Olfactory marker protein is critical for functional maturation of olfactory sensory neurons in mice

Many rodents, birds, marsupials, and humans, are altricial animals. Born closed-eyed, immobile, and helpless, many altricial species depend critically on their olfactory system for survival. Interestingly, the olfactory system is immature at birth, and undergoes a maturation process while the animal matures to become self reliant. In behavioral studies, newborn rats are responsive to olfactory cues with low sensitivity, but improve their detection thresholds for natural and synthetic odors within the first two weeks of birth. At birth, olfactory discrimination is also poor, as rat pups fail to prefer conspecifics to huddle with until two weeks of age. At the cellular level, extracellular recordings of unlabeled embryonic olfactory sensory neurons show a gradual shift from broad tuning to narrow tuning in odor preference. My dissertation is directed at investigating how the function of the olfactory sensory neurons (OSNs) in the olfactory epithelium of mice matures in the first month of life. Olfactory Marker Protein (OMP), an abundant protein unique to OSNs, has a developmentally regulated expression pattern that coincides with major events in the development of the olfactory system. I have investigated whether OMP is required for functional maturation, and if its deletion results in functionally immature OSNs. Using patch clamp technique in transgenic mouse lines where one olfactory receptor population is identifiable by fluorescent labeling, I have found that individual OSNs undergo a functional maturation process in the first month of a mouse\u27s life, in terms of odor response kinetics, sensitivity, and selectivity. OMP seems critical for this maturation process, as OSNs lacking OMP expression are arrested in an immature functional state. In ongoing biochemical and electrophysiological studies, altered adenylate cyclase regulation may be an important factor underlying the immature OMP-KO phenotype. It is interesting to consider these findings in the context of the maturation of the olfactory system necessary for survival in the altricial mouse