TY - JOUR
T1 - Multiple Slits regulate the development of midline glial populations and the corpus callosum
AU - Unni, Divya K.
AU - Piper, Michael
AU - Moldrich, Randal X.
AU - Gobius, Ilan
AU - Liu, Sha
AU - Fothergill, Thomas
AU - Donahoo, Amber Lee S.
AU - Baisden, John M.
AU - Cooper, Helen M.
AU - Richards, Linda J.
N1 - Funding Information:
We thank Prof. Marc Tessier-Lavigne, Genentech, for providing riboprobes as well as the Slit1 , Slit2 and Slit1/2 mutant mice and for supplying the Slit3 mutant mice that were generated and provided with permission by Prof. David Ornitz, Washington University, St Louis. We thank Dr. Vasi Sundaresan and Dr. Bill Andrews, Kings College London and University College London, for providing the Robo1 −/− mice, Dr. Niels Danbolt for the GLAST antibody and Prof. Fujio Murakami for the Robo1 antibody. We are grateful to Rowan Tweedale for critical reading of the manuscript and for members of the Goodhill Laboratory (Queensland Brain Institute) for their assistance in the analysis of the explant assay. This work was supported by grants 456026 and 631466 to LJR and 456040 to HC and LJR from the National Health and Medical Research Council (NHMRC) of Australia . MP is supported by a Career Development Award and LJR is supported by a Principal Research Fellowship from the NHMRC. HC is supported by a Smart State Fellowship from the Queensland Government . DU was supported by University of Queensland International Post Graduate and International Living Allowance Scholarships , IG was supported by a University of Queensland Research Scholarship and ALSD was supported by an Australian Postgraduate Research Award .
PY - 2012/5/1
Y1 - 2012/5/1
N2 - The Slit molecules are chemorepulsive ligands that regulate axon guidance at the midline of both vertebrates and invertebrates. In mammals, there are three Slit genes, but only Slit2 has been studied in any detail with regard to mammalian brain commissure formation. Here, we sought to understand the relative contributions that Slit proteins make to the formation of the largest brain commissure, the corpus callosum. Slit ligands bind Robo receptors, and previous studies have shown that Robo1-/- mice have defects in corpus callosum development. However, whether the Slit genes signal exclusively through Robo1 during callosal formation is unclear. To investigate this, we compared the development of the corpus callosum in both Slit2-/- and Robo1-/- mice using diffusion magnetic resonance imaging. This analysis demonstrated similarities in the phenotypes of these mice, but crucially also highlighted subtle differences, particularly with regard to the guidance of post-crossing axons. Analysis of single mutations in Slit family members revealed corpus callosum defects (but not complete agenesis) in 100% of Slit2-/- mice and 30% of Slit3-/- mice, whereas 100% of Slit1-/-; Slit2-/- mice displayed complete agenesis of the corpus callosum. These results revealed a role for Slit1 in corpus callosum development, and demonstrated that Slit2 was necessary but not sufficient for midline crossing in vivo. However, co-culture experiments utilising Robo1-/- tissue versus Slit2 expressing cell blocks demonstrated that Slit2 was sufficient for the guidance activity mediated by Robo1 in pre-crossing neocortical axons. This suggested that Slit1 and Slit3 might also be involved in regulating other mechanisms that allow the corpus callosum to form, such as the establishment of midline glial populations. Investigation of this revealed defects in the development and dorso-ventral positioning of the indusium griseum glia in multiple Slit mutants. These findings indicate that Slits regulate callosal development via both classical chemorepulsive mechanisms, and via a novel role in mediating the correct positioning of midline glial populations. Finally, our data also indicate that some of the roles of Slit proteins at the midline may be independent of Robo signalling, suggestive of additional receptors regulating Slit signalling during development.
AB - The Slit molecules are chemorepulsive ligands that regulate axon guidance at the midline of both vertebrates and invertebrates. In mammals, there are three Slit genes, but only Slit2 has been studied in any detail with regard to mammalian brain commissure formation. Here, we sought to understand the relative contributions that Slit proteins make to the formation of the largest brain commissure, the corpus callosum. Slit ligands bind Robo receptors, and previous studies have shown that Robo1-/- mice have defects in corpus callosum development. However, whether the Slit genes signal exclusively through Robo1 during callosal formation is unclear. To investigate this, we compared the development of the corpus callosum in both Slit2-/- and Robo1-/- mice using diffusion magnetic resonance imaging. This analysis demonstrated similarities in the phenotypes of these mice, but crucially also highlighted subtle differences, particularly with regard to the guidance of post-crossing axons. Analysis of single mutations in Slit family members revealed corpus callosum defects (but not complete agenesis) in 100% of Slit2-/- mice and 30% of Slit3-/- mice, whereas 100% of Slit1-/-; Slit2-/- mice displayed complete agenesis of the corpus callosum. These results revealed a role for Slit1 in corpus callosum development, and demonstrated that Slit2 was necessary but not sufficient for midline crossing in vivo. However, co-culture experiments utilising Robo1-/- tissue versus Slit2 expressing cell blocks demonstrated that Slit2 was sufficient for the guidance activity mediated by Robo1 in pre-crossing neocortical axons. This suggested that Slit1 and Slit3 might also be involved in regulating other mechanisms that allow the corpus callosum to form, such as the establishment of midline glial populations. Investigation of this revealed defects in the development and dorso-ventral positioning of the indusium griseum glia in multiple Slit mutants. These findings indicate that Slits regulate callosal development via both classical chemorepulsive mechanisms, and via a novel role in mediating the correct positioning of midline glial populations. Finally, our data also indicate that some of the roles of Slit proteins at the midline may be independent of Robo signalling, suggestive of additional receptors regulating Slit signalling during development.
KW - Axon guidance
KW - Cerebral cortex
KW - Commissure formation
KW - Diffusion magnetic resonance imaging
KW - Indusium griseum glia
KW - Midline formation
UR - http://www.scopus.com/inward/record.url?scp=84862811622&partnerID=8YFLogxK
U2 - 10.1016/j.ydbio.2012.02.004
DO - 10.1016/j.ydbio.2012.02.004
M3 - Article
C2 - 22349628
AN - SCOPUS:84862811622
SN - 0012-1606
VL - 365
SP - 36
EP - 49
JO - Developmental Biology
JF - Developmental Biology
IS - 1
ER -