Activation of the Wnt/β-catenin signaling reporter in developing mouse olfactory nerve layer marks a specialized subgroup of olfactory ensheathing cells

Wnt reporter TOPgal mice carry a β-galactosidase (βgal) gene under the control of the Wnt/β-catenin signaling responsive elements. We found that the intensely immunolabeled βgal⁺ cells were co-immunolabeled with Nestin and formed a tangentially oriented single-cell layer in the "connecting or docking zone" where the olfactory sensory axons attached to the brain surface during mid-gestation. During early postnatal development, βgal⁺ cells were located in the inner olfactory nerve layer (ONLi) and co-labeled with olfactory ensheathing cell (OEC) markers S100β and NPY but not with lineage-specific markers for neurons, oligodendrocytes, astrocytes, and microglia, demonstrating that the TOPgal marked a subpopulation of OECs. By confocal microscopy, we found that TOPgal activated processes extended along the developing glomerulus and formed multiple tunnel-like structures that ensheathe and bridge olfactory sensory axonal bundles from ONLi to the glomerulus, which may play a key role in glomerulus formation and convergent sorting of the peripheral olfactory axons.