In the chick, heart mesoderm is induced by signals from the anterior endoderm. Although BMP-2 is expressed in the anterior endoderm, BMP activity is necessary but not sufficient for heart formation. Previous work from our lab has suggested that one or more additional factors from anterior endoderm are required. Crescent is a Frizzled-related protein that inhibits Wnt-8c and is expressed in anterior endoderm during gastrulation. At the same stages, expression of Wnt-3a and Wnt-8c is restricted to the primitive streak and posterior lateral plate, and is absent from the anterior region where crescent is expressed. Posterior lateral plate mesoderm normally forms blood, but coculture of this tissue with anterior endoderm or infection with RCAS-crescent induces formation of beating heart muscle and represses formation of blood. Dkk-1, a Wnt inhibitor of a different protein family, similarly induces heart-specific gene expression in posterior lateral plate mesoderm. Furthermore, we have found that ectopic Wnt signals can repress heart formation from anterior mesoderm in vitro and in vivo and that forced expression of either Wnt-3a or Wnt-8c can promote development of primitive erythrocytes from the precardiac region. We conclude that inhibition of Wnt signaling promotes heart formation in the anterior lateral mesoderm, whereas active Wnt signaling in the posterior lateral mesoderm promotes blood development. We propose a model in which two orthogonal gradients, one of Wnt activity along the anterior-posterior axis and the other of BMP signals along the dorsal-ventral axis, intersect in the heart-forming region to induce cardiogenesis in a region of high BMP and low Wnt activity.

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Our findings suggest that cCer maintains a delicate balance of different TGF-beta family members involved in laterality decisions, and reveal the existence of partially overlapping molecular pathways regulating left-right asymmetry in the head and trunk of the embryo.

Osteotomies have a role in the active patient with degenerative joint disease of the medial or lateral knee who, for reasons of age or activity level, is not yet a good candidate for prosthetic arthroplasty. Recognition and treatment of malalignment associated with ligamentous instability is essential if long-term good outcomes are to be expected from ligamentous reconstruction. Also, treatment of concomitant malalignment and the unloading of the operative site is now recognized as an important adjunct to any cartilage-preserving surgery. This review examines the use of osteotomies about the knee in the athletic patient. Indications, contraindications, preoperative planning, surgical techniques, and complications are reviewed.

Periarticular osteotomies, either a high tibial osteotomy for a varus deformity or a distal femoral osteotomy for a valgus deformity, are performed for symptomatic unicompartmental degenerative joint disease (DJD) of the knee. These procedures provide pain relief by realigning the mechanical axis and unloading the degenerative compartment. Although arthroplasty has become a reliable procedure for DJD, premature wear and revision remain a concern for younger individuals as well as for individuals who desire to participate in high impact activities. Long-term follow-up studies have shown good results for osteotomy at over 10 years of follow-up. Periarticular osteotomies are a reliable and durable way to provide symptomatic relief for these younger and more active patients with symptomatic DJD of the knee.