Sophisticated Lessons from Simple Organisms: Appreciating the Value of Curiosity-Driven Research Robert J
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© 2017. Published by The Company of Biologists Ltd | Disease Models & Mechanisms (2017) 10, 1381-1389 doi:10.1242/dmm.031203 SPECIAL ARTICLE Sophisticated lessons from simple organisms: appreciating the value of curiosity-driven research Robert J. Duronio1, Patrick H. O’Farrell2, Greenfield Sluder3 and Tin Tin Su4,* ABSTRACT revolutionary advances in medicine, in addition to the incremental For hundreds of years, biologists have studied accessible organisms and unsteady progress that medicine typically makes. Despite this such as garden peas, sea urchins collected at low tide, newt eggs, history of success, science is increasingly being tasked to focus on and flies circling rotten fruit. These organisms help us to understand application rather than discovery (Fang and Casadevall, 2010; Hand the world around us, attracting and inspiring each new generation of et al., 2013; Minogue and Wolinsky, 2010). It is therefore with a biologists with the promise of mystery and discovery. Time and time sense of urgency that we write this article to defend the winning ‘ ’ again, what we learn from such simple organisms has emphasized strategy of discovery first . our common biological origins by proving to be applicable to Our understanding of human diseases and the ability to treat them more complex organisms, including humans. Yet, biologists are hinges on a foundation of knowledge about basic biology. This increasingly being tasked with developing applications from the knowledge has been gained largely by research using organisms that known, rather than being allowed to follow a path to discovery of the as are experimentally tractable in ways that humans or human cells can yet unknown. Here, we provide examples of important lessons never be. Those who do not know the history of yeast, flies and other learned from research using selected non-vertebrate organisms. We non-vertebrate organisms and their contributions to biomedicine argue that, for the purpose of understanding human disease, simple may consider such studies as unworthy of participation or of organisms cannot and should not be replaced solely by human cell- funding. Given the growing excitement about human stem-cell- based culture systems. Rather, these organisms serve as powerful based cell culture systems, particularly organoids (Box 1), some discovery tools for new knowledge that could subsequently be tested may argue that organisms that do not recapitulate all of the for conservation in human cell-based culture systems. In this way, complexity of humans will cease to be useful in the near future. This curiosity-driven biological research in simple organisms has and will line of thought is not only incorrect but could hamper scientific continue to pay huge dividends in both the short and long run for progress. improving the human condition. In this article, we highlight the continuing value of curiosity-driven research, with a focus on widely used non-vertebrate experimental KEY WORDS: C. elegans, Drosophila, Invertebrates, Sea urchin, organisms. These are often referred to as ‘model organisms’ (Box 1) Yeast to highlight their utility in discovering and understanding fundamental biological principles that also apply to other Introduction organisms, particularly humans, and to mechanisms of disease. The emphases and directions of medical practice are influenced not Although we use this term for the remainder of the article, we wish to only by scientific evidence but also by factors such as financial emphasize that research using such organisms need not be motivated interests and societal trends. For example, interventions such as solely for the purpose of modeling human biology in order to cupping, the application of suction cups to the skin, have gained significantly enhance our understanding of human disease. popularity not due to scientific evidence (Lee et al., 2011), but based We will illustrate the utility of each model organism with seminal on popular figures promoting the practice. In contrast, impactful historical examples, rather than providing a comprehensive progress in medicine invariably follows major advances in overview. We hope to motivate the reader to look into additional biological understanding due to scientific discovery. Examples contributions. Indeed, it is hard to think of an aspect of biology that extend from Pasteur’s recognition of the infectious basis of many has not benefited from studies in model organisms, be it behavior diseases to the recent discovery of CRISPR/Cas9-based genome (e.g. Kravitz and Fernandez, 2015), aging (e.g. Kenyon, 2011) or editing (see Box 1 for a glossary of terms) (McNutt, 2015; Porter, memory (e.g. Dubnau and Tully, 1998). Highlighting past 1961). Such advances in our understanding of biology have driven achievements will not necessarily encourage future work. Therefore, we also discuss potential future breakthroughs that might come from curiosity-driven research in model organisms. 1Departments of Biology and Genetics, Integrative Program for Biological and This is not to say that we disagree with the well-supported Genome Sciences, and Lineberger Comprehensive Cancer Center, UNC Chapel contention that no one can predict at the time of discovery how Hill, NC 27599-3280, USA. 2Department of Biochemistry and Biophysics, University of California, San Francisco, CA 94158-2517, USA. 3Department of Radiology, applicable findings from basic research will turn out to be. For University of Massachusetts Medical School, Worcester, MA 01655, USA. example, John S. Dexter, investigating mutant notched wings of 4Department of Molecular Cellular and Developmental Biology, University of fruit flies (Dexter, 1914), could not have predicted the prominent Colorado, Boulder, CO 80309-0347, USA. role of the Notch cell surface receptor in cancer (Nowell and Radtke, *Author for correspondence ([email protected]) 2017; Ranganathan et al., 2011). We do not have such foresight either. Nonetheless, it is worth pondering what more we can learn T.T.S., 0000-0003-0139-4390 from model organisms, particularly in the era of human stem cells, This is an Open Access article distributed under the terms of the Creative Commons Attribution organoids and facile genome editing using CRISPR/Cas9-based License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed. technologies. Disease Models & Mechanisms 1381 SPECIAL ARTICLE Disease Models & Mechanisms (2017) 10, 1381-1389 doi:10.1242/dmm.031203 The first study asked a simple but fundamental question: which Box 1. Glossary genes control how one cell becomes two? Leland Hartwell and his Centrosomes: multi-protein structures that determine spindle polarity in colleagues recognized that the way budding yeast grew and divided mitosis through their function as primary microtubule-organizing centers would allow the identification of mutants that are defective in the of the cell. cell division cycle by simply observing the cells (Hartwell et al., Chromatin: DNA complexed with associated proteins, particularly 1970, 1973). The researchers took advantage of a useful feature of histones. Cleavage furrow: the constriction that cleaves the cell between the yeast. Because yeast can grow at different temperatures, one can separated sister chromosomes at the end of mitosis. isolate conditional mutants (Box 1) in which a gene product is active Conditional mutants: mutants that show the phenotype of interest only at a low temperature but becomes inactive at a high temperature. under specific conditions. These temperature-sensitive conditional mutants could be grown CRISPR/Cas9: clustered regularly interspaced short palindromic repeat and propagated at the low temperature and their defects examined (CRISPR)/CRISPR-associated protein 9. This term is used to refer to a after a shift to the high temperature. Because yeast cells are small genome editing tool. Differential interference contrast (DIC): a type of microscopy that uses and easy to grow, Hartwell and his colleagues were able to isolate polarized light to distinguish subcellular features in transparent objects. many temperature-sensitive mutants (Fig. 1A). By simply observing Epigenetic regulation: alteration in gene transcription due to changes cells at the high temperature, these researchers identified mutants in chemical modification of DNA or associated proteins. that were blocked at different stages of the cell cycle (Fig. 1B). This Epistasis: a genetic analysis method in which the phenotype of a mutant genetic screen, combined with genetic tools such as epistasis defective in two genes of interest is compared to the phenotype of single analysis (Box 1), allowed Hartwell and colleagues to identify mutants in each gene. The results can be used to infer the order in which virtually all of the genes involved in controlling the cell division the products of the two genes act in a biological pathway. ‘ ’ Genetic screen: an experimental technique in which individuals are cycle, or the CDC genes (Hartwell et al., 1970, 1973). A parallel selected from a mutagenized population based on a specific phenotype. analysis led by Paul Nurse and colleagues using similar methods Mechanical fragmentation: method used to cut sea urchin zygotes into identified the CDC genes in fission yeast (Lee and Nurse, 1987; viable fragments containing different nuclear makeups to, for example, Nurse, 1975). dissect the contribution of nucleus vs cytoplasm. The identification