FIGURE 5

FIGURE 5

The microbiota modulates oligodendrocyte maturation and myelination across species. (A) Relative gene expression (RT‐qPCR) of glia, myelin, and neurotransmitter markers in GF and conventionally‐raised (CON) whole larvae at 5 dpf. (B) Schematic of the lateral larval zebrafish showing the region of interest and the method for calculating the g‐ratio. Imaging was conducted at the urogenital opening level, around somite 15. (C) Representative images of whole‐body myelin (white—Tg(mbp:memScarlet); nacre) in GF and CON larvae at 5 dpf. Scale bar, 300 µm. (D) Quantification of the total area of myelin (µm²) proportional to larval length at 5 dpf. (E) Super‐resolution confocal live‐imaging depicting the diameter of the Mauthner axon (magenta—Tg(hspGFF62A:Gal4)); Tg(UAS:mem‐Scarlet)) with myelination (green—Tg(mbp:eGFP‐CAAX)) at somite 15 at 5 dpf. The white boxed region depicts the area where analysis was performed (somite 15). Scale bar, 10 µm. (F,G) Quantification of Mauthner (F) axon diameter growth and (G) number of synaptic boutons at somite 15 at 5 dpf. (H) Representative images of the Mauthner axon tracing (region outlined with magenta) along with myelin sheath tracing (region outlined with green) for both GF and CON larvae at 5 dpf. Scale bar, 10 µm. (I–K) Quantification of (I) myelin diameter (J) myelin thickness, and (K) (g‐ratio) in GF larvae compared to controls at 5 dpf. Data presented as Mean ± SEM. Sample size: RT‐qPCR; n = 10–13, Whole body myelin; n = 21–26 larvae, confocal Imaging; n = 16–18 axons from individual larvae. Microbiota; *p < 0.05, **p < 0.01, ***p < 0.001. Detailed statistical analysis can be found in Supplementary Table S1.