The development of the paired fins in the zebrafish (Danio rerio).
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In the present study, we describe the structure and normal development of the zebrafish (Danio rerio) paired fins. Particularly, we focus on the structure of the apical epidermis and on endoskeletal morphogenesis. Endoskeletal development proceeds differently in the pectoral and pelvic fins. Whereas in both fins major parts of the endoskeletal girdle develop within the fin bud mesenchyme, the pattern of chondrogenic condensations observed in the pelvic fins directly reflects the adult endoskeletal pattern. In the pectoral fin, a morphogenetic detour is taken via a functional larval endoskeleton, the endoskeletal disc. It arises in the fin bud mesenchyme from a chondrogenic anlage common with the girdle. The disc chondrifies and represents the functional endoskeleton of the larval pectoral fin. The pectoral fin endoskeleton is expanded as well as restructured during larval stages in a process which involves decomposition of cartilage matrix in the endoskeletal disc. Our comparisons of apical fold morphology with reports on other teleosts and tetrapod apical ridges show them to be homologous on the structural level. Comparisons of endoskeletal development of the zebrafish with reports on teleosts, actinopterygians and chondrichthyans show that endoskeletal morphogenesis in the zebrafish pectoral fin follows a morphogenetic process which is wide-spread among actinopterygians. (+info)
Equatorius: a new hominoid genus from the Middle Miocene of Kenya.
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A partial hominoid skeleton just older than 15 million years from sediments in the Tugen Hills of north central Kenya mandates a revision of the hominoid genus Kenyapithecus, a possible early member of the great ape-human clade. The Tugen Hills specimen represents a new genus, which also incorporates all material previously referable to Kenyapithecus africanus. The new taxon is derived with respect to earlier Miocene hominoids but is primitive with respect to the younger species Kenyapithecus wickeri and therefore is a late member of the stem hominoid radiation in the East African Miocene. (+info)
Prolyl 4-hydroxylase is an essential procollagen-modifying enzyme required for exoskeleton formation and the maintenance of body shape in the nematode Caenorhabditis elegans.
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The multienzyme complex prolyl 4-hydroxylase catalyzes the hydroxylation of proline residues and acts as a chaperone during collagen synthesis in multicellular organisms. The beta subunit of this complex is identical to protein disulfide isomerase (PDI). The free-living nematode Caenorhabditis elegans is encased in a collagenous exoskeleton and represents an excellent model for the study of collagen biosynthesis and extracellular matrix formation. In this study, we examined prolyl 4-hydroxylase alpha-subunit (PHY; EC 1.14.11.2)- and beta-subunit (PDI; EC 5.3.4.1)-encoding genes with respect to their role in collagen modification and formation of the C. elegans exoskeleton. We identified genes encoding two PHYs and a single associated PDI and showed that all three are expressed in collagen-synthesizing ectodermal cells at times of maximal collagen synthesis. Disruption of the pdi gene via RNA interference resulted in embryonic lethality. Similarly, the combined phy genes are required for embryonic development. Interference with phy-1 resulted in a morphologically dumpy phenotype, which we determined to be identical to the uncharacterized dpy-18 locus. Two dpy-18 mutant strains were shown to have null alleles for phy-1 and to have a reduced hydroxyproline content in their exoskeleton collagens. This study demonstrates in vivo that this enzyme complex plays a central role in extracellular matrix formation and is essential for normal metazoan development. (+info)
Evolutionary exploitation of design options by the first animals with hard skeletons.
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The set of viable design elements available for animals to use in building skeletons has been fully exploited. Analysis of animal skeletons in relation to the multivariate, theoretical "Skeleton Space" has shown that a large proportion of these options are used in each phylum. Here, we show that structural elements deployed in the skeletons of Burgess Shale animals (Middle Cambrian) incorporate 146 of 182 character pairs defined in this morphospace. Within 15 million years of the appearance of crown groups of phyla with substantial hard parts, at least 80 percent of skeletal design elements recognized among living and extinct marine metazoans were exploited. (+info)
Dorsal patterning defects in the hindbrain, roof plate and skeleton in the dreher (dr(J)) mouse mutant.
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dreher is a spontaneous mouse mutation in which adult animals display a complex phenotype associated with hearing loss, neurological, pigmentation and skeletal abnormalities. During early embryogenesis, the neural tube of dreher mutants is abnormally shaped in the region of the rhomboencephalon, due to problems in the formation of a proper roof plate over the otic hindbrain. We have studied the expression of Hox/lacZ transgenic mouse strains in the dreher background and shown that primary segmentation of the neural tube is not altered in these mutants, although correct morphogenesis is affected resulting in misshapen rhombomeres. Neural crest derivatives from rhombomere 6, such as the glossopharyngeal ganglion, are defective, and the dorsal neural tube marker Wnt1 is absent from this segment. Selected trunk neural crest populations are also altered, as there is a lack of pigmentation in the thoracic region of mutant mice. Skeletal defects include abnormal cranial bones of neural crest origin, and improper fusion of the dorsal aspects of cervical and thoracic vertebrae. Taken together, the gene affected in the dreher mutant is responsible for correct patterning of the dorsal-most cell types of the neural tube, that is, the neural crest and the roof plate, in the hindbrain region. Axial skeletal defects could reflect inductive influence of the dorsal neural tube on proper fusion of the neural arches. It is possible that a common precursor population for both neural crest and roof plate is the cellular target of the dreher mutation. (+info)
Osteochondroma in a skeleton from an 11th century Croatian cemetery.
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We present a case of a well-preserved bone tumor in a skeleton from a Croatian skeletal series dated to the 11th century AD. The tumor is located on the anterior side of the neck of the right femur. The gross morphology of the tumor - a round, lumpy, cauliflower-like appearance with a fairly smooth external surface - is consistent with osteochondroma. The diagnosis is supported by x-ray and CAT-scan findings, which show thickened trabeculae and an internal structure of cancellous bone interspersed with areas of dense compact bone. Comparison with x-rays from a patient surgically treated in 1999 for an osteochondroma with the same localization shows that the characteristics of the tumor have remained unchanged from the 11th century. (+info)
Early Permian bipedal reptile.
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A 290-million-year-old reptilian skeleton from the Lower Permian (Asselian) of Germany provides evidence of abilities for cursorial bipedal locomotion, employing a parasagittal digitigrade posture. The skeleton is of a small bolosaurid, Eudibamus cursoris, gen. et sp. nov. and confirms the widespread distribution of Bolosauridae across Laurasia during this early stage of amniote evolution. E. cursoris is the oldest known representative of Parareptilia, a major clade of reptiles. (+info)
Prevalence of large-joint osteoarthritis in Asian and Caucasian skeletal populations.
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OBJECTIVE: To determine ethnic variations of large-joint osteoarthritis (OA) in past populations. METHODS: One thousand two hundred and nine adult skeletons, excavated from archaeological sites in Japan, China and France were assessed for OA as defined by the presence of eburnation. RESULTS: Within Asian skeletal populations, elbow OA and patellofemoral joint OA were more common in hunter-gatherers than in agriculturalists. Compared with Caucasians, the Asian skeletal population had a higher prevalence of tibiofemoral joint OA. CONCLUSION: The relative frequencies of OA within and between ethnic groups at certain joint sites have changed over time from the past to the present. (+info)