Overview on the modern era of evelopmental biology- pptx

Overview

1. OVERVIEW ON THE MODERN ERA OF DEVELOPMENTAL BIOLOGY EMERGED THROUGH MULTIDISCIPLINARY APPROACHES Submitted to: Dr. Chandini V.K. Assistant Professor Department Of Botany Submitted by: Ananya J.S. Roll No: 5 Department Of Botany

2. Overview Developmental biology Modern developmental biology Preview of developmental biology Embryology – approaches References 1

3. Developmental Biology Development biology is a fundamental aspect of biology.
Depends upon complex mechanisms and many layers of “biological information” that are superimposed one upon another. Field of biology that studies how a single cell (the fertilized egg) gives rise to a fully grown organism. It brings understanding between genotypes and phenotypes. 2

4. Modern Developmental Biology Modern developmental biology is mostly experimental.
Embryogenesis (embryo formation) determines the overall body plan.
Organogenesis (organ formation) determines subsections of the body (examples: vertebrate limb, Drosophila eye). 3

5. Developmental biology provides understandable explanations to varies aspects of cell biology, genetics, physiology, ecology, evolution, histology and anatomy.
Developmental biology and genetics have become closely related to form a distinct biological discipline, called developmental genetics.
It has also provided convincing explanations to various problems of evolution and phylogeny. Ecology is also related to developmental biology. 4

6. Preview Of Developmental Biology The embryogenesis of animal species includes various stages or phases: 1. Gametogenesis 2. Fertilization 3. Cleavage 4. Gastrulation 5. Organogenesis 6. Growth
7. Differentiation
8. Morphogenesis
9. Metamorphosis 5

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8. Embryology Study of animal development traditionally has been called embryology. In recent years, developmental biology use as the discipline that studies embryonic and other developmental processes. Three major ways of embryology are Anatomical approaches Experimental approaches Genetic approaches 7

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10. Anatomical Approaches There are several strands that together constitute the anatomical approaches to development. Comparative embryology Evolutionary embryology Teratology Mathematical modelling 9

11. Comparative Embryology Study of how anatomy changes during the development of different organisms. Here, a comparative embryologist may study which tissues form the nervous system in the fly or in the frog. Charles Darwin’s theory of evolution restructured comparative embryology and gave it a new focus. 10

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13. Evolutionary Embryology Study of how changes in development may cause evolutionary changes and of how an organism’s ancestry may constrain the types of changes that are possible. One of the most important distinctions made by the evolutionary embryologists was the difference between analogy and homology. Both terms refer to structures that appear to be similar. Homologous structures are those organs whose underlying similarity arises from their being derived from a common ancestral structure. 12

14. Eg ; the wing of a bird and the forelimb of a human are homologous. Moreover, their respective parts are homologous. Analogous structures are those whose similarity comes from their performing a similar function, rather than their arising from a common ancestor. Eg ; the wing of a butterfly and the wing of a bird are analogous. Homologies must be made carefully and must always refer to the level of organization being compared. 13

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16. For instance, the bird wing and the bat wing are homologous as forelimbs, but not as wings. In other words, they share a common underlying structure of forelimb bones because birds and mammals share a common ancestry. However, the bird wing developed independently from the bat wing. Bats descended from a long line of nonwinged mammals, and the structure of the bat wing is markedly different from that of a bird wing. 15

17. One of the most celebrated cases of embryonic homology is that of the fish gill cartilage, the reptilian jaw, and the mammalian middle ear. First, the gill arches of jawless fishes became modified to form the jaw of the jawed fishes. In the jawless fishes, a series of gills opened behind the jawless mouth. When the gill slits became supported by cartilaginous elements, the first set of these gill supports surrounded the mouth to form the jaw.
There is ample evidence that jaws are modified gill supports 16

18. Teratology Study of birth defects. These anatomical abnormalities may be caused by mutant genes or by substances in the environment that interfere with development. The study of abnormalities is often used to discover how normal development occurs. Agents responsible for these abnormalities are called teratogens. 17

19. In 1961, Lenz and McBride independently accumulated evidence that thalidomide, prescribed as a mild sedative to many pregnant women, caused an enormous increase in a previously rare syndrome of congenital anomalies. The most noticeable of these anomalies was phocomelia , a condition in which the long bones of the limbs are deficient or absent. Over 7000 affected infants were born to women who took this drug, and a woman need only have taken one tablet to produce children with all four limbs deformed. 18

20. 19 Phocomelia condition

21. Other abnormalities induced by the ingestion of thalidomide included heart defects, absence of the external ears, and malformed intestines. The integration of anatomical information about congenital malformations with our new knowledge concerning the genes responsible for development has had a revolutionary effect and is currently restructuring medicine. This integration is allowing us to discover the genes responsible for inherited malformations, and it permits us to identify the steps in development being disrupted by teratogens. 20

22. Mathematical Modeling Describe developmental phenomena in terms of equations. Certain patterns of growth and differentiation can be explained by interactions whose results are mathematically predictable. The revolution in graphics technology has enabled scientists to model certain types of development on the computer and to identify mathematical principles upon which those developmental processes are based. 21

23. Pattern formation and growth are two areas in which such mathematical modeling has given biologists interesting insights into some underlying laws of animal development. By focusing on a few developmental systems and the corresponding models that have been developed, this illustrates the potential and possibilities in developing an intuition about interactions among biochemical components and their emergent properties. Most animals grow by increasing their volume while retaining their proportions. 22

24. D’Arcy Thompson (1942) similarly showed that the spiral growth of shells (and fingernails) can be expressed mathematically (r=a), and that the ratio of the widths between two whorls of a shell can be calculated by the formula r= e^2 cot 23

25. If the shape is preserved because all components grow at the same rate, called isometric growth. Growth is not a uniform phenomenon and not all parts of body grow at same rate. Different growth rates of parts within the same organism, called allometric growth. 24

26. Growth of male fidder crab, Uca pugnax also an example for allometric growth When the data plotted (the body mass on the x axis, the mass on the y axis), one obtains a straight hose slope is the a/c ratio.
In the male, a/c ratio is 6:1. This means that the mass of chela increases six times faster than the mass of rest of the body. 25

27. Principles Of Developmental Anatomy Organisms must function as they form their organs. They have to use one set of structures while constructing others.
Preformation is not in the anatomical structures, but in the instructions to form them. The inheritance of the fertilized egg includes the genetic potentials of the organism.
The preformed nuclear instructions include the ability to respond to environmental stimuli in specific ways. Allometric growth can create dramatic changes in the structure of organisms. 26

28. Experimental Approaches Anatomical approaches gave rise to experimental approaches. Four major techniques involved in experimental embryology; 1. Defect experiment 2. Isolation 3. Recombination
4. Transplantation 27

29. One destroys a portion of the embryo and then observes the development of the impaired embryo. Defect Experiment 28

30. Isolation Experiment One removes a portion of the embryo and then observes the development of the partial embryo and the isolated part. 29

31. One observes the development of the embryo after replacing an original part with a part from a different region of the embryo. Recombination Experiment 30

32. One portion of the embryo is replaced by a portion from a different embryo. This fourth technique was used by some of the same scientists when they first constructed fate maps of early embryos Transplantation Experiment 31

33. Principles Of Development – Experimental Anatomy Developing organisms are adapted to the ecological niches in which they develop. Before cells overtly differentiate into the many cell types of the body, they undergo a “covert” commitment to a certain fate. In autonomous specification, morphogenetic determinants are apportioned to different blastomeres during cell cleavage. In conditional specification, the fate of a cell often depends upon its neighbors Different cell types can sort themselves into regions by means of cell surface molecules such as cadherins . These molecules can be critical in patterning cells into tissues and organs. 32

34. Genetic Approaches Genetic approaches built on the foundations of earlier two approaches. All the processes that are essential for development cell division, growth, differentiation, pattern formation and morphogenesis Proteins are encoded by genes, so development is controlled to a large degree by gene expression. Many genes shown to have important roles in development encode two particular types of protein, transcription factors and components of signaling pathways. 33

35. Transcription factors are important because they control gene expression, and therefore act as coordinators of developmental processes. Signaling pathways are necessary for cells to perceive external signals, either from other cells or from the environment. Two strands; Mutagenesis Transgenics 34

36. Mutagenesis Process by which the genetic information of an organism is changed, resulting in a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens. It can also be achieved experimentally using laboratory procedures. In nature mutagenesis can lead to cancer and various heritable diseases, but it is also a driving force of evolution. 35

37. This immediately found use as a genetic tool to induce mutations in specific ways which in turn can be to determine the phenotype of the organism, the function of the genes and even the nucleotides. Two types Site-directed mutagenesis Random and extensive mutagenesis 36

38. Site-directed Mutagenesis Site-directed mutagenesis is a molecular biology method that is used to make specific and intentional changes to the DNA sequence of a gene and any gene products. Also called site- specific mutagenesis or oligonucleotide-directed mutagenesis, it is used for investigating the structure and biological activity of DNA, RNA, and protein molecules, and for protein engineering 37

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40. Random And Extensive Mutagenesis Useful approach when many mutations are desired. There is less control over the resulting modifications. It does not require the researcher to have any prior knowledge about the structural properties of the DNA sequence being targeted This technique has helped map out critical residues of proteins 39

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42. Transgenics Process of introducing foreign or exogenous DNA into an animals genome is called transgenesis . Transgenics is the process of introducing an exogenous gene called a transgene into a living organism so that the organism will exhibit a new property and transmit that property to its offspring.
Transgenic animals include rats, pigs and sheeps . 41

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44. Transgenic animals are useful as disease models and producers of substances for human welfare.
Some transgenic animals are produced for specific economic traits. For example, transgenic cattle were created to produce milk containing particular human proteins, which may help in the treatment of human emphysema.
Other transgenic animals are produced as disease models. For example, genetically engineered mouse, called Onco Mouse carrying a gene that promotes the development of various human cancers. 43

45. Transgenic Mice: A transgenic mice is one that carries a foreign gene that has been deliberately inserted into its genome. The foreign gene is constructed using recombinant DNA methodology. There are three basic methods of producing transgenic mice: DNA microinjection
Embryonic stem cell-mediated gene transfer
Retrovirus-mediated gene transfer 44

46. DNA Microinjection Direct microinjection of a chosen gene construct from another member of the same species or from a different species, into the pronucleus of a fertilized ovum. The introduced DNA may lead to the over- or under-expression of certain genes or to the expression of genes entirely new to the animal species. The manipulated fertilized ovum is transferred into the oviduct of a recipient female, or foster mother that has been induced to act as a recipient by mating with a vasectomized male. 45

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48. Embryonic Stem Cell Mediated Gene Transfer This method involves prior insertion of the desired DNA sequence by homologous recombination into an in vitro culture of embryonic stem (ES) cells.
Stem cells are undifferentiated cells that have the potential to differentiate into any type of cell (somatic and germ cells) and therefore to give rise to a complete organism.
These cells are then incorporated into an embryo at the blastocyst stage development. 47

49. The result is a chimeric animal. ES cell-mediated gene transfer is the method of choice for gene inactivation, the so-called knock-out method. 48

50. Retrovirus Mediated Gene Transfer To increase the probability of expression, gene transfer is mediated by means of a carrier or vector, generally a virus or a plasmid.
Retroviruses are commonly used as vectors to transfer genetic material into the cell, taking advantage of their ability to infect host cells in this way. Offspring derived from this method are chimeric, i.e., not all cells carry the retrovirus.
Transmission of the transgene is possible only if the retrovirus integrates into some of the germ cells. 49

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52. Principles Of Developmental Genetics Differential gene expression from genetically identical nuclei creates different cell types. Differential gene expression can occur at the levels of gene transcription, nuclear RNA processing, mRNA translation, and protein modification. Specific transcription factors can recognize specific sequences of DNA in the promoter and enhancer regions. They activate or repress transcription from the genes to which they have bound 51

53. References Gilbert, S. (2006). Developmental Biology (9 th ed.). Sunderland, Mass. Sinauer . Twyman , R. (2001), Instant Notes in Developmental Biology. Oxford: Bios Scientific. https://www.sciencedirect.com/journal/developmental-biology https://www.ncbi.nlm.nih.gov/books/NBK10097/ 52

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