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ARTICLES |
Department of Molecular, Cellular, and Developmental Biology and Life Sciences Institute, University of Michigan, Ann Arbor, MI 48109-2216
Submitted December 5, 2004; Revised July 12, 2005; Accepted July 19, 2005
| ABSTRACT |
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Key Words: systems biology functional genomics bioinformatics active learning cooperative learning yeast graduate undergraduate
| INTRODUCTION |
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With these technologies drawing a strong foothold in modern molecular biology, a growing subdiscipline of genomics is seeking to integrate large-scale data sets in order to achieve a more complete representation of the cell as a whole. This integrative approach to genomic biology is one branch of the subdiscipline termed "systems biology" (Ideker et al., 2001; Kitano, 2002). The rationale behind this integrative approach is simple: While no one data set can comprehensively define a cellular pathway or response, several complementary data sets may be integrated in order to reveal such pathways or provide insight into a response or process unobtainable from the consideration of a single given data set. For example, DNA microarray analysis may be used to identify genes differentially regulated at the level of transcription; however, it cannot be used to identify genes regulated posttranscriptionally (e.g., by protein phosphorylation). In contrast, mass spectrometry is extremely useful as a means of identifying proteins modified by phosphorylation but is not applicable as a means of directly identifying differentially transcribed genes. Considered in union, however, data sets derived by microarray analysis and mass spectrometry may provide an indication of both transcriptional and posttranscriptional regulatory events and, therefore, a more comprehensive understanding of the genes and regulatory mechanisms driving a given cell response.
Systems biology is rapidly increasing in popularity. While it is difficult, if not impossible, to conclusively trace the lineage of this field, most studies in systems biology reference back to the work of Ideker et al. (2001), in which the authors implemented an integrative genomics strategy to define pathway components involved in galactose utilization in yeast. In the years since, the term systems biology has been used in over 110 published articles, and several institutes are now dedicated to this genomic discipline. The widespread application of systems biology is unlikely to diminish in the immediate future, with the increasing numbers of integrative genomic studies under way.
As promising research paradigms are developed, it is both our responsibility and privilege as educators to communicate this work. The advent of systems biology provides us with just such an opportunity; however, many obstacles do exist in accurately presenting this material to graduate and upper-level undergraduate students. In particular, it is difficult to convey effectively the unique advantage provided by systems biology: namely, that by integrating the data from multiple approaches, we can potentially generate novel findings beyond those that can be derived from the examination of any one individual data set. Furthermore, in order to appreciate such studies, students must possess a basic understanding of the approaches in use; typically, an introduction to these approaches is not provided in lower-division biology courses.
Recently, a number of educators have reported the benefits of "active learning" as applied to the teaching of undergraduate and graduate biology (Klionsky, 2002; Lord, 1994; Malacinski and Zell, 1996; Wyckoff, 2001). Briefly, active learning refers to the application of any teaching strategy in which students actively participate in academic exercises or projects rather than passively listen to an instructor's lecture (Baines et al., 2004; Harwood, 2003; Malacinski, 2003). Defined as such, active learning draws from a wide range of teaching practices; a comprehensive overview of these teaching strategies is provided in Paulson and Faust (2002). Active-learning techniques encompass individual exercises designed to foster effective listening practices, written exercises designed to promote student retention of lecture material, and group exercises in which students may learn from one another. In particular, the latter approach represents a subset of active learning termed "cooperative learning" (Sharan, 1994). In cooperative learning, students typically work in groups of three or more to complete fairly complex tasks, such as multistep exercises, research projects, and presentations (McKinney and Graham-Buxton, 1993). By performing these tasks in groups, the students may utilize the specific expertise of their respective classmates a particular advantage in considering material that is inter-disciplinary in nature.
Here, I present a cooperative-learning-based approach suitable for the introductory overview of systems biology at the graduate or upper-division undergraduate level. As an introduction to systems biology, I asked my graduate class at the University of Michigan, Ann Arbor, to reconstruct a cellular pathway using a modification of the "jigsaw" learning method. The class was broken into small groups, and each group was asked to interpret a different sample data set. Each group's independent findings were subsequently presented before the class as a whole to be ultimately integrated into a single comprehensive interpretation of the pathway. The message in this exercise became clear very quickly: The sum conclusions drawn by integrating the various data sets outweighed the individual conclusions drawn from any one data set in isolation. In total, this exercise proved very successful in actively engaging students as well as in disseminating relevant information. Furthermore, the approach provides a readily modifiable template for the instruction of many genomic disciplines at a variety of student levels.
| CLASS FORMAT/STRUCTURE |
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| MODIFIED JIGSAW GROUP PROJECTS |
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To instill within my students an appreciation of the potential benefit in a systems biology-based approach, I utilized a teaching strategy featuring a modified form of the jigsaw approach (Clarke, 1994). In this learning method, the class is divided into small groups; each group is asked to complete a discrete part of a total project. Once all groups have completed their assigned tasks, the findings from each group are presented before the class as a whole to be integrated into a finished project. By analogy, the individual group findings may be thought of as pieces in a jigsaw puzzle; the jigsaw puzzle can only be solved by properly integrating the various component findings.
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| LARGE-SCALE DATA SETS |
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DNA Microarray Analysis
Students were presented with sample results from a comparative
hybridization of RNA extracted from a strain deleted for a given gene and RNA
extracted from a wild-type strain (Figure
1A). Students were told that complementary DNA (cDNA) prepared
from the wild-type RNA had been labeled with a green fluor; cDNA prepared from
the deletion strain RNA had been labeled with a red fluor. In the data set
presented to the students, hybridization results for each gene (corresponding
to a "spot" on the array) were listed with an accompanying color:
red, green, or yellow. According to the indicated labeling scheme, a red spot
indicates an increased concentration of deletion strain RNA and, therefore, a
gene whose expression is induced in the deletion strain. Similarly, a green
spot indicates a gene repressed in the deletion strain, while a yellow spot
indicates a gene whose expression level is unchanged between the two strains.
These microarray data are intended to reflect a classic approach in which
polymerase chain reaction products are spotted onto a glass microscope slide
(DeRisi et al.,
1997).
By analyzing the relative expression pattern of each gene in the various deletion strains, students can formulate a transcriptional network of pathway components. The network drawn from the complete set of gene deletion/microarray analysis is shown in Figure 1B.
Yeast Two-Hybrid/Mass Spectrometric Analysis
A second group of students was presented with sample results from a
large-scale two-hybrid analysis of all pathway components in pairwise
combination (Figure 2A). The
two-hybrid system described here utilizes a simple HIS3 reporter,
such that growth on medium lacking histidine may serve as an indicator of
two-hybrid reporter activity and a corresponding protein-protein interaction.
The hypothetical analysis presented to my students encompassed all possible
pairwise combinations between the 26 genes included in this pathway; results
were depicted as a grid of 676 assays, wherein colony growth indicates a
protein-protein interaction.
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In addition, students were given a small set of data from a mass spectrometric analysis of pathway components identifying three phosphorylated proteins (T, B, and F) and one ubiquitinylated protein (I). Conclusions drawn from these two-hybrid and mass spectrometric analyses are indicated in Figure 2B.
Homology Searching
Finally, a third group of students was presented with output from a series
of homology searches using the basic local alignment search tool (BLAST;
Altschul et al.,
1990). Specifically, BLAST protein (BLASTP) alignments were
generated for five genes: B, C, F, H, and Q; the other genes were said to
possess no orthologs. Complete amino acid sequences were available for each
gene. A typical BLASTP alignment output is shown in
Figure 3A. The alignments were
created using actual yeast genes of a type identical to the hypothetical gene
in the student data set. For example, in the pathway constructed here, gene C
is intended to be an E3 ubiquitin-protein ligase; therefore, I downloaded the
amino acid sequence of the yeast E3 ligase Rsp5p and used this sequence to
query the nonredundant SwissProt database by BLAST. By interpreting the
resulting sequence alignment output, students can identify the function of
gene C as an E3 ubiquitin ligase. The conclusions drawn from these BLAST
alignments are listed in Figure
3B.
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| STUDENT RESPONSE |
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Of the 16 students enrolled in Bioinformatics 526, 13 were full-time students in the Bioinformatics Program at the University of Michigan. These 13 students were asked to assess critically the active-learning sessions after completion of this course. One student was absent during the systems biology classes; three students could not be reached for comment. The remaining nine students completed an anonymous survey assessing the utility and effectiveness of this teaching strategy. Results from this survey are presented in Figure 5.
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As indicated, respondents were unanimously positive in regards to the active-learning-based approach, affirming that the group strategy was both effective and beneficial (Figure 5A). One student wrote that the active-learning approach "allowed an individual group to focus on its problem, brainstorm, collaborate but then come back and hear about the other groups, which allowed for depth and breadth." Another student stated that an understanding of methods for data interpretation "can best be learned through a hands-on approach." One student suggested that it would be helpful to distribute the data sets prior to class a valid suggestion that can be easily incorporated into future sessions.
To enable quantitative assessment, students were asked to utilize a numeric scale in comparing active-learning and lecture-based classes in Bioinformatics 526 (Figures 5B, C). Students did not draw a distinction between the two teaching strategies in regards to information transfer, finding both approaches to be equally informative. Opinion was mildly split in regards to the efficiency of each approach; the class generally felt that the active-learning sessions were a more efficient use of time, although three students offered contrasting viewpoints. Opinion was decidedly uniform, however, when students were asked to select the teaching approach they preferred. Not one student preferred a lecture-based approach, and 75% of the class (six of nine respondents) strongly favored a cooperative-learning format. In interpreting these results, it should be noted that my class sessions were taught using active-learning approaches; the lecture-based sessions in Bioinformatics 526 were presented by other instructors, and the comparisons indicated here must be viewed in this light.
To assess retention of course material, each surveyed student was asked to define systems biology and list an advantage and disadvantage of this genomics approach. Each student was able to define systems biology at a level consistent with the expectations of this course. Nearly all respondents emphasized the integrative nature of the discipline and were equally accurate in identifying advantages (e.g., identification of whole-pathway effects and interpathway cross-talk) and disadvantages (e.g., expense, computational requirements, the preponderance of false-positive results in genomic data sets).
By other metrics as well, student response was extremely positive. Students undertook the jigsaw exercise with genuine enthusiasm; in fact, two groups asked for additional time to continue their respective analyses. After 30 min, student groups remained unanimously focused on their assigned data sets. I overheard two students commenting to each other: "It's amazing how time flies when you're really working." Furthermore, each group was accurate in interpreting the data, suggesting that the students were indeed gaining valuable experience in analyzing realistic experimental results. By the end of class, several students were able to point out a minor error I had made in integrating the various data sets. It is possible that the success of this exercise results, in part, from the fact that the audience consisted of a small group of bioinformatics students; it will be interesting to consider the success of these class exercises when used on a larger group of undergraduate students.
To gain additional insight into the effectiveness of my cooperative-learning-based strategy, I met individually with several members from this class. From even a cursory conversation, it was evident that these students had grasped a basic understanding of systems biology. One student went so far as to discuss with me methods by which a systems biology-based approach might be incorporated into his own doctoral research. Another student commented upon the limitations of bioinformatics within systems biology and on the need for computational methods by which the process of data integration can be automated. This level of understanding far exceeded my expectations for an introductory overview of such a challenging field.
| A FLEXIBLE TEMPLATE FOR ACTIVE LEARNING |
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Obviously, the data sets used for this exercise need not be identical to the ones I have selected they are included in this manuscript strictly as a suggested model. In fact, for future classes, I intend to utilize data sets related to a genuine eukaryotic pathway; I expect the added authenticity of the data will enhance student interest and enthusiasm (Campbell, 2003). Furthermore, additional data sets may be incorporated into this exercise; for example, large-scale data sets describing protein localization and abundance may complement the data sets described here.
| CONCLUSIONS |
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| ACKNOWLEDGMENTS |
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| FOOTNOTES |
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Address correspondence to: Anuj Kumar (anujk{at}umich.edu).
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