Migration of nerve growth cones requires detergent-resistant membranes in a spatially defined and substrate-dependent manner

Motility of nerve growth cones (GCs) is regulated by region-specific activities of cell adhesion molecules (CAMs). CAM activities could be modified by their localization to detergent-resistant membranes (DRMs), specialized microdomains enriched in signaling molecules. This paper deals with a question of whether DRMs are involved in GC migration stimulated by three CAMs; L1, N-cadherin (Ncad), and β1 integrin. We demonstrate that L1 and Ncad are present in DRMs, whereas β1 integrin is exclusively detected in non-DRMs of neurons and that localization of L1 and Ncad to DRMs is developmentally regulated. GC migration mediated by L1 and Ncad but not by β1 integrin is inhibited after DRM disruption by micro-scale chromophore-assisted laser inactivation (micro-CALI) of GM1 gangliosides or by pharmacological treatments that deplete cellular cholesterol or sphingolipids, essential components for DRMs. Characteristic morphology of GCs induced by L1 and Ncad is also affected by micro-CALI–mediated DRM disruption. Micro-CALI within the peripheral domain of GCs, or even within smaller areas such as the filopodia and the lamellipodia, is sufficient to impair their migration. However, micro-CALI within the central domain does not affect GC migration. These results demonstrate the region-specific involvement of DRMs in CAM-dependent GC behavior

Cell adhesion molecules regulate Ca2+-mediated steering of growth cones via cyclic AMP and ryanodine receptor type 3

Axonal growth cones migrate along the correct paths during development, not only directed by guidance cues but also contacted by local environment via cell adhesion molecules (CAMs). Asymmetric Ca2+ elevations in the growth cone cytosol induce both attractive and repulsive turning in response to the guidance cues (Zheng, J.Q. 2000. Nature. 403:89–93; Henley, J.R., K.H. Huang, D. Wang, and M.M. Poo. 2004. Neuron. 44:909–916). Here, we show that CAMs regulate the activity of ryanodine receptor type 3 (RyR3) via cAMP and protein kinase A in dorsal root ganglion neurons. The activated RyR3 mediates Ca2+-induced Ca2+ release (CICR) into the cytosol, leading to attractive turning of the growth cone. In contrast, the growth cone exhibits repulsion when Ca2+ signals are not accompanied by RyR3-mediated CICR. We also propose that the source of Ca2+ influx, rather than its amplitude or the baseline Ca2+ level, is the primary determinant of the turning direction. In this way, axon-guiding and CAM-derived signals are integrated by RyR3, which serves as a key regulator of growth cone navigation

Brain development in mice lacking L1–L1 homophilic adhesion

A new mouse line has been produced in which the sixth Ig domain of the L1 cell adhesion molecule has been deleted. Despite the rather large deletion, L1 expression is preserved at normal levels. In vitro experiments showed that L1–L1 homophilic binding was lost, along with L1-α5β1 integrin binding. However, L1–neurocan and L1–neuropilin binding were preserved and sema3a responses were intact. Surprisingly, many of the axon guidance defects present in the L1 knockout mice, such as abnormal corticospinal tract and corpus callosum, were not observed. Nonetheless, when backcrossed on the C57BL/6 strain, a severe hydrocephalus was observed and after several generations, became an embryonic lethal. These results imply that L1 binding to L1, TAG-1, or F3, and L1-α5β1 integrin binding are not essential for normal development of a variety of axon pathways, and suggest that L1–L1 homophilic binding is important in the production of X-linked hydrocephalus

Autonomous right-screw rotation of growth cone filopodia drives neurite turning

The clockwise turning of neurites is caused by the rotations of filopodia as they extend and sweep across the substratum

Future change of daily precipitation indices in Japan: a stochastic weather generator-based bootstrap approach to provide probabilistic climate information

This study proposes the stochastic weather generator (WG)-based bootstrap approach to provide the probabilistic climate change information on mean precipitation as well as extremes, which applies a WG (i.e., LARS-WG) to daily precipitation under the present-day and future climate conditions derived from dynamical and statistical downscaling models. Additionally, the study intercompares the precipitation change scenarios derived from the multimodel ensemble for Japan focusing on five precipitation indices (mean precipitation, MEA; number of wet days, FRE; mean precipitation amount per wet day, INT; maximum number of consecutive dry days, CDD; and 90th percentile value of daily precipitation amount in wet days, Q90). Three regional climate models (RCMs: NHRCM, NRAMS and TWRF) are nested into the high-resolution atmosphere-ocean coupled general circulation model (MIROC3.2HI AOGCM) for A1B emission scenario. LARS-WG is validated and used to generate 2000 years of daily precipitation from sets of grid-specific parameters derived from the 20-year simulations from the RCMs and statistical downscaling model (SDM: CDFDM). Then 100 samples of the 20-year of continuous precipitation series are resampled, and mean values of precipitation indices are computed, which represents the randomness inherent in daily precipitation data. Based on these samples, the probabilities of change in the indices and the joint occurrence probability of extremes (CDD and Q90) are computed. High probabilities are found for the increases in heavy precipitation amount in spring and summer and elongated consecutive dry days in winter over Japan in the period 2081-2100, relative to 1981-2000. The joint probability increases in most areas throughout the year, suggesting higher potential risk of droughts and excess water-related disasters (e. g., floods) in a 20 year period in the future. The proposed approach offers more flexible way in estimating probabilities of multiple types of precipitation extremes including their joint probability compared to conventional approaches

Recycling of the Cell Adhesion Molecule L1 in Axonal Growth Cones

The cell adhesion molecule (CAM) L1 plays crucial roles in axon growth in vitro and in the formation of major axonal tracts in vivo. It is generally thought that CAMs link extracellular immobile ligands with retrogradely moving actin filaments to transmit force that pulls the growth cone forward. However, relatively little is known about the fate of CAMs that have been translocated into the central (C)-domain of the growth cone. We have shown previously that L1 is preferentially endocytosed at the C-domain. In the present study, we further analyze the subcellular distribution of endocytic organelles containing L1 at different time points and demonstrate that internalized L1 is transported into the peripheral (P)-domain of growth cones advancing via an L1-dependent mechanism. Internalized L1 is found in vesicles positioned along microtubules, and the centrifugal transport of these L1-containing vesicles is dependent on dynamic microtubules in the P-domain. Furthermore, we show that endocytosed L1 is reinserted into the plasma membrane at the leading edge of the P-domain. Monitoring recycled L1 reveals that it moves retrogradely on the cell surface into the C-domain. In contrast, the growth cone advancing independently of L1 internalizes and recycles L1 within the C-domain. For the growth cone to advance, the leading edge needs to establish strong adhesive interactions with the substrate while attachments at the rear are released. Recycling L1 from the C-domain to the leading edge provides an effective way to create asymmetric L1-mediated adhesion and therefore would be critical for L1-based growth cone motility

Neural cell adhesion molecule L1: Signaling pathways and growth cone motility

The neural cell adhesion molecule L1 plays a key role in nervous system development including neuronal migration, neurite growth, and axonal fasciculation. L1 is expressed on most developing axons, and homophilic binding of L1 molecules on adjacent axons is likely to play a key role in axon extension. It is now well documented that a number of second‐messenger systems are involved in L1‐stimulated neurite growth in vitro. However, it is unclear how L1 homophilic or heterophilic binding trigger signals that regulate the mechanical forces that produce axon extension. In this report, we will review recent advances in understanding L1‐associated signals, L1 interactions with the cytoskeleton, and the molecular mechanisms underlying growth cone motility. J. Neurosci. Res. 49:1–8, 1997. © 1997 Wiley‐Liss Inc

A Neuronal Form of the Cell Adhesion Molecule L1 Contains a Tyrosine-Based Signal Required for Sorting to the Axonal Growth Cone

The neural cell adhesion molecule L1, which is present on axons and growth cones, plays a crucial role in the formation of major axonal tracts such as the corticospinal tract and corpus callosum. L1 is preferentially transported to axons and inserted in the growth cone membrane. However, how L1 is sorted to axons remains unclear. Tyr(1176) in the L1 cytoplasmic domain is adjacent to a neuron-specific alternatively spliced sequence, RSLE (Arg-Ser-Leu-Glu). The resulting sequence of YRSLE conforms to a tyrosine-based consensus motif (YxxL) for sorting of integral membrane proteins into specific cellular compartments. To study a possible role of the YRSLE sequence in L1 sorting, chick DRG neurons were transfected with human L1 cDNA that codes for full-length L1 (L1(FL) ), a non-neuronal form of L1 that lacks the RSLE sequence (L1(ΔRSLE)), mutant L1 with a Y1176A substitution (L1(Y1176A) ), or L1 truncated immediately after the RSLE sequence (L1(ΔC77)). L1(FL) and L1(ΔC77), both of which possess the YRSLE sequence, were expressed in the axonal growth cone and to a lesser degree in the cell body. In contrast, expression of both L1(ΔRSLE) and L1(Y1176A) was restricted to the cell body and proximal axonal shaft. We also found that L1(ΔRSLE) and L1(Y1176A) were integrated into the plasma membrane in the cell body after missorting. These data demonstrate that the neuronal form of L1 carries the tyrosine-based sorting signal YRSLE, which is critical for sorting L1 to the axonal growth cone