Fig. 1. Tbx6 transgenic construct and expression pattern. (A) The Tbx6 genomic locus (top) showing the positions of the exons (blue boxes), start of transcription (black arrow) and positions of the XbaI (X) sites used for cloning the Tbx6 transgenic construct (bottom). The Tbx6 transgenic construct consists of the entire coding region, upstream and downstream flanking regions and a lacZ reporter gene, which has a minimal promoter and a polyadenylation sequence. (B-D) Transgenic embryos, derived from the Tg46 founder line, were dissected from E7.5-9.5 and stained for ß-galactosidase activity. (B) Side view (posterior is towards the right) of an E7.5 mouse embryo showing X-gal staining predominantly within the primitive streak, but also widely scattered throughout the embryo. (C) By E8.5, staining is found within the primitive streak and PSM, with some stained cells found in the newly formed somites (red arrowhead). (D) Similarly, at E9.5, X-gal staining is seen in the primitive streak region and PSM, but also extending into the caudal-most somites. (E) Whole-mount in situ hybridization of endogenous Tbx6 expression in an E9.5 wild-type embryo, showing the anterior limit of Tbx6 transcripts in the PSM prior to somite segmentation (red arrowhead indicates the position of the newly formed somite). (F) Whole-mount in situ hybridization of lacZ expression in a Tg46 transgenic embryo is largely limited to the primitive streak and PSM with transcripts downregulated in the newly formed somite (red arrowhead).

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