Nkx2.1-ires-Flp knock-in mice express Flp Recombinase from the endogenous NK2 homeobox 1 (Nkx2-1) promoter/enhancer elements. Nkx2.1 expressing cells are GABAergic neurons along the medial-ganglionic eminence and the preoptic areas (MGE-POA) in both the ventricular zone radial glia (RG) progenitors and subventricular zone intermediate progenitors (IP). Homozygous mice are viable and fertile. FLP is expressed in cells in MGE-derived neurons including parvalbumin (PV) and somatostatin (SST) neurons, with no expression in caudal-ganglionic eminence (CGE)-derived vasoactive intestinal polypeptide (VIP) neurons detected. When Nkx2.1-ires-Flp mice are bred with mice containing frt-flanked sequence(s), Flp-mediated recombination will result in deletion of the flanked sequence(s) in the Nkx2.1-expressing cells of the offspring.
These mice were bred to Ai65(RCFL-tdT)-neo mice (Stock No. 021875) (after removal of the loxP-flanked STOP codon by breeding with Nkx6-2-CreERT2 mice (Stock No. 017536)) in order to study the fate of progenitor cells at the MGE/POA intersection. tdTomato-labeled MGE progenitors give rise to neurons in layers 1-3 show horizontally oriented morphology. L2/3 SST cells have Martinotti cell morphology with an ascending axon that arborizes in L1.
In contrast, when Ai65(RCFL-tdT)-neo mice were first bred with ER81-CreER mice (Stock No. 013048) many of the progenitors produce neurons in deep layers (layer 4-6), and are mostly multipolar cells with radiating axons in L5. They give rise to more PV than SST cells, and less than 10% of L2/3 putative Martinotti neurons cells.
