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(Circulation Research. 2005;96:898.)
© 2005 American Heart Association, Inc.

Integrative Physiology

Homeobox Protein Hop Functions in the Adult Cardiac Conduction System

Fraz A. Ismat, Maozhen Zhang, Hyun Kook, Bin Huang, Rong Zhou, Victor A. Ferrari, Jonathan A. Epstein, Vickas V. Patel

From the Division of Cardiology (F.I.), Department of Pediatrics, The Children’s Hospital of Philadelphia, Philadelphia, Pa; Division of Cardiovascular Medicine (M.Z., B.H., V.A.F., J.A.E., V.V.P.) and the Department of Radiology (R.Z.), University of Pennsylvania, Philadelphia, Pa; and the Department of Pharmacology and Medical Research Center for Gene Regulation (H.K.), Chonnam National University Medical School, Gwangju, South Korea.

Correspondence to Vickas V. Patel, MD, PhD, 906 Biomedical Research Bldg II/III, 421 Curie Blvd, Philadelphia, PA 19104. E-mail vickas.patel{at}uphs.upenn.edu

Hop is an unusual homeobox gene expressed in the embryonic and adult heart. Hop acts downstream of Nkx2–5 during development, and Nkx2–5 mutations are associated with cardiac conduction system (CCS) defects. Inactivation of Hop in the mouse is lethal in half of the expected null embryos. Here, we show that Hop is expressed strongly in the adult CCS. Hop^–/– adult mice display conduction defects below the atrioventricular node (AVN) as determined by invasive electrophysiological testing. These defects are associated with decreased expression of connexin40. Our results suggest that Hop functions in the adult CCS and demonstrate conservation of molecular hierarchies between embryonic myocardium and the specialized conduction tissue of the mature heart.

Key Words: Hop • conduction • connexin40 • Nkx2–5 • mouse mutants

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Understanding Conduction System Development: A Hop, Skip and Jump Away?

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