Figure 2.

(a) Analysis of transgenic offspring. After microinjection of purified YAC DNA, integrity and copy number of the transgenes were tested in the transgenic mice. Copy numbers are indicated between brackets below the names of each transgenic line. Markers used for testing YAC transgene integrity are listed, and their positions, relative to SOX9, are indicated. +, Marker present in the tested mice; −, absent marker. Tissues showing modifications in SOX9/lacZ expression are also reported. +, Normal tissue; −, altered tissue. (b–e) Comparison between expression derived from mouse endogenous Sox9 gene and the 600-kb human YAC transgene. (b and d) In situ hybridization using a Sox9 RNA probe on wild-type embryos. (c and e) β-Galactosidase staining of embryos from line A46 transgenic for one copy of the 600-kb YAC. (b and c) Embryos (10.5 dpc). (d and e) Embryos (11.5 dpc). SOX9/lacZ expression is detected at the correct time in the mesenchyme of the head, the otic vesicles, and branchial arches. Expression is also found in the neural tube, notochord, migrating sclerotomal cells, and developing ribs. Whereas expression in the limb buds is highly similar at 10.5 dpc, differences in the patterns occur from 11.5 dpc. At that stage, SOX9/lacZ is strongly expressed in the mesenchymal condensation of the long bones and expression in the hand and foot plates is detected only from 12.5 dpc. In contrast, from 11.5 dpc, mouse Sox9 expression is strongly expressed in the hand and foot plates, the developing long bones only expressing weakly Sox9. This difference may be caused by species-specific elements or by the lack, on the YAC, of control elements involved in SOX9/Sox9 expression during limb development.