title: Developmental guidance of the retroflex tract at its bending point involves Robo1-Slit2-mediated floor plate repulsion.
abstract: The retroflex tract contains medial habenula efferents that target the hindbrain interpeduncular complex and surrounding areas. This tract displays a singular course. Initially, habenular axons extend ventralwards in front of the pretectum until they reach the basal plate. Next, they avoid crossing the local floor plate, sharply changing course caudalwards (the retroflexion alluded by the tract name) and navigate strictly antero-posteriorly across basal pretectum, midbrain and isthmus. Once they reach rhombomere 1, the habenular axons criss-cross the floor plate several times within the interpeduncular nuclear complex as they innervate it. Here we described the timing and details of growth phenomena as these axons navigate to their target. The first dorsoventral course apparently obeys Ntn1 attraction. We checked the role of local floor plate signaling in the decision to avoid the thalamic floor plate and bend caudalwards. Analyzing the altered floor and basal plates of Gli2 knockout mice, we found a contralateral projection of most habenular axons, plus ulterior bizarre navigation rostralwards. This crossing phenotype was due to a reduced expression of Slit repulsive cues, suggesting involvement of the floor-derived Robo-Slit system in the normal guidance of this tract. Using Slit and Robo mutant mice, open neural tube and co-culture assays, we determined that Robo1-Slit2 interaction is specifically required for impeding that medial habenular axons cross the thalamic floor plate. This pathfinding mechanism is essential to establish the functionally important habenulo-interpeduncular connection.
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Moreno-Bravo
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain.
authors.forename: Jesus E
authors.initials: JE
authors.lastname: Martinez-Lopez
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain.
authors.forename: M Pilar
authors.initials: MP
authors.lastname: Madrigal
authors.affiliation: Department of Biology, University of Nevada, Reno, NV, 89557, USA.
authors.forename: Minkyung
authors.initials: M
authors.lastname: Kim
authors.affiliation: Department of Biology, University of Nevada, Reno, NV, 89557, USA.
authors.forename: Grant S
authors.initials: GS
authors.lastname: Mastick
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain.
authors.forename: Guillermina
authors.initials: G
authors.lastname: Lopez-Bendito
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain.|Instituto Murciano de Investigación Biomédica IMIB-Arrixaca, Murcia, Spain.
authors.forename: Salvador
authors.initials: S
authors.lastname: Martinez
authors.affiliation: Instituto de Neurociencias de Alicante, Universidad Miguel Hernández-CSIC, Sant Joan d'Alacant, 03550, Alicante, Spain. epuelles@umh.es.
authors.forename: Eduardo
authors.initials: E
authors.lastname: Puelles
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism; D019556:COS Cells; D002465:Cell Movement; D002522:Chlorocebus aethiops; D018920:Coculture Techniques; D018507:Gene Expression Regulation, Developmental; D005838:Genotype; D005865:Gestational Age; D019262:Habenula / Q000196:embryology / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051741:Kruppel-Like Transcription Factors / Q000172:deficiency / Q000235:genetics; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D010641:Phenotype; D011971:Receptors, Immunologic / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D013788:Thalamus / Q000196:embryology / Q000378:metabolism*; D046509:Tissue Culture Techniques; D014162:Transfection; D000075746:Zinc Finger Protein Gli2; D000097905:Roundabout Proteins; D000098552:Slit Homolog 2 Protein
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D051741:Kruppel-Like Transcription Factors; D009419:Nerve Tissue Proteins; D011971:Receptors, Immunologic; D000075746:Zinc Finger Protein Gli2; D000097905:Roundabout Proteins; D000098552:Slit Homolog 2 Protein; C000618551:Gli2 protein, mouse
keywords: Axon guidance; Floor plate; Habenula; Retroflex tract; Robo-Slit