The Prl-Cre transgene expresses Cre recombinase selectively in the lactotrope lineage. A. Schematic of the Prl-Cre transgene. A CRE ORF was inserted into the second exon of the Prl gene in an mPrl BAC behind the native Prl translation initiation codon (see Methods). The curved arrow indicates the direction of Prl transgene transcription. The Prl BAC transgene preserves extensive sequences flanking the Prl locus (not shown in diagram; see Results). B. Immunofluorescence microscopy of dispersed pituitary cells from a Prl-Cre/ZsGreen compound transgenic mouse. The ZsGreen fluorescent reporter is preceded by a lox-stop-lox element such that ZsGreen is only expressed in cells that express the Cre recombinase. Lactotrope (PRL+) cells are indicated by orange arrows, and somatotrope (GH+) cells are indicated by white arrows. C. Quantification of somatotropes and lactotropes expressing ZsGreen reporter in a Prl-Cre/ZsGreen compound transgenic mouse (n = 350 cells PRL+ and 350 GH+ cells analyzed). BAC, bacterial artificial chromosome; GH, growth hormone; ORF, open reading frame; PRL, prolactin.