Molecular Recognition in Biological Systems and Bioinformatics

Immunofluorescence staining of Math5 (red) and Pou4f2 (green) on an E14.5 mouse retinal section. Expression of these two transcriptional factors represents two stages of retinal ganglion cell (RGC) development.

Developmental Biology, Neural Development, Genomics, Mouse genetics, Transcription regulation.

We are interested in how global gene expression advances from one state to the next in time and space and promotes the specification and differentiation of individual neural cell types from multi-potent neural progenitor cells. We use the mouse retina as our model system and our current work focuses on the gene regulatory network (GRN) involved in the formation of one retinal cell type, retinal ganglion cells (RGCs). RGCs are one of the seven cell types in the retina. They are the only projection neurons in the retina and connect the retina to the brain through the optic nerve. Death of RGCs is the cause of vision loss in glaucoma, one of the most common eye diseases.

In our research, we employ a combined approach of genetics, genomics and bioinformatics to study how the RGC fate is specified and how the fate-committed RGC precursors differentiate into fully functional RGCs. Previously, several key transcription factors functioning at different stages of RGC development have been identified; Math5 is essential for RGC fate specification, whereas Pou4f2 and Isl1 are required for their differentiation. We have characterized the roles of these factors in the RGC GRN by gene expression profiling and revealed that the GRN is complex and interconnected, in which the key transcription factors occupy the key node positions. Math5 is upstream of Pou4f2 and Isl1, and renders the retinal progenitor cells competent for the RGC fate. Pou4f2 and Isl1 functions after RGCs are born by activating genes essential for differentiation. Pou4f2 and Isl1 regulate two distinct but overlapping sets of genes and define two different gene regulation branches downstream of Math5.

Current projects in the lab are aimed at further understanding how these transcription factors specifically regulate their target genes and how they interact with each other. Our goal is to establish a global view of the RGC gene regulatory network, in which the downstream targets of the key regulators, distinct pathways and their interactions, as well as the feed-back and feed-forward circuits are defined. We hope that eventually we will be able to use the knowledge learned from these studies to develop new therapies for various retinal diseases.

Mouse

Math5 (Atoh7), Pou4f2 (Brn3b), Isl1 (Islet1)

Retinal development, Neural development, Neural diseases

Gene knockout, Histology, Immunofluorescence, Microarray, QPCR, In situ hybridization

HEK 293 cells, Mouse ES cells , Neural stem cells

Glaucoma, Neural degeneration

1. Mu, X. and Klein, W.H. (2008). Gene regulatory networks and the development of retinal ganglion cells. In: Eye, Retina, and Visual System of the Mouse (ed. L. M. Chalupa and R. W. Williams), pp. 321-332. MIT Press, Cambridge, MA.

2. Mu, X.*, Fu, X., Beremand, P.D., Thomas, T.L., and Klein, W.H.* (2008). Gene regulation logic in retinal ganglion cell development: Isl1 defines a critical branch distinct from but overlapping with Pou4f2. PNAS, 105, 6942-6947. (* corresponding authors).

3. Fu, X., Sun, H., Klein, W.H., and Mu, X.* (2006). ß-catenin is essential for lamination but not neurogenesis in mouse retinal development. Dev Biol, 299, 424-437. (* corresponding author).

4. Mu, X., Fu, X., Sun, H., Beremand, P.D., Thomas, T.L., and Klein, W.H. (2005). A gene network downstream of transcription factor Math5 regulates retinal progenitor cell competence and ganglion cell fate. Dev Biol 280, 467-481.

5. Mu, X., Fu, X., Sun, H., Liang, S., Maeda, H., Frishman, L, and Klein, W.H. (2005). Ganglion cells are required for normal progenitor cell proliferation but not cell-fate determination or patterning in the developing mouse retina. Curr Biol, 15, 525-530.

6. Mu, X., Beremand, P.D., Zhao, S., Pershad, R., Scarpa, A., Sun, H., Liang, S., Thomas, T.L., and Klein, W.H. (2004). Discrete gene sets depend on POU domain transcription factor Brn3b/Brn-3.2/POU4f2 for their expression in the mouse embryonic retina. Development, 131, 1197-1210.

7. Mu, X.* and Klein, W.H. (2004). A genetic regulatory hierarchy for retinal ganglion cell specification and differentiation. Semin Cell Dev Biol 15, 115-123. (*corresponding author).

8. Mu, X., Zhao, S., Pershad, R., Hsieh, T.-F., Scarpa, A., Wang, S.W., White, H.R., Beremand, P.D., Thomas, T.L., Gan, L., and Klein, W.H. (2001). Gene expression in the developing mouse retina by EST sequencing and microarray analysis. Nucleic Acids Res, 29, 4983-4993.

9. Mu, X., Spanos, S.A., Shiloach, J., and Kimmel, A. (2001). CRTF is a novel transcription factor that regulates multiple stages of Dictyostelium development. Development, 128, 2569-2579.

10. Mu, X., Lee, B., Louis, J.M., and Kimmel, A.R. (1998). Sequence-specific protein interaction with a transcriptional enhancer involved in the auto-regulated expression of cAMP receptor 1 in Dictyostelium. Development, 125, 3689-3698.