Sandra Leal, Ph.D.

Assistant Professor, Department of Biological Sciences

Research

My devoted students, myself, and my colleagues affiliated with the Leal lab are contributing to the field of developmental biology at the same time, just as we are all learning from the work. Since the 1954 publication of the seminal paper “Two or Three Bristles” by Curt Stern, a student of Thomas Hunt Morgan (the grandfather of modern genetics and a Southerner), the cellular, genetic, and molecular basis that form the pattern of approximately 450 interommatidial mechanosensory bristles within the hexagonal, multicellular array of the Drosophila compound eye has been an intriguing and complex area of study in the area of pattern formation. To this day, the mechanisms of bristle pattern formation of that compound eye are unknown. These are exciting times, as our basic research has reported landmark findings that will help unravel these mysteries of eye development and tissue pattern formation, with implications for scientific understanding of sensory organ development in general and by future translational studies to develop treatments to thwart cancer in particular. We are truly a “lab of firsts.”
In 2010 we initiated the nation’s first study examining the role of the T-box transcription factor (TF) gene midline (mid) in regulating Drosophila eye development (in Drosophila genetics, genes are italicized and the proteins they express are presented in regular type). These eye developmental studies were part of our research on the developing central nervous system (CNS) using the fruit fly as a model system. We are the first research group to report pioneering findings in an important foundation paper on eye development published in the prestigious journal Mechanisms of Development (Das et al., 2013). The foundation paper contributes to the knowledge base of TF regulation of eye development, an understudied area of research with only two other papers available in the scientific literature to this date.

I have proposed for the first time in this paper an original “Cell Selection Theory” (Das et al., 2013). I have also had the opportunity to name a potentially new cell type, strongly indicated by research results that we are working to render definitive. The name I have chosen for the cell is the “Grandmother Pre-SOP” cell or GPS cell. By the name, one understands the cell divides to produce a Ganglian Mother Cell (GMC). The GMC is also referred to as a sensory organ precursor (SOP) cell. The GMC or SOP cell divides to gives rise to distinct daughter cells. Five highly specialized daughter cells arrange themselves physically into a tight cohort to generate a mechanosensory bristle complex composed of a hair shaft, a socket, a neuron, a protective sheath for the neuron, and a glial cell. About 450 bristle complexes decorate a hexagonal array of eye cells in the adult fly. The organization of eye cells creates a visually stunning pattern described as a “neurocrystalline lattice,” (Ready et al., 1976) with bristle cells occupying alternate vertices of hexagonal units of cells (for an image of the eye see publication of Das 2013). We are now poised to understand how bristles are selected and geometrically arranged within the eye tissue. We have ascertained that mid plays a key role as a regulator of cell signaling. By investigating the role of mid, and by proving my proposed Cell Selection Theory, we will for the first time have a more detailed understanding as to how the beautiful bristle pattern is established. We will be the first to solve this long-standing mystery in the area of tissue pattern formation of the Drosophila eye.

Besides the creation of an exquisite pattern of eye bristles, we are very interested in studying GPS cells for another important reason. We believe each GPS cell is the functional antithesis of a cancer cell. While cancer cells divide and grow without restriction to form tumors, the GPS cell behaves in exactly the opposite manner. Early in development, it transitions into hibernation mode while all other cells within the eye tissue surrounding it are dividing and differentiating to become photoreceptor neurons (PNs). Like our human PNs, the PNs of the fruit fly transmit light and color to the brain for visual processing. After PNs have become specified, the GPS cells awaken in response to a currently unidentified signal to divide, giving rise to daughter cells that generate mechanosensory bristles within the eye. These bristles are critical for helping the fly navigate. If our lab can use fluorescent probes to specifically identify the GPS cells that give rise to the adult eye bristles during early development, we can physically isolate them using sophisticated microsurgical techniques under an ultra-high-power microscope with high resolution optics to magnify cells. Once isolated, we can measure changes in specific gene expression within GPS cells to discover what “makes them tick” or more importantly, to discover how they transition into and out of the quiescent state. Having a synopsis of genes that are expressed and those not expressed, like a thumbprint, will help us to develop innovative experimental strategies to hijack cancer cells by affecting the repertoire of their gene expression and placing them into a permanent state of hibernation.

We have shown, for the first time, that the mid gene is an essential member of the Notch-Delta lateral inhibition signaling pathway that specifies sensory organ precursor (SOP) cell fates. This is in addition to discovering potential GPS cells. Our work contributes significantly to the classic model of SOP cell fate specification, a specification supported by nearly 20 years of cumulative research by leading scientists in the field of developmental biology. We are the third lab group (not the first, but among the first ones) to publish a paper showing that mid suppresses cell death - quite a unique function for members of the T-box gene family. Results were previously reported only for mouse Tbx3 and Brachyury-T T-box genes (Conlon and Smith, 1999; Carlson et al., 2002; Das et al., 2013). We present further unequivocal evidence that mid functions as a pro-survival factor that thwarts cell death when cells are experiencing physiological stress (Chen et al., submission date November/December 2013). Moreover, we also hypothesize mid functions as a surveyor of cell growth and proliferation. When cells grow abnormally or overproliferate, we predict that the Mid protein regulates the expression of specific gene targets to prevent these cells from developing into a cancer. USM graduate student Petra Visic is working on a research thesis project to validate this hypothesis. We found that the mid gene interacts with bric-a-brac-1 and bric-a-brac-2 whose conserved human counterpart genes express a key domain implicated in the etiology of specific cancers. Mutations in other T-box genes are also known to result in cancer.

Additional Research:
My contributions to the field of developmental biology are not limited to the “eyes of the flies.” I am the first to identify mid as a new and novel regulator of cell-fate specification in the developing embryonic CNS (Leal et al., 2009). I brought the mid-CNS project with me to Southern Miss, and I completed the research studies in the Department of Biological Sciences from 2007-2009. My independent contribution as a junior faculty at Southern Miss toward the completion of this publication within yet another prestigious journal, Developmental Biology (Leal et al., 2009). Now that I have also identified numerous mid-interacting genes after undertaking a major two-year, time- and labor-intensive genetic screening approach, I am now prepared to return to my first developing tissue of interest, the CNS, to determine how these genes collaborate with mid to regulate neuronal specification and axon guidance. In addition, a productive collaboration with my colleague Dr. William Brooks (Calgary University, Canada) resulted in a co-authored paper published in the highest impact-rated journal in the field of developmental biology, Development. In that paper we reported that mid regulates pattern formation of the developing leg tissue (Svendson et al., 2009).

With such contributions to the field come opportunities for dissemination, which in turn, bring recognition to Southern Miss. I have co-authored three papers in high-impact rated journals, a book chapter (Neckameyer and Leal, 2009), and 35 abstracts. I have presented at one international, nine national, one regional, four local, and five in-house (at Southern Miss) scientific research conferences. I recently accepted an invitation to submit a review article in the highly respected journal Experimental Eye Research, with an anticipated submission date of the article this November or December with the assistance of my graduate student Brielle Menengazzi (2013). The output of the lab will support publishing at least one significant paper every year at a level equivalent to my peers conducting research at tier-one level research institutions.

Funding:
Funding for this research, typical to many laboratories, comes from a variety of sources. The lab has benefited from faculty start-up funds granted by Southern Miss, and from several honorable intramural awards including the Aubrey Keith Lucas and Ella Ginn Lucas Endowment for Faculty Excellence in 2013 and a Grant Development Award. I also received extramural funding from the Ford Foundation with matching funds from Southern Miss (Principal Investigator or PI, 2008), the National Science Foundation (NSF) (PI, 2009-2012) and a recent seed grant from the MS-INBRE program funded by a National Institute of Health grant awarded to Dr. Shearer (PI) and Dr. Elasri (co-PI) from the Department of Biological Sciences (2013-2014). Without this support, the contributions of the lab to the field of developmental biology would not be possible. I am awaiting notification from the NSF on a pending CAREER Award and will be submitting numerous grants to both federal and private funding sources this year and next (2013-2014) to gain additional research support for the lab.

In summary, I am looking forward to training future undergraduate researchers as I have a strong track record of having trained 40 undergraduates from USM and a few from William Carey where at least 75% of previous students are now enrolled in medical school, graduate school, and other professional schools including schools of optometry. I have also trained 9 Honor’s students who published high-quality theses and I am a champion of the Honor’s College. I welcome students of all ages and abilities to enjoy the rewards of science!

References Cited

Das, S., Chen, Q.B., Saucier, J.D., Drescher, B., Zong, Y., Morgan, S., Forstall, J., Meriwether, A., Toranzo, R., and Leal, S.M. 2013. The Drosophila T-box transcription factor Midline functions within the Notch-Delta signaling pathway to specify sensory organ precursor cell fates and regulates cell survival within the eye imaginal disc. Mechanisms of Development Epub (in press).

Carlson, H., Ota, S., Song, Y., Chen, Y., and Hurlin, P.J. 2002. Tbx3 impinges on the p53 pathway to suppress apoptosis, facilitate cell transformation and block myogenic differentiation. Oncogene 21:3827-3835.

Chen, Q.B., Das, S., Zong, Y., Menegazzi, B., Smith, R.B., Visic, P., Odom, K., Buti, W., Buford, K., Morgan, S., and Leal, S.M. The Drosophila T-box Transcription Factor Midline Functions within Stress-Reactive Signaling Pathways to Regulate Cellular Homeostasis. Estimated Submission Date to the journal Mechanisms of Development: November or early December, 2013.

Conlon, F.L. and Smith J.C. 1999. Interference with brachyury function inhibits convergent extension, causes apoptosis, and reveals separate requirements in the FGF and activin signaling pathways. Developmental Biology 213:85-100.

Leal, S.M., Qian, L., Lacin, H., Bodmer, R., Skeath, J.B. 2009. Neuromancer1 and Neuromancer2 Regulate Cell Fate Specification in the Developing Embryonic CNS of Drosophila melanogaster. Developmental Biology 325:138-150.

Neckameyer W.S. and Leal, S.M. Biogenic amines as circulating hormones in insects. In, “Hormones, Brain, and Behavior”, Academic Press, D. Pfaff, A. Arnold, A. Etgen, S. Farbach, R. Moss, and R. Rubin, Eds. 2009.

Ready, D.F., Hanson, T.E., and Benzer, S. 1976. Development of the Drosophila retina, a neurocrystalline lattice. Developmental Biology 53:217-240.

Stern, C. 1954. Two or three bristles. American Scientist 42:213-247.

Svendsen, P.C., Formaz-Preston, A., Leal, S.M., and Brook, W.J. (2009) The Tbx20 homologs midline and H15 specify ventral fate in the Drosophila melanogaster leg. Development 136:2689-2693.

Selected Publications:

Das, S., Chen, Q.B., Saucier, J.D., Drescher, B., Zong, Y., Morgan, S., Forstall, J., Meriwether, A., Toranzo, R., and Leal, S.M. 2013. The Drosophila T-box transcription factor Midline functions within the Notch-Delta signaling pathway to specify sensory organ precursor cell fates and regulates cell survival within the eye imaginal disc. Mechanisms of Development Epub (in press).

Chen, Q.B., Das, S., Zong, Y., Menegazzi, B., Smith, R.B., Visic, P., Odom, K., Buti, W., Buford, K., Morgan, S., and Leal, S.M. The Drosophila T-box Transcription Factor Midline Functions within Stress-Reactive Signaling Pathways to Regulate Cellular Homeostasis. Estimated Submission Date to the journal Mechanisms of Development: November or early December, 2013.

Leal, S.M., Qian, L., Lacin, H., Bodmer, R., Skeath, J.B. 2009. Neuromancer1 and Neuromancer2 Regulate Cell Fate Specification in the Developing Embryonic CNS of Drosophila melanogaster. Developmental Biology 325:138-150.

Neckameyer W.S. and Leal, S.M. Biogenic amines as circulating hormones in insects. In, “Hormones, Brain, and Behavior”, Academic Press, D. Pfaff, A. Arnold, A. Etgen, S. Farbach, R. Moss, and R. Rubin, Eds. 2009.

Svendsen, P.C., Formaz-Preston, A., Leal, S.M., and Brook, W.J. (2009) The Tbx20 homologs midline and H15 specify ventral fate in the Drosophila melanogaster leg. Development 136:2689-2693.