Jackson was interested in understanding the properties that distinguish early retinal progenitors from their late counterparts and their potential to generate early and late born neurons. Using co-culture and transplantation approaches,Jackson demonstrated that contrary to previously held notion, the late retinal stem cells/progenitors are not irreversibly committed to generate late born neurons but may appear as such under the constraints dictated by their niche. Therefore, given the conducive environment they can differentiate into early born neurons. Using transcription profiling and perturbation of function analyses,Jackson showed that the two populations of retinal stem cells/progenitors are distinct in their molecular make-up and utilize intracellular signaling, such as that initiated by Notch receptor, towards different ends. While early retinal stem cells/progenitors use Notch signaling to keep them uncommitted, their late counterparts require it to differentiate into Muller glia. In addition, he observed that the chromatin remodeling ATPase, Brm constitutes an integral part of the differentiation program in the developing retina.
Xing's interest was in therapeutic application of retinal stem cells/progenitors. She was interested in identifying alternative renewable sources of retinal progenitors. Based on the notion that embryonic ectoderm possesses default neural potential, Xing demonstrated that stem cells/progenitors in limbus of the adult eye, when removed from the niche, can generate multipotential neural progenitors. She has shown that these cells can differentiate into retinal neurons in vitro and in vivo. In addition, her works demonstrate that these cells can also be use as reagents for treating Parkinson's disease as they have the potential to differentiate into dopaminergic neurons. This alternative renewable source of neural progenitors raises the prospect of autologous stem cell therapy to treat neurodegenerative diseases. Xing has also demonstrated that embryonic stem cells can also be used as a source for generating retinal neurons; ES cell-derived neural progenitors can differentiate into rod photoreceptors and bipolar cells when they are cultured along with neonatal retinal cells. Recently, Xing demonstrated the presence of growth factor-responsive neural progenitors in the periphery of postnatal retina, providing an evidence for the existence of a vestige of the ciliary margin zone, found in amphibians and teleosts, in the mammalian retina.
Dhammika was interested in the regulation of Wnt signaling in retinal stem cells/progenitors. She cloned transcripts corresponding to Wise1 from the rat retina. Wise1 encodes a secretary protein that influences the binding of Wnts with Frizzled receptors. Dhammika showed that the levels of Wise1 expression correspond to the temporal aspects of differentiation in the developing retina and increase when enriched retinal stem cells/progenitors are placed in differentiation conditions, both observations suggested that Wise1 participates the differentiation of retinal stem cells/progenitors. Dhammika and Ani have observed that one of the mechanisms by which Wise1 may influence differentiation is by attenuating Wnt signaling. This may involve Wise1-dependent interference in Wnt-Frizzled interactions, compromising the canonical Wnt pathway.
Sreekumaran was interested in understanding the functional properties of retinal stem cells/progenitors in different conditions. It has been shown by others that electrophysiological properties of progenitors can differ from their descendents and the differentiation of ion currents in progenitors can be influenced by growth factors and other culture conditions. Sreekumaran, using whole cell patch clamp recordings showed that the early and late retinal stem cells/progenitors have distinct electrophysiological properties in proliferating and differentiating conditions. Such distinct electrophysiological properties correlate with differential transcription profiles of early and late retinal stem cells/progenitors in the context of genes encoding different voltage- and ligand-gated channels.
Harsha examined the role of bHLH transcription factors in retinal development. She cloned NeuroD cDNA from rat and primate retina and mapped the temporal and spatial aspects of NeuroD expression in the developing rat retina. Using in situ hybridization, immunocytochemical localization and perturbation of expression analyses, Harsha and Jim Rogers demonstrated that NeuroD plays an important role in the rod photoreceptor differentiation.
Jim was interested in the biology of stem cells in general. He played a critical role in establishing the neurosphere culture of retinal stem cells/progenitors. He studied the proliferation and multipotentiality of these cells and demonstrated through the limiting dilution analysis (LDA) that the self-renewal is a non-cell autonomous property of retinal progenitors and thus explained why clones could not be generated when retinal progenitors are cultured at low density. This has led us to a project, currently pursued by Ganapati, to identify factors that may contribute to self-renewal of retinal progenitors. Jim participated in understanding the role of NeuroD in retinal development and demonstrated the involvement of this bHLH factor in the generation of rod photoreceptors. Jim also participated in retinal transplantation studies that demonstrated that cultured retinal stem cells/progenitors survive in the host retina and show the potential to differentiate along the photoreceptor lineage.
Jianuo brought her expertise of molecular biology to the lab and established transfection of neurospheres and ES cells protocols. She and Xing collaborated in determining the retinal potential of ES cells.
Connie studied the role of Notch signaling in retinal development. Using co-culture, antisense-mediated attenuation in gene expression and perturbation of function analyses, Connie showed that Notch signaling is required for keeping the early retinal progenitors uncommitted and the attenuation in Notch signaling constitutes a critical event for promoting their differentiation along RGC lineage. She demonstrated that Numb, a negative regulator of Notch signaling, through the differential utilization of its splice variants, might influence proliferation and differentiation of retinal stem cells/progenitors during neurogenesis and maturation of post-mitotic neurons. She also participated in studies that showed the involvement of bHLH transcription factors, Mash1 and NeuroD in the differentiation of retinal progenitors.
Justin was MS student/tech. Justin established the retinal explant culture protocol in the lab and studied the role of bHLH factor, Ath3 in the development of retina.
Frank was a MS student/tech. He was interested in understanding the role of LPA in retinal development, particularly, in regulating the proliferation and differentiation of retinal stem cells/progenitors. He demonstrated that LPA inhibits the differentiation of retinal stem cell/progenitors and this effect is associated with the mitogenic effects of LPA on these cells.
Gaurav was a MS student. He was interested in the perturbation of gene expression in vivo to understand their roles in retinal development. He studied microinjection and electroporation techniques in chick retina.
Dorisa was a summer undergraduate student, on her way to medical school. She established the chick model of retinal development in our lab that was instrumental in establishing the role of Notch signaling in the maintenance and differentiation of retinal progenitors.
Sanaz, a medical student and batch-mate of Dorisa, did a summer research project in the lab. She participated in the study that showed that the bHLH transcription factor, Mash1, characterizes the transient intermediate state of retinal progenitors, on way to differentiation, during late retinal histogenesis. Mash1 expression is under the influence of extrinsic cues. EGF attenuates Mash1 expression in transient precursors, shifting them towards the progenitor state.
Hao was a summer undergraduate student. Using chronic BrdU injection in adult rats, Hao observed BrdU-positive cells in the pigmented ciliary epithelium. He observed that the number of BrdU-positive cells increased when ciliary epithelium explants were cultured in the presence of mitogen. These observations led to the identification of a quiescent population of neural stem cells in the adult eye.
Fariha was a summer undergraduate student. She showed, contrary to existing notion, that bHLH factor, Mash1, is expressed during early stage of retinal histogenesis and thus involved in the generation of early born neurons.
Saima was a medical student from Russia who did summer research in the lab. Saima worked with Hao to understand the proliferative responsiveness of ciliary epithelium stem cells.
Allison was a BRIN summer scholar. She studied immortalized human retinal progenitors for their proliferative properties and differentiation potential. She, along with Faraz, a high school summer student, observed that these cells proliferate in the presence of FGF2 and EGF and when co-cultured with rat retinal cells show the potential to differentiate, as ascertained by expression of immunoreactivities corresponding to those that characterize bipolar cells, amacrine cells and rod photoreceptors.
Faraz is a summer high school student. He has collaborated with Allison in characterizing the human retinal progenitors. He has learnt cellular and molecular biology techniques and help Sumitra and Ani in their projects. While in middle school, he proposed the hypothesis that all tissues have stem cells and showed that adult heart does harbor proliferating cells.
Justin was a summer high school student. He collaborated with Sumitra in determining the proliferative status of neural progenitors in acetyl cholinesterase null mice.
Scott is a BRIN summer scholar. Scot is using his expertise and knowledge of information technology and computer to establish regulatory network and hierarchy, involved in the development of the mammalian retina.
Faisal is a summer scholar with expertise in IT and computer. He collaborated with Scott to establish a regulatory network and hierarchy, involved in the development of the mammalian retina.
Jordan M. Katz
Jordan was a summer student. He established the morphometric and quantitative measurements of neurosphere culture. He worked with Xing.
Han helped us set our lab and in our experiments involving the role of Mash1 in retinal development.
Tracy helped us during our initial phase of understanding the role of Notch signaling in retinal development.
Lin helped us when we were developing and acquiring retinal transplantation expertise and in the characterization of ciliary epithelium stem cells.
Tami helped us during the phase when we were characterizing early and late retinal stem cells/progenitors
Dr. Ashraf B. Abdel-Naim
Dr. Ashraf is an Associate Professor in the Department of Pharmacology, Ain Shams University, Cairo, Egypt. Dr. Ashraf studied effects of various pharmaceutical agents on neural progenitors.