XB-ART-53846Dev Neurobiol January 1, 2017; 77 (11): 1308-1320.
Neuronal degeneration and regeneration induced by axotomy in the olfactory epithelium of Xenopus laevis.
The olfactory epithelium (OE) has the remarkable capability to constantly replace olfactory receptor neurons (ORNs) due to the presence of neural stem cells (NSCs). For this reason, the OE provides an excellent model to study neurogenesis and neuronal differentiation. In the present work, we induced neuronal degeneration in the OE of Xenopus laevis larvae by bilateral axotomy of the olfactory nerves. We found that axotomy induces specific- neuronal death through apoptosis between 24 and 48h post-injury. In concordance, there was a progressive decrease of the mature-ORN marker OMP until it was completely absent 72h post-injury. On the other hand, neurogenesis was evident 48h post-injury by an increase in the number of proliferating basal cells as well as NCAM-180- GAP-43+ immature neurons. Mature ORNs were replenished 21 days post-injury and the olfactory function was partially recovered, indicating that new ORNs were integrated into the olfactory bulb glomeruli. Throughout the regenerative process no changes in the expression pattern of the neurotrophin Brain Derivate Neurotrophic Factor were observed. Taken together, this work provides a sequential analysis of the neurodegenerative and subsequent regenerative processes that take place in the OE following axotomy. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1308-1320, 2017.
PubMed ID: 28719101
Article link: Dev Neurobiol
Species referenced: Xenopus laevis
Genes referenced: bdnf casp3.2 fuz gap43 krt61 ncam1 omp
Antibodies: Bdnf Ab2 BrdU Ab2 Casp3 Ab1 Gap43 Ab1 Krt5.2 Ab1 Ncam1 Ab1 Omp Ab1
Article Images: [+] show captions
|Figure 2 Axotomy triggers apoptosis in the OE and exacerbates proliferation of basal cells. Apoptotic cells labeled with cleaved-casp3 (cleaved-casp31 cells) in the OE under normal physiological conditions (A), and after 24 h (B), 48 h (C), and 72 h (D) post-axotomy; proliferating cells labeled with BrdU (BrdU1 cells) in the OE under normal physiological conditions (E), and after 48 h (F), 72 h (G) and 7 days (H) post-axotomy, scale bars: 20 mm; quantification of cleaved-casp31 cells per mm of OE perimeter (I) and BrdU1 cells per mm of OE perimeter (J) in control and axotomized animals after different recovery periods, different letters indicate statistically significant differences between groups, n54 for each group, ANOVA and Tuckey test, P<0.05. [Color figure can be viewed at wileyonlinelibrary.com]|
|Figure 5 The olfactory function is lost and recovered in X. laevis larvae following axotomy. Change of buccal pumping frequency was analyzed in the presence of food stimulus (see “Frequency of buccal pumping” section) in control and axotomized animals following different periods of recovery, different letters indicate statistically significant differences between groups, n510 for each group, ANOVA and Tuckey test, P<0.05.|
|Figure 6 The distribution of BDNF expression in the OE is not altered following axotomy. BDNF immunolabeling (green) and Cytoketatin II (SC marker, CytkII) (magenta) in the OE under normal physiological conditions (A), and 48 h (B), 7 days (C), and 28 days (D) post-axotomy, scale bar: 50 mm. [Color figure can be viewed at wileyonlinelibrary.com]|
|Figure 7 Dynamic of neuronal degeneration and regeneration in the OE following axotomy. The dynamic of the regenerative process that takes place in the OE of X. laevis larvae after bilateral axotomy of the olfactory nerves is summarized in a timeline. The points on the timeline represent the evaluated recovery periods (24, 48, 72 h, 7, 21, and 28 days). Fuzzy boundaries of the boxes mean that processes do not necessarily begin or end in the exact time point evaluated.|
|Fig. S1. Negative controls for immunohistochemistry and immunofluorescence by omitting primary antibodies. Primary antibodies were omitted (Ct(-)) and no specific immunostaining is visible after incubation with the secondary antibodies biotinylated (biot.) coupled with streptavidin- horseradish peroxidase (Str- HRP) or coupled with a fluorophore (rhodamine or Alexa 488).|
|Fig. S2. Western blot of OMP and GAP-43 from X. laevis larvae olfactory system showing immune reactive bands of the corresponding molecular weight.|
|Fig. S3. Structure and organization of the olfactory system of X. laevis larvae. Longitudinal sections of X. laevis larvae at premetamorphosis (stage 50 and 54) and metamorphic climax (stage 60); the top row belongs to a more dorsal section, the middle row to a medial section and the lower row to a more ventral section; principal cavity (PC), middle cavity (MC), vomeronasal organ (VNO), olfactory nerve (ON), olfactory bulb (OB); staining: Masson–Goldner’s trichrome stain, scale bar: 100µm.|