The single OLFR124 expressed exon was replaced with a cassette encoding green fluorescent protein followed by an IRES and taulacZ so that olfactory sensory neurons with the Olfr124 locus actively transcribed can be identified by their expression of either reporter, even though no OLFR124 protein is expressed.
Peter Mombaerts, Max Planck Research Unit for Neurogenetics
OLFR124 expressing olfactory sensory neurons are normally found in the ventral zone of the main olfactory epithelium, densely packed in the septal organ, and OLFR124 expressing axons coalesce into one large glomerulus on the lateral surface of the ventral olfactory bulb and two to four glomeruli clustered in the medial olfactory bulb. OLFR124 expressing cells have been found to respond to a wide array of compounds and at a wide concentration range. The single OLFR124 expressed exon was replaced with a cassette encoding green fluorescent protein followed by an IRES and taulacZ so that olfactory sensory neurons with the Olfr124 locus actively transcribed can be identified by their expression of either reporter, even though no OLFR124 protein is expressed. Olfactory sensory neurons actively transcribing this null reporter allele occupy a more basal position in the main olfactory epithelium and the sensory organ than controls, showing that the migratory pattern is impacted by the alteration in olfactory receptor expression. The number of neurons transcribing this locus in the main olfactory epithelium and especially the sensory organ is significantly reduced compared with OLFR124 expressing cells in mice with an intact Olfr124 locus tagged with an IRES-tauGFP. Null alleles of Olfr124 permit a very high rate of secondary olfactory receptor expression, with the subset of expressed secondary alleles differing between the main olfactory epithelium and sensory organ. The olfactory sensory neurons expressing this null allele have an increased rate of apoptosis compared with those transcribing this locus and expressing an intact OLFR124 receptor, with heterozygotes having a 1.3-fold increase in apoptotic cells and homozygotes a 1.9-fold increase.
This null allele was generated by replacing the endogenous coding sequence with a green fluorescent protein-IRES-tau-lacZ cassette for co-expression of both reporters, along with an ACNF cassette which self-excised during male germline transmission. Homologous recombination was done in 129P2-derived E14 ES cells, the chimeric founder was bred with C57BL/6J and this strain was maintained on a B6;129P2 segregating background until sperm were cryopreserved in 2007.
|Allele Name||targeted mutation 2, Peter Mombaerts|
|Allele Type||Targeted (Reporter, Null/Knockout)|
|Allele Synonym(s)||delta-GFP-lacZ; GFP-IRES-tauLacZ->SR1|
|Gene Symbol and Name||Olfr124, olfactory receptor 124|
|Strain of Origin||129P2/OlaHsd|
|Molecular Note||The locus was replaced with an EGFP, IRES and tau-lacZ. The final allele lacks the self-excising neomycin resistance cassette inserted downstream of lacZ.|