title: Ten-m3 is required for the development of topography in the ipsilateral retinocollicular pathway.
abstract: BACKGROUND
  The alignment of ipsilaterally and contralaterally projecting retinal axons that view the same part of visual space is fundamental to binocular vision. While much progress has been made regarding the mechanisms which regulate contralateral topography, very little is known of the mechanisms which regulate the mapping of ipsilateral axons such that they align with their contralateral counterparts.
  
  
  RESULTS
  Using the advantageous model provided by the mouse retinocollicular pathway, we have performed anterograde tracing experiments which demonstrate that ipsilateral retinal axons begin to form terminal zones (TZs) in the superior colliculus (SC), within the first few postnatal days. These appear mature by postnatal day 11. Importantly, TZs formed by ipsilaterally-projecting retinal axons are spatially offset from those of contralaterally-projecting axons arising from the same retinotopic location from the outset. This pattern is consistent with that required for adult visuotopy. We further demonstrate that a member of the Ten-m/Odz/Teneurin family of homophilic transmembrane glycoproteins, Ten-m3, is an essential regulator of ipsilateral retinocollicular topography. Ten-m3 mRNA is expressed in a high-medial to low-lateral gradient in the developing SC. This corresponds topographically with its high-ventral to low-dorsal retinal gradient. In Ten-m3 knockout mice, contralateral ventrotemporal axons appropriately target rostromedial SC, whereas ipsilateral axons exhibit dramatic targeting errors along both the mediolateral and rostrocaudal axes of the SC, with a caudal shift of the primary TZ, as well as the formation of secondary, caudolaterally displaced TZs. In addition to these dramatic ipsilateral-specific mapping errors, both contralateral and ipsilateral retinocollicular TZs exhibit more subtle changes in morphology.
  
  
  CONCLUSIONS
  We conclude that important aspects of adult visuotopy are established via the differential sensitivity of ipsilateral and contralateral axons to intrinsic guidance cues. Further, we show that Ten-m3 plays a critical role in this process and is particularly important for the mapping of the ipsilateral retinocollicular pathway.
authors.affiliation: Discipline of Physiology, School of Medical Sciences and Bosch Institute, University of Sydney, New South Wales, Australia.
authors.forename: Nuwan
authors.initials: N
authors.lastname: Dharmaratne
authors.forename: Kelly A
authors.initials: KA
authors.lastname: Glendining
authors.forename: Timothy R
authors.initials: TR
authors.lastname: Young
authors.forename: Heidi
authors.initials: H
authors.lastname: Tran
authors.forename: Atomu
authors.initials: A
authors.lastname: Sawatari
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Leamey
mesh_terms: D000818:Animals; D001369:Axons; D001931:Brain Mapping; D005786:Gene Expression Regulation; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D012160:Retina / Q000254:growth & development / Q000378:metabolism*; D012165:Retinal Ganglion Cells / Q000378:metabolism; D013477:Superior Colliculi / Q000378:metabolism*; D015348:Vision, Binocular / Q000235:genetics; D014795:Visual Pathways / Q000502:physiology*
chemical_list: D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C525233:Tenm3 protein, mouse