Abnormal vessel morphology and patterning defects in EXT1^MCko. Macroscopic analysis of E13.5 control (A) and EXT1^MCKO embryos revealed edema (, B) and hemorrhages (white arrowhead, B) in the skin; n > 3. Transverse sections demonstrate increased interstitial space (D, ) and loose connective tissue in the epidermis of EXT1^MCko (F) compared with the control littermate (C,E); n = 2. Endomucin staining (G-N, red) of E13.5 mutant embryos revealed abnormal patterning of the superficial vessels at the back along the spinal cord (G-H). (I-J) Higher-magnification images of the boxed area in panels G and H. The skin vasculature of the control littermates is uniform in its size and diameter (K). In contrast, EXT1^MCko display irregular-shaped, tortuous vessels with fluctuation in their diameter (arrowheads, L). EXT1^MCko exhibit excessive filopodia extension (N), indicating aberrant sprouting processes, which are reflected in embryonic skin sections showing a widespread network of blood vessels through the entire depth of the skin (P). On the contrary, the skin vasculature in control embryos is restricted to a two-dimensional network (M,O); n > 5. Visualization of lymphatic vessels (LYVE-1, green) revealed an increase in lymphatic vessels in EXT1^MCko embryonic skin (R) compared with control littermates (Q); however, colabeling with endomucin (red) showed separation of lymphatic and blood vessels and no defects in lymphangiogenesis. E indicates epidermis; D, dermis; S, subcutis. n = 2.