Cell lineage

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 Cell Lineage

  • CellLineage of an organism is the pattern of cell division during its development 
  • In lineage tracing, a single cell is marked in such a way that the mark is transmitted to the cell’s progeny , resulting in a set of labelled clones.
  • Provides information about number of progeny of the founder cell, their location and their differentiation status.
  • Applied to stem cell research and in modelling cellular heterogeneity in cancer.
  • Began with Whitman’s description of cleavage patterns in leech embryos. Later lineage were described in nematodes, sea urchins and ascidians.
Why Caenorhabditis elegans ?
  • Small, relatively simple and precisely structured organism. Anatomy has been described in detail and one can map out the exact lineage of every cell in the body.
  • Development is highly determinant , and cell fate decisions are autonomous from the surroundings.
  • Number of somatic cell is highly limited . Make the analyses straight forward and accurate.
  • Fate of every cell in the embryo has been determind using the timelapse microscopy.

Method to study Cell Lineage

  •  Direct observation:-
  • Direct observation or by reconstruction from fixed specimens.
  • Required embryos that were very small , transparent and rapidly developing.
  • Nomarski differential interference contrast microscopy allows imagining transparent specimens.
  • Time lapse microscopy in multiple focal planes has been has allowed entire cell lineage of individual animals to be recorded digitally.
  • Clonal analysis 
  • In large Opaque or slowly developing embryos where direct observation of cell divisions is not feasible.
  • Necessary to mark individual cells by physical or genetic means , and later the progeny are identified by expression of the marker.
  • Cells can be labelled by injection with a non-diffusing dye such as a fluorescein-conjugated dextran.
  • Progeny of a single cell forms a clone.
  • Possible issue is that the dye gets progressively  diluted with each division.
  • Used to study cheek and my million neutral development.

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