The hallmark of myelinated axons is their organization into molecularly distinct domains, a pre-requisite for the rapid propagation of action potentials. The paranodal domains establish the axo-glial septate junctions (AGSJs) through interactions involving axonal Contactin-associated protein (Caspr), Contactin (Cont), and glial Neurofascin NF155. The nodal domain is organized by neuronal NF186, voltage gated sodium (Nav) channels, and Ankyrin G (AnkG), a cytoskeletal adaptor protein. We showed that loss of Caspr and NF155 results in loss of AGSJs, mislocalization of the juxtaparanodal proteins, disorganization of the paranodal axonal cytoskeleton, and degeneration of myelinated axons, but nodal organization remains relatively unaffected. Recently, we showed that Band 4.1B, a paranodal/ juxtaparanodal cytoskeletal protein, is essential for the stability of AGSJs and juxtaparanodal organization. We show here that Whirlin, another cytoskeletal protein, is required for paranodal compaction and cytoskeletal stability. In further studies, we demonstrated that loss of nodal NF186 abolished clustering of Nav channels and AnkG at the nodes, allowing the flanking paranodal AGSJs to invade the nodal space. Most importantly, we show here that in vivo loss of AnkG does not abolish node formation, but may affect nodal stability. While significant advancements have been made regarding the composition and organization of axonal domains, there still remain fundamental questions regarding how the transmembrane components at these domains interact with local cytoskeleton to initiate domain organization, and to ensure long-term stability and maintenance of axonal architecture. Based on our published and preliminary studies, our central hypothesis is that the transmembrane components and local axonal cytoskeleton are critical for axonal domain organization, their stability and function. We will use genetic, molecular and cell biological methods to determine the specific role of paranodes, nodes and their associated cytoskeletal proteins in domain stabilization and maintenance, and the efficacy of restoration of key axonal domains by re-expression of NF155 and NF186 in progressively weak adult mouse mutants. We will accomplish our goals in the following specific aims: (1) What are the consequences of loss of cytoskeletal scaffolding proteins and loss of NF155 during adult life on the maintenance and function of paranodal AGSJs? (2) What are the consequences of loss of nodal cytoskeletal proteins and loss of NF186 during adult life on the stability and function of nodes in myelinated axons? and (3) Are adult myelinated axons with extended periods of disorganized domain structure able to re-organize axonal domains to restore nerve conduction? Collectively, our studies will provide insights that bear directly on the mechanisms by which axonal domains are formed and maintained, and how these structures can be reorganized and nerve function restored. In the future, these studies will advance our understanding of how demyelinating diseases, such as multiple sclerosis (MS) lead to axonal domain disorganization and guide the development of therapeutic interventions.

Public Health Relevance

The studies described in this application relate to the molecular mechanisms that govern the establishment and organization of distinct axonal domains in myelinated nerve fibers. This unique axonal domain structure allows saltatory propagation of nerve impulses in myelinated axons. Better understanding of the mechanisms that underlie this organization may help to design future therapeutic strategies to myelin-related diseases or demyelination disorders like for example multiple sclerosis (MS) where remyelination is required and the axonal domain structure must be preserved and nerve functions restored.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
2R01GM063074-11A1
Application #
8630674
Study Section
Cellular and Molecular Biology of Glia Study Section (CMBG)
Program Officer
Sesma, Michael A
Project Start
2001-05-01
Project End
2018-02-28
Budget Start
2014-04-10
Budget End
2015-02-28
Support Year
11
Fiscal Year
2014
Total Cost
$331,848
Indirect Cost
$108,098
Name
University of Texas Health Science Center San Antonio
Department
Physiology
Type
Schools of Medicine
DUNS #
800772162
City
San Antonio
State
TX
Country
United States
Zip Code
78229
Saifetiarova, Julia; Liu, Xi; Taylor, Anna M et al. (2017) Axonal domain disorganization in Caspr1 and Caspr2 mutant myelinated axons affects neuromuscular junction integrity, leading to muscle atrophy. J Neurosci Res 95:1373-1390
Banerjee, Swati; Mino, Rosa E; Fisher, Elizabeth S et al. (2017) A versatile genetic tool to study midline glia function in the Drosophila CNS. Dev Biol 429:35-43
Saifetiarova, Julia; Taylor, Anna M; Bhat, Manzoor A (2017) Early and Late Loss of the Cytoskeletal Scaffolding Protein, Ankyrin G Reveals Its Role in Maturation and Maintenance of Nodes of Ranvier in Myelinated Axons. J Neurosci 37:2524-2538
Banerjee, Swati; Venkatesan, Anandakrishnan; Bhat, Manzoor A (2017) Neurexin, Neuroligin and Wishful Thinking coordinate synaptic cytoarchitecture and growth at neuromuscular junctions. Mol Cell Neurosci 78:9-24
Schmid, Annina B; Bland, Jeremy D P; Bhat, Manzoor A et al. (2014) The relationship of nerve fibre pathology to sensory function in entrapment neuropathy. Brain 137:3186-99
Buttermore, Elizabeth D; Thaxton, Courtney L; Bhat, Manzoor A (2013) Organization and maintenance of molecular domains in myelinated axons. J Neurosci Res 91:603-22
Green, James A; Yang, Jun; Grati, M'hamed et al. (2013) Whirlin, a cytoskeletal scaffolding protein, stabilizes the paranodal region and axonal cytoskeleton in myelinated axons. BMC Neurosci 14:96
Buttermore, Elizabeth D; Piochon, Claire; Wallace, Michael L et al. (2012) Pinceau organization in the cerebellum requires distinct functions of neurofascin in Purkinje and basket neurons during postnatal development. J Neurosci 32:4724-42
Grati, M'hamed; Shin, Jung-Bum; Weston, Michael D et al. (2012) Localization of PDZD7 to the stereocilia ankle-link associates this scaffolding protein with the Usher syndrome protein network. J Neurosci 32:14288-93
Chen, Yu-Chi; Lin, Yong Qi; Banerjee, Swati et al. (2012) Drosophila neuroligin 2 is required presynaptically and postsynaptically for proper synaptic differentiation and synaptic transmission. J Neurosci 32:16018-30

Showing the most recent 10 out of 33 publications