Fig. 2. HtrA1 expression during the development of skeletal elements. (A) Whole-mount in situ hybridization of the 13.5 dpc forelimb. (B) Section of A. (C) In situ hybridization of a transverse section of the 14.5 dpc limb. (D) In situ hybridization of a 14.5 dpc rib section. (E) Immunostaining of a 15.5 dpc rib section. The localization of HtrA1 protein is in good agreement with that of mRNA shown in D. (F) In situ hybridization of the 17.5 dpc hind limb. Inset shows a magnified view of the boxed area. Low expression can be seen in a thin layer of the articular surface (arrowhead in inset). (G,H,I) Immunostaining of adult tibia. HtrA1 is detected in the bone matrix of the diaphysis and epiphysis. ac, articular cartilage; bm, bone marrow; c, cartilage nodule; ca, calcaneus; cu, cuboid; et, extensor tendon primordium; gp, growth plate; hc, hypertrophic cartilage; j, joint developing region; l, lateral cuneiform; oc, ossification center; pc, proliferating cartilage; pch, perichondrium; po, periosteum; t, tendon; III, digit III; 3m, 3rd metatarsal.