Devbiol LE1

• Developmental Biology


  Field of biology that has evolved from embryology (study of embryos)
• Embryo


  Early stage when the developing animal does not yet resemble the adult of the species
• Traditional Definition of Developmental Biology

  Study of structural changes in embryonic development

  
• Contemporary Definition of Developmental Biology

  Study of embryonic developmental processes of integrated complex phenomena

  
• How a single cell (simple) gets transformed into multicellular embryonic stage (complex)


  Embryology evolved into developmental biology (an analysis of biological development)
• How individual cells (simple) gets transformed into specialized cells (in structure & function)


  Embryology evolved into developmental biology (an analysis of biological development)
• Significance of Increasing the Knowledge in Embryology/Animal Developmental Biology:
• Foundations for:
• Embryology or developmental biology usually starts on the onset of fertilization ending in birth (mammals), hatching (avians and reptiles), and metamorphosis (amphibians)

  
• Development is made up of a series of uninterrupted correlated events
• Ontogenic development


  Development of a new individual from a fertilized oocyte (in the case of sexual reproduction) or development of a new individual from budding of from a parent organism (in the case of asexual reproduction)
• Phylogenetic development


  Evolutionary development of a species. Development from a simple form of life to a diversity of more complex forms of life.
• Major Accomplishments of Ontogenic Development

  • Generation of cell number (growth)
  • Cellular diversity within generation (differentiation)
  • Cellular order within generation (morphogenesis)
  • Continuity of life
• Mosaic Development


  The fate of a cell depends upon specific cytoplasmic determinants (unequally or asymmetrically distributed in the daughter cells) in the zygote
• If a part of the embryo is removed in mosaic development, certain cell types would be lacking in later stage of development
• If a blastomere is isolated in mosaic development, it cannot develop
• Regulative Development


  The fate of a cell depends upon interactions with neighbor cells, not by what piece of cytoplasm it has
• Characteristic feature of vertebrates is that when a blastomere is isolated early in cleavage, it can form a new complete individual
• Key Processes of Development

  • Cleavage division
  • Pattern formation (body axes formation)
  • Morphogenesis
  • Cell differentiation
  • Growth
• Embryonic cells are already in their destined location during cell differentiation
• Preformed Guidelines


  Directive influences on development that are present right at the start of ontogeny, such as maternal genes/maternal effect genes and oocyte cytoarchitecture
• Progressively-formed Guidelines


  Directive influences on development that appear gradually in every step of ontogeny, such as zygotic genes
• Anterior-Posterior axis is coupled to Gastrulation, where the developmental potential and inducing properties of cells in the dorsal lip of blastopore change with time
• Signaling factors


  • Wnt
  • FGF
  • ILGFs
  • BMP
• Gene products expressed at the dorsal lip of the blastopore

  • Chordin
  • Noggin
  • Follistatin
• Fate


  What cells would become, the range of cell types that a particular embryonic cell can give rise to, dependent on cell asymmetries, unequal cytoplasmic determinants, inductive information, and morphogens
• Potency


  Ability of a cell to follow a developmental pathway
• Levels of Potency


  • Totipotent
  • Pluripotent
  • Multipotent
  • Unipotent
• Oct4 is required for the maturation of ICM (inner cell mass), and Cdx2 is required for the maturation of TE (trophoectoderm)
• Determination


  Gradual commitment to a certain cell fate, geared to follow a certain developmental pathway
• Capacity and Competence


  1. Primary induction

  2. Secondary induction

  3. Reciprocal interaction

  4. Epithelial mesenchymal interaction
• Embryonic Induction


  Evocative influence of cells, within a cell or a cell with a neighboring cell and between cell
• Regulative Development


  Potential of a cell is much greater than what is indicated in its normal fate (if controlled exclusively by inductive signals)
• Mosaic Development


  Embryonic cells can develop only according to their early fate; their fate is determined very early (if controlled exclusively by cytoplasmic determinants)
• Concepts of Inevitability


  • Apoptosis (programmed cell death)
  • Biological clock
  • Intercellular clock
  • Presence of normal homeobox genes
  • Positional information
• Functions of Programmed Cell Death (PCD) During Development:
• At metamorphosis in Drosophila melanogaster, larval structures are destroyed and novel structures are raised from undifferentiated cells termed marginal discs
• In PNS Development, neurons are overproduced and survival depends on competition for limited amounts of survival-promoting factors produced in target tissues
• Somite segmentation is controlled by a biological clock with the expression of a specific group of genes that oscillates in a 2-hr cycle
• Cell-intrinsic Timers


  Intracellular developmental programs that change precursor cells over time