Biomedical subjects

Joshua A Weiner

Publications and source records attributed to Joshua A Weiner.

7 recordsLinked to original sources

PubMed2004

Cell adhesion molecules in synapse formation.

Neuronal transmission relies on signals transmitted through a vast array of excitatory and inhibitory neuronal synaptic connections. How do axons communicate with dendrites to build synapses, and what molecules regulate this interaction? There is a wealth of evidence suggesting that cell adhesion molecules (CAMs) provide much of the information required for synapse formation. This review highlights the molecular mechanisms used by CAMs to regulate presynaptic and postsynaptic differentiation.

Animals↗

PubMed2004

Axon fasciculation defects and retinal dysplasias in mice lacking the immunoglobulin superfamily adhesion molecule BEN/ALCAM/SC1.

The immunoglobulin superfamily adhesion molecule BEN (other names include ALCAM, SC1, DM-GRASP, neurolin, and CD166) has been implicated in the control of numerous developmental and pathological processes, including the guidance of retinal and motor axons to their targets. To test hypotheses about BEN function, we disrupted its gene via homologous recombination and analyzed the resulting mutant mice. Mice lacking BEN are viable and fertile, and display no external morphological defects. Despite grossly normal trajectories, both motor and retinal ganglion cell axons fasciculated poorly and were occasionally misdirected. In addition, BEN mutant retinae exhibited evaginated or invaginated regions with photoreceptor ectopias that resembled the "retinal folds" observed in some human retinopathies. Together, these results demonstrate that BEN promotes fasciculation of multiple axonal populations and uncover an unexpected function for BEN in retinal histogenesis.

Activated-Leukocyte Cell Adhesion Molecule↗

PubMed2004

A putative ariadne-like E3 ubiquitin ligase (PAUL) that interacts with the muscle-specific kinase (MuSK).

Formation of the postsynaptic membrane at the skeletal neuromuscular junction (NMJ) requires activation of the muscle-specific receptor tyrosine kinase (MuSK). Few intracellular mediators or modulators of MuSK actions are known. E3 ubiquitin ligases may serve this role, because activities of several receptor tyrosine kinases, G-protein-coupled receptors and channels are modulated by ubiquitination. Here, we report identification of a putative Ariadne-like ubiquitin ligase (PAUL) that binds to the cytoplasmic domain of MuSK. PAUL is expressed in numerous tissues of developing and adult mice, and is present at NMJs in muscle fibers but is not confined to them.

Amino Acid Sequence↗

PubMed2003

Synaptic adhesion molecules.

Formation, differentiation and plasticity of synapses, the specialized cell-cell contacts through which neurons communicate, all require interactions between pre- and post-synaptic partners. Several synaptically localized adhesion molecules potentially capable of mediating these interactions have been identified recently. Functional studies suggest roles for some of them in target recognition (e.g. SYG-1 and sidekicks), formation and alignment of synaptic specializations (e.g. SynCAM, neuroligin and neurexin), and regulation of synaptic structure and function (e.g. cadherins and syndecan).

Amino Acid Sequence↗

PubMed2002

Gamma protocadherins are required for survival of spinal interneurons.

The murine genome contains approximately 70 protocadherin (Pcdh) genes. Many are expressed in the nervous system, suggesting that Pcdhs may specify neuronal connectivity. Here, we analyze the 22 contiguous genes of the Pcdh-gamma cluster. Individual neurons express subsets of Pcdh-gamma genes. Pcdh-gamma proteins are present in most neurons and associated with, but not confined to, synapses. Early steps in neuronal migration, axon outgrowth, and synapse formation proceed in mutant mice lacking all 22 Pcdh-gamma genes. At late embryonic stages, however, dramatic neurodegeneration leads to neonatal death. In mutant spinal cord, many interneurons are lost, but sensory and motor neurons are relatively spared. In cultures from mutant spinal cord, neurons differentiate and form synapses but then die. Thus, Pcdh-gamma genes are dispensable for at least some aspects of connectivity but required for survival of specific neuronal types.

Animals↗

PubMed2002

Sidekicks: synaptic adhesion molecules that promote lamina-specific connectivity in the retina.

A major determinant of specific connectivity in the central nervous system is that synapses made by distinct afferent populations are restricted to particular laminae in their target area. We identify Sidekick (Sdk)-1 and -2, homologous transmembrane immunoglobulin superfamily molecules that mediate homophilic adhesion in vitro and direct laminar targeting of neurites in vivo. sdk-1 and -2 are expressed by nonoverlapping subsets of retinal neurons; each sdk is expressed by presynaptic (amacrine and bipolar) and postsynaptic (ganglion) cells that project to common inner plexiform (synaptic) sublaminae. Sdk proteins are concentrated at synaptic sites, and Sdk-positive synapses are restricted to the 2 (of > or =10) sublaminae to which sdk-expressing cells project. Ectopic expression of Sdk in Sdk-negative cells redirects their processes to a Sdk-positive sublamina. These results implicate Sdks as determinants of lamina-specific synaptic connectivity.

Amacrine Cells↗

PubMed2002

Lysophosphatidic acid influences the morphology and motility of young, postmitotic cortical neurons.

Lysophosphatidic acid (LPA) is a bioactive lysophospholipid that produces process retraction and cell rounding through its cognate receptors in neuroblastoma cell lines. Although the expression profile of LPA receptors in developing brains suggests a role for LPA in central nervous system (CNS) development, how LPA influences the morphology of postmitotic CNS neurons remains to be determined. Here we have investigated the effects of exogenous LPA on the morphology of young, postmitotic neurons in primary culture. When treated with LPA, these neurons responded by not only retracting processes but also producing retraction fiber "caps" characterized by fine actin filaments emanating from a dense core. Retraction fiber caps gradually vanished due to the outward spread of regrowing membranes along the fibers, suggesting a role for caps as scaffolds for regrowth of retracted processes. Furthermore, LPA also affects neuronal migration in vitro and in vivo. Taken together, these results implicate LPA as an extracellular lipid signal affecting process outgrowth and migration of early postmitotic neurons during development.

Actin Cytoskeleton↗