Fig. 4. Genetic lineage tracing in heterozygous and homozygous Olig3 mutant mice. (A) Strategy used to generate the Olig3^CreERT2 allele. Schematic representation of the wild-type Olig3 locus, the targeting vector, and the mutant Olig3 alleles before (Olig3^CreERT2neo) and after (Olig3^CreERT2) removal of the neomycin (neo) cassette. The coding exon of Olig3 (red) was interrupted by the insertion of a CreERT2-FRT-neo-FRT cassette. Indicated are CreERT2 (yellow) and the neo resistance cassette surrounded by FRT sequences (FRT-neo-FRT); in addition, a diphtheria toxin A (DTA, light green) cassette was included for negative selection. (B) Immunohistological analysis of rhombomere 7 in Olig3^CreERT2/+ mice at E11.5 using antibodies against Cre and Olig3. (C-J) Analysis of the medulla oblongata and pons of control (Olig3^CreERT2/+; Rosa26R) and Olig3 mutant (Olig3^CreERT2/-; Rosa26R) mice at E18.5. Recombination was induced at E10.5 by tamoxifen, and expression of the active lacZ gene was identified by X-Gal staining (blue). (K,L) Immunohistological analysis using antibodies against Pax2 and NF68 (Nefl). To improve the visibility of neurons, a false color was assigned to the black background of the original photograph. Arrowheads and arrows indicate the solitary (sol) and spinal trigeminal (spV) tracts, respectively. Cu, cuneate nucleus; ECu, external cuneate nucleus; ION, inferior olivary nucleus; NTS, nucleus of the solitary tract; LRt, lateral reticular nucleus; PB, parabrachial nucleus; PGN, pontine gray nucleus; RTN, reticulotegmental nucleus; CB, cerebellum; EGL, external granular layer. Scale bars: 50 µm in B; 200 µm in D,J,L.