Differential Responsiveness to the Chemorepellent Semaphorin 3A Distinguishes Ipsi- and Contralaterally Projecting Axons in the Chick Midbrain

Developmental Biology

Sigrid Henke-Fahle¹  Andreas W Püschel¹  Kai-Wulf Beck¹ 

[1] Department of Ophthalmology, University of Tübingen, Schleichstrasse 12, D-72076, Tübingen, Germany

关键词: axon guidance;    chemorepulsion;    Sema3A-deficient mice;    Neuropilin-1;    Netrin-1;    Slit2;    floor plate;    diencephalon;    optic tectum;    tegmentum;    ipsilateral projection;    midline crossing;   

DOI  :  10.1006/dbio.2001.0376

学科分类：生物科学（综合）

来源: Academic Press

【 摘 要 】

Inthechickdorsalmesencephalon,theoptictectum,thedevelopingaxonsmustchoosebetweenremainingonthesamesideofthemidlineorgrowingacrossit.Theipsilaterallyprojectingaxons,formingthetectobulbartract,coursecircumferentiallytowardtheventrallysituatedfloorplatebutbeforereachingthebasalmesencephalon,thetegmentum,graduallyturncaudally.Here,theyfollowthecourseofthemediallongitudinalfasciculus(MLF),locatedparalleltothefloorplate.Byinvivolabelingoftectalaxons,wecoulddemonstratethattheseaxonsariseprimarilyinthedorsaltectum.Totesttheideathatchemorepellentmoleculesareinvolvedinguidanceofthenondecussatingaxons,weperformedcocultureexperimentsemployingtectalexplantsfromvariouspositionsalongthedorso-ventralaxis.AxonsemanatingfromdorsaltectalexplantswerestronglyrepelledbydiencephalictissuecontainingtheneuronsthatgiverisetotheMLFwhereasventraltectalaxonsshowedonlyamoderateresponse.Thisinhibitoryeffectwassubstantiallyneutralizedbytheadditionofanti-neuropilin-1antibodies.AsimilardifferentialresponseofaxonswasobservedwhentectalexplantswerecoculturedwithcellaggregatessecretingthechemorepellentSemaphorin3A(Sema3A).Sema3BandSema3C,respectively,didnotinhibitgrowthoftectalaxons.Inaddition,neitherthefloorplatenorSlit2-secretingcellaggregatesinfluencedoutgrowthofdorsalfibers.InSema3A-deficientmice,DiI-labelingrevealedthatdorsalmesencephalicaxonscrosstheMLFinsteadofturningposteriorlyuponreachingthefibertract,thusbehavingliketheventrallyoriginatingcontralaterallyprojectingaxons.AdifferentialresponsivenessoftectalaxonstoSema3AmostlikelyreleasedbytheMLFthuscontributestopathfindingintheventralmesencephalon.

【 授权许可】

Unknown