# Plexin B3 guides axons to cross the midline in vivo

## TL;DR

This study shows that Plexin B3 helps axons cross the midline in zebrafish embryos, suggesting it may act as a receptor for Sema3E in axon guidance.

## Contribution

The paper identifies Plexin B3 as a potential receptor for Sema3E in axon guidance and proposes zebrafish as a model for studying its role.

## Key findings

- Plexin B3 is highly expressed in retinal ganglion cells during midline crossing in zebrafish embryos.
- Plexin B3 functions in axon guidance and may act as a receptor for Sema3E with Neuropilin1 as a co-receptor.
- Zebrafish are proposed as a suitable model for studying Sema3E and Plexin B3 mechanisms.

## Abstract

During the development of neural circuits, axons are guided by a variety of molecular cues to navigate through the brain and establish precise connections with correct partners at the right time and place. Many axon guidance cues have been identified and they play pleiotropic roles in not only axon guidance but also axon fasciculation, axon pruning, and synaptogenesis as well as cell migration, angiogenesis, and bone formation. In search of receptors for Sema3E in axon guidance, we unexpectedly found that Plexin B3 is highly expressed in retinal ganglion cells of zebrafish embryos when retinal axons are crossing the midline to form the chiasm. Plexin B3 has been characterized to be related to neurodevelopmental disorders. However, the investigation of its pathological mechanisms is hampered by the lack of appropriate animal model. We provide evidence that Plexin B3 is critical for axon guidance in vivo. Plexin B3 might function as a receptor for Sema3E while Neuropilin1 could be a co-receptor. The intracellular domain of Plexin B3 is required for Semaphorin signaling transduction. Our data suggest that zebrafish could be an ideal animal model for investigating the role and mechanisms of Sema3E and Plexin B3 in vivo.