Msx1 haploinsufficiency modifies the Pax9-deficient cardiovascular phenotype.

Area of Science:

• Developmental Biology
• Genetics
• Cardiovascular Biology

Background:

• Embryogenesis involves coordinated gene and tissue interactions.
• Transcription factors Pax9 and Msx1 play critical roles in mouse craniofacial and tooth development.
• Pax9 deficiency in mice leads to craniofacial, tooth, palate, and cardiovascular defects.

Purpose of the Study:

• Investigate the impact of genetic background on Pax9-deficient cardiovascular phenotype.
• Determine the effect of Msx1 haploinsufficiency on Pax9-deficient cardiovascular defects.
• Explore the underlying mechanisms of these developmental interactions.

Main Methods:

• Comparative analysis of Pax9-deficient mice on different genetic backgrounds (C57Bl/6 vs. CD1).
• Generation of Pax9-deficient mice with Msx1 haploinsufficiency.
• Assessment of cardiovascular defects (outflow tract, aortic arch arteries) and neural crest cell migration.

Main Results:

• Congenic CD1-Pax9^-/- mice showed reduced outflow tract defects but unchanged aortic arch defects compared to C57Bl/6.
• Msx1 haploinsufficiency in Pax9^-/- mice reduced interrupted aortic arch incidence and altered arch artery origins.
• These changes correlated with rescued third pharyngeal arch neural crest cell migration and smooth muscle cell coverage.

Conclusions:

• Msx1 haploinsufficiency mitigates aortic arch artery defects in Pax9^-/- mice, likely by supporting neural crest cell migration.
• Pax9 deficiency affects neural crest-derived structures (hyoid bone, thyroid cartilage).
• Pharyngeal endoderm acts as a signaling center influencing neural crest cell behavior during development.