Fate mapping neurons and glia derived from Dbx1-expressing progenitors in mouse preBötzinger complex.

The brainstem preBötzinger complex (preBötC) generates the inspiratory breathing rhythm, and its core rhythmogenic interneurons are derived from Dbx1-expressing progenitors. To study the neural bases of breathing, tamoxifen-inducible Cre-driver mice and Cre-dependent reporters are used to identify, record, and perturb Dbx1 preBötC neurons. However, the relationship between tamoxifen administration and reporter protein expression in preBötC neurons and glia has not been quantified. To address this problem, we crossed mice that express tamoxifen-inducible Cre recombinase under the control of the Dbx1 gene (Dbx1CreERT2) with Cre-dependent fluorescent reporter mice (Rosa26tdTomato), administered tamoxifen at different times during development, and analyzed tdTomato expression in the preBötC of their offspring. We also crossed Rosa26tdTomato reporters with mice that constitutively express Cre driven by Dbx1 (Dbx1Cre) and analyzed tdTomato expression in the preBötC of their offspring for comparison. We show that Dbx1-expressing progenitors give rise to preBötC neurons and glia. Peak neuronal tdTomato expression occurs when tamoxifen is administered at embryonic day 9.5 (E9.5), whereas tdTomato expression in glia shows no clear relationship with tamoxifen timing. These results can be used to bias reporter protein expression in neurons (or glia). Tamoxifen administration at E9.5 labels 91% of Dbx1-derived neurons in the preBötC, yet only 48% of Dbx1-derived glia. By fate mapping Dbx1-expressing progenitors, this study illustrates the developmental assemblage of Dbx1-derived cells in preBötC, which can be used to design intersectional Cre/lox experiments that interrogate its cellular composition, structure, and function.