Comparison And Significance Of Expression Of Slit And Sema3A In The Spinal Cord Of Embryonic Chicken

The specificity of neuronal connections is the striking physical feature of the nervous system. Many developmental processes contribute to establishing these precise patterns of connections,but none is more important than the guidance of axons from their points of origin to their appropriate targets. The specificity required to achieve the correct wiring is quite extraordinary,in that many axons need to grow long distance,bypassing numerous targets along the way,before reaching and forming connections with appropriate synaptic paterns.The nervous system has developed elaborate mechanism to solve the problem .At the cellular level,one basic strategy is to break the long journey into several manageable steps.Thus axons receive guidance at intervals along the way. Some axons that grow early in the embryo serve as scaffold for late-growing axons.Others grow along cell surface or extracellular matrices.Sometimes so-called guidepost cells serve as sites at which axons make divergent choices,such as midline cells.The axon receives and responds to these guidance clues with a specialized terminal apparatus, the growth cone. The growth cone is both a sensory and motor structure.lt bears numerous receptors to whichenvironmental cues binds .And it contains signal transduction systems converting signals into integrate instructions that steer the growth of growth cones.In this way the growing axons can integrate multiple cues to traverse complex terrain to their destinations.In the most general terms,the molecules that guide axons act by eitherpromoting or inhibiting neurite outgrowth.Some molecules promoteoutgrowth of some axons but inhibit others. Slit and Sema3A are suchguidance cues that have multiple functions in vitro.In order to study thepossible functions in vivo ,we detected the mRNA expression pattern ofthe neural growth guidance cues Slit and Sema3A in the spinal cord ofembryonic chicken . Antisense and sense Dig-labeled RNA probes to Slitand Sema3A mRNA were produced . The expression of Slit and Sema3Agenes in the spinal cord of embryonic chicken at different stages wasdetected by the method of in situ hybridization. With the result that theSlit gene was expressed mainly around the midline structure,appearing asmidline dominance,and that Sema3A mRNA was expressed with ventralpredominance, we postulated that Slit and Sema3A play important rolesin the axonal pathfmding and establishment of neural circuits in spinalcord development.