Nogo-A Regulates Neural Precursor Migration in the Embryonic Mouse Cortex

Although Nogo-A has been intensively studied for its inhibitory effect on axonal regeneration in the adult central nervous system, little is known about its function during brain development. In the embryonic mouse cortex, Nogo-A is expressed by radial precursor/glial cells and by tangentially migrating as well as postmigratory neurons. We studied radially migrating neuroblasts in wild-type and Nogo-A knockout (KO) mouse embryos. In vitro analysis showed that Nogo-A and its receptor components NgR, Lingo-1, TROY, and p75 are expressed in cells emigrating from embryonic forebrain–derived neurospheres. Live imaging revealed an increased cell motility when Nogo-A was knocked out or blocked with antibodies. Antibodies blocking NgR or Lingo-1 showed the same motility-enhancing effect supporting a direct role of surface Nogo-A on migration. Bromodeoxyuridine (BrdU) labeling of embryonic day (E)15.5 embryos demonstrated that Nogo-A influences the radial migration of neuronal precursors. At E17.5, the normal transient accumulation of radially migrating precursors within the subventricular zone was not detectable in the Nogo-A KO mouse cortex. At E19, migration to the upper cortical layers was disturbed. These findings suggest that Nogo-A and its receptor complex play a role in the interplay of adhesive and repulsive cell interactions in radial migration during cortical development

Enhanced Functional Recovery in MRL/MpJ Mice after Spinal Cord Dorsal Hemisection

Adult MRL/MpJ mice have been shown to possess unique regeneration capabilities. They are able to heal an ear-punched hole or an injured heart with normal tissue architecture and without scar formation. Here we present functional and histological evidence for enhanced recovery following spinal cord injury (SCI) in MRL/MpJ mice. A control group (C57BL/6 mice) and MRL/MpJ mice underwent a dorsal hemisection at T9 (thoracic vertebra 9). Our data show that MRL/MpJ mice recovered motor function significantly faster and more completely. We observed enhanced regeneration of the corticospinal tract (CST). Furthermore, we observed a reduced astrocytic response and fewer micro-cavities at the injury site, which appear to create a more growth-permissive environment for the injured axons. Our data suggest that the reduced astrocytic response is in part due to a lower lesion-induced increase of cell proliferation post-SCI, and a reduced astrocytic differentiation of the proliferating cells. Interestingly, we also found an increased number of proliferating microglia, which could be involved in the MRL/MpJ spinal cord repair mechanisms. Finally, to evaluate the molecular basis of faster spinal cord repair, we examined the difference in gene expression changes in MRL/MpJ and C57BL/6 mice after SCI. Our microarray data support our histological findings and reveal a transcriptional profile associated with a more efficient spinal cord repair in MRL/MpJ mice

What the literature tells us about score sheet design

Score sheets are an essential tool of animal welfare. They allow transparent assessments to be made of animal health and behavior during animal experiments and they define interventions when deviations from normal status are detected. As such, score sheets help to refine animal experiments as part of the 3R (replacement, reduction and refinement) concept. This mini review aims at summarizing the scarce literature available on score sheet design

Fold changes for the 10 most up- and down-regulated genes in MRL/MpJ compare to C57BL/6 mice after spinal cord hemisection.

<p>The complete data set is available at <a href="http://genechip.salk.edu/rawdata/Thuret_MRL.zip" target="_blank">http://genechip.salk.edu/rawdata/Thuret_MRL.zip</a>.</p><p>Expression changes of genes of interest were also verified by quantitative RT-PCR (Q-PCR). When applicable, the Q-PCR fold changes are presented in brackets [ ].</p

Enhanced regeneration of corticospinal tract (CST) axons in MRL/MpJ mice after SCI.

<p><b>a</b>, <b>b</b>, Sagittal sections of BDA-labeled CST axons in C57BL/6 (<b>a</b>) and MRL/MpJ (<b>b</b>) mice. Two weeks after tracing, dorsal hemisections were performed. The CST was analyzed at 4 dpi ( = 18 days after tracing). In both mouse strains, axons are visible rostral and caudal from the injury site. No BDA-labeled fibers were found at the injury site, confirming that the CST was completely transected. <b>c</b>, <b>d</b>, Sagittal sections of BDA-labeled CST axons in injured C57BL/6 (<b>c</b>) and MRL/MpJ (<b>d</b>) mice at 54 dpi. Here, BDA tracing was performed right after SCI. C57BL/6 CST axons retracted from the lesion (arrowhead in <b>c</b>). In contrast, some MRL/MpJ CST fibers crossed through the lesion site (arrowhead in (<b>d</b>)). <b>e</b>, <b>f</b>, Montage of sagittal sections of BDA-labeled CST axons in C57BL/6 (<b>e</b>) and MRL/MpJ (<b>f</b>) mice at 109 dpi. Higher magnifications are shown in <b>g</b> (from boxed area in <b>e</b>) and <b>h</b> (from boxed area in <b>f</b>). We found no BDA-positive fibers below the injury site in C57BL/6 spinal cord (<b>e</b>, <b>g</b>), in contrast to MRL/MpJ mice (<b>f</b>, <b>h</b>). <b>i</b>, <b>j</b>, Data represent percentage of fibers and are reported as a function of the distance from the lesion at 54 dpi (i) and 109 dpi (j). MRL/MpJ mice exhibited significantly more regenerating axons at 0.5 mm caudal from the lesion site. Rostral end of the spinal cord is to the left. The arrows point at the injury site. Asterisks denote significant differences between MRL/MpJ and C57BL/6, P<0.02 (two-way ANOVA, Bonferroni Post-hoc). Scale bar, 250 µm (<b>a</b>–<b>d</b>); 300 µm (<b>e</b>, <b>f</b>); 100 µm (<b>g</b>, <b>h</b>).</p

Higher cell proliferation in intact spinal cord but lower increase in cell proliferation after SCI in MRL/MpJ mice.

<p><b>a</b>, <b>b</b>, Immunohistochemical staining for BrdU (arrowheads) on cross sections at the mid-thoracic level of intact spinal cord in C57BL/6 (<b>a</b>) and MRL/MpJ (<b>b</b>) mice 24 h after the last of 6 daily BrdU injections. <b>c</b>, Graphs show the amount of BrdU-labeled nuclei per mm³ in the intact spinal cord at the thoracic level 24 h and 4 weeks after the last BrdU injection. MRL/MpJ mice showed a 1.5× higher level of cell proliferation than C57BL/6. Cell survival was assessed at 4 weeks and there was no significant difference between the two strains. <b>d</b>, Number of BrdU-labeled nuclei per mm³ in the injured spinal cord 1, 54 and 109 dpi. BrdU was injected after injury and for the 6 following days. MRL/MpJ spinal cord showed less cell proliferation at 1 and 54 dpi. <b>e</b>, <b>f</b>, Sagittal sections of the lesion epicenter at 54 dpi stained for BrdU in C57BL/6 (<b>e</b>) and MRL/MpJ (<b>f</b>) mice. Asterisks denote significant difference between MRL/MpJ and C57BL/6, P<0.05 (Student's t-test). Scale bar, 260 µm.</p

Reduced astrocytic differentiation in MRL/MpJ injured spinal cord.

<p>Sagittal sections of the lesion epicenter at 54 dpi (<b>a</b>–<b>l</b>) and 109 dpi (<b>m</b>–<b>r</b>) labeled for BrdU (green) and lineage markers (red): GFAP (<b>a</b>–<b>f</b>), NG2 (<b>g</b>–<b>l</b>), OX-42 (<b>m</b>–<b>r</b>) in C57BL/6 (<b>a</b>–<b>c</b>, <b>g</b>–<b>i</b>, <b>m</b>–<b>o</b>) and MRL/MpJ (<b>d</b>–<b>f</b>, <b>j</b>–<b>l</b>, <b>p</b>–<b>r</b>) mice. Higher magnifications of cells marked by the arrowheads are shown in boxed inserts. <b>s</b>–<b>v</b>, Graphs represent the quantification of BrdU-labeled cells stained for a specific marker at 54 dpi (<b>s</b>, <b>u</b>) and 109 dpi (<b>t</b>, <b>v</b>) shown as percentage of all BrdU-labeled cells (<b>s</b>, <b>t</b>) and as absolute number of co-stained BrdU-labeled nuclei per mm³ (<b>u</b>, <b>v</b>). At 54 dpi, C57BL/6 mice showed more NG2/BrdU- and GFAP/BrdU-positive cells than MRL/MpJ mice. At 109 dpi, C57BL/6 mice had still more GFAP/BrdU-expressing cells than MRL/MpJ mice; however, OX-42/BrdU-positive cells were only found in MRL/MpJ spinal cord (2.7±0.9%). Asterisks denote significant difference between MRL/MpJ and C57BL/6, P<0.05 (Student's t-test). Scale bar, 100 µm (<b>a</b>–<b>i</b>); 50 µm (<b>p</b>–<b>r</b>); 50 µm for boxed area (<b>a</b>–<b>i</b>); 25 µm for boxed area (<b>p</b>–<b>r</b>).</p

Enhanced functional recovery after SCI in MRL/MpJ mice.

<p><b>a</b>, The latency to fall off the rotarod is depicted as a function of time for intact (baseline) and injured MRL/MpJ and C57BL/6 mice. In both strains intact mice improved their performance over the course of the 88 days of training, but the C57BL/6 performed better at all time points tested. The injured MRL/MpJ reached their baseline level by the end of the 88 days of testing, whereas the injured C57BL/6 did not. <b>b</b>, Rotarod performance of injured mice is expressed as a ratio of baseline performance. Injured MRL/MpJ performed significantly better than injured C57BL/6 at 12, 18, 53, 60, 67, 74 and 88 dpi (*P<0.002). Injured MRL/MpJ significantly improved between 4 dpi and 88 dpi (#P<0.002), whereas injured C57BL/6 did not improve during that period. <b>c</b>, The number of foot-faults made during grid walking is reported as a function of time for intact (baseline) and injured MRL/MpJ and C57BL/6 mice. Both intact strains improved their ability to cross the grid with fewer foot-faults, but intact MRL/MpJ made more foot-faults throughout the entire training period. The injured MRL/MpJ reached their baseline level already by 12 dpi, whereas the injured C57BL/6 still had not reached their baseline level by the end of the testing period at 18 dpi. <b>d</b>, Grid walking performance of injured mice is expressed as a ratio to baseline performance. Injured MRL/MpJ performed significantly better than injured C57BL/6 at 12 and 18 dpi (p<0.05). Injured MRL/MpJ had significantly improved between 4 dpi and 12 dpi, 18 dpi (p<0.05), whereas injured C57BL/6 did not improve during that period. <b>e</b>, Estimation of bladder fullness is reported as a function of time after SCI in MRL/MpJ and C57BL/6 mice. All MRL/MpJ mice recovered autonomic bladder function by 3 dpi, whereas in C57BL/6 mice, autonomic bladder function did not returned until 6 dpi (Mann Whitney test, p-value = 0.028). Data present mean ± SEM. * denotes significant difference between MRL/MpJ and C57BL/6 and # denotes significant differences in MRL/MpJ performance between time points (P value: two-way ANOVA, Bonferroni post-hoc analysis).</p