A. Factual Knowledge

This week, I learned the definitions of  totipotent and pleuripotent. Totipotent refers to the cells formed shortly after fertilization that have the ability to specialize into any kind of cell. It has the most potency of any cell type. Pleuripotent, on the other hand, are the cells that result when totipotent cells first begin to differentiate. Pleuripotent cells can give rise to many different cell types, but is more differentiated than totipotent cells.

I know I have acquired this factual knowledge because I am able to compare and contrast totipotent and pleuripotent cell types (as done above) and also because I am able to apply their definitions to a real-world example. For instance, when C. elegans eggs become fertilized, the resulting zygote is totipotent. Once it divides into 2 cells, the cells are no longer totipotent because they can only grow into their respective ‘sides’ of the worm. In contrast, a human embryo can contain multiple cells but still have identical totipotency in all the cells– which is why an embryo in early developmental stages can split to form two whole individuals rather than two halves of a single person. It is only later in development that the cells become pleuripotent, at which point removal of certain cells may result in physical deformations in the mature fetus.

B. Conceptual knowledge

This week I learned what kinds of information we can obtain from the three broad types of experimental approaches: Look/stain and look, remove something, and add something. From “look” approaches, we can acquire lots of different information such as the location of structure, the appearance of structure, the location or distribution of proteins, the expression pattern of mRNA, the movement of different molecules, and much more. When something is removed. we learn what functions that unit is necessary for. This is in contrast to when you add something, in which case we learn what functions that unit might be sufficient for.

I have acquired this information because I am able to use this conceptual knowledge when analyzing data or exercising my ‘skills’. For example, if you were to present me with a case study in which the deletion of gene Y results in X phenotype, I could tell you that gene Y is necessary for the wild-type phenotype X. Likewise, I would be able to say that in an experiment where you add component A to result in affect B, component A is sufficient to induce affect B.

C. Skills

One skill I have acquired this week is the ability to know how to interpret experimental data– specifically, what data might mean and what limitations certain results have. As an extension of this skill, I also have learned how to identify how one might clarify or resolve the limitations of a particular experiment.

Some examples that I have to demonstrate this ability is:

• Be able to look at the relationships between cell potency and time/stage after fertilization, when transplanting genetic material into egg cells. In this case, it is important to realize that while we can conclude that as time increases potency decreases, we do NOT know that DNA is necessarily being deactivated. It may be that DNA is gradually being discarded as cells become more differentiated. In order to determine whether it is DNA being inactivated, or `DNA being discarded (or something else entirely), DNA could be quantified or sequenced to compare the DNA content between cell stages.
• Be able to conclude the phenotypic effects of the loss of the Rspo2 gene in frogs. Although the results show asymmetrical facial and limb development, it would be best to say that Rspo2 is involved in general facial and lib development, rather than say “it results in the right leg and left face being deformed”. This is because the asymmetrical deformations may be due in part to environmental effects, and that the asymmetry might be partially stochastic (random) regarding which side it effects.