Quantitative analysis of expression of NeuroD, GAP43 and receptor tyrosine kinase B in developing mouse olfactory neuroepithelium.
OBJECTIVE
The mammalian olfactory neuroepithelium (OE), which harbors olfactory receptor neurons (ORNs), has the unusual characteristic of continuous neurogenesis throughout its lifetime. This unique feature provides an excellent model for neuronal differentiation. Recently, we found dual-phase expression of NeuroD, a member of the basic helix-loop-helix transcription factor family, in the developing mouse OE, suggesting multiple roles of NeuroD during the development of mammalian ORNs.


METHODS
In order to better understand the molecular mechanism of the development of ORNs, we performed quantitative analysis of expression of NeuroD, GAP43 and receptor tyrosine kinase B (TrkB), as well as 5-bromo-2'-deoxyuridine (BrdU)-labeled cells, in the developing mouse OE from gestational Day 10 to postnatal Day 28.


RESULTS
During the embryonic period, NeuroD expression is mostly confined to the basal compartment. During the neonatal period, NeuroD expression is detected in two compartments: the middle compartment and the basal compartment. GAP43-expressing cells were located between these two NeuroD-positive layers. TrkB-expressing cells were located above the NeuroD-positive layer in the middle compartment. As the mice grew, the numbers of NeuroD-expressing cells and BrdU-labeled cells in the basal compartment significantly decreased, while the number of NeuroD-expressing cells in the middle compartment gradually increased. The number of TrkB-expressing cells dramatically increased. The number of GAP43-expressing cells also gradually increased. However, the relative proportion of GAP43 cells decreased as the OE developed.


CONCLUSIONS
NeuroD is a useful molecular marker for studying olfactory neurogenesis.
Department of Otolaryngology-Head and Neck Surgery, Kobe University Graduate School of Medicine, Japan.
Rie
R
Yasui
Masumi
M
Hasegawa
Kiyoshi
K
Doi
Ken-ichiro
K
Shimizu
Naoki
N
Ohtuski
Haruhiko
H
Ishida
Ken-ichi
K
Nibu
D000818:Animals; D000831:Animals, Newborn; D051792:Basic Helix-Loop-Helix Proteins; D001973:Bromodeoxyuridine; D019922:GAP-43 Protein / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D051379:Mice; D008807:Mice, Inbred BALB C; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009831:Olfactory Mucosa / Q000196:embryology / Q000254:growth & development / Q000378:metabolism*; D020813:Receptor, trkB / Q000235:genetics / Q000378:metabolism*
D051792:Basic Helix-Loop-Helix Proteins; D001973:Bromodeoxyuridine; D019922:GAP-43 Protein; D009419:Nerve Tissue Proteins; D020813:Receptor, trkB; C093564:Neurogenic differentiation factor 1