Abstract
Abstract: :
Purpose: The Pitx2 homeobox gene is expressed in neural crest and mesoderm during eye development, and loss of Pitx2 results in severe eye defects in tissues derived from these lineages. We generated mice with tissue–specific deletion of Pitx2 in neural crest or mesoderm in order to more clearly understand the function of this essential gene in each embryonic precursor pool. Methods: Gene targeting was used to generate a conditional Pitx2 allele (Pitx2flox) by introducing loxP sites flanking the critical homeodomain–containing exon 5 into the endogenous gene locus. Pitx2flox mice were mated to mice transmitting neural crest or mesoderm specific Cre transgenes, resulting in somatic conversion of Pitx2flox to the non–functional Pitx2null allele in the respective embryonic precursor pools. Eye primordia from somatic mutant mice and wild type siblings were assessed by comparative histology, as well as analysis of molecular markers. Results: Somatic knockouts of Pitx2 in neural crest and mesoderm were readily isolated and mutants of each class have significant eye phenotypes. Patterning and differentiation of multiple eye structures are affected in each class. However, the phenotypes of the two mutant classes are distinct from each other and from that of Pitx2null/null mice. Affected individuals of each somatic mutant class also survive significantly longer that do systemic Pitx2–null mutants. Conclusions: Identification of phenotypes in each mutant class establishes that Pitx2 function is required in both neural crest and mesoderm during eye development. However, the differences between the phenotypes indicate that the roles of Pitx2 in each embryonic precursor population are different. The longer survival of these mice will allow assessment of potential roles for Pitx2 in later steps in eye development. These somatic mutants provide an essential means for further dissection of Pitx2 function in the eye.
Keywords: genetics • transcription factors • transgenics/knock–outs