The proposed aims build on investigations during the previous funding period on the identification of a single ligand-receptor pair, EphB1-ephrinB2 that directs repulsion of ventrotemporal (VT) retinal ganglion cell (RGC) growth cones at the optic chiasm midline. EphB1, expressed strictly on VT RGCs, interacts with the ligand ephrinB2 on radial glia at the chiasm midline to direct formation of the uncrossed projection. Mechanisms of midline crossing that guide RGC axons across the optic chiasm midline remain unclear. We have identified NrCAM as necessary for the establishment of the late crossed projection from VT retina. NrCAM is also expressed in RGCs outside the VT crescent.
In Aim 1. a, the function of two other CAMs, TAG- 1 and Neurofascin, expressed similarly to NrCAM, will be investigated for their involvement in crossing the midline. In addition, we localized Sema6D at the chiasm midline and its receptor, Plexin-A1, is expressed in all crossing RGCs. In vitro, Sema6D inhibits the growth of RGCs that project across the midline.
In Aim 1. b., the actions of Sema6D and Plexin-A1 in mediating the crossed RGC projection will be studied. CAMs have been shown to collaborate with semaphorins in other crossing systems. This issue will be addressed in Aim 1.c. Transgenic mice, culture assays, and methods for gene delivery (electroporation in utero and ex utero) developed in our lab will be used to provide a comprehensive view of the crossing process in the chiasm. The formation of eye-specific terminations in the dLGN is a direct consequence of retinal axon decussation in the optic chiasm. In our studies on the uncrossed projection, we asked how aberrant midline decussation affects specific innervation patterns in the dLGN. In EphB1 gain- and loss-of-function models, RGCs misproject to the wrong side of the midline yet terminate in appropriate eye-specific zones. These results implicate molecular """"""""tags"""""""" for eye-specific innervation. As a foundation for further analysis, in Aim 2.a., we will chronicle the ingrowth, arbor formation and segregation of mouse retinogeniculate axons at the single-fiber level, as this information is lacking.
In Aim 2. b., we will identify molecules that may implement eye-specific innervation of the dLGN, by 1) localization of candidates studied in Aim 1, and 2) transcriptional profiling of specific tissue regions.
In Aim 2. c. and d., we will then determine the role of candidate molecules by perturbing them and by altering neural activity. The phenomenon of coordinate action by multiple guidance families such as Semaphorins and CAMs, presents a new level of analysis of axon navigation in higher vertebrate retinal pathways, where divergence is controlled by two distinct molecular systems. The proposed experiments thus address fundamental questions on how the binocular pathways develop.

Public Health Relevance

This research aims to understand how growing retinal ganglion cells from each eye converge at the X- shaped optic chiasm, and then diverge toward targets on the same and opposite side of the brain. Proper binocular vision is dependent on a normal distribution of retinal axons at the optic chiasm, and if altered, reduced visual acuity and depth perception ensue. These studies use this model to investigate the molecular factors that help guide axons to their appropriate route and synaptic targets in the brain.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Research Project (R01)
Project #
5R01EY012736-23
Application #
8293261
Study Section
Central Visual Processing Study Section (CVP)
Program Officer
Steinmetz, Michael A
Project Start
1999-07-01
Project End
2014-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
23
Fiscal Year
2012
Total Cost
$415,092
Indirect Cost
$157,271
Name
Columbia University (N.Y.)
Department
Pathology
Type
Schools of Medicine
DUNS #
621889815
City
New York
State
NY
Country
United States
Zip Code
10032
Iwai-Takekoshi, Lena; Balasubramanian, Revathi; Sitko, Austen et al. (2018) Activation of Wnt signaling reduces ipsilaterally projecting retinal ganglion cells in pigmented retina. Development 145:
Sitko, Austen A; Kuwajima, Takaaki; Mason, Carol A (2018) Eye-specific segregation and differential fasciculation of developing retinal ganglion cell axons in the mouse visual pathway. J Comp Neurol 526:1077-1096
Lee, Melissa A; Sitko, Austen A; Khalid, Sania et al. (2018) Spatiotemporal distribution of glia in and around the developing mouse optic tract. J Comp Neurol :
Kuwajima, Takaaki; Soares, Célia A; Sitko, Austen A et al. (2017) SoxC Transcription Factors Promote Contralateral Retinal Ganglion Cell Differentiation and Axon Guidance in the Mouse Visual System. Neuron 93:1110-1125.e5
Wang, Qing; Marcucci, Florencia; Cerullo, Isadora et al. (2016) Ipsilateral and Contralateral Retinal Ganglion Cells Express Distinct Genes during Decussation at the Optic Chiasm. eNeuro 3:
Crair, Michael C; Mason, Carol A (2016) Reconnecting Eye to Brain. J Neurosci 36:10707-10722
Iwai-Takekoshi, Lena; Ramos, Anna; Schaler, Ari et al. (2016) Retinal pigment epithelial integrity is compromised in the developing albino mouse retina. J Comp Neurol 524:3696-3716
Marcucci, Florencia; Murcia-Belmonte, Veronica; Wang, Qing et al. (2016) The Ciliary Margin Zone of the Mammalian Retina Generates Retinal Ganglion Cells. Cell Rep 17:3153-3164
Panza, Paolo; Sitko, Austen A; Maischein, Hans-Martin et al. (2015) The LRR receptor Islr2 is required for retinal axon routing at the vertebrate optic chiasm. Neural Dev 10:23
Soares, Célia A; Mason, Carol A (2015) Transient ipsilateral retinal ganglion cell projections to the brain: Extent, targeting, and disappearance. Dev Neurobiol 75:1385-401

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