Figure 2
From: Epithelial–mesenchymal transformation and apoptosis in rat urethra development
Immunohistochemical staining of rat penis sections with CK-pan at ED 19. (a–i) Representation of sections from distal to proximal (× 200). (a) Transverse section of the tip of the penis is oval with a layer of epithelium surrounding the mesenchyme. (b) A shallow invagination (arrow, indicating the urethral plate) has appeared at the ventral penis. (c) The invagination of bilateral urethral plate has deepened (arrow). (d) “U”-shaped fold (arrow) is formed. (e) Urethral plate has grown and the fold has invaginated into the mesenchyme. (f) With elongation of the urethral plate, “O”-shaped urethra cavity is formed, but is not intact. (g) The two layered-urethral plates have drawn nearer, but do not meet. (h) Urethral plate is fused and the urethral seam can be seen; the center of urethral plate is the primitive urethra. (i) Urethral seam has remodeled and forms the inner mature urethra (arrowhead). CK-pan, pan-cytokeratin; ED, embryonic day; US, urethral seam.
