BIOM 2208 - Differentiation and Developmental Biology MODULE ONE: PRINCIPLES OF DEVELOPMENTAL BIOLOGY Lecture one · Development: organisation of cells into functional units through spatial and temporal expression of genes in specific microenvironments SPACIAL AND TEMPORAL EXPRESSION OF GENES · The default state of genes is a repressed state (genes are in chromatin = DNA and protein) . DNA is wrapped around many histone octamers to create a "ring" of histone octamers with DNA wrapped around them. Then another protein (another type of histone) links them together . This is a tight structure that has to be unwound for DNA to be transcribed as machinery can't get in < unwindases unwind the DNA in various histone regions to allow for transcription and thus expression of the genes WHAT DOES DIFFERENTIAL GENE EXPRESSION DO? · Induction: where a group of cells or tissues become committed to a functional unit (e.g. neural tissue) and this involves inducers . Regionalisation: of tissues (e.g. in the CNS the brain and spinal cord regions are formed) involves morphogens. < regionalise the tissue along a different axis · Differentiation: of specific cell types/phenotypes within regions involving growth factors etc. FUNDAMENTAL PRINCIPLES OF DEVELOPMENTAL BIOLOGY 1. Development is progressive (involves proliferation, differentiation, migration, cell death) and is primed by maternal factors 2. Development involves gene networks or circuits that are reutilised in different tissues 3. Development relies on organising centres 4. Development is self-organised DEVELOPMENT IS PROGRESSIVE (1) . 40 trillion cells in the human body < this all comes from 1 cell. Thus, one cell produces 40 trillion cells in an 8 to 9-month period · Development is progressive. I.e. takes time to get to a fully grown adult (to get 40 trillion cells) and there longer it takes, usually the more complex/intricate the structure/shape. · Large cell number is produced by starting with a small number of major cell types · "teams" of cell < the body partitions the cells into groups and each cluster performs a different function · In vertebrates there are 3 primary cell types: o Ectoderm (skin and neural tissue) o Mesoderm (muscle, bone, blood) o Endoderm (gut and organ tissue) How do cells get their identity? o Have to have some way of identifying it (mechanism of labelling the identity of that cell) o E.g. neuron in the cortex < neuron cells in one area will be different to those in another, need to label them both differently to see what gives them their identity. o Need to do this progressively throughout time (through different stages of development) o Example of one of the ways to solve this problem: tracking the lineage of cells. Trying to find out where the adult cells progressed from/started out from by tracking their lineage (they did this with a species of worm and traced back 600+ cells to 1 cell) < Lineage tracing (used to use an ink to track) FATE MAP . Tracing the lineage creates a fate map . Fate mapping is