Longitudinal skeletal growth and growth plate morphological characteristics of chondro-tissue specific CUL7 knockout mice

Background: 3 M syndrome is first reported in 1975，which characterized by severe pre- and postnatal growth retardation, skeletal malformation and facial dysmorphism. These three genes (CUL7, OBSL1 and CCDC8) have been identified to be respond for 3 M syndrome, of which CUL7 is accounting for approximately 70%. To date, the molecular mechanism underlying the pathogenesis of 3 M syndrome remains poorly understood. Previous studies showed that no Cul7^-/- mice could survive after birth, because of growth retardation at late gestational stage and respiratory distress after birth. The establishment of the animal model of cartilage specific Cul7 knockout mice (Cul7^fl/fl;Col2a1-CreERT2 mice) has confirmed that Cul7^fl/fl;Col2a1-CreERT2 mice can be selective in a time- and tissue-dependent manner, which can provide an experimental basis for further research on severe genetic diseases related to growth plates.

Objective: To establish a model of Cul7^fl/fl;Col2a1-CreERT2 mice based on Cre/LoxP system, and to further observe its phenotype and morphological changes in growth plate.

Methods: The Cul7^fl/fl;Col2a1-CreERT2 mice were taken as the experimental group, while the genotype of Cul7^fl/+;Col2a1-CreERT2 mice were used as the control group. The gross morphological features and X-ray films of limbs in the two groups were observed every week for 3-6 consecutive weeks, and the length of the mice from nose to the tail, the length of femur and tibia were recorded. In the meantime, The histological morphology of tibial growth plates was compared between the two groups.

Results: A preliminary model of Cul7^fl/fl;Col2a1-CreERT2 mice was established. The Cul7^fl/fl;Col2a1-CreERT2 mice had abnormally short and deformed limbs (P<0.05), increased thickness of growth plate, the disorderly arranged chondrocyte columns, decreased number of cells in the proliferation zone, changes in the shape from flat to round, obviously expanded extracellular matrix, and disordered arrangement, thickening and loosening of bone trabecula at the proximal metaphysis of the femur.

Conclusions: The knockout of Cul7 gene may affect both the proliferation of chondrocytes and the endochondral osteogenesis, confirming that Cul7 is essential for the normal development of bone in the body.