Annexe : Wiring Mechanisms for Olfaction and Vision

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Questions and Answers

What did Weth et al. (2014) hypothesize?

The superior colliculus is the target for RGC axons in mammals.

Conditional knockout mice lack EphrinA5 in the retina.

Axon-axon interactions are crucial for topographic mapping. (correct)

EphrinA5 is essential for topographic mapping.

What was the primary focus of the research conducted by Suetterlin and Drescher (2014)?

Replicating the findings of Friedrich Bonhoeffer and colleagues.

Providing experimental evidence for the involvement of axon-axon interactions in topographic map formation. (correct)

Investigating the role of EphrinA5 in retinal development.

Examining the impact of EphrinA5 knockout on the superior colliculus.

What specific technique did Suetterlin and Drescher (2014) employ in their research?

Electrophysiological recordings of neuronal activity.

Direct observation of axon-axon interactions.

Immunostaining to visualize specific proteins.

Genetic manipulation of EphrinA5 expression. (correct)

In the context of the research, what is the significance of the superior colliculus?

It serves as the target of RGC (retinal ganglion cell) axons in mammals. (D) Signup and view all the answers

What is the connection between the research by Suetterlin and Drescher (2014) and the work of Friedrich Bonhoeffer and colleagues?

Suetterlin and Drescher (2014) built upon previous observations made by Friedrich Bonhoeffer and colleagues using a new experimental approach. (D) Signup and view all the answers

What is the main takeaway from this research regarding the role of axon-axon interactions in topographic map formation?

Axon-axon interactions play a crucial role in topographic map formation, as supported by the experimental evidence. (B) Signup and view all the answers

What is the purpose of using conditional knockout mice in this study?

To study the effects of removing EphrinA5 specifically in the retina or the superior colliculus. (B) Signup and view all the answers

How does the research by Suetterlin and Drescher (2014) contribute to the understanding of topographic map formation?

It demonstrates the importance of axon-axon interactions in establishing topographic maps. (C) Signup and view all the answers

Which of the following is the key difference between the olfactory and visual systems, as discussed in the text?

The olfactory system prioritizes topographic mapping, while the visual system prioritizes spatial segregation. (B) Signup and view all the answers

What is the role of EphA receptors and EphrinA ligands in the visual system?

They act as repellent molecules, preventing axons from entering specific regions. (D) Signup and view all the answers

What is the consequence of higher EphA receptor levels in retinal ganglion cell axons?

Stronger repulsion from posterior areas of the tectum. (C) Signup and view all the answers

What is the significance of the Bonhoeffer stripe assay?

It confirmed the chemoaffinity hypothesis, demonstrating a gradient of repulsive molecules in the tectum. (C) Signup and view all the answers

Which of the following statements is supported by the text regarding the role of EphA receptor and EphrinA ligand levels in axon targeting?

The relative levels of Ephrins are more critical than absolute levels of receptors and ligands. (D) Signup and view all the answers

What is the primary focus of the new model proposed by Weth et al. (2014) for visual system wiring?

The importance of a combination of axon-target and axon-axon interactions in visual system wiring. (D) Signup and view all the answers

What is the significance of the Bonhoeffer lab's in vitro observations in the development of the new model for visual system wiring?

They contributed to the development of the new model by providing insights into the mechanisms of axon-axon interactions. (A) Signup and view all the answers

What is the main difference between the traditional view of topographic map formation and the newer model proposed by Weth et al. (2014)?

The newer model emphasizes the role of axon-axon interactions, while the traditional model focuses solely on axon-target interaction. (C) Signup and view all the answers

What is the key contribution of the study by Weth et al. (2014) to the understanding of visual system wiring?

It proposed a new model for visual system wiring that incorporates both axon-target and axon-axon interactions. (B) Signup and view all the answers

What does the new model for visual system wiring suggest about the role of axon-axon interactions in the development of the topographic map?

Axon-axon interactions are crucial for the formation of the map and influence the final projection pattern. (B) Signup and view all the answers

What was the main conclusion Roger Sperry drew from his experiments that led to the chemoaffinity hypothesis?

Axons are guided to their targets by a specific chemical attraction between cells. (B) Signup and view all the answers

Which of the following is NOT a key component of the chemoaffinity hypothesis?

Axons navigate to their targets by following the blood vessels. (B) Signup and view all the answers

What is the role of Eph receptors and Ephrins in axonal guidance?

They act as repellents, guiding axons away from certain regions. (D) Signup and view all the answers

According to the article, what is the main difference in sensitivity to repellents between nasal and temporal retinal ganglion cell (RGC) axons?

Temporal axons are more sensitive to repellents than nasal axons. (A) Signup and view all the answers

What experimental method contributed to the discovery of the EphrinA-mediated repulsion of temporal axons?

Using a Bonhoeffer stripe assay where nasal axons grew on stripes containing membranes from the anterior and posterior tectum. (A) Signup and view all the answers

How did the discovery of Ephrins and Eph receptors change the understanding of axonal guidance?

It confirmed Sperry's chemoaffinity hypothesis and provided a specific molecular mechanism for axon guidance. (C) Signup and view all the answers

What remains an unresolved issue in understanding how axons expressing EphA receptors innervate the tectum?

The reason why axons expressing EphA receptors are attracted to the tectum despite the presence of repellents. (B) Signup and view all the answers

What is the significance of the work by Suetterlin and Drescher (2014) in the context of the chemoaffinity hypothesis?

It extended Sperry's hypothesis by demonstrating the role of EphrinA expressed on nasal axons in guiding axons. (B) Signup and view all the answers

Which of the following correctly describes the role of EphA receptors and EphrinA ligands in the visual system?

EphA receptors and EphrinA ligands are only responsible for rostrocaudal mapping, while EphrinBs and EphBs are responsible for lateral-medial mapping. (D) Signup and view all the answers

What is the main difference between the targeting of axons in the visual system and the olfactory system?

In the visual system, axons are guided to their target cells based on spatial information, forming a topographic map, while in the olfactory system, axons converge based on odorant sensitivity, not spatial location. (B) Signup and view all the answers

What is the proposed function of the countergradients of EphA receptors and EphrinA ligands in the tectum and retina?

Their specific function is currently unknown but they are hypothesized to play a role in the fine-tuning and refinement of the initial axon connections in the tectum. (B) Signup and view all the answers

What does the phrase "cis-interactions" refer to in the context of this passage?

Interactions between EphA receptors and EphrinA ligands on the same cell, such as on an RGC axon. (A) Signup and view all the answers

Which of these features differentiates olfactory sensory neurons from RGC axons?

RGC axons form a topographic map in the tectum, while olfactory sensory neurons form a discrete map in the olfactory bulb. (B) Signup and view all the answers

Which of the following is NOT a specific type of Eph receptor mentioned in the text?

EphrinA receptors (B) Signup and view all the answers

Which of the following statements is TRUE regarding the role of Eph receptors and ligands in the visual system?

Both EphrinA/EphA and EphrinB/EphB interactions contribute to the precise spatial mapping of RGC axons to the tectum. (C) Signup and view all the answers

What is the significance of the study's finding that nasal RGC axons in mice lacking EphrinA5 in both the retina and SC were not more affected than those lacking EphrinA5 only in the SC?

It suggests EphrinA5 in the retina does not contribute to nasal RGC axon targeting. (C) Signup and view all the answers

What is the proposed mechanism behind the caudal overshooting of temporal RGC axons in mice lacking EphrinA5 in both the retina and SC?

Lack of axon-axon repulsion caused by the absence of EphrinA5 in the SC. (B) Signup and view all the answers

Which of the following is a characteristic of axon-axon interactions in the olfactory system?

Axon-axon interactions are responsible for the global distribution of OSN axons in the olfactory bulb. (A) Signup and view all the answers

What is the suggested role of olfactory receptors in olfactory sensory neuron axon guidance?

They act as attractant cues, guiding axons to specific regions of the olfactory bulb. (D) Signup and view all the answers

How does the study contribute to our understanding of axon guidance mechanisms?

It highlights the complexity of axon guidance, involving both classical and non-classical cues. (C) Signup and view all the answers

What is a key difference between the study's findings on temporal and nasal RGC axons?

Temporal RGC axons exhibit caudal overshooting in the absence of EphrinA5, while nasal RGC axons do not. (D) Signup and view all the answers

What is the suggested reason for nasal RGC axons being less affected by the absence of EphrinA5 in both the retina and SC compared to those only lacking EphrinA5 in the SC?

Nasal RGC axons are more reliant on other guidance cues for their targeting. (C) Signup and view all the answers

What is the primary conclusion drawn from the study's observations on temporal RGC axons?

EphrinA5 plays a critical role in mediating axon-axon repulsion for temporal RGC axons. (C) Signup and view all the answers

Study Notes

Wiring Mechanisms for Olfaction and Vision

EphrinAs and Eph receptors play crucial roles in wiring the visual system.
Sperry's chemoaffinity hypothesis proposes two molecular gradients guide retinal ganglion cell (RGC) axons to their targets in the visual system.
EphrinAs are expressed in an anterior-low/posterior-high gradient in the tectum.
EphA3 receptors are expressed in a nasal-low/temporal-high gradient in the retina.
RGC axons target specific locations in the tectum based on level of EphA receptors. Nasal axons extend further due to lower EphA receptors.
Temporal axons are repelled by the posterior tectum due to high EphA levels.
Axon-axon interactions contribute significantly to topographic map formation in the visual system.
EphrinA5 plays a role in regulating the spatial distribution of RGC axons, with interactions between nasal and temporal axons contributing to the anterior-posterior axis.

Olfactory System Wiring

Olfactory sensory neurons (OSNs) converge in the olfactory bulb forming discrete rather than topographic maps.
Spatial information is not required in olfactory wiring.
Olfactory receptors may be responsible for guiding OSN axons to the glomeruli.
Axon-axon interactions in the olfactory system are involved in global patterning.

Comparison of Visual and Olfactory Systems

Visual system wiring requires maintaining spatial information in the target.
Olfactory wiring does not require maintaining spatial information.
Both systems demonstrate axon-axon interactions contributing to targeting.
Axon-axon interactions in the olfactory system are involved in global patterning, while in the visual system they are local.

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Description

Explore the intricate wiring mechanisms involved in the olfactory and visual systems. Learn about the roles of EphrinAs and Eph receptors in guiding retinal ganglion cell axons and how these interactions shape topographic maps in the brain. This quiz delves into the molecular gradients and axon-axon relationships that are essential for sensory mapping.