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. Author manuscript; available in PMC: 2013 Jul 1.
Published in final edited form as: Mech Dev. 2012 May 26;129(5-8):75–97. doi: 10.1016/j.mod.2012.05.005

Figure 5. A sharp spatial gradient of Tbx5 is necessary and sufficient to septate the ventricle.

Figure 5

(A) In the mouse, although the T-box transcription factor Tbx5 is expressed in the cardiac crescent at embryonic day 8.0 (E8.0), it is rapidly extinguished by E8.5 except in the sinus venosus, atrium (a), and the portion of the ventricular chamber destined to be the left ventricle (v) (B). The embryo in Panel C is from slightly later on E8.5 than the embryo in Panel B. (D) E11.5 embryo. (E) In evolution, the emergence of a separated left ventricle correlates with the gradual spatial restriction of the expression of Tbx5. The infant shown with haploinsufficiency for TBX5 (Holt-Oram Syndrome) has muscular ventricular septal defects, holes in the trabecular septum. la=left atrium; lv=left ventricle; ot=outflow tract; ra=right atrium; rv=right ventricle. Panels A through D are from Bruneau et al. (1999) and are reproduced with permission. Panel E is modified from Zina Deretsky, National Science Foundation, after Benoit Bruneau, Gladstone Institute of Cardiovascular Disease (http://www.nsf.gov/news/news_images.jsp?cntn_id1/4115520&org1/4IOS).