Abstract
Reelin, an extracellular glycoprotein is essential for migration and correct positioning of neurons during development. Since the olfactory system is known as a source of various migrating neuronal cells, we studied Reelin expression in the two chemosensory olfactory systems, main and accessory, during early developmental stages of human foetuses/embryos from Carnegie Stage (CS) 15 to gestational week (GW) 14. From CS 15 to CS 18, but not at later stages, a transient expression of Reelin was detected first in the presumptive olfactory and then in the presumptive vomeronasal epithelium. During the same period, Reelin-positive cells detach from the olfactory/vomeronasal epithelium and migrate through the mesenchyme beneath the telencephalon. Dab 1, an adaptor protein of the Reelin pathway, was simultaneously expressed in the migratory mass from CS16 to CS17 and, at later stages, in the presumptive olfactory ensheathing cells. Possible involvements of Reelin and Dab 1 in the peripheral migrating stream are discussed.
Highlights
During development of the olfactory system, peripheral neurosensory axons arising from the invaginated placode reach the presumptive olfactory area of the telencephalon, mediating olfactory bulb (OB) development
From CS15 to CS17, the basal telencephalon in front of the olfactory placode (OP) and olfactory epithelium (OE) consisted in a peripheral marginal zone (MZ) as defined by Meyer et al [24] and a ventricular proliferating zone (Fig 1G and 1H); OBs were present at Carnegie Stage (CS) 20–21 and identified by the strongly calretinin-labeled peripheral olfactory fibre layer (Fig 1I)
We show that during early olfactory development in human, neuronal cells arising from the presumptive OE/vomeronasal epithelium (VNE) express Reelin; this is a temporally and spatially regulated phenomenon doi:10.1371/journal.pone.0135710.g005
Summary
During development of the olfactory system, peripheral neurosensory axons arising from the invaginated placode reach the presumptive olfactory area of the telencephalon, mediating olfactory bulb (OB) development. In the main olfactory system, neurosensory cells in the olfactory epithelium (OE), sending axons to the main OB, make synapses with the dendrite of mitral/tufted cells, whereas in the accessory olfactory system, axons arising from the neurosensorial cells of the vomeronasal epithelium (VNE), lying in the vomeronasal organ (VNO), make synapses with mitral/tufted cells in the accessory olfactory bulb. The olfactory placode (OP), and later the VNO and OE are well known as sources of various migrating neurons toward the telencephalon; among them are GnRH neurons that migrate along the vomeronasal-terminal nerve (VN/TN) [2]. Several guidance molecules have been proposed for guiding olfactory axons and neurons through the mesenchyme toward the PLOS ONE | DOI:10.1371/journal.pone.0135710. Several guidance molecules have been proposed for guiding olfactory axons and neurons through the mesenchyme toward the PLOS ONE | DOI:10.1371/journal.pone.0135710 August 13, 2015
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