[1] History of Developmental Biology.pdf

History of Developmental Biology Edited by: La Vera U. Sombito AY 2024-25  DEFINITIONS: Embryology – descriptive study of development Developmental Biology- study of processes and mechanisms behind development; mostly experimental Phylogenetic development- gradu...

History of Developmental Biology Edited by: La Vera U. Sombito AY 2024-25  DEFINITIONS: Embryology – descriptive study of development Developmental Biology- study of processes and mechanisms behind development; mostly experimental Phylogenetic development- gradual evolutionary history of a species Ontogenetic development- transformation of an organism within its own lifetime  Phases of ontogenetic development: Gametogenesis, Fertilization, Cleavage, Gastrulation, Organogenesis, Growth and Histological Differentiation *Metamorphosis/ Regeneration Scope Of Developmental Biology Developmental biology unites the disciplines of molecular/cellular biology, genetics, and morphology.  Molecular and cell biology tell us about how individual genes and cells work. In development this means inducing factors, their receptors, signal transduction pathways, and transcription factors.  Genetics tells us directly about the function of an individual gene and how it relates to the activities of other genes. Morphology is both a consequence and a cause of the molecular events.  The first processes of development create a certain simple morphology, which then serves as the basis on which further rounds of signaling and responses can occur, creating a progressively more complex morphology.  A sciencewith lots of questions that need to be answered…  Development DOES NOT happen by magic. Information and mechanisms at the cellular and/or molecular levels are needed to accomplish development.  HISTORICAL BACKGROUND 1. Aristotle (340 BC)  Do all parts of a developing organism come into existence together and simply grow larger?  Is development a stepwise process characterized by progressive organization and an increase in complexity? He observed that new structures arose progressively in embryos (e.g. blood, blood vessels, heart, blood vessels around organs). This supported epigenesis (17th century), i.e., the organism develops in a stepwise fashion from an unorganized state. He believed that the embryo was formed from menstrual blood interacting with a male vital factor present in the semen. This creative force forms the maternal substance into embryonic body parts. 2. Bonnet & Swammerdam: (17 th century) Preformation Theory: embryonic parts are already present in the sperm or egg (animalculists or ovists) which simply grow in size in development. Leeuwenhoek and other early microscopists claimed to have seen the homunculus. HOMUNCULUS 3. Caspar Friedrich Wolff (1759) Similar to epigenetic theory but postulated that a development force inherent in the matter of the embryo directs the laying down of body parts in sequence. He laid the foundation for the Germ Layer Theory by showing that the material out of which the embryo is constructed is, in an early stage of development, arranged in the form of leaf-like layers.  Descriptive and Comparative Embryology 4. Karl Ernst von Baer (1828) - most coherent embryological data Baer’s law: More general features that are common to all members of groups of animals are developed in the embryo earlier than the more special features which distinguish the members of the group. Ex: brain & spinal cord, notochord, segmented muscles, aortic arches (present in all vertebrates) develop earlier than hair, feathers, limbs (which are present in various classes) 5. Fritz Muller (1864), Ernst Haeckel (1868) Biogenetic law: features that are inherited from the common ancestor of the group have an ancient origin, and develop earliest during ontogeny Example: “Big 4” characteristics of all embryonic chordates (notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail) appear similar despite differences in adult appearance. Divergent features are adaptations of the embryo to its surroundings (e.g. placenta) However, an embryo does not “pass through” the adult stages observed in lower animals.  ONTOGENY RECAPITULATES PHYLOGENY RECAPITULATION THEORY - the development of individual organisms (ontogeny) follows (recapitulates) the same phases of the evolution of larger ancestral groups of related organisms (phylogeny); basis of the biogenetic law 6. August Weismann (1883) Germ plasm theory - every germ cell during early development receives a complete set of units of heredity (“ids” or Mendel’s “genes”) Development involves orderly unpacking of an embryo as dictated by ids; interactions between parts make epigenetic development possible Each egg nucleus contain discrete localized determinants which result to unequal distribution of nuclear components during cleavage Cells cannot change their fate if a blastomere is lost (mosaic model of development)  Experimental Embryology 7. Wilhelm Roux (1905) Heat-killed one of the 2 blastomeres of a frog’s egg. Surviving cell developed half of a complete embryo Results either support both preformation and mosaic development, or reflect use of crude techniques which possibly caused defects in the other half. 8. H. Driesch (1891), Endres (1895), Spemann (1901), Schmidt (1903) If cleavage cells of a sea urchin were completely separated, each develop into a whole embryo (regulative model of development). Massive cell rearrangements and migrations precede or accompany specifications of development, allowing cells to acquire different functions.  Analytical (modern) Developmental Biology 9. T.H. Morgan (1919), Watson & Crick (1953) – units of heredity composed of sequence of DNA base triplets are transformed into an array of proteins, which acting partly on their own or through other chemical components, transforms the system that is an adult organism.  Experimental and analytical embryology demonstrated the existence of embryonic induction: chemical signals that controlled the pathways of development of cells within the embryo. The 20 th century experiments showed where and when these signals operated, but they could not identify the signals nor the molecular nature of the responses to them.  Molecular biology had started with the discovery of the 3-D structure of DNA in 1953, and became a practical science of gene manipulation in the 1970s. Once the toolkit had been assembled it could be applied to a whole range of biological problems.  The path of development could be experimentally altered by the introduction of new genes, or the selective removal of genes, or by an alteration of the regulatory relationships between genes.  APPLICATIONS:  Understanding of the genetic or chromosomal basis of many human birth defects which are due to mutations in genes that control development. It is now possible to screen for some of these, using DNA of the embryo or chorionic villi, using molecular biology techniques.  Identification of several new growth regulatory substances, some of which have entered clinical practice. For example the hematopoietic growth factors erythropoietin and granulocyte–macrophage colony- stimulating factor (GM- CSF) have both been used for some years to treat patients whose blood cells are depleted by cancer chemotherapy. Some other growth factors, such as the fibroblast growth factors (FGFs) have been used to assist the healing of wounds.  Discovered stem cell biology which has now become a huge science in its own right, with many potential medical applications.  FUTURE IMPACT:  Pharmaceutical industry can design potential new therapeutic drugs effective against cancer or degenerative diseases such as diabetes, arthritis, and neurodegeneration.  Prenatal screening towards elimination of human congenital defects.  Production of human cells, tissues, or organs for transplantation, e.g., making pancreatic β-cells for treatment of diabetes, dopaminergic neurons for treatment of Parkinson’s disease, and cardiomyocytes for treatment of heart disease.  Methods maybe fused with tissue engineering which can potentially generate more complex tissues and organs starting with the constituent cell types.  Produce pharmaceuticals in the milk of sheep, or vaccines in eggs.  Human genetic manipulation may cause some serious ethical and legal problems.  Summary Points: Development is epigenetic. Although it is regulated by the nucleus, it takes place primarily in the cytoplasm. It involves interactions between parts. The parts arise within gradient patterns or fields. Differentiation is in essence the development of the macromolecular pattern within the cell.  SOME LINGERING THOUGHTS… 1. Developmental Biology is not only a scientific discipline. It is also a social discourse that is deeply embedded in cultural concerns. 2. Reproductive cloning, assisted reproductive technology (ART), abortion, stem cell differentiation, genetic enhancement, gene therapy, environmental estrogens, sex selection, and teratogenesis all converge on developmental biology. 3. it is crucial that we should be educated toward having more social responsibility than we have ever wanted.