Distribution of OMP-, PGP 9.5- and CaBP-like immunoreactive chemoreceptor neurons in the developing human olfactory epithelium.

We have examined the distribution of olfactory marker protein (OMP), protein gene product 9.5 (PGP 9.5) and calcium-binding protein D-28k (CaBP) in the olfactory epithelium of mid- to late fetal and newborn humans using immunocytochemistry. Olfactory chemoreceptor neurons (ORNs) in a 24-week-old female fetus, a 31-week-old male fetus and a newborn male were examined. OMP-like immunoreactivity (-LI) and PGP 9.5-LI were distributed throughout ORNs at all ages. CaBP-like immunoreactivity, however, was found only in clustered or isolated fetal ORNs; in the newborn, CaBP-LI was seen only in isolated ORNs sparsely distributed throughout the OE. These findings demonstrate that human ORNs express OMP-LI nearly 4 weeks earlier in development than previously reported. PGP 9.5-LI is coincidentally abundant within these cells, suggesting it may have an important role in mature ORNs. Because the number of ORNs expressing CaBP-LI decreases during perinatal development, CaBP may be important in intracellular calcium regulation during ORN growth and maturation in the developing OE.