The centromere protein B (CENP-B) is a centromeric DNA/binding protein. It recognizes a 17-bp sequence motif called the CENP-B box, which is found in the centromeric region of most chromosomes. It binds DNA through its amino terminus and dimerizes through its carboxy terminus. CENP-B protein has been proposed to perform a vital role in organizing chromatin structures at centromeres. However, other evidence does not agree with this view. For example, CENP-B is found at inactive centromeres on stable dicentric chromosomes, and also mitotically stable chromosomes lacking alpha-satellite DNA have been reported. To address the biological function of CENP-B, we generated mouse null mutants of CENP-B by homologous recombination. Mice lacking CENP-B were viable and fertile, indicating that mice without CENP-B undergo normal somatic and germline development. Thus, both mitosis and meiosis are able to proceed normally in the absence of CENP-B.
Developmental Biology: In the article "Spatial and temporal pattern of expression of the cellular retinoic acid-binding protein and the cellular retinol-binding protein during mouse embryogenesis" by Ana V. Perez-Castro, Leslie E. TothRogler, Li-na Wei, and M. Chi Nguyen-Huu, which appeared in number 22, November 1989, ofProc. NatI. Acad. Sci. USA (86,(8813)(8814)(8815)(8816)(8817)
A region of fibrocartilage develops in bovine deep flexor tendon where the tissue wraps around bone and is subjected to compressive and shear forces in addition to tension. There is no fibrocartilage at this location in fetal tendon or in adjacent adult tendon that is subjected to tensional load only. We investigated the development of fibrocartilage in tendon using in situ hybridization to localize cells that express collagen and proteoglycan genes typical of either tendon or cartilage. The signal for type I collagen and decorin was high in cells throughout fetal and newborn tendon, as is expected in a growing tissue composed predominantly of type I collagen. No signal for aggrecan was seen in either fetal or newborn tendon. No hybridization with any of the probes for collagen or proteoglycan was detected in cells in the tensional region of adult tendon, indicating that the cells in this tissue are normally quiescent. However, the cells in the fibrocartilage of adult tendon displayed a high level of expression for types I and II collagen, decorin, biglycan, and aggrecan. This suggests that the fibrocartilage in adult tendon is a dynamic tissue. Expression of type IIA collagen is considered a marker of prechondrocytes. Type IIA collagen gene expression was present throughout both the tensional and compressed regions of fetal and newborn tendon but was absent in cartilage and adult tendon. This suggests that cells located throughout fetal tendon may have the capacity to develop as chondrocytes. Fibrocartilage signal was detected for type I collagen in 75% of the cells and for type II collagen in 50% of the cells at one location in adult tendon, suggesting that some cells in this tissue could have expressed mRNA for both type I and type II collagen.
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