Xpo7 is highly induced during terminal erythroid differentiation, highly erythroid specific, and uses an erythroid-specific start site. (A) FACS of in vivo fetal liver erythropoiesis. Briefly, mouse fetal liver was sorted by flow cytometry into 5 separate populations corresponding to progressive stages of definitive erythroid development using CD71/TER119 staining patterns (regions R1-R5). (B) RNA-seq levels (from Wong et al⁷ ) of all nuclear exportins during murine definitive erythropoiesis. (C) qPCR of Xpo7 mRNA transcript during terminal erythropoiesis. (D) Tissue expression (measured by qPCR) of Xpo7 transcript in several different mouse tissues. (E) Browser depicting the genomic structure of the murine Xpo7 gene, which consists of 28 exons spanning over 112 kb, transcribed from the reverse strand, from right to left. Boxed area shows close-up of (F), with black bars depicting previously annotated exons; gray bar shows an alternative first exon transcribed only in late erythroblasts. (F) RNA-seq data (numbers on left are log2[RPKM values]) from the earliest committed erythroid precursors (BFU-Es) through early precursors (CFU-Es) to TER119-positive late erythroblasts (from Flugare et al¹³ ), showing reads corresponding to each exon of Xpo7. Note the alternative exon depicted in the University of California, Santa Cruz gene prediction tracks (arrow) is transcribed only in TER119⁺ late erythroblasts. The sequence of the alternative exons 1a and 1b is included in supplemental Table 1. BFU-E, erythroid burst forming unit; CFU-E, erythroid colony forming unit.