Dissertation Defense Announcement
To:  The George Mason University Community

Candidate: Eswar Prasad Ramachandran Iyer
Program:    PhD Biosciences

Date:   Friday April 20, 2012
Time:   9:00 a.m.
Place:   George Mason University
             Krasnow Institute for Advanced Study, Room 229
             Fairfax campus
Dissertation Director: Dr. Daniel N. Cox
Committee members: Dr. Emanuel Petricoin III, Dr. Karl J. Fryxell, Dr. James L. Olds
Title: "Dissecting Transcriptional Mechanisms Regulating Class-Specific Dendrite Development: A Systems Approach"

The dissertation is on reserve in the Johnson Center Library, Fairfax campus.
The doctoral project will not be read at the meeting, but should be read in advance.

All members of the George Mason University community are invited to attend.


Dendrites act as the primary sites of sensory and synaptic inputs to a neuron. Drosophila dendritic arborization (da) sensory neurons have emerged as an excellent model for investigating the molecular bases of dendrite development. Forward genetic screens, although extremely valuable, have limitations and genetic pleiotropy remains a significant impediment to identifying key molecular mechanisms regulating such complex developmental processes. To circumvent this problem, we have developed and applied a novel neuronal cell-type specific transcriptional expression profiling strategy coupled to a targeted and systematic in vivo RNAi functional validation screen to facilitate molecular dissection of the mechanisms regulating class-specific da neuron dendritogenesis.  Microarray analyses reveal transcriptional regulation as one statistically over-represented functional category in class IV da neurons with a remarkable 420 transcription factors significantly expressed in this single sensory neuron subclass. To validate the putative role(s) of these transcription factors in regulating class IV dendrite development, we performed a class IV specific RNAi screen against 343 of the 420 expressed transcription factors. Intriguingly, at least 269 transcription factors were found to be required for proper dendritic patterning of class IV sensory neurons, including 53 genes with no previously known function.  These transcription factors mediate a broad spectrum of functions including dendritic field coverage, branching, routing, tiling, and cell fate specification. In addition, over 60% of the identified transcription factors are evolutionarily conserved in vertebrates, with many implicated in nervous system diseases. As a result of these analyses, the novel zinc-BED domain containing transcription factor, CG3995, emerged as the most significant regulator of class IV dendrite development. In order to further understand the role of CG3995 in regulating class-specific dendrite development, we systematically characterized CG3995 loss-of-function and gain-of-function phenotypes. Our results suggest that CG3995 functions primarily to regulate dendritic scaling. We conducted a series of genetic, molecular and biochemical experiments to investigate the mechanisms underlying the CG3995 scaling phenotype. We identified at least two independent mechanisms by which CG3995 regulates class-specific dendrite development and scaling. Firstly, CG3995 interacts genetically with the homeodomain containing transcription factor cut to regulate class-specific dendrite development. Interestingly, Cut was found to positively regulate CG3995 expression, and CG3995 was found to negatively regulate Cut expression. In the second proposed pathway, our data indicate that CG3995 may function as an essential component of a ribosomal protein complex. Collectively, these studies provide a deeper mechanistic understanding of the complex roles transcriptional regulators play in directing distinct aspects of dendrite development.