Developmental Neurobiology: Axon Guidance, Forebrain Patterning, and Pituitary Developement
My laboratory uses zebrafish as a simple vertebrate system to study how the forebrain and pituitary gland develop, and to investigate how axons are guided across the midline to form the forebrain commissures and optic chiasm. Accessible and rapid early development, combined with beautiful imaging characteristics and the ability to manipulate gene expression, make zebrafish a powerful model system for the study of early brain formation.
Pituitary Induction and Patterning
The vertebrate pituitary gland is the "master" endocrine gland and controls a wide range of metabolic functions, from growth, to reproduction, to stress responses. The zebrafish is a relatively untapped resource in the study of endocrine development, and has profound advantages for research into pituitary development. In particular, the genetic and optical accessibility of the embryo makes it possible to observe and manipulate the earliest events in pituitary formation (see time-lapse movie). Importantly, pituitary structure is highly conserved across vertebrate species, making studies in zebrafish directly relevant to human development.
Our analysis of zebrafish forebrain mutants led to the discovery that the small protein Sonic Hedgehog (Shh) is a critical player in the early induction of the pituitary placode, as well as in the differentiation of a subset of endocrine cell types. This role for Shh is conserved across vertebrates, with defects in human Shh signaling leading to congenital disorders affecting pituitary development. In addition, aberrant Shh signaling in the adult pituitary is associated with common pituitary adenomas. A major project in the lab is to investigate the cellular and molecular mechanisms by which Shh regulates this endocrine gland, both in the embryo and post-embryonically. This research is aiding our understanding of human birth defects and is beginning to shed light on how mis-regulation of Shh signaling can lead to pituitary tumors.
Axon and Glial Guidance in the forebrain
We continue to use the zebrafish achiasmatic mutants as tools for investigating the mechanisms that guide axons across the midline of the forebrain. We recently showed that the belladonna (bel) mutation affects the lhx2 gene. In both lhx2 and shh mutants, the axon growth substrate is disrupted in specific ways, providing clues as to the axon guidance mechanisms that are required for proper midline crossing. In particular, we have characterized a unique population of glial cells that spans the midline just prior to axon crossing, and shown that this glial bridge is disrupted in the achiasmatic mutants. We are currently investigating how these glial cells find their correct positions in the forebrain and how they subsequently help establish of the optic chiasm and forebrain commissures.
Shen, M.C., Ozacar, A.T, Boeras, C, Pink, J., Thomas, J., Kohtz, J., and Karlstrom R.O. 2013. Heat Shock Mediated Conditional Regulation of Hedgehog/Gli Signaling in Zebrafish. Developmental Dynamics, 242(5): 539-49. PMID: 23441066
Breves, J.P., Serizier, S.B., Goffin, V., McCormick, S.D., Karlstrom, R.O. 2013. Prolactin regulates transcription of the ion uptake Na+/Cl- cotransporter (ncc) gene in zebrafish gill. Mol. Cell Endocrinology, 369(1-2): 98-106. PMID: 23395804
Bergeron, S.A., Tyurina, O.V., Miller, E., Bagas, A., Karlstrom, R.O. 2011. Brother of cdo (umleitung) is cell-autonomously required for Hedgehog-mediated ventral CNS patterning in the zebrafish. Development, Jan;138(1): 75-85. Epub. 2010, Nov 29. PMID: 21115611
Barresi, M.J., Burton, S., Dipietrantonio, K., Amsterdam, A., Hopkins, N., Karlstrom, R.O. 2010. Essential genes for astroglial development and axon pathfinding during zebrafish embryogenesis. Dev. Dyn., Oct;239(10): 2603-18. PMID: 20806318.
Gates, K.P., Mentzer, L., Karlstrom, R.O., Sirotkin, H.I. 2010. The transcriptional repressor REST/NRSF modulates hedgehog signaling. Developmental Biology, Apr 15;340(2): 293-305. Epub. 2010, Feb 1. PMID: 20122919.
Placinta, M., Shen, M.C., Achermann, M., Karlstrom, R.O. 2009. A laser pointer driven microheater for precise local heating and conditional gene regulation in vivo. Microheater driven gene regulation in zebrafish. BMC Dev Biol., Dec 30; 9:73. PMID: 20042114.
Wang, Z., Glenn, H., Brown, C., Valavanis, C., Liu, J.X., Seth, A., Thomas, J.E., Karlstrom, R.O.,, Schwartz, L.M. 2009. Regulation of muscle differentiation and survival by Acheron. Mech. Dev., Aug-Sep; 126(8-9): 700-9. Epub. 2009, May 28. PMID: 19481601
Devine, C.A., Sbrogna, J.L., Guner, B., Osgood, M., Shen, M-C., and Karlstrom, R.O. 2009. A dynamic Gli code interprets Hh signals to regulate induction, patterning, and endocrine cell specification in the zebrafish pituitary. Developmental Biology, (accepted 11/4/08).
Guner, B., Ozacar, A.T., Thomas, J.E., and Karlstrom, R.O. 2008. Graded Hh and Fgf signaling independently regulate pituitary cell fates and help establish the PD and PI of the zebrafish adenohypophysis. Endocrinology, 149(9): 4435-51.
Bergeron, S.A., Milla, L.A., Villegas, R., Shen, M-C., Burgess, S.M., Allende, M.L., Karlstrom, R.O., and Palma, V. 2008. Expression profiling identifies novel Hh/Gli regulated genes in developing zebrafish embryos. Genomics, 91(2): 165-77.
Guner, B. and Karlstrom, R.O. 2007. Cloning of zebrafish nkx6.2 and a comprehensive analysis of the conserved transcriptional response to Hedgehog/Gli signaling in the zebrafish neural tube. Mechanisms of Development, 7(5): 596-605.
Seth, A., Culverwell, J., Walkowicz, M., Toro, S., Rick, J.M., Neuhauss, S., Varga, Z., and Karlstrom, R.O. 2006. belladonna/lhx2 is required for neural patterning and midline axon guidance in the zebrafish forebrain. Development, 133: 725-735.
Cerda, G.A., Thomas, J.E., Allende, M.A., Karlstrom, R.O., Palma, V. 2006. Electroporation of DNA, RNA, and morpholinos into zebrafish embryos. Methods, 39: 207-211.
Barresi, M.J., Hutson, L., Chien, C-B., and Karlstrom, R.O. 2005. Hedgehog regulated Slit expression determines commissure and glial cell position in the zebrafish forebrain. Development, 132(16): 3643-56.
Vanderlaan, G.M., Tyurina, O.V., Karlstrom, R.O., and Chandrasekhar, A., 2005. Gli Function is Essential for Motor Neuron Induction in Zebrafish. Developmental Biology, 282(2): 550-70.
Tyurina, O.V., Guner, B., Popova, E., Feng, J., Schier, A.F., Kohtz, J.D., and Karlstrom, R.O. 2005. Zebrafish Gli3 functions as both an activator and a repressor in Hedgehog signaling. Developmental Biology, 277: 537-556.
Feng, J., White, B., Tyurina, O., Guner, B., Larson, T., Lee, H., Karlstrom, R. O., and Kohtz, J. 2004. Synergistic and antagonistic roles of the Sonic hedgehog N and C-terminal lipids. Development, 131(17): 4357-70.
Sekimizu, K, Nishioka, N, Sasaki, H, Takeda, H, Karlstrom, R.O. and Kawakami, A. 2004. The zebrafish iguana locus encodes Dzip1, a novel zinc finger protein required for proper regulation of hedgehog signaling. Development, 131: 2521.
Ungos, J.M., Karlstrom, R.O. , and Raible, D.W. 2003. Hedgehog signaling is directly required for the development of zebrafish dorsal root ganglia neurons. Development. 130: 5351-5362.
Sbrogna, J.L., Barresi, M.J.F., and Karlstrom, R.O. 2003. Multiple roles for hedgehog signaling in zebrafish pituitary development. Developmental Biology. 254(1): 19-35.
Karlstrom, R.O., Tyurina, O., Kawakami, A., Nishioka, N., Talbot, W.S., Sasaki, H., and Schier, A.F. 2003. Genetic analysis of zebrafish gli1 and gli2 reveals and divergent requirements for gli genes in vertebrate development. Development. 130: 549-1564.
Culverwell, J., and Karlstrom, R.O. 2002. Making the connection: Retinal axon guidance in the zebrafish. Sem. Cell and Developmental Biol. 13(6): 497-506.
diIorio, P.J., Moss, J.B., Sbrogna, J.L., Karlstrom, R.O., and Moss, L.G. 2002. Sonic hedgehog Is Required Early in Pancreatic Islet Development. Developmental Biology, 2002 Apr 1 244(1): 75-84.
Kondoh, H., Ukhikawa, M., Yoda, H., Furutani-Seiki, M., and Karlstrom, R.O. 2000. Zebrafish mutations in gli-mediated hedgehog signaling lead to lens transdifferentiation from the adenohypophysis anlage. Mechanisms of Development 96: 165-174.
Karlstrom, R.O., Talbot, W.S. and Schier, A.F. 1999. Synteny cloning of zebrafish you-too: Mutations in the hedgehog target gli2 affect ventral forebrain patterning. Genes and Development 13: 388-393.
Karlstrom, R.O., Trowe, T. and Bonhoeffer, F. 1997. Genetic analysis of axon guidance in the zebrafish. Trends in Neurosciences 20: 3-8.
Karlstrom, R.O. and Kane, D.A. 1996. A time-lapse flip-book of zebrafish development. Development 123: 2-460.
Karlstrom, R.O., et al. 1996. Zebrafish mutations affecting retinotectal axon pathfinding. Development 123: 427-438.