Overview and Questions
research aim is to understand the mechanisms underlying the long-term
regulation of neuropeptide signaling. In this research, we are
using the powerful molecular and genetic techniques available in a
model genetic organism, the fruit
fly, Drosophila melanogaster.
as neuromodulators and hormones, neuropeptides are key regulators
of diverse processes, including growth, reproduction, stress, energy
balance, sleep, and circadian rhythms. While there are exceptions,
peptidergic cells as a rule, and neurosecretory cells in particular,
synthesize prodigious amounts of neuropeptides. This is often to support
chronic secretion or to overcome dilution of neuropeptides upon their
release into the general circulation. One of the most fundamental
characteristics of many neuropeptide systems is their inherent flexibility,
which enables organisms to dramatically alter neuropeptide expression
in response to internal and external cues. The resulting changes in
the gain of neuropeptide signaling form an integral component of the
neuroendocrine and physiological feedback loops that establish and
regulate many homeostatic mechanisms. This form of regulation has
been intensively investigated in a few amenable systems, and contributions
of factors such as CREB
and steroids to changes in neuropeptide gene expression are well documented.
Nevertheless, in many other systems, the heterogeneity and scattered
distribution of peptidergic cells has restricted progress toward a
general molecular understanding of the mechanisms governing changes
in neuropeptide expression and secretion, and new tools and approaches
are three critical and largely unanswered questions that must be addressed
for a full understanding of how neuropeptide systems are regulated.
First, how is the development of neuropeptide-secreting (peptidergic)
cells controlled? Second, what are the mechanisms underlying long-term
changes in neuropeptide expression? Third, to what extent are genes
that are involved in the development of peptidergic cells reused to
perform similar functions in mature cells. We seek to address these
questions in model systems where novel features of molecular signaling
pathways can be isolated and readily studied, and where we can take
full advantage of remarkable new tools that allow us to either raise
or lower gene expression in specific neuropeptide-secreting cells,
and also to dictate the precise timing of these changes.
Current Research Projects
controls neuropeptide levels. Anti-leucokinin neuropeptide immunostaining
in brain (insets) and ventral CNS of heterozygous control (+/-)
and homozygous dimm mutant (-/-) larvae.
1. Peptidergic cell regulation
In many professional secretory cells, the majority of new protein
synthesis is devoted to the manufacture and storage of secreted proteins.
Thus, there appear to be genetic factors that control robust expression
of neuropeptides and other components of the regulated secretory pathway.
We have identified a Drosophila basic helix-loop-helix (bHLH)
gene, dimmed (dimm), with an expression pattern
that corresponds precisely with neuronal and endocrine cells that
accumulate large amounts of secretory peptides. Through genetic and
cell biological methods, we have shown that dimm controls
levels of a wide variety of neuropeptides and peptide biosynthetic
enzymes within these diverse cells and that its actions appear to
be confined to that aspect of cellular differentiation. Therefore,
dimm appears to be an integral component of a novel and general
mechanism by which secretory cells acquire and maintain the pro-secretory
state. In our studies of dimm, and of the putative mouse
ortholog, Mist1, we are using a variety of genetic, molecular
and cell biological tools to further understand how neuropeptide levels
are regulated in developing and mature animals.
2. Neuropeptide signaling pathways
controlling insect wing expansion behavior.
Through their life-cycles, insects must go through repeated molts
in order to accommodate increases in body size and changes in external
morphology. At the end of each molt, insects perform highly stereotyped
of behavior in order to shed the old external cuticle. These events
are triggered and controlled by neuropeptides. During the molt to
the adult stage, many insects also perform additional neuropeptide-mediated
behaviors to expand their wings. These are fascinating biological
processes, and many of us have vivid childhood memories of watching
emerging from its chrysalis. However, they also present a unique
opportunity for genetic analysis of neuropeptide signaling pathways
controlling animal behavior. We are using genetic tools to define
the relationships among cells controlling these behaviors and to identify
novel mechanisms controlling neuropeptide signaling in this system.
Research Openings in the Lab
There are exciting opportunities available in my
lab for postdoctoral, graduate, and undergraduate research on dimm,
wing expansion, and related questions. These include:
Genetic and molecular screens for additional
factors that function with dimm in controlling secretion
in neuroendocrine and endocrine cells.
Cell biological studies to further dissect
the role of dimm and other proteins in controlling the
regulated secretion of neuropeptides.
Genetic, cell biological and molecular studies
of the mouse dimm orthologue and its roles in controlling
neuropeptide levels in embryos and adults.
Molecular genetics and genomics
to study the roles of neuropeptides (and the cells
that secrete them) in controlling behavior, physiology and development.
more information on opportunities for undergraduate and graduate research
in my lab, please feel free to call
me, send me an e-mail (hewes<<at>>ou.edu),
or drop in for a visit.
- Zhao, T., Gu, T., McAdams, K.L., Moran, E.P., and Hewes, R.S. (2010). The Split ends (SPEN) transcriptional coregulator suppresses Myosin II-dependent axon outgrowth during neurosecretory cell remodeling in Drosophila. Accepted pending minor revisions.
- Hewes, R.S. (2008). The buzz on fly neuronal remodeling. TRENDS
in Endocrinology and Metabolism 19:317-323
- Zhao, T., Gu, T., Rice, H.C., McAdams, K.L., Roark, K.M., Lawson,
K., Gauthier, S.A., Reagan, K.L., and Hewes, R.S. (2008). A Drosophila
gain-of-function screen for candidate genes controlling steroid-dependent
neuroendocrine cell remodeling. Genetics 178:883-901.
- Shakiryanova, D., Klose, M., Zhou, Y., Gu, T., Deitcher, D.L.,
Atwood, H.L., Hewes, R.S. and Levitan, E.S. (2007). Presynaptic
ryanodine receptor-activated calmodulin kinase II increases vesicle
mobility and potentiates neuropeptide release. Journal of Neuroscience
- Hewes, R.S., Gu, T., Brewster, J.A., Qu, C. & Zhao, T. (2006).
Regulation of secretory protein expression in mature cells by DIMM,
a bHLH neuroendocrine differentiation factor. Journal of Neuroscience
- Gauthier, S.A., and Hewes, R.S. (2006). Transcriptional regulation
of neuropeptide and peptide hormone expression by the Drosophila
dimmed and cryptocephal genes. Journal of Experimental
Biology 209(10):1803-1815 (and cover photo). This article was
also featured in the column, Inside JEB [K Phillips (2006).
DIMM Regulates Neuropeptide Levels. J. Exp. Biol. 209(10):i-a].
- Sturman, D.A., Shakiryanova, D., Hewes, R.S., Deitcher, D.L. &
Levitan, E.S. (2006). Nearly neutral secretory vesicles in Drosophila
nerve terminals. Biophysical Journal 90(6):L45-L47. (pdfs)
- Shakiryanova, D., Tully, A., Hewes, R.S., Deitcher, D.L. &
Levitan, E.S. (2005). Activity-dependent liberation of synaptic
neuropeptide vesicles. Nature Neuroscience 8:173-178.
Upper left Transmission electron micrograph
of an insect neuroendocrine cell axon packed with numerous large dense
core granules containing the neuropeptide, bursicon (image by P. Taghert,
circa 1980; reprinted with permission).
Upper right Confocal micrograph of a portion
of the larval central nervous system showing the expression pattern
of dimmed (green) and multiple neuropeptides ending in the C-terminal
sequence, RF-amide (red). Double-stained cells are yellow.
Page author: R.S. Hewes