Targeted mutation reveals essential functions of the homeodomain transcription factor Shox2 in sinoatrial and pacemaking development.
BACKGROUND
Identifying molecular pathways regulating the development of pacemaking and coordinated heartbeat is crucial for a comprehensive mechanistic understanding of arrhythmia-related diseases. Elucidation of these pathways has been complicated mainly by an insufficient definition of the developmental structures involved in these processes and the unavailability of animal models specifically targeting the relevant tissues. Here, we report on a highly restricted expression pattern of the homeodomain transcription factor Shox2 in the sinus venosus myocardium, including the sinoatrial nodal region and the venous valves.


RESULTS
To investigate its function in vivo, we have generated mouse lines carrying a targeted mutation of the Shox2 gene. Although heterozygous animals did not exhibit obvious defects, homozygosity of the targeted allele led to embryonic lethality at 11.5 to 13.5 dpc. Shox2-/- embryos exhibited severe hypoplasia of the sinus venosus myocardium in the posterior heart field, including the sinoatrial nodal region and venous valves. We furthermore demonstrate aberrant expression of connexin 40 and connexin 43 and the transcription factor Nkx2.5 in vivo specifically within the sinoatrial nodal region and show that Shox2 deficiency interferes with pacemaking function in zebrafish embryos.


CONCLUSIONS
From these results, we postulate a critical function of Shox2 in the recruitment of sinus venosus myocardium comprising the sinoatrial nodal region.
Blaschke
Rüdiger J
RJ
Human Genetics, University of Heidelberg, Heidelberg, Germany.
Hahurij
Nathan D
ND
Kuijper
Sanne
S
Just
Steffen
S
Wisse
Lambertus J
LJ
Deissler
Kirsten
K
Maxelon
Tina
T
Anastassiadis
Konstantinos
K
Spitzer
Jessica
J
Hardt
Stefan E
SE
Schöler
Hans
H
Feitsma
Harma
H
Rottbauer
Wolfgang
W
Blum
Martin
M
Meijlink
Frits
F
Rappold
Gudrun
G
Gittenberger-de Groot
Adriana C
AC
D000818:Animals; D001919:Bradycardia / Q000196:embryology / Q000235:genetics; D018031:Connexin 43 / Q000032:analysis; D017630:Connexins / Q000032:analysis; D047108:Embryonic Development / Q000235:genetics; D005318:Fetal Heart / Q000473:pathology; D018507:Gene Expression Regulation, Developmental; D018390:Gene Targeting; D005804:Genes, Lethal; D006321:Heart / Q000196:embryology*; D006329:Heart Conduction System / Q000196:embryology / Q000503:physiopathology; D006330:Heart Defects, Congenital / Q000196:embryology / Q000235:genetics; D006351:Heart Valves / Q000196:embryology; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D051379:Mice / Q000196:embryology; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009206:Myocardium / Q000473:pathology; D032383:Myocytes, Cardiac / Q000166:cytology; D010641:Phenotype; D012849:Sinoatrial Node / Q000196:embryology; D014157:Transcription Factors / Q000032:analysis / Q000235:genetics / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology; D029961:Zebrafish Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000097003:Gap Junction alpha-5 Protein
D018031:Connexin 43; D017630:Connexins; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D014157:Transcription Factors; D029961:Zebrafish Proteins; D000097003:Gap Junction alpha-5 Protein; C484469:Nkx2-5 protein, mouse; C484663:Shox2 protein, mouse; C519383:Shox2 protein, zebrafish