Postdoctoral Position Available

Steven Reppert, M.D.

Academic Role: Professor

Faculty Appointment(s) In:
   Neurobiology

Other Affiliation(s):
   Interdisciplinary Graduate Program
   Program in Neuroscience

NEW:  NIH ARRP funding of monarch genome

Molecular Neuroethology

In an integrated set of studies, our laboratory is using anatomical, cellular, molecular, electrophysiological, genetic and behavioral approaches to more fully understand the biological basis of monarch butterfly (Danaus plexippus) migration, with a focus on the butterfly's navigational abilities and its ancestral circadian clock.  Active projects include:

Monarch Circadian Clockwork

Rationale. Paradigm shifting studies in the monarch butterfly have enhanced our view of the evolution and function of CRYPTOCHROME (CRY) proteins in animals (Zhu et al., 2008).  The butterfly's clock mechanism posits two CRY proteins as critical for circadian timing, giving rise to a NOVEL clockwork (Fig. 1). Thus, in the same species, the two functionally distinct CRYs can be analyzed.  In monarchs, a Drosophila-like CRY, designated CRY1, functions as a likely circadian photoreceptor, while a vertebrate-like CRY, designated CRY2, appears to function as the major transcriptional repressor of the clockwork transcriptional feedback loop.  The analysis of distinct CRY function has been further aided by a monarch cell line (DpN1 cells), which expresses a light-driven clock, in which both monarch CRY1 and CRY2 function; no other light-sensitive insect cell line has been described. Our continued studies will expand our knowledge of the unique properties of the CRY proteins by further defining distinct CRY mechanisms of action in lepidopterans (butterflies and moths) using molecular, biochemical, genetic, and behavioral approaches. Because of the parallel, complementary nature of circadian clock discoveries between flies and mammals, which we believe can now be extended to lepidopterans, our overriding hypothesis is that further analysis of the two families of animal CRY proteins that are represented in insects will advance our fundamental understanding of animal clock mechanisms.

Employ an RNAi screen to discover novel components of the insect CRY1 light-signaling pathway.  We postulate that novel components of the CRY1-dependent circadian input pathway remain to be elucidated. The light-driven clock in DpN1 cells, along with a recently constructed monarch expressed sequence tag library (see below), allow for the development of an unbiased, high-throughput RNAi screen to discover novel components of light-induced CRY1 signaling that allow the molecule to function as a circadian photoreceptor. Mechanistic details of novel component function will be further analyzed in DpN1 cells.  Candidate components will be characterized in Drosophila strains harboring loss-of-function mutations of the fly homologs.

Use a proteomics approach to identify novel interactors within the insect CRY2/CLK:CYC transcriptional complex.   We hypothesize that yet to be discovered insect CRY2 interactive proteins are essential for its role as a major transcriptional repressor of the clockwork transcriptional feedback loop.  With DpN1 cells, we will use tandem affinity purification and coimmunoprecipitation to identify additional CRY2-, CLOCK-, and CYCLE-interacting proteins.  Finding novel interactors may help define the transcriptional repressive role of CRY not only in insects, but also in mammals, in which the mechanism of CRY repression is not well understood.

Public health relevance:   The monarch butterfly clock mechanism affords unique opportunities to further our understanding of fundamental clock mechanisms in animals.  Defining the molecular and biochemical basis of circadian timing in animals has important implications.  In terms of fundamental brain mechanisms, the circadian system is among the most tractable models for providing a complete understanding of the cellular and molecular events connecting genes to behavior.  Thorough dissection of the genetic basis of circadian behavior may help decipher this connection for more complex behaviors.  There are also important biomedical implications:  Understanding the molecular clock has already increased our knowledge of how clock gene mutations contribute to disorders of the timing of sleep and could increase our knowledge of how clock gene mutations contribute to psychopathology (e.g., major depression and seasonal affective disorder).  Likewise, such understanding should lead to new strategies for pharmacological manipulation of the human clock to improve the treatment of jet lag and shift-work ailments, and of clock-related sleep and psychiatric disorders.

Monarch Navigation

Rationale.  During their fall migration, monarch butterflies travel distances approaching 4000 km.  The remarkable navigational abilities of monarch butterflies are part of a genetic program that is initiated in migrations.  We believe that the centerpiece of the navigational process is time-compensated sun compass orientation.  The ability of migrants to successfully navigate to their overwintering sites in central Mexico requires that the underlying genetically program is constantly being recalibrated by environmental factors.

Time-compensated sun compass orientation.   We continue to use a flight simulator to examine this important aspect of monarch navigation.  We are determining whether a time-compensated sun compass is used in the spring by migrants on the way back from Mexico to the Southern US and its utilization in subsequent summer generations that travel from the Southern US to the Northern limits of their habitat.  We are also examining whether the use and orientation direction of the sun compass is influence by daylength in monarchs.

Brain clocks and circuits.   Using a strategy that relied on the coexpression of PER, TIM, and CRY1, four cells in the dorsolateral region of monarch butterfly brain (the pars lateralis, PL) were identified as the putative location of circadian clocks (Sauman et al., 2005) (Fig. 2).  Further study showed that CRY2 is also expressed in those cells, in which it cycles in and out of the nucleus at the appropriate times to regulate the clockwork feedback loop (Zhu et al., 2008).  Clock proteins are also expressed in large neurosecretory cells in the pars intercerebralis (PI); these cells may be part of a circadian network that contributes to circadian behaviors.  Importantly, the CRY proteins mark neural pathways that may be relevant for migration and circadian behaviors.  CRY1-positive fibers connect the PL clock cells to axons from polarization-sensitive photoreceptors in the dorsolateral medulla.  CRY1-positive fibers also connect the PL to the PI that may be critical for the photoperiodic regulation of reproductive diapause and the initiation of the migratory state.  A CRY2 –staining neural pathway may connect the PL clocks to the central complex, ultimately regulating circadian behaviors (e.g., daily flight activity, metabolic rhythms, and the sleep-wake cycle).

Antennal clocks. It has been assumed that the circadian clock that provides time compensation for time-compensated sun compass orientation resides in the brain (specifically the PL), although this assumption has never been examined directly. We recently discovered that the antennae are necessary for proper time-compensated sun compass orientation in migratory monarch butterflies, that antennal clocks exist in monarchs, and that they likely provide the primary timing mechanism for sun compass orientation (Merlin et al., 2009). These unexpected findings pose a novel function for the antennae and open a new line of investigation into clock-compass connections that may extend widely to other insects that use this orientation mechanism.  They also suggest the existence of a crucial but hitherto unknown neural circuit between the antennae and the central complex system (Fig. 3) that is now under investigation.

Central Complex.  Based on studies in locusts and crickets, it appears that the sun compass resides in the central complex.  The central complex is a midline structure consisting of the protocerebral bridge, the central body, which has upper and lower subdivisions, and the noduli.  We are defining in more detail with confocal microscopy and three-dimensional reconstruction the anatomy of the central complex in the monarch butterfly.  Input, intermediate and output neurons to the central complex are being defined and electrophysiological recordings of relevant neurons that process skylight information has begun.  Our ultimate goal is to define how information about time and space are integrated in the brain of migratory butterflies, allowing them to maintain a southerly flight bearing over the course of the day.  Elucidating the neural pathway connecting antennal clocks to the central complex looms large in this context.

Magnetoreception.   As migrants "funnel" into Texas in October, do they switch navigation strategies - the so-called "beacon effect"?  Could this be geomagnetic in whole or part?  We have developed an assay system in which light-dependent magnetoreception can be monitored and its molecular underpinnings deciphered (See Gegear et al., 2008).

Social interactions.   Migratory monarch butterflies are gregarious, while summer butterflies are not.  Migrants spend their nights in roosts along the migration flyway.  They migrate in large swarms, which increase in size the closer they get to Mexico.  Do social interactions among butterflies influence their navigation.  Flight simulator experiments could help determine whether social interactions actually influence time-compensated sun compass orientation mechanisms.  We are also investigating whether pheromones are important.

Real-time monitoring of navigation.  We are developing tools for monitoring free-flying monarchs over long distances.

Monarch Migration Genes

Rationale.  To fully understand migration, we need to determine the gene expression patterns that define the migratory "state".

Transcriptional Profiling. We recently showed that increasing juvenile hormone activity to induce summer-like reproductive development in normally juvenile hormone-deficient fall migrants does not alter directional flight behavior or its time-compensated orientation, as monitored in a flight simulator. Reproductive summer butterflies, in contrast, uniformly fail to exhibit directional, oriented flight. To define molecular correlates of behavioral state, we used microarray analysis of 9417 unique cDNA sequences (see Monarch brain expressed sequence tag library, below). Gene expression profiles reveal a suite of 40 genes whose differential expression in brain correlates with oriented flight behavior in individual migrants, independent of juvenile hormone activity, thereby molecularly separating fall migrants from summer butterflies.   We also identified 23 juvenile hormone-dependent genes in brain, which separate reproductive from non-reproductive monarchs; genes involved in longevity, fatty acid metabolism, and innate immunity are upregulated in non-reproductive (juvenile-hormone deficient) migrants. Our results link key behavioral traits with gene expression profiles in brain that differentiate migratory from summer butterflies and thus show that seasonal changes in genomic function help define the migratory state.  See Zhu et al., 2009.

miRNAs.  MicroRNAs (miRNAs) regulate gene expression by inhibiting translation, and each miRNA can regulate a complement of proteins.  In other systems, miRNAs are involved in epigenetic developmental events.  We are therefore addressing the possibility that miRNAs may be involved in initiating/mediating the migratory state in monarch butterflies.

Accessing the Monarch Genome

Rationale.  Accessing the monarch genome is essential for moving the clockwork, navigation and migration issues into contemporary biology.  Such access is necessary for the monarch butterfly to become a model organism to study circadian clock and migration mechanisms.

Develop a targeted gene inactivation strategy in lepidopterans. In collaboration with Dr. Scot Wolfe in the Program in Gene Function & Expression, we are developing a novel gene targeting approach that uses a zinc finger nuclease (ZFN) strategy in the silkworm Bombyx mori, a genetically tractable species, to define the essential nature of CRY2 for clockwork function in lepidopterans.   The effects of such gene targeting on two circadian behaviors, the timing of egg hatching and adult eclosion, will be monitored, as well as the effects on the molecular clock mechanism itself.  Once developed, the ZFN strategy will be a powerful tool for targeting additional clock genes in Bombyx and ultimately targeting genes in monarchs.  The method can also be used to knock-in reporters into clock gene loci.

Develop artificial diet for monarchs.   An artificial diet for consistently rearing monarchs from egg to adults is essential for the utilization of genetic approaches.  We need to be able to maintain monarch "lines" in the laboratory.  Such a diet is being established by Orley (Chip) Taylor at Monarch Watch.

Monarch Genomic Resources

Rationale. Developing more comprehensive genomic resources for the monarch butterfly is a fundamental step to fully utilize this system to address important issues in contemporary biology (e.g., sun compass orientation, and circadian clock mechanisms).

Monarch brain expressed sequence tag library (http://titan.biotec.uiuc.edu/butterfly/)
We have developed a brain expressed sequence tag (EST) resource to identify genes involved in migratory behaviors (Zhu et al., 2008).   A brain EST library was constructed from summer (non-migrating) and fall (migrating) butterflies. The monarch butterfly EST Information Management Application (ESTIMA) can be found at: http://titan.biotec.uiuc.edu/cgi-bin/ESTWebsite/estima_start?seqSet=butterfly 
Of 9,484 unique sequences, 6068 had positive hits with the non-redundant protein database; the EST database likely represents ~ 52% of the gene-encoding potential of the monarch genome. The brain transcriptome was cataloged using Gene Ontology and compared to Drosophila.  Monarch genes were well represented in all categories, including those implicated in behavior. This EST resource contains individually arrayed cDNA clones that can be used to generate dsRNAs to induce RNAi.  The EST library is therefore an essential resource for the development of a high-throughput RNAi screen in DpN1 cells for delineating novel components of the CRY1 signaling pathway and will help define additional monarch CRY2 interactors important for transcriptional repressive activity.

The monarch genome.  We have received NIH ARRP funds to generate a high depth sequence of the monarch butterfly genome using a combination of state-of-the-art "next generation" sequencing technologies, and then appropriately assemble, annotate and interpret the genome. To fully develop the monarch butterfly as a model organism to study circadian clock mechanisms and the associated molecular mechanisms of sun compass navigation used during migration, a sequenced and fully annotated genome is needed.

The sequencing and annotation project is being performed in collaboration with Jeffrey L. Boore of the University of California Berkeley and CEO of Genome Project Solutions, Inc. through a consortium agreement for bioinformatics support.  Genome Project Solutions (http://genomeprojectsolutions.com/) is a service provider of genome-level bioinformatics and developer of a new suite of genome analysis tools.

A public database will be available to access all sequence and annotation information, as it becomes available.

Figure 1.  Proposed monarch butterfly circadian clock mechanism.  The main gear of the clock mechanism is an autoregulatory transcription feedback loop in which CLK and CYC heterodimers drive the transcription of the per, tim, and cry2 genes through E box enhancer elements; in addition to per, there are CACGTG E box elements within the 1.5 kb 5’ flanking regions of the butterfly tim and cry2 genes (data not shown).  TIM (T), PER (P), and CRY2 (C2) form complexes in the cytoplasm and CRY2 is shuttled into the nucleus where it shuts down CLK:CYC-mediated transcription.  PER is progressively phosphorylated and likely helps translocate CRY2 into nucleus.  CRY1 (C1) is a circadian photoreceptor which, upon light exposure (lightning bolt) causes TIM degradation to gain access to the central clock mechanism.  The thick gray arrows represent output functions for CRY1 and for CRY2.

Figure 2. Brain clocks and circuits. Schematic representation of neurons and fibers expressing different circadian clock proteins in monarch butterfly brain. Regions expressing TIM, PER, CRY1 and/or CRY2 are highlighted in red. In these areas the four clock proteins partially colocalize. Areas expressing TIM or CRY1 are indicated in pink. In these regions the two clock proteins do not colocalize. CRY1 positive fibers are represented by continuous orange lines. Projections of dorsal rim area photoreceptors are indicated by dotted orange lines. Neurons and fibers expressing exclusively CRY2 are represented in blue and within the central body are shown as blue circles and blue hatching. Areas positive exclusively to TIM and PER are indicated in light blue and green, respectively. PL, pars lateralis; PI, pars intercerebralis; SOG, subesophageal ganglion; CB, central body; LO, lobula; ME, medulla; LA, lamina; RE, retina (Kyriacou CP, J Biol 2009, 8:55).

Figure 3. Clock-sun compass interactions.

Publications

Cover Articles:

Click the magazine covers to link to the online journal which will open in a frameset.

Representative Publications:

Reppert, S.M. (2006) A colorful model of the circadian clock. Cell 124:233-236.   (See Monarch Project)

Sauman, I., Briscoe, A.D., Zhu, H., Shi, D., Froy, O., Stalleichen, J., Yuan, Q., Casselman, A., Reppert, S.M. (2005) Connecting the navigational clock to sun compass input in monarch butterfly brain. Neuron 46:457-467.  (See Monarch Project)

Froy, O., Gotter, A.L., Casselman, A.L., and Reppert, S.M. (2003) Illuminating the circadian clock in the monarch butterfly migration. Science 300: 1303-1305.  (See Monarch Project)

Etchegaray, J.P., Lee, C., Wade, P.A., and Reppert, S.M. (2003) Rhythmic histone acetylation underlies transcription in the mammalian circadian clock. Nature 421: 177-182.

Lee, C., Etchegaray, J.-P., Cagampang, F.R.A., Loudon, A.S.I., and Reppert S.M. (2001) Post-translational mechanisms regulate the mammalian circadian clock. Cell 197: 855-867.

Clayton, J.D., Kyriacou, C.P., and Reppert, S.M. (2001) Keeping time with the human genome. Nature 409: 829-831.

Shearman, L.P., Sriram, S., Weaver, D.R., Maywood, E.S., Chaves, I., Zheng, B., Kume, K., Lee, C.C., van der Horst, G.T. Hastings, M.H., and Reppert, S.M. (2000) Interacting molecular loops in the mammalian circadian clock. Science 288: 1013-9.

Gotter, A.L., Manganaro, T., Weaver, D.R., Kolakowski, L.F., Possidente, B., Sriram, S., MacLaughlin, D.T., and Reppert, S.M. (2000) A time-less function for mouse Timeless. Nat. Neurosci. 3: 755-6.

Liu, C., and Reppert, S.M. (2000) GABA synchronizes clock cells within the suprachiasmatic circadian clock. Neuron 25: 123-8.

Gotter, A.L., Levine, J.D., and Reppert, S.M. (1999) Sex-linked period genes in the silkmoth, Antheraea pernyi: implications for circadian clock regulation and the evolution of sex chromosomes. Neuron 24: 953-65.

Kume, K., Zylka, M.J., Sriram, S., Shearman, L.P., Weaver, D.R., Jin, X., Maywood, E.S., Hastings, M.H., and Reppert, S.M. (1999) mCRY1 and mCRY2 are essential components of the negative limb of the circadian clock feedback loop. Cell 98: 193-205.

******See PubMed:for complete publication list (reppert sm).

Press/Outreach

Radio Broadcasts:

NPR Morning Addition, May 23, 2003 - Monarch migration

NPR Morning Addition, May 5, 2005 - Monarch migration

NPR Science Friday, January 11, 2008 - Monarch migration

Voice of America, July 28, 2008 - Magnetoreception

Video Broadcasts:

CSH Symposium Interview, 2008 - Monarch migrations

Art inspired by our work:

Newspaper, popular science articles:

New York Times Magazine, Awakening to Sleep, Verlyn Klinkenborg, January 5, 1997

Discover Magazine, Mind Over Time, Mark Caldwell, July 1999 issue.

Washington Post, Butterflies Guided Body Clocks, Sun; Scientist Shine Light on Monarchs' Pigrimage, Guy Gugliotta, May 23, 2003.

Boston Globe, Timing is everything, Emily Anthes, August 20, 2007.

Toronto Star, Monarch's map to Mexico, Peter Calamai, January 8, 2008.

The Daily Telegraph, UK, Monarch butterflies use human clock to migrate, Roger Highfield, January 8, 2008.

Wall Street Journal, Using Butterfly Time, We Can Learn Secrets of Our Own 'Clocks', Robert Lee Hotz, February 8, 2008.

Philadelphia Inquirer, Amazing journey of the monarch butterfly, Faye Flam, Jan 21, 2008.

ScienceNow, Guided by the light, Rachel Zelkowitz, July 22, 2008.

Miller-McCune, The ticking compass inside a Butterfly, David Richardson, July 19, 2008.

TheScientist, Southbound genes, Amber Dance, April 8, 2009.

Nature News, Butterflies’ migrational timekeeper found, Lizzie Buchen, September 24,2009.

Wired Science, Butterflies Use Antenna GPS to Guide Migration, Hadley Leggett, September 24, 2009.

Potential Rotation Projects

Three-dimensional reconstructions of Monarch butterfly brains (under supervision of Postdoctoral Fellow:  Stanley Heinze)  See Below

In vitro reconstruction of the purple sea urchin (Strongylocentrotus purpuratus) circadian clock. (under supervision of Postdoctroral Fellow: Christine Merlin)  See Below

Project: Three-dimensional reconstructions of Monarch butterfly brains

With Postdoctoral Fellow: Stanley Heinze

Monarch butterflies are well known for their most spectacular fall migrations, during which they cover thousands of kilometers across unfamiliar terrain in order to reach their winter habitats in Mexico. For this task these animal use time compensated sky compass navigation. This allows them to calculate their traveling direction by using information derived from the changing position of the sun during the day. Not only the sun itself serves as compass cue, but also the sky polarization pattern, as has been shown by behavioral experiments (Reppert et al, 2004). The summer form of the Monarch butterfly, however, is non migratory and has been also shown to lack directional flight behavior (Zhu et al, 2009).

The neuronal basis of sky compass navigation and directional flight behavior is completely unknown in the Monarch butterfly and shall be addressed in this project. microarray analysis of brains has revealed that several genes are differentially expressed in brains of migrants and summer butterflies, suggesting that the neuronal machinery of the brain differs between the two forms (Zhu et al, in press). This is likely to result in changes of synaptic density in brain regions involved in migratory behavior. As it is known from other species, in particular the desert locust, that the central complex and the anterior optic tubercle are crucially involved in processing of sun compass cues, this project will focus on these two brain areas (Homberg, 2004; Pfeiffer et al, 2005; Heinze and Homberg, 2007; Pfeiffer and Homberg, 2007).

One way to estimate the number of synapses and fine branches within specific brain areas is a detailed volumetric analysis of these regions. Therefore digital, three-dimensional reconstructions of the central complex and the anterior optic tubercle will be carried across a population of butterflies, resulting in average shape and volume data of these regions (Huetteroth and Schachtner, 2005, Kurylas et al., 2008). The results will be eventually compared between summer butterflies and migrants in order to establish neuronal correlates of their different migratory states.

During the course of this two-month project, the complete dataset for summer butterflies is going to be obtained, providing the base for the comparison with the migratory form, which only occurs within a short period during fall. The student will learn to perform immunocytochemical brain labeling with antibodies against synaptic proteins and neurotransmitters. These fluorescent stainings will be analyzed with high resolution confocal microscopy, and the resulting image stacks will be used for three dimensional reconstructions with sophisti­cated graphics software (Amira5.1). Emphasis will be laid on obtaining a sound under­standing of insect brain neuroanatomy and developing the capabilities to independently pursue immunocytochemical studies of insect brains, starting with the dissection of brains up to the final statistical analysis of volumetric data.

References

Heinze S, Homberg U (2007) Maplike representation of celestial E-vector orientations in the brain of an insect. Science 315:995-997.

Homberg U (2004) In search of the sky compass in the insect brain. Naturwiss 91:199-208.

Huetteroth W, Schachtner J (2005) Standard three-dimensional glomeruli of the Manduca sexta antennal lobe: a tool to study both developmental and adult neuronal plasticity. Cell Tissue Res 319:513-24.

Kurylas AE, Rohlfing T, Krofczik S, Jenett A, Homberg U (2008) Standardized atlas of the brain of the desert locust, Schistocerca gregaria. Cell Tissue Res 333:125-145.

Pfeiffer K, Kinoshita M, Homberg U (2005) Polarization-sensitive and light-sensitive neurons in two parallel pathways passing through the anterior optic tubercle in the locust brain. J Neurophysiol 94:3903-3915.

Pfeiffer K, Homberg U (2007) Coding of azimuthal directions via time-compensated combination of celestial compass cues. Curr Biol 17:960-965.

Reppert SM, Zhu H, White RH (2004) Polarized light helps monarch butterflies navigate. Curr Biol 14:155-158.

Zhu H, Gegear RJ, Casselman A, Kanginakudru S, Reppert SM (2009) Defining behavioural and molecular differences between summer and migratory monarch butterflies. BMC Biology 7:14.

Project:  A rotation project is now open in the lab to work on the in vitro reconstruction of the purple sea urchin (Strongylocentrotus purpuratus) circadian clock.

Rotation Project under Supervision of Postdoctroral Fellow: Christine Merlin

Most of organisms possess an internal clock controlling physiological and behavioral outputs. The main gear at the core of the clock is a simple autoregulatory feedback loop involving a set of clock genes, in which positive elements drive the transcription of negative elements that rhythmically feed back to inhibit the action of the former with a time delay of about 24h.

Recent activities in our lab led to the discovery of a new type of clockwork mechanism in the monarch butterfly and yielded insights into the evolution of the circadian clock in insects (1-3). In order to extend our knowledge on the evolution of circadian clocks in the animal kingdom, we are interested to look at the clockwork mechanism in more ancient species. The sea urchin appears to be a suitable model for that purpose as it belongs to an evolutionary ancient group and its genome has been fully sequenced and annotated (4), therefore allowing the identification of its clock genes by database searches. Indeed, a preliminary study performed in the lab identified into the genome of S. purpuratus a set of clock genes that could potentially represent a new way to build a clock. To test this hypothesis, we are thus seeking to reconstruct this clock in vitro with the cloned clock genes identified.

The rotation student will be in charge of the cloning of the genes into appropriate expression vectors as well as the reconstruction of the transcriptional feedback loop in vitro using a luciferase reporter assay in Schneider 2 cells, in which the genes will be expressed transiently.

The student can expect to be trained in molecular biology, biochemistry, cell culture, and in vitro assays, in addition to be exposed to a rich scientific environment as exemplified by the diversity of projects developed in the lab (see our website).

Motivated students with strong interests in molecular approaches are encouraged to apply.

Zhu H., Yuan Q., Briscoe A.D., Froy O., Casselman A., and Reppert S.M. (2005) The two CRYs of the butterfly. Curr. Biol., 15:R953-R954.

Yuan Q., Metterville D., Briscoe A.D., and Reppert, S.M. (2007) Insect cryptochromes: Gene duplication and loss define diverse ways to construct insect circadian clocks. Mol. Biol. Evol., 24:948-955.

Zhu H., Sauman I., Yuan Q., Casselman A., Emery-Le M., Emery P., and Reppert S.M. (2008) Cryptochromes define a novel circadian clock mechanism in monarch butterflies that may underlie sun compass navigation. PLoS Biol., 6:e4.

The genome of the Sea Urchin Strogylocentrotus purpuratus. (2006) Sea Urchin Genome Sequencing Consortium. Science, 314:941-952.

Laboratory Personnel:

Academic Background

Office: LRB 728 A-D Rm 728
Phone: 508-856-6148
E-mail: Steven.Reppert@umassmed.edu

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Postdoctoral Position Available A postdoctoral position is available to study in this laboratory. Contact Dr. Reppert for additional details.