Fig. 4.
Overexpression of Has2 impairs formation of precartilage condensations and chondrogenesis by limb mesenchymal cells in vitro. (A–H) Phase contrast microscopy images of micromass cultures of stage 22–24 limb bud mesenchymal cells established at 5 × 104 cells/10 μl (A–D) or 2.5 × 104 cells/10 μl (E–H) infected with a control RCAS retrovirus (A,C; E,G) or a Has2 RCAS retrovirus (B,D; F,H). The RCAS control cultures form numerous precartilage condensations of closely packed rounded cells on day 2 (A) or day 3 (E), which subsequently enlarge and differentiate into cartilage nodules which deposit a refractile matrix (C,G). In contrast, only a few very small condensations form in cultures infected with the Has2 RCAS vector (B,F), and there a striking decease in the number of refractile cartilage nodules that differentiate (D,H).