Nkx2-5 mutation causes anatomic hypoplasia of the cardiac conduction system.
Heterozygous mutations of the cardiac transcription factor Nkx2-5 cause atrioventricular conduction defects in humans by unknown mechanisms. We show in KO mice that the number of cells in the cardiac conduction system is directly related to Nkx2-5 gene dosage. Null mutant embryos appear to lack the primordium of the atrioventricular node. In Nkx2-5 haploinsufficiency, the conduction system has half the normal number of cells. In addition, an entire population of connexin40(-)/connexin45(+) cells is missing in the atrioventricular node of Nkx2-5 heterozygous KO mice. Specific functional defects associated with Nkx2-5 loss of function can be attributed to hypoplastic development of the relevant structures in the conduction system. Surprisingly, the cellular expression of connexin40, the major gap junction isoform of Purkinje fibers and a putative Nkx2-5 target, is unaffected, consistent with normal conduction times through the His-Purkinje system measured in vivo. Postnatal conduction defects in Nkx2-5 mutation may result at least in part from a defect in the genetic program that governs the recruitment or retention of embryonic cardiac myocytes in the conduction system.
Jay
Patrick Y
PY
Department of Cardiology, Children's Hospital, Boston, Massachusetts 02115, USA. patrick.jay@childrens.harvard.edu
Harris
Brett S
BS
Maguire
Colin T
CT
Buerger
Antje
A
Wakimoto
Hiroko
H
Tanaka
Makoto
M
Kupershmidt
Sabina
S
Roden
Dan M
DM
Schultheiss
Thomas M
TM
O'Brien
Terrence X
TX
Gourdie
Robert G
RG
Berul
Charles I
CI
Izumo
Seigo
S
D000818:Animals; D017630:Connexins / Q000032:analysis; D004562:Electrocardiography; D006329:Heart Conduction System / Q000473:pathology*; D018398:Homeodomain Proteins / Q000235:genetics* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009154:Mutation; D000097003:Gap Junction alpha-5 Protein
D017630:Connexins; D018398:Homeodomain Proteins; D000097003:Gap Junction alpha-5 Protein