General Biology Laboratory BIO 112 Morehouse College
1
Laboratory Orientation Case Study
There are two parts to this case study. Your typewritten responses to both parts are
due in laboratory next week.
Case Study Part 1: The Method of Science
In Class: Work in groups of four students and address the Scientific Methods issues and
the Academic Honesty issues. There will be an open discussion of these issues after the
groups.
Homework: Write responses to the Scientific Methods questions and write an original
summary of the research article. Your typewritten responses must be in your own words.
The following is the complete abstract from “Role of actin filaments in the axonal
transport of microtubules” (Hasaka, Myers and Baas, 2004):
“Microtubules originate at the centrosome of the neuron and are then released for
transport down the axon, in which they can move both anterogradely and
retrogradely during axonal growth. It has been hypothesized that these movements
occur by force generation against the actin cytoskeleton. To test this, we analyzed
the movement, distribution, and orientation of microtubules in neurons
pharmacologically depleted of actin filaments. Actin depletion reduced but did not
eliminate the anterograde movements and had no effect on the frequency of
retrograde movements. Consistent with the idea that microtubules might also
move against neighboring microtubules, actin depletion completely inhibited the
outward transport of microtubules under experimental conditions of low
microtubule density. Interestingly, visualization of microtubule assembly shows
that actin depletion actually enhances the tendency of microtubules to align with
one another. Such microtubule-microtubule interactions are sufficient to orient
microtubules in their characteristic polarity pattern in axons grown overnight in
the absence of actin filaments. In fact, microtubule behaviors were only chaotic
after actin depletion in peripheral regions of the neuron in which microtubules are
normally sparse and hence lack neighboring microtubules with which they could
interact. On the basis of these results, we conclude that microtubules are
transported against either actin filaments or neighboring microtubules in the
anterograde direction but only against other microtubules in the retrograde
direction. Moreover, the transport of microtubules against one another provides a
surprisingly effective option for the deployment and orientation of microtubules in
the absence of actin filaments.”
Scientific Methods
1. What are the questions and problems being addressed by the research described in
this article? Identify both the narrow and the broader issues addressed by this
research.
