Collins Lab Blog

Cell biology – technical details

The historical roots of cell biology lay in anatomy; basically the discipline where a biological specimen is taken apart and examined in order to deduce information about its constituent parts. The scientific challenge of this mode of investigation is to move the examination from the purely descriptive into the realm of the informative.

Take the following simple example of the growth of Saccharomyces cerevisiae cells. These single cell eukaryotes grow and divide by a process whereby new cells emerge from a small patch on the side of the progenitor cell; a process giving rise to the colloquial name of budding yeast.

A progenitor cell (aka the “mother cell’) expands until reaching a threshold size. At this point, the mother cell maintains constant size and growth is directed towards a new ovoid shape that emerges from the mother cell. This is affectionately referred to as “the bud”. The bud grows in size following which cell division occurs at the “neck” region connecting the two ovoid shapes and the bud is now officially an independent daughter cell.

If we take a growing population of budding yeast and examine them under the microscope, we see a variety of single ovoid shapes, some smaller, some larger and some double ovoid shapes; all cells at different stages of growth.  Such an  examination is straightforward and can be made by anybody with a simple microscope.

Now the scientific investigation can begin. The number of cells of each shape are a direct reflection of the length of time taken for each stage of the cell cycle. We could sort the population and count the number of cells in each category. We could identify mutant populations that block cell growth at a particular stage of the process and watch the cells just prior to that stage accumulate in number. These are classic avenues of investigation in biology. But, there’s an important catch, the technical execution of the experiment. Schematically, we’d expect our field of cells in the microscope to look something like the picture on the left, but in reality, when we peer down the microscope, we see something the picture on the right.

The technical problem is that in our experiment, we cannot distinguish between two ovoid shapes representing independent cells that are happen to lie very close together and two ovoid shapes that represent the mother cell and a large bud that are connected by a neck. This problem significantly affects the accuracy of our experiment.

To illustrate what I mean, examine the two pictures below. One of these images shows two cells next to each other and one image shows a mother cell connected to a large budding daughter cell.

Which is which and how can we tell the difference? Answers in the next post, in the meantime, if anyone would like to take a stab at this question please leave a comment. The best answer will win a brand new Sarstedt maker pen, which is, in my opinion, the finest fine-tip marking pen for lab use.

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