No abstract

This is the first study documenting the rates of variation of the AA in Ireland. Variation of AA branching is of radiological and surgical significance, particularly in the diagnosis and treatment of thoracic and head and neck diseases. Awareness of these variations is particularly relevant for interventionalists who access these vessels during endovascular surgery.

Glycosylation is a major post‐translational modification in which a carbohydrate known as a glycan is enzymatically attached to target proteins which regulate protein folding and stability. Glycans are strongly expressed in the developing nervous system where they play multiple roles during development. The importance of these glycan epitopes in neural development is highlighted by a group of conditions known as congenital disorders of glycosylation which lead to psychomotor difficulties, mental retardation, lissencephaly, microencephaly and epilepsy. One of these glycan epitopes, known as Lewis X, is recognised by the FORSE‐1 antibody and is regionally expressed in the developing nervous system. In this study, we report the regional and temporal expression patterns of FORSE‐1 immunolabelling during the periods of neurogenesis, gliogenesis and axonogenesis in developing mouse nervous system. We demonstrate the localisation of FORSE‐1 on subsets of neuroepithelial cells and radial glial cells, and in compartments corresponding to axon tract formation. These spatial, temporal and regional expression patterns are suggestive of roles in the determination of different cell lineages and in the patterning of white matter during development, and help provide insights into the neuroanatomical regions affected by congenital disorders of glycosylation.

During vertebrate development, sensory axons project from the peripheral nervous system (PNS) into the spinal cord at the dorsolateral margin via the dorsal roots. They then ascend to the brain in separate tracts depending on sensory modality. This segregation of sensory axons is essential for appropriate perception and reflex activity. We show that radial glial cells support the formation of these tracks by forming scaffolds which channel various axon fasciculi through the spinal cord along the rostrocaudal axis. Semaphorins are the largest family of axon guidance cues expressed during central nervous system (CNS) formation. Class 6 semaphorins are found throughout the developing CNS and play vital roles in the guidance of growing axons in the brain, yet their roles in the spinal cord are relatively unknown. We investigated the role of Sema6A and its canonical receptor PlexinA2 during spinal cord development by comparing the organisation of radial glia and axon tracts in WT, Sema6A‐/‐and PlexinA2‐/‐ mice. This study shows that Sema6A is inhibitory to TAG‐1 expressing sensory axons entering the spinal cord from the dorsal roots and is a key regulator of sensory axon growth through the spinal cord during development. This effect is independent of its receptor PlexinA2. Sema6A is expressed on boundary cap cells in the dorsal root ganglion and the phenotype described here suggests that it acts as a barrier between the CNS and the PNS. The axonal growth guidance properties of Sema6A and the radial glial cell scaffold suggest they may be therapeutic targets for axonal regeneration following spinal cord injury.