Cooperation between p27 and p107 during Endochondral Ossification Suggests a Genetic Pathway Controlled by p27 and p130

University of Santiago de Compostela, Santiago, Galicia, Spain
Molecular and Cellular Biology (Impact Factor: 4.78). 08/2007; 27(14):5161-71. DOI: 10.1128/MCB.02431-06
Source: PubMed


Pocket proteins and cyclin-dependent kinase (CDK) inhibitors negatively regulate cell proliferation and can promote differentiation.
However, which members of these gene families, which cell type they interact in, and what they do to promote differentiation
in that cell type during mouse development are largely unknown. To identify the cell types in which p107 and p27 interact,
we generated compound mutant mice. These mice were null for p107 and had a deletion in p27 that prevented its binding to cyclin-CDK
complexes. Although a fraction of these animals survived into adulthood and looked similar to single p27 mutant mice, a larger
number of animals died at birth or within a few weeks thereafter. These animals displayed defects in chondrocyte maturation
and endochondral bone formation. Proliferation of chondrocytes was increased, and ectopic ossification was observed. Uncommitted
mouse embryo fibroblasts could be induced into the chondrocytic lineage ex vivo, but these cells failed to mature normally.
These results demonstrate that p27 carries out overlapping functions with p107 in controlling cell cycle exit during chondrocyte
maturation. The phenotypic similarities between p107−/− p27D51/D51 and p107−/− p130−/− mice and the cells derived from them suggest that p27 and p130 act in an analogous pathway during chondrocyte maturation.

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    • "A main function of p16INK4a is to specifically inhibit cell cycle progression by targeting G1 CDK4/6 activities [35] and therefore maintain retinoblastoma (pRb), p107, and p130 under their active unphosphorylated forms [36]. These three pocket proteins are known to control chondrocyte cell fate decision during bone growth [37-39]. Interestingly, two other CKIs—p27KIP1 and p57KIP2—are also part of the cell cycle regulation during terminal differentiation through CDK inhibition leading to pocket proteins activation [40,41]. "
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    • "p107 has also been implicated in the control of bone and cartilage development. Double knockout p107-/-;p130-/- embryos as well as p107-/-;p27-/- embryos display defects in ossification of the long bones and chondrocyte proliferation [102,103]. During chondrogenesis, FGF signaling induces a potent cell cycle arrest, and dephosphorylation of p107 is one of the earliest distinguishing events during this process, occurring 10-11 hours sooner than dephosphorylation of Rb and p130 [104]. "
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