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      Review and experimental evaluation of the embryonic development and evolutionary history of flipper development and hyperphalangy in dolphins (Cetacea: Mammalia)

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      genesis
      Wiley-Blackwell

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          A distinct cohort of progenitor cells participates in synovial joint and articular cartilage formation during mouse limb skeletogenesis.

          The origin, roles and fate of progenitor cells forming synovial joints during limb skeletogenesis remain largely unclear. Here we produced prenatal and postnatal genetic cell fate-maps by mating ROSA-LacZ-reporter mice with mice expressing Cre-recombinase at prospective joint sites under the control of Gdf5 regulatory sequences (Gdf5-Cre). Reporter-expressing cells initially constituted the interzone, a compact mesenchymal structure representing the first overt sign of joint formation, and displayed a gradient-like distribution along the ventral-to-dorsal axis. The cells expressed genes such as Wnt9a, Erg and collagen IIA, remained predominant in the joint-forming sites over time, gave rise to articular cartilage, synovial lining and other joint tissues, but contributed little if any to underlying growth plate cartilage and shaft. To study their developmental properties more directly, we isolated the joint-forming cells from prospective autopod joint sites using a novel microsurgical procedure and tested them in vitro. The cells displayed a propensity to undergo chondrogenesis that was enhanced by treatment with exogenous rGdf5 but blocked by Wnt9a over-expression. To test roles for such Wnt-mediated anti-chondrogenic capacity in vivo, we created conditional mutants deficient in Wnt/beta-catenin signaling using Col2-Cre or Gdf5-Cre. Synovial joints did form in both mutants; however, the joints displayed a defective flat cell layer normally abutting the synovial cavity and expressed markedly reduced levels of lubricin. In sum, our data indicate that cells present at prospective joint sites and expressing Gdf5 constitute a distinct cohort of progenitor cells responsible for limb joint formation. The cells appear to be patterned along specific limb symmetry axes and rely on local signaling tools to make distinct contributions to joint formation.
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            Kinematics of foraging dives and lunge-feeding in fin whales.

            Fin whales are among the largest predators on earth, yet little is known about their foraging behavior at depth. These whales obtain their prey by lunge-feeding, an extraordinary biomechanical event where large amounts of water and prey are engulfed and filtered. This process entails a high energetic cost that effectively decreases dive duration and increases post-dive recovery time. To examine the body mechanics of fin whales during foraging dives we attached high-resolution digital tags, equipped with a hydrophone, a depth gauge and a dual-axis accelerometer, to the backs of surfacing fin whales in the Southern California Bight. Body pitch and roll were estimated by changes in static gravitational acceleration detected by orthogonal axes of the accelerometer, while higher frequency, smaller amplitude oscillations in the accelerometer signals were interpreted as bouts of active fluking. Instantaneous velocity of the whale was determined from the magnitude of turbulent flow noise measured by the hydrophone and confirmed by kinematic analysis. Fin whales employed gliding gaits during descent, executed a series of lunges at depth and ascended to the surface by steady fluking. Our examination of body kinematics at depth reveals variable lunge-feeding behavior in the context of distinct kinematic modes, which exhibit temporal coordination of rotational torques with translational accelerations. Maximum swimming speeds during lunges match previous estimates of the flow-induced pressure needed to completely expand the buccal cavity during feeding.
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              Wnt/beta-catenin signaling is sufficient and necessary for synovial joint formation.

              A critical step in skeletal morphogenesis is the formation of synovial joints, which define the relative size of discrete skeletal elements and are required for the mobility of vertebrates. We have found that several Wnt genes, including Wnt4, Wnt14, and Wnt16, were expressed in overlapping and complementary patterns in the developing synovial joints, where beta-catenin protein levels and transcription activity were up-regulated. Removal of beta-catenin early in mesenchymal progenitor cells promoted chondrocyte differentiation and blocked the activity of Wnt14 in joint formation. Ectopic expression of an activated form of beta-catenin or Wnt14 in early differentiating chondrocytes induced ectopic joint formation both morphologically and molecularly. In contrast, genetic removal of beta-catenin in chondrocytes led to joint fusion. These results demonstrate that the Wnt/beta-catenin signaling pathway is necessary and sufficient to induce early steps of synovial joint formation. Wnt4, Wnt14, and Wnt16 may play redundant roles in synovial joint induction by signaling through the beta-catenin-mediated canonical Wnt pathway. Copyright 2004 Cold Spring Harbor Laboratory Press
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                Author and article information

                Journal
                genesis
                genesis
                Wiley-Blackwell
                1526954X
                January 2018
                January 25 2018
                : 56
                : 1
                : e23076
                Article
                10.1002/dvg.23076
                cdfb7f44-b32d-4511-b824-e5c26a9db5fe
                © 2018

                http://doi.wiley.com/10.1002/tdm_license_1.1

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