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
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
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.