Endoderm differentiates into a transient epidermis in the mouse perineum

Area of Science:

• Developmental Biology
• Mammalian Embryogenesis
• Epithelial Differentiation

Background:

• The embryonic cloaca in eutherian mammals is divided by the urorectal septum into genitourinary and anorectal canals.
• The urorectal septum forms the perineum, separating the anus from external genitalia, and incorporates cloacal endoderm into its epidermis.
• The fate of these endodermal cells within the perineal epidermis has been enigmatic.

Purpose of the Study:

• To investigate the differentiation and fate of cloacal endodermal cells in the developing mammalian perineum.
• To elucidate the cellular mechanisms underlying perineal epidermis development and its replacement by ectoderm.
• To explore potential sex-specific differences in perineal development.

Main Methods:

• Live imaging of mouse embryos to track cell movements.
• Single-cell tracking analysis to quantify cell velocities and directions.
• Immunohistochemistry to identify epidermal cell markers (basal, spinous, granular) in endodermal cells.

Main Results:

• Cloacal endodermal cells differentiate into functional epidermis expressing characteristic epidermal markers.
• This endodermal epidermis is transient, undergoing terminal differentiation and desquamation postnatally.
• Ectodermal cells exhibit directed lateral-to-medial migration, converging to replace the endodermal epidermis, with similar patterns observed in both sexes.

Conclusions:

• Cloacal endoderm forms a unique, non-renewing transient epidermis at the perineal midline.
• Perineal epidermis development involves convergent extension driven by differential cell movements between endodermal and ectodermal populations.
• These findings offer insights into perineum development and the origins of sex-specific epidermal phenotypes.