Tagging Stem Cells - Science
In 1963, Drs. Becker, Till and McCulloch published a seminal paper about the identification of stem cells demonstrating its properties of proliferation and differentiation.(1) The Tagging Stem Cell exhibit is a simplified explanation of the experiment using abstracted images of hematopoietic cells and an accompanying narrative intended for a general audience.
This page is about some of the science details embedded in the images. To see the images with a more general narrative, please the Exhibit page.
Illustration of hematopoietic cells represented by a few physical features. The elusive stem cell is theoretically included on the far right in a group of cells that are relatively nondescript.
Cell types from left to right:
- Megakaryoctyes - much bigger than stem cells and have multiple nuclei
- Erythroblasts - appears distinctly blue
- Neutrophilic myelocytes (large) and N. metamylocytes (small) - dots representing granules and generally bigger than stem cells
- Lymphoid progenitors, lymphoblasts, possibly a stem cell and other non-descript progenitor cells
Conceptual image of marrow cells after irradiation. Each "nucleus" is coloured with a different pattern representing the random and unique chromosomal damage caused by radiation.
Illustration of four different colonies grown from the irradiated marrow cells. Within a colony, there are different types of hematopoietic cells but every cell has the same "karyotype" illustrating that they are clones of a single cell. Different markings are used between colonies suggesting that each colony originated from a different and unique stem cell.
Other minor details include illustrating some cells in active stages of cell division. And the colonies have different compositions of cells lines, as described in a subsequent paper published in 1969 by Fowler et.al. (2)
To further illustrate the stem cell properties of differentiation and proliferation, the last slide shows a single colony after 14 days. Although this was not discussed in the 1963 Becker et. al. paper, it was discussed in other articles by Till and McCulloch.
Three features from the research are incorporated in this slide:
- there are many more cells than the day 11 colonies,
- the cells are more mature and
- there is greater heterogeneity of cell types.
Of special note are the blue erythropoietic cells shown at various stages of discarding their nucleus and becoming mature red blood cells represented by double pink circles.
- Becker, A.J., E.A. McCulloch, and J.E. Till 1963 Cytological demonstration of the clonal nature of spleen colonies derived from transplanted mouse marrow cells. Nature, 197:452-454. See original paper here: tspace.library.utoronto.ca/bitstream/1807/2779/2/Nature_1963_197_452.pdf .
- Fowler, J.H., A.M. Wu, J.E. Till, E.A. McCulloch and L. Siminovitch. 1967 Journal of Cellular Physiology, 69: 65-72
Unfortunately, this journal paper is not available for free. Obtaining this article was quite difficult. See blog page: Denied Access. Are you kidding me? (coming soon)
Further online information
Video by FCIHR. Dr. Till explains the structure of the experiment and shares anecdotes that make the experiment much more memorable. I highly recommend it.