Col10a1 gene expression and chondrocyte hypertrophy during skeletal development and disease

The type X collagen gene, COLIOA1, is specifically expressed by hypertrophic chondrocytes during endochondral ossification. Endochondral ossification is a well-coordinated process that involves a cartilage intermediate and leads to formation of most of the skeleton in vertebrates during skeletogenesis. Chondrocyte hypertrophy is a critical stage of endochondral ossification linking both bone and cartilage development. Given its specific association with chondrocyte hypertrophy, type X collagen plays essential roles in endochondral ossification. It was previously shown that transgenic mice with mutant type X collagen develop variable skeleton-hematopoietic abnormalities indicating defective endochondral ossification, while mutations and abnormal expression of human COLIOA1 cause abnormal chondrocyte hypertrophy that has been seen in many skeletal disorders, including skeletal chondrodysplasia and osteoarthritis. In this review, we summarized the skeletal chondrodysplasia with COLIOA1 gene mutation that shows growth plate defect. We also reviewed recent studies that correlate the type X collagen gene expression and chondrocyte hypertrophy with osteoarthritis. Due to its significant clinical relevance, the type X collagen gene regulation has been extensively studied over the past two decades. Here, we focus on recent progress characterizing the cis-enhancer elements and their binding factors that together confer hypertrophic chondroeyte-specific murine type X collagen gene （CollOal） expression. Based on literature review and our own studies, we surmise that there are multiple factors that contribute to hypertrophic chondrocyte-specific CoHOal expression. These factors include both transactivators （such as Runx2, MEF2C etc.） and repressors （such as AP1, NFATcl, Sox9 etc.）, while other co-factors or epigenetic control of CollOal expression may not be excluded.

Action recognition from arbitrary views using 3D-key-pose set

Recovering three-dimensional （3D） human pose sequence from arbitrary view is very difficult, due to loss of depth information and self-occlusion. In this paper, view-independent 3D-key-pose set is selected from 3D action samples, for the purpose of representing and recognizing those same actions from a single or few cameras without any restriction of the relative orientations between cameras and subjects. First, 3D-key-pose set is selected from the 3D human joint sequences of 3D training action samples that are built from multiple viewpoints. Second, 3D key pose sequence, which matches best with the observation sequence, is selected from the 3D-key- pose set to represent the observation sequence of arbitrary view. 3D key pose sequence contains many discriminative view-independent key poses but cannot accurately describe pose of every frame in the observation sequence. Considering the above reasons, pose and dynamic of action are modeled respectively in this paper. Exemplar-based embedding and probability of unique key pose are applied to model pose property. Complementary dynamic feature is extracted to model these actions that share the same poses but have different dynamic features. Finally, these action models are fused to recognize observation sequence from a single or few cameras. Effectiveness of the proposed approach is demonstrated with experiments on IXMAS dataset.