Background: The Six1Eya1 transcription complex is essential for proper embryogenesis of various organ systems and appears to play a role in perineal patterning.
. Methods: Six1^-/- mice were generated by replacing the Six1 coding region with IRES-LacZ/PGK-neo sequence. Six1 gene expression patterns were recapitulated by X-gal staining which detects the Bgalactosidase activity of the lacZ gene product. Six1+/- and Eya1+/- mice where crossed to generate the genotypes: Six1+/-Eya+/-, Six1-/-Eya1+/-, Six1+/-Eya1-/-, and Six1-/-Eya1-/-. Perineal and anorectal anatomy of Six1Eya1 mutants was examined by H&E staining. To establish if Six1 is expressed in the anorectum or lower urinary tract serial sections of embryos at e12.5 were stained for X-gal.
Results: X-gal staining reveals Six1 expression in the perineum, anterior abdominal wall, genital tubercle (Figure 1) and the urorectal septum. The perineal and anorectal anatomy of new-born Six1 and Eya1 mutants are summarized in Figure 2. In the wild type embryo ( Figure 2A and C) there are two distinct openings in the perineum: the anus (A) and the urethra (U). Eya-/- mice display a common opening for the rectum and urethra (Panels B and D). The degree of severity seems to increase if the mouse is heterozygous for the Six1 gene with Six1-/-Eya1-/- mice showing the most severe phenotypes.
Conclusion: Mice with mutations of Six1 and Eya1 genes display varying mutations of the perineum. The above findings suggest a role for the Six1Eya1 transcription complex in proper patterning of the perineum.