Embryonic development of mouse external genitalia: insights into a unique mode of organogenesis

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Abstract
SUMMARY The mammalian external genitalia are specialized appendages for efficient copulation, internal fertilization and display marked morphological variation among species. In this paper, we described the embryonic development of mouse genital tubercle (GT), an anlage of the external genitalia utilizing the scanning electron microscope (SEM) analysis. It has been shown that the Distal Urethral Epithelium (DUE) may fulfill an essential role in the outgrowth control of the GT. Our present SEM analysis revealed a small distal protrusion at the tip of the GT of normal embryos as well as some morphological differences between male and female embryonic external genitalia. Previous analysis shows that the teratogenic dose of Retinoic Acid (RA) induces a drastic marformation of the urethral plate, but not gross abnormalities for GT outgrowth. Interestingly, a small distal protrusion at the tip of GT was clearly observed also after RA treatement. Furthermore, we showed that treatment with anti‐androgen flutamide resulted in the demasculinization of the GT in males. The unique character of GT development and the sexual dimorphism are discussed. Keyword: external genitalia; genital tubercle; urethral plate; outgrowth; morphogenesis; Fgf; retinoic acid; androgen