- 1 Development
- 1.1 Objectives
- 1.2 Concepts
- 1.3 Mitosis and Meiosis
- 1.4 Zygote
- 1.5 Mitosis
- 1.6 Patterning
- 1.7 Induction and Cell Signaling
- 1.8 Cell migration and shape change
- 1.9 Morphogenesis by Apoptosis
- 1.10 Glossary
- 1.11 2017 Course Content
This lecture is about how the embryo makes use of cellular mechanisms (described during this term) to construct itself.
It is concerned with concepts rather than detail.
You should appreciate how these cellular mechanisms integrate to produce the whole organism.
The image above shows the first cell that forms following fertilization, and that cell's offspring 8 weeks later.
- Understand the utility of model organisms in research on developmental mechanisms
- Understand the conceptual importance of somatic cell nuclear transfer (cloning) experiments
- Understand the concept of how lineage restriction is controlled by the expression of DNA-binding transcription factors
- Brief understanding of how transcription factor expression can be controlled by signaling pathways
- Brief understanding of cell movements in development
- Brief understanding of how apoptosis can create shape
- Cell proliferation careful control of cell division is needed to ensure that tissues achieve their correct size at the right time and in the right place.
- Tissue differentiation - specialization of cells and expression of tissue-specific genes e.g. globin gene in blood cells.
- Patterning - temporal and spatial expression of DNA-binding proteins e.g. the homeobox (Hox) genes.
- Induction and cell signaling
- Short range by cell-cell contact e.g. delta/notch
- Long range by diffusible morphogen e.g. sonic hedgehog
- Cell migration and shape change – cells (or parts of cells e.g. neurons) need to move through other tissues to reach the right location e.g. germ cells and limb myoblasts.
- Morphogenesis by selective apoptosis (programmed cell death) – shapes can be created by the formation of temporary structures that are later removed by coordinated apoptosis e.g. formation of digits
Mitosis and Meiosis
Mitosis 2 Daughter cells identical to parent (diploid)
Meiosis Germ cell division (haploid)
- Reductive division
- Generates haploid gametes (egg, sperm)
- Each genetically distinct from parent
- Genetic recombination (prophase 1)
- Exchanges portions of chromosomes maternal/paternal homologous pairs
- Independent assortment of paternal chromosomes (meiosis 1)
Cell Birth - Mitosis and Meiosis 1st cell division- Meiosis
Homologous chromosomes pairing unique to meiosis
- Each chromosome duplicated and exists as attached sister chromatids before pairing occurs
- Genetic Recombination shown by chromosomes part red and part black
- chromosome pairing in meiosis involves crossing-over between homologous chromosomes
(For clarity only 1 pair of homologous chromosomes shown)
Comparison of Meiosis/Mitosis
- After DNA replication 2 nuclear (and cell) divisions required to produce haploid gametes
- Each diploid cell in meiosis produces 4 haploid cells (sperm) 1 haploid cell (egg)
- Each diploid cell mitosis produces 2 diploid cells
Male and Female Meiosis
- Links: Gametogenesis
Chromosomal Sex Determination
| Chromosome Y Chromosome
|| Chromosome X Chromosome
- All cells formed from the zygote do so by mitosis.
- Cell proliferation is strictly regulated
- Unregulated/abnormal proliferation is oncogenesis or Cancer
Cell Cycle - External Regulators
- Cell replacement in different tissues
- regulated by growth factors
- can be specific for specific cell types
Growth Factors and Cell Cycle Progress
- External factors can also regulate progression through cycle
- Growth factors primarily act on cells in G0 and G1
- The restriction point is the timepoint in G1 when cells no longer respond to withdrawal of growth factors by returning to G0, but progress to S phase.
- thought to involve retinoblastoma protein (pRb)
Growth Factor Model
- Fibroblasts in culture
- Serum (Prepared by clotting)- Proliferation
- Plasma (Prepared by centrifugation, no clotting)- no proliferation
- allows platelets to release secretory granules
- Platelet-derived growth factor (PDGF)
- Connective tissue cells express PDGF receptors which bind the small PDGF glycoprotein
Other Growth Factors
- Interleukin-2 (IL-2)
- Stimulates T lymphocytes
- Nerve Growth Factor (NGF)
- Promotes neuronal survival and growth
- Epidermal Growth Factor (EGF)
- Vascular Endothelial Growth Factor (VEGF)
- Insulin-like growth factors (IFG-1, IGF-2)
Cell Cycle- Internal Regulators
- 1980s - studies in Xenopus eggs and starfish oocytes:
- purification of M phase-promoting factor (MPF);
- identification of its components as cyclin B and CDC2 (also called cyclin-dependent kinase, Cell Division Cycle)
Induction and Cell Signaling
Many developmental signals are reused at different times and different locations.
Membrane Receptors Signaling between cells, cells and matrix, tissues, and systemically, is key to the developmental and differentiation process.
Some signals final actions are as transcription factors.
Cell migration and shape change
Skeletal Muscle Stages
- Myoblast - individual progenitor cells
- Myotube - multinucleated, but undifferentiated contractile apparatus (sarcomere)
- Myofibre (myofiber, muscle cell) - multinucleated and differentiated sarcomeres
- primary myofibres - first-formed myofibres, act as a structural framework upon which myoblasts proliferate, fuse in linear sequence
- secondary myofibers - second later population of myofibres that form surrounding the primary fibres.
- Muscle Stem Cell - Satellite Cell
Morphogenesis by Apoptosis
Apoptosis in digit development
- Cell lineage – a linear sequence of cell fate that traces progressive states of differentiation. Analogous to the "ancestry" of a cell – e.g. liver cells are derived from the endodermal lineage.
- Embryonic patterning – the underlying mechanism by which a shapeless ball of cells is provided with the information required to develop into its appropriate anatomical form and structure.
- Cell commitment (specification) – the process by which a cell becomes dedicated to becoming some other more mature cell type due to its position in the embryo or as a result of its cell lineage: reversible if exposed to a different environment e.g. grafted into another location.
- Cell determination – the process by which a cell becomes irreversibly locked into a particular cell fate: precedes differentiation. However, the cell shows no outward signs of what they are destined to be.
- Differentiation - the process by which a less specialized cell undergoes a recognizable change (of shape and/or function) into a more specialized cell type: irreversible (under normal circumstances).
- Morphogenesis – The overall process by which the embryo resolves itself into a mature shape
2017 Course Content
Lectures: Cell Biology Introduction | Cells Eukaryotes and Prokaryotes | Cell Membranes and Compartments | Cell Nucleus | Cell Export - Exocytosis | Cell Import - Endocytosis | Cytoskeleton Introduction | Cytoskeleton - Microfilaments | Cytoskeleton - Microtubules | Cytoskeleton - Intermediate Filaments | Cell Mitochondria | Cell Junctions | Extracellular Matrix 1 | Extracellular Matrix 2 | Cell Cycle | Cell Division | Cell Death 1 | Cell Death 2 | Signal 1 | Signal 2 | Stem Cells 1 | Stem Cells 2 | Development | 2017 Revision
Dr Mark Hill 2015, UNSW Cell Biology - UNSW CRICOS Provider Code No. 00098G