1.4 Fate Maps & Cell Lineages

Question 0

Name and describe the major morphogenetic processes regulated by Mesenchymal cells.

Answer 0

1. Condensation - where the mesenchyme cells become a single epithelial tube, sheet, sphere, etc. (Cartilage mesenchyme)
2. Hyperplasia - Mitosis produces more cells (cell division, e.g. Limb mesenchyme)
3. Apoptosis - cells die (e.g., interdigital mesenchyme)
4. Migration - cells move to particular places @ particular times (e.g., heart mesenchyme)
5. Matrix secretion & degradation - synthesis or removal of extra cellular layer (e.g., cartilage mesenchyme)
6. Hypertrophy - growth (cells get larger, e.g. Fat cells)

Question 1

Describe the 2 major cell types in the embryo. Define each of them to highlight their differences.

Answer 1

1. Epithelial cells - tightly connected cells that form sheets or tubes.
2. Mesenchymal cells - unconnected cells that act independently.

Question 2

Name & describe the major morphogenetic processes regulated by epithelial cells.

Answer 2

1. Dispersal - Epithelium becomes mesenchyme (entire structure).
2. Delamination - part of the epithelium becomes mesenchyme.
3. Growth or shape change - Cells remain attached as morphology is altered. (E.g., neurulation)
4. Intercalation - rows of epithelia merge to form fewer rows (e.g., vertebrate gastrulation)
5. Mitosis - Cell division within a row or column (e.g., vertebrate gastrulation)
6. Matrix secretion and degradation - Synthesis or removal of extra cellular matrix (e.g., vertebrate organ formation)
7. Migration - Formation of free edges (e.g., chick ectoderm)
8. Matrix secretion & degradation - vertebrate

Question 3

Name and describe four techniques (in evolutionary progression) for developing species-specific fate maps.

Answer 3

1. Direct observation of living embryos - like tunicate (sea squirt) Styela partita, zebrafish, chick, etc. E.G. Conklin given 1st credit for this in 1905.
2. Dye marking - Vogt (1929) traced the fate of different amphibian cells utilizing vital dyes. These became more diluted over divisions. Fluorescent dyes improve upon this.
3. Genetic labeling -in 1920s Hilde Mangold & Hans Spemann created chimeric embryos with 2 species of newt. A best example is utilizing quail embryo inside chick embryo.
4. Transgenic DNA chimeras - transfer DNA to a cell that expresses GFP when run.