Cloning the full-length cDNA for rat connective tissue growth factor: implications for skeletal development

Area of Science:

• Genetics
• Molecular Biology
• Skeletal Biology

Background:

• Mammalian osteopetroses are skeletal disorders characterized by increased bone mass due to reduced osteoclastic bone resorption.
• Osteoblast dysfunction and developmental abnormalities are also observed in various osteopetrosis forms.

Purpose of the Study:

• To investigate skeletal gene expression differences between osteopetrosis (op) mutant rats and normal littermates.
• To identify specific genes involved in the pathogenesis of osteopetrosis.

Main Methods:

• Utilized mRNA-differential display on RNA from calvaria and long bones of op mutant and normal rats.
• Employed 5'-RACE to assemble a consensus sequence for rat connective tissue growth factor (CTGF) cDNA.
• Confirmed CTGF message over-expression using Northern blot analysis and examined its expression in various tissues and primary osteoblast cultures.

Main Results:

• Identified rat CTGF as a selectively expressed cDNA in bone, homologous to known CTGF genes.
• Demonstrated an 8- to 10-fold overexpression of CTGF message in op mutant bone compared to normal bone.
• Observed CTGF upregulation in op mutant kidney and its differential expression in primary osteoblast cultures, regulated by prostaglandin E(2).

Conclusions:

• CTGF may play a previously unrecognized role in normal skeletal modeling and remodeling.
• The dramatic overexpression of CTGF in the op mutant skeleton is likely secondary to uncoupled bone resorption and formation, leading to dysregulated osteoblast gene expression and function.