A Developmental Switch of Axon
Targeting in the Continuously
Regenerating Mouse Olfactory System
Limei Ma,1 Yunming Wu,1 Qiang Qiu,1 Hayley Scheerer,1 Andrea Moran,1 C. Ron Yu1,2*
The mammalian olfactory system has the natural capacity to regenerate throughout the
animal’s life span. Despite constant neurogenesis, olfactory sensory neurons project to precise,
stereotypical positions in the brain. Here, we identify a critical period of olfactory sensory axon
targeting during postnatal development in mouse. Perturbing axon projection beyond postnatal
day 7 permanently disrupts targeting specificity of the sensory neurons. In addition, we find
that the establishment of the convergence map requires perinatal sensory neurons. Late-born
neurons appear to connect with prospective glomeruli based on homotypic interactions among
neurons expressing the same odorant receptor. Our results reveal a developmental switch in
axon guidance and a mechanism of circuit integration of adult-born neurons.
Neural regeneration holds the potential to repair dysfunctional or damaged nervous ystems. A key step that must be achieved
for an effective cure is to allow new neurons to
make precise and functional connections. Adult
neurogenesis in mammals occurs in the olfactory
epithelium, dentate gyrus of the hippocampus, and
subventricular zone of the lateral ventricle (1–3).
In olfactory epithelium, sensory neurons are continuously generated to replace aging cells and in
response to axonal or peripheral damages (4–7).
These neurons must project to the olfactory bulb
and establish precise and functional connections
with a glomerulus containing axons expressing
the same olfactory receptor (OR) gene (6, 8). This
regenerative capacity is essential in maintaining
the topographic map in the bulb and consistency
in odor perception. Here, we show that axon-
targeting mechanisms used for the initial estab-
lishment differ from those used for subsequent
maintenance of the olfactory map.
The topographic projection from the olfactory
epithelium to the bulb is established perinatally in
mouse (8, 9). Beginning at embryonic day 17,
olfactory sensory neurons expressing the same OR
gene converge onto the same glomerulus (8–12).
In the olfactory epithelium, neurogenesis peaks
around postnatal day 14 (P14), gradually subsides,
and continues at a steady rate after weaning at
P21 (2). The newly generated sensory neurons
project into existing glomeruli to maintain constant innervation of the bulb (13). Although some
evidence supports lifelong plasticity of the olfactory map (3, 14), other evidence suggests that the
sensory neuron projection may not be properly
1Stowers Institute for Medical Research, 1000 East 50th Street,
Kansas City, MO 64110, USA. 2Department of Anatomy and
Cell Biology, University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS 66160, USA.
*Corresponding author. E-mail: firstname.lastname@example.org
Fig. 1. Silencing spontaneous activity of olfactory sensory neurons
during postnatal development permanently alters axonal projection.
(A) Representative images of P2-GFP glomeruli in Kir2.1 mice showing divergent projection patterns in postnatal day 2 (P2) and adult (8-week-old,
8wks) mice. (B) In situ hybridization using antisense riboprobe against Kir2.1
(i and ii, purple) and immunofluorescent staining of Kir2.1 protein (iii and
iv, red) in the olfactory epithelium of Kir2.1 mice treated with or without
doxycycline (DOX) diet. Duration of treatment is indicated. (C) Representative
images of P2-GFP neuron projection in the olfactory bulb from (i) controls,
Kir2.1 mice treated with doxycycline (ii) at P0 for 8 weeks, (iii) at P21 for
5 weeks, and (iv) at P21 for 12 weeks. Green: GFP; blue: 4ʹ,6ʹ-diamidino-2-
phenylindole (DAPI). Scale bars, 100 mm.