This action funds an NSF Minority Postdoctoral Research Fellowship for FY 2008. The fellowship supports a research and training plan in a host laboratory for the Fellow who also presents a plan to broaden participation in biology. The title of the research and training plan for this fellowship to Labib Rouhana is "Analysis of mRNA regulation required for regeneration and stem cell maintenance in planarian flatworms." This research will be conducted at the University of Illinois under the sponsorship of Dr. Phil Newmark, and the University of Kyoto under the sponsorship of Dr. Kiyokazu Agata.
Planarians are simple bilateral flatworms with nervous, digestive and reproductive systems, capable of regenerating and remodeling entire organisms from small body fragments. This amazing capability is attributable to a population of stem cells which make up approximately 30% of their body. Studies in planarians are relevant to human stem cell biology and regenerative medicine, as over 80% of genes known to be required for proper regeneration and stem cell maintenance in planarians are also present in the human genome. This research is seeking to understand the crucial role that this level of regulation plays during planarian regeneration by: 1) identifing the mRNAs associated with proteins (named Bruno, Pumilio, and Nanos) that are required for proper regeneration in planarians; 2) determining the effects of the RNA-binding proteins on their respective mRNA targets; and 3) testing the role of their targets in regeneration.
The training objectives include increased understanding of planarian biology and molecular biology. The broader impacts include increasing the number of minorities at the pre-doctoral and post-doctoral level through innovative outreach programs in addition to the new knowledge to be gained about this organism and regeneration.
Normally, all the cells that make up an organism have the same genetic information (i.e. genome), but a neuron is very different from an intestinal cell, and this is because different cells turn on different genes. What mechanisms allow for specific genes to be activated in order to produce the proteins needed for a specific cell shape and function? To answer this question, I decided to study regulation of gene expression in planarians. Planarians are free-living flatworms that possess amazing regenerative abilities (Figure 1). Although this may sound like science fiction, planarians actually use their regenerative ability to reproduce asexually. They stick their tail to a surface and pull-away to tear themselves in half. The resulting products from such event will regenerate missing parts within a week and ultimately give rise to two planarians. The regenerative ability of these animals is fueled by a population of stem cells known as "neoblasts", which comprise 20-30% of all cells in their bodies. These cells proliferate continuously, but some of their progeny give rise to specified planarian cell types (e.g. neurons, muscle cells, intestinal cells, sperm and eggs) in a process called differentiation. Messenger RNA (mRNA) is the intermediate molecule for gene expression. Specific DNA sequences in the genome (genes) serve as foundation for the production of mRNA of the same sequence. In most cases, proteins are synthesized from such mRNAs, and go on to carry the function encoded by their respective gene. For many years, scientists assumed that progression from DNA to RNA to Protein was automatic. However, recent studies have revealed that significant regulation happens at the level of mRNA. Neoblasts express an array of tissue-specific RNA-binding proteins, and contain characteristic macromolecular structures made up of RNA and protein (reviewed by Shibata et al., 2010). I hypothesized that RNA processing factors common to planarians and humans are important for the regulation of noeblasts, and found that such was the case (Figure 2). My work in the laboratory of Dr. Kiyokazu Agata (Kyoto University) determined that Argonaute-2, a protein that represses protein synthesis from mRNAs identified by matching small RNA molecules (called microRNAs), is required for maintenance of planarian stem cell identity and regeneration (Rouhana et al., 2010). I also characterized mRNA regulators required for regeneration but not for maintenance of neoblast identity or number. I believe that some of these regulators mediate destruction of mRNAs that dictate stem cell identity during the process differentiation. Thus, their absence leads to planarians full of stem cells that are not able differentiate and consequently fail to regenerate (Rouhana et al., 2010). Alternatively, mRNAs repressed by Argonaute-2 may encode for factors that promote differentiation, and their premature de-repression may lead to differentiation and loss of neoblasts. Finally, my work at the laboratory of Dr. Phillip A. Newmark (Howard Hughes Medical Institute/University of Illinois) determined that stabilization of the aforementioned macromolecular structures correlates the ability of a second class of small RNAs (called Piwi-interacting RNAs) to prevent events that could genomic instability in planarian stem cells (Rouhana et al, submitted). Collectively, these results (and those of others) have revealed that stem cells of somr understudied animals are regulated by proteins better known for functions in the germ-line (reviewed by Juliano and Wessel, 2010). The concept of a stem cell is not restricted to what is known from in vitro studies of embryonic or induced pluripotent stem cells. New perspectives such as the one resulting from this project could greatly benefit the field of regenerative medicine. This work was presented to hundreds of students during the course of this project. I personally visited elementary schools and showcased the work of my host laboratories in events open to the general public in Illinois and California. The response obtained from people of all ages was inspiring. I am naturalized American citizen, originally from Mexico, who is able to pursue a career in science and academia thanks to efforts aimed at increasing the number of under-represented minorities in science. Financial support for these efforts comes from taxpayers, and I would like to thank them and the National Science Foundation for their support. REFERENCES Juliano C. and Wessel G. (2010). Versatile germline genes. Science 329, 640-641. Newmark P. A. and Sanchez Alvarado A. (2002). Not your father's planarian: a classic model enters the era of functional genomics. Nature Review Genetetics 3, 210-9. Rouhana L., Shibata N., Nishimura O., and Agata K. (2010). Different requirements for conserved posttranscriptional regulators in planarian regeneration and stem cell maintenance. Developmental Biology 341, 429-43. Rouhana L., Vieira A. P., and Newmark P. A. (2011). Symmetric dimethylarginine methylation and the involvement of chromatoid bodies in piRNA regulation of planarian stem cells. Submitted. Shibata N., Rouhana L., and Agata K. (2010). Cellular and molecular dissection of pluripotent adult somatic stem cells in planarians. Development Growth Differentiation 52, 27-41. Last Modified: 12/08/2011 Submitted by: Labib Rouhana The reference listed as: Rouhana L., Vieira A. P., and Newmark P. A. (2011). Symmetric dimethylarginine methylation and the involvement of chromatoid bodies in piRNA regulation of planarian stem cells. Submitted. Is replaced by the revised version: Rouhana L., Vieira A. P., Roberts-Galbraith R. H, and Newmark P. A. (2012). PRMT5 and the role of symmetric dimethylarginine in chromatoid bodies of planarian stem cells. Development (in press).
