The Indian hedgehog (Ihh) signal plays a vital role in regulating proliferation 
and hypertrophy of chondrocytes. To investigate its function in postnatal 
chicken (Gallus gallus) chondrocytes, cyclopamine was used to inhibit Ihh 
signaling. The MTT and ALP assays revealed the downgrade-proliferation and 
upgrade-differentiation of chondrocytes. To further elucidate the mechanism, the 
mRNA expression levels of Ihh, parathyroid hormone related protein (PTHrP), 
Gli-2, Bcl-2, Bone Morphogenetic Protein 6 (BMP-6), type X collagen (Col X) and 
type II collagen (Col II) were detected by quantitative real-time RT-PCR 
analysis, and the protein expressions of Ihh, Col X, and Col II were determined 
using Western blot analysis. After the Ihh signal was blocked, chondrocytes 
demonstrated high expression levels of PTHrP and Col X and low levels of Gli-2, 
BMP-6, Bcl-2 and Col II although Ihh expression was increased. Based on these 
results, the Ihh signal is essential for balancing chicken chondrocyte 
proliferation and hypertrophy, and the regulatory function of PTHrP acts in an 
Ihh-dependent manner. Furthermore, BMP-6 and Bcl-2 played roles in maintaining 
the development of chondrocytes and may be downstream regulatory factors of Ihh 
signaling.