Extraocular muscle morphogenesis and gene expression are regulated by Pitx2 gene dose.
OBJECTIVE
PITX2 gene dose plays a central role in Axenfeld-Rieger syndrome. The purpose of this study was to test the hypothesis that the effects of Pitx2 gene dose on eye development can be molecularly dissected in available Pitx2 mutant mice.


METHODS
A panel of mice with Pitx2 gene dose ranging from wild-type (+/+) to none (-/-) was generated. Eye morphogenesis was assessed in animals with each Pitx2 gene dose. We also compared global gene expression in eye primordia taken from e12.5 Pitx2+/+, Pitx2+/-, Pitx2-/- embryos using gene microarrays. The validity of microarray results was confirmed by qRT-PCR.


RESULTS
Morphogenesis of all extraocular muscle bundles correlated highly with Pitx2 gene dose, but there were some differences in sensitivity among muscle groups. Superior and inferior oblique muscles were most sensitive and disappeared before the four rectus muscles. Expression of muscle-specific genes was globally sensitive to Pitx2 gene dose, including the muscle-specific transcription factor genes Myf5, Myog, Myod1, Smyd1, Msc, and Csrp3.


CONCLUSIONS
Pitx2 gene dose regulates both morphogenesis and gene expression in developing extraocular muscles. The expression of key muscle-specific transcription factor genes is regulated by Pitx2 gene dose, suggesting that sufficient levels of PITX2 protein are essential for early initiation of the myogenic regulatory cascade in extraocular muscles. These results document the first ocular tissue affected by Pitx2 gene dose in a model organism, where the underlying mechanisms can be analyzed, and provide a paradigm for future experiments designed to elucidate additional effects of Pitx2 gene dose during eye development.
Diehl
Adam G
AG
Department of Ophthalmology and Visual Sciences, University of Michigan Medical School, Ann Arbor 48105, USA.
Zareparsi
Sepideh
S
Qian
Min
M
Khanna
Ritu
R
Angeles
Rowena
R
Gage
Philip J
PJ
D000818:Animals; D005260:Female; D019084:Fluorescent Antibody Technique, Indirect; D018628:Gene Dosage; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000235:genetics*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009024:Morphogenesis / Q000235:genetics*; D009124:Muscle Proteins / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D009801:Oculomotor Muscles / Q000196:embryology* / Q000254:growth & development; D011247:Pregnancy; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014157:Transcription Factors / Q000235:genetics; D000097577:Homeobox Protein PITX2
D018398:Homeodomain Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; D014157:Transcription Factors; D000097577:Homeobox Protein PITX2