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 
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.