions . There are also certain types of cells that can differentiate into many types of cells. These cells are known as "pluripotent" or stem cells in animals ( meristemic cells in higher plants).

17. While this type of cell can divide to produce new differentiated generations, they retain the ability to divide and maintain the stem cell population making them some of the most important cells . Examples of stem and progenitor cells include: Hematopoietic Stem Cells - These are from the bone marrow and are involved in the production of red and white blood cells as well as the platelets.

18. Mesenchymal Stem Cells - Also from the bone marrow, these cells are involved in the production of fat cells, stromal cells as well as a given type of bone cell . Epithelial Stem Cells - These are progenitor cells and are involved in the production of certain skin cells

19. Muscle Satellite Cells - These are progenitor cells that contribute to differentiated muscle tissue. The process of cell differentiation starts with the fertilization of the female egg . As soon as the egg is fertilized, cell multiplication is initiated resulting in the formation of a sphere of cells known as the blastocyst.

20. It is this sphere of cells that attach to the uterine wall and continues to differentiate. As the blastocyst differentiates, it divides and specializes to form a zygote that attaches to the womb for nutrients. As it continues to multiply and increase in size, the differentiation process results in the formation of different organs.

21. Specification and Determination During the differentiation process, cells gradually become committed towards developing into a given cell type. Here , the state of commitment may be described as "specification" representing a reversible type of commitment or "determination" representing irreversible commitment.

22. Although the two represent differential gene activity, the properties of cells in this stage is not completely similar to that of fully differentiated cells. For instance, in the specification state, cells are not stable over a long period of time. There are two mechanisms that bring about altered commitments in the different regions of the early embryo.

23. These include : Cytoplasmic localization Induction Cytoplasmic Localization - This occurs during the earliest stage of embryo development. Here, the embryo divides without growth and undergoes cleavage divisions that produce blastomeres (separate cells). Each of these cells inherit a given region of the cytoplasm of the original cell that may contain cytoplasmic determinants

24. Once the embryo becomes a morula (solid mass of blastomeres ) it is composed of two or more differently committed cell populations. The cytoplasmic determinants may contain mRNA or protein a given state of activation that influence specific development.

25. INDUCTION In induction, a substance secreted by one group of cells causes changes in the development of another group. During early development, induction tends to be instructive in that tissue assumes a given state of commitment in the presence of the signal . .

26. During the final phase of cell differentiation, there is formation of several types of differentiated cells from one population of stem cells of the precursor . Here, terminal differentiation occurs both in embryonic development as well as in tissues during postnatal life . Control of the process largely depends on a system of lateral inhibition. That is, cells differentiating along a given pathway send out signals which repress similar differentiation by the neighboring cells.

27. A good example of this is with the developing CNS of vertebrates (central nervous system). In this system, neurons cells from the tube of neuroepithelium possess a surface receptor known as Notch and a cell surface molecule known as Delta that can bind to the Notch of adjacent cells and activate them.

28. GENE EXPRESSION REGULATES CELL DIFFERENTIATION Cell differentiation occurs during multiple stages of development. During cell differentiation, the cell size and shape changes dramatically, as does its ability to respond to signaling molecules. Signaling molecules are molecules that bring messages to cells that help the cell know which activities and processes to perform.

29. Signaling molecules carry a message to a cell receptor, which interprets the message through a signal transduction pathway Gene expression is the process in which the information stored in DNA is used to produce a functional gene product. Gene expression plays a critical role in the morphological changes that take place in a developing embryo and fetus and in the differentiation of stem cells to form specialized cells.

30. In general the cell differentiation occurs only when a specific genes are switched off and on

31. TYPES OF CELL DIFFERENTIATION MORPHOLOGICAL DIFFERENTIATION : During the cells multiplication in blastomeres individual cells and group of cells become structurally different from other cells Eg : a common startin g point in generalized ectoderm, nerve cells, and epidermal cells acquire distinguishing features of size, shape, Internal architecture.

32. BEHAVIOURAL DIFFERENTIATION : Although all cells exhibit common basic attributes such as metabolism and irritability special functional capabilities are eventually superposed on these general properties Eg : nerve cells come to transport electrical disturbances, muscles to contract, glands to secrete special products

33. CHEMICAL DIFFERENTIATION: The elaboration and assortment of chemical differences lie in the morphological and behavioural differences that ultimately emerge the acquisition of special biochemical properties by the cells proceeds the appearance of a neural tube, heart.

34. HOW CELLS GET DIFFERENTIATED AS SOMATIC AND GERM CELLS ? During the development of zygote, in the stage of blastomere (which is after 90minutes after fertilization) the cells get divided by MITOSIS and they form stem cells After certain divisions of mitosis they undergo MEIOSIS and they become germ cells.

35. What is the role of DNA in cell differentiation ? Nearly all cell types in a large organism contain the same DNA, yet they express their genes differently Gene expression describes the way in which genetic information is put into action. DNA is first transcribed into mRNA. The codons of mRNA specify the sequence of amino acids in a protein. Proteins, in turn, play a key role in producing an organism’s traits

36. What is the role of RNA in cell differentiation? Changes in the pattern of gene expression affect the types and amounts of RNA produced by a cell . Recall that DNA is transcribed into mRNA. mRNA then provides instructions that direct the production of proteins in the process of translation.

37. The types and number of proteins a cell generates help to determine how a cell differentiates . New research suggests that RNA can directly affect cell differentiation by shutting down the expression of targeted genes through a process called RNA interference

38. What is the role of the environment in cell differentiation ? A cell’s internal and external environment can affects its pattern of gene expression and cell differentiation . For example, during development in many animals, the concentration of certain transcription factors in the cytoplasm of the egg cell determines basic body plan—which part of the embryo will become head, tail, front, and back.

39. External environment, specifically temperature, during the development of turtles and some other reptiles helps to determine the sex of hatching offspring

40. Undifferentiated adult stem cells make it possible to continue to form specialized, differentiated cells. In humans, there are high concentrations of these adult stem cells in the skin, brain, and bone marrow.

41. Recent research has shown that in many cases adult skin cells can be induced to reverse their differentiation process and assume many of the properties of embryonic cells. The resultant cells are known as “induced pluripotent stem cells,” or iPS cells . Induced pluripotency is now the subject of intense research around the world.