Marnie Halpern Staff Member Department of Embryology, Carnegie Institution of Washington Adjunct Professor Department of Biology CMDB Graduate Program Faculty B.S. McMaster University M.S. McMaster University Ph.D. Yale University

[Research Interests] [Representative Publications] [Lab Members]

RESEARCH INTERESTS

Genetic approaches in the zebrafish, Danio rerio enable us to explore how regional specializations arise in the developing neural tube. The zebrafish is ideal for these studies because of its short generation time and ability to produce large numbers of progeny. Eggs are fertilized externally and the resultant embryos develop rapidly and are optically clear, allowing direct visualization of neural development and rapid identification of mutant phenotypes.

In vertebrate embryos, evidence suggests that the notochord, a derivative of axial mesoderm, influences differentiation of the overlying neurectoderm. In particular, notochord is thought to be important for induction of the floor plate, the specialized cells at the ventral midline of the neural tube. Floor plate cells in turn provide essential signals for axon guidance at the spinal cord midline and for differentiation of motoneurons. A member of the Hedgehog family of proteins, Sonic hedgehog (SHH), is thought to be the candidate-inducing signal for floor plate and motoneurons.

Surprisingly, zebrafish mutants that lack notochords exhibit relatively normal neural development, including differentiation of floor plate and motoneurons. We carried out a detailed analysis of shh expression at gastrulation in relation to expression of tiggy-winkle hedgehog (twhh), another zebrafish hh gene. Cells in the newly forming embryonic axis sort out into discrete hedgehog-expressing layers: shh is expressed by the deep axial mesoderm which gives rise to notochord, whereas twhh is expressed in overlying cells that gives rise to floor plate. Thus, specification of floor plate appears to commence at gastrulation, prior to notochord differentiation. Using gene inactivation methods, we have further shown that HH activity is not essential for floor plate formation in zebrafish.

Another signaling pathway has been implicated in floor plate development from the genetic identification of zebrafish cyclops (cyc). Mutant cyclops embryos lack the ventral brain and floor plate. In collaboration with Chris Wright and coworkers (Vanderbilt University), we determined that cyc encodes a nodal-related member of the TGF beta family of signaling peptides. Injection of cyc RNA rescues the ventral brain and floor plate of cyc mutants. Coinjection of tracer RNAs reveals that cyc overexpression in either the ventral neural tube or notochord is insufficient for rescue. However, recovery of the ventral brain and floor plate correlates with the presence of tracer gene activity in derivatives of the prechordal plate, which itself comes from the early gastrula organizer. We propose that it is within this organizer region that patterning of the ventral neural tube occurs, and in agreement, cyc is normally expressed in these cells. We are continuing our studies on the timing and mechanisms that pattern the zebrafish floor plate through overexpression and cell transplantation studies.

Curiously, the nodal signaling pathway is also activated transiently on the left side of the zebrafish forebrain, in the epithalamic region. We have to begun to examine how this molecular left-right asymmetry is regulated and its functional significance.

Other projects in the lab involve studies of the genetic regulation of myelination and of forebrain morphogenesis.

REPRESENTATIVE PUBLICATIONS

Gamse, J.T., C. Thisse, B. Thisse and M.E. Halpern 2003. The parapineal mediates left-right asymmetry in the zebrafish diencephalon. Development 130:1059-1068.

Farber, S.A., R.A. DeRose, E.S. Olson and M.E. Halpern 2003. The zebrafish annexin gene family.  Genome Res, 13:1082-1096.

Halpern, M.E., J.O. Liang and J.T. Gamse 2003. Leaning to the left: laterality in the zebrafish forebrain. Trends Neurosci. 26: 308-313. 

Fisher, S.A., P. Jagadeeswaran and M.E. Halpern 2003. Radiographic analysis of zebrafish skeletal defects.  Dev Biol. in press

Gamse, J.T., Y.-C. Shen, C. Thisse, B. Thisse, P.A. Raymond, M.E. Halpern and J.O. Liang 2002. Otx5 regulates genes that show circadian expression in the zebrafish pineal complex. Nature Genetics 30: 117-121.

Brösamle, C. and M.E. Halpern 2002. Characterization of myelination in the developing zebrafish. Glia 39: 47-57.

Wright, C. and Halpern, M.E. 2002. Specification of Left-Right Asymmetry in “Pattern formation in zebrafish". Ed. L. Solnica-Krezel. Springer-Verlag.

Etheridge, L.A. T. Wu, J.O. Liang, S. Ekker and M.E. Halpern 2001. Floor plate develops upon depletion of Tiggy-winkle and Sonic hedgehog. Genesis 30: 164-169.

Farber, S.A., M. Pack, S.-Y. Ho, I.D. Johnson, H.S. Hendrickson, E.K. Hendrickson and M.E. Halpern 2001. Genetic Analysis of Digestive Physiology Using Fluorescent Phospholipid Reporters. Science 292: 1385-1388.

Liang, J.O., A. Etheridge, L. Hantsoo, A.L. Rubinstein, S. J. Nowak, J.C. Izpisua-Belmonte and M.E. Halpern. 2000. Asymmetric Nodal signaling in the zebrafish diencephalon positions the pineal organ.  Development 127: 5101-5112.

Sampath*, K., A.L. Rubinstein*, A.M.S. Cheng*, J.O. Liang*, K. Fekany, L. Solnica-Krezel, V. Korzh, M.E. Halpern and C.V.E. Wright 1998. Induction of the zebrafish ventral brain and floor plate requires Cyclops/Nodal signalling. Nature 395: 185-189. (*co-first authors)

Lab Members

Postdoctoral Fellows:
Ararat Ablooglu
Christian Brösamle
Joshua Gamse
Jiaojiao Zhang
 
Graduate Student:
Vanessa Matos-Cruz
Valarie Miller-Bertoglio completed Ph.D. 2000)

Technicians:
David Coyle (fish facility)
Lea Fortuno
Michelle Macurak