Development (finished)

• Cell division: process of creating two daughter cells from a parent cell
• Cell differentiation: process by which a cell acquires its specialized functions
• Gene expression: process by which genetic material is used to drive cellular functions
• Morphogen: signaling factor that directs cell fate at a distance from their source of production
• Inductive Signaling: process through which a cell or group of cells secretes factors that influence neighboring cells
• Regional Determination: once embryonic tissues reach a certain stage of development they are committed to form their adult structures independent of their environment
• Gastrulation: process by which the bilaminar embryonic disc becomes the three key germ cell alyers needed to generate all the tissues/organs in the body
• Neural crest cells: embryonic cell populations that are formed between the developing neural tube and the epidermis

  • Cells migrate along very specific restricted pathways (routes) to give rise to many of the craniofacial structures
• Hox Genes: specialized set of genes that contain a homeodomain motif (homeobox) that carry a permanent record of positional information used to specify patterning
• The face is not recognizable until around 8 weeks
• All cells have the same genes, but each cell will respond differently based on their environment
• The genome provides the blueprint for the cell and is the entire set of genetic material in a cell
• The complement of expressed RNA and protein defines the identity of each cell
• Homologous developmental pathways and mechanisms operate in all vertebrate species to direct similar morphological changes

  • This permits the use of other animal models to study different disorders
• Multicellular organisms are enriched in proteins mediating cell communication
• Signaling pathways have been highly conserved throughout evolution
• The duration cells receive signals and the signals onset between species is what will induce diversity between different animals
• Secreted Wnt ligands bind to cell surface receptors which can stimulate specific gene expression
• Embryogenesis Steps:

  • Cell proliferation
  • Cell specialization
  • Cell interaction
  • Cell movement
  • (sometimes apoptosis to fine-tune development)
• Homeobox code: patterned expression of HOX protein family of transcription factors

  • Discovered by Ed Lewis (recieved Nobel Prize in 1995)
• Expression of the Hox genes is colinear with their order on the chromosome
• In the study with the fruit fly and Hox genes, the mutation caused a disruption of a regulatory element that caused the gene to be expressed more anteriorly
• Hox proteins are DNA binding transcriptional regulators
• Homeotic transformation: the replacement of one body part with another
• The homeotic selector genes control the identity of segments along the anteroposterior axis.
• All positional identity aspects in vertebrae are establish by Hox genes except for the face
• The face has its own homeobox-related code that defines the separate identity of the jaws and establishes the identity of the teeth
• Drosophila has 8 Hox genes (1-8) while humans have 4 Hox genes (A-D)
• Inductive signaling by morphogens can act over many cell distances
• The amount of cell signaling will affect how much gene expression will happen
• Morphogen: signaling factor that directs cell fate and tissue development at a distance from their source
• Nearby cells will have a higher level of gene expression, so distant cells will have a lower level of gene expression
• Gene expression is both distant-dependent and duration-dependent
• All aspects of craniofacial complex are defined by axes:

  • Left-right
  • Dorsal-ventral
  • Anterior-posterior
• Clinical treatments consider:

  • Form
  • Symmetry
• During the first 7 days of development, the zygote just undergoes cell division
• During E4, the morula has 32 cells
• During E6, the blastocyst has 64 cells
• During the morula and blastocyst stages is when assymetry can start to be seen
• The blastocyte doesn't undergo differentiation until it's implanted in the uterus