Spatio-temporal expression of activating transcription factor 5 in the skeletal development of mouse limb.

There are no data about the expression pattern of activating transcription factor 5 (Atf5) during limb development. The aim of the present study was to describe the expression of Atf5 throughout mouse limb development. Some specimens were examined for the expression of type II collagen alpha1 (Col2a1), sex-determining region Y-related high-mobility-group-box 9 (Sox9), and activating transcription factor 2 (Atf2) by in situ hybridization. ATDC5 cells, mouse limb buds, and epiphyseal cartilage were examined for the expression of Atf5alpha and Atf5beta by quantitative real-time PCR. Atf5 transcripts were detected in condensed mesenchymal cells, cartilage primordia, proliferative, prehypertrophic, and articular chondrocytes, but not in hypertrophic chondrocytes. Atf5 was predominantly expressed by osteoblasts in the primary spongiosa. At the postnatal stage, Atf5 was expressed in epiphyseal chondrocytes and osteoblasts lining the bone trabeculae. Spatial distribution of Col2a1, Sox9, and Atf2 transcripts closely corresponded to that of Atf5 within developing limbs, except for bony tissues. In cartilage, Atf5alpha is the dominant form in the embryonic stage as well as in the postnatal stage.