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p53 influences mice skeletal development
1Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia 19104, USA.
Abstract:
The p53 tumor suppressor gene encodes a transcriptional activator whose targets include genes that regulate cell cycle progression and apoptosis. Since we have shown that a critical event in the life history of the chondrocyte is programmed cell death, we asked the question: does loss of the p53 gene influence skeletogenesis? Female p53(+/-) mice were mated with p53(+/-) male mice and 17-day-old fetal mice were studied. Exencephaly was the most profound skeletal defect of the p53 null mutation. This defect was due to failure of formation of the bones that comprise the mouse calvarium. There was also loss of the hyoid bone, and defective mineralization of the manubrium sternum and the terminal phalanges. In the homozygous state (-/-), in the absence of exencephaly, the number of skeletal deformities was markedly reduced. Aside from the gross changes associated with null status, the mutants exhibited alterations in bone length and width. Small differences in the size and orientation of the mineral crystals in embryonic bone, as evaluated by small-angle X-ray scattering, were found to disappear after birth. To explain these observations, we evaluated the extent of apoptosis in the tibial growth plates using the TUNEL stain. In the growth plate of the p53(-/-) homozygote, there was minimal labeling of the hypertrophic layer. Since the p53(-/-) TUNEL stain pattern at 17 days was very similar to the pattern of labeling of the p53(+/+) at 15 days, we concluded that the growth defect reflected a delay in cartilage maturation rather than a change in chondrocyte phenotype. On this basis, we predict that after birth, in mice that survive, differences in bone length would become minimal, and at maturity, the length of the long bones of (+/+) and (-/-) mice would be similar.
Insights
Loss of the p53 tumor suppressor gene in mice leads to severe skeletal defects, including exencephaly, due to delayed cartilage maturation. These growth defects in p53 null mice resolve postnatally, resulting in normal long bone length at maturity.
Area of Science:
- Developmental Biology
- Genetics
- Skeletal Biology
Background:
- The p53 tumor suppressor gene is crucial for regulating cell cycle and apoptosis.
- Chondrocyte programmed cell death is a critical event in skeletogenesis.
- The role of p53 in embryonic skeletal development remains largely unexplored.
Purpose of the Study:
- To investigate the influence of p53 gene loss on mammalian skeletogenesis.
- To determine if p53 deficiency impacts chondrocyte apoptosis and cartilage maturation.
Main Methods:
- Generation and analysis of p53 heterozygous (p53(+/-)) and homozygous (p53(-/-)) knockout mice.
- Skeletal phenotyping of 17-day-old fetal mice, including gross examination and X-ray scattering.
- Assessment of apoptosis in tibial growth plates using TUNEL staining.
Main Results:
- p53 null mutation caused profound skeletal defects, most notably exencephaly (failure of calvarium formation).
- Other defects included hyoid bone loss and abnormal mineralization of the sternum and phalanges.
- TUNEL staining revealed minimal apoptosis in the hypertrophic zone of p53(-/-) growth plates, indicating delayed cartilage maturation.
Conclusions:
- p53 deficiency significantly disrupts embryonic skeletogenesis, primarily through delayed chondrocyte maturation.
- While initial skeletal development is impaired, surviving p53 null mice are predicted to exhibit normalized long bone length by maturity.
- These findings highlight p53's critical role in regulating chondrocyte apoptosis and timely skeletal development.