%0 Journal Article
%T Ectodermal Wnt6 is an early negative regulator of limb chondrogenesis in the chicken embryo
%A Poongodi Geetha-Loganathan
%A Suresh Nimmagadda
%A Bodo Christ
%A Ruijin Huang
%A Martin Scaal
%J BMC Developmental Biology
%D 2010
%I BioMed Central
%R 10.1186/1471-213x-10-32
%X In this paper, we investigated the molecular nature of the inhibitory influence of the ectoderm on limb chondrogenesis in the avian embryo in vivo. We show that ectoderm ablation in the early limb bud leads to increased and ectopic expression of early chondrogenic marker genes like Sox9 and Collagen II, indicating that the limb ectoderm inhibits limb chondrogenesis at an early stage of the chondrogenic cascade. To investigate the molecular nature of the inhibitory influence of the ectoderm, we ectopically expressed Wnt6, which is presently the only known Wnt expressed throughout the avian limb ectoderm, and found that Wnt6 overexpression leads to reduced expression of the early chondrogenic marker genes Sox9 and Collagen II.Our results suggest that the inhibitory influence of the ectoderm on limb chondrogenesis acts on an early stage of chondrogenesis upsteam of Sox9 and Collagen II. We identify Wnt6 as a candidate mediator of ectodermal chondrogenic inhibition in vivo. We propose a model of Wnt-mediated centripetal patterning of the limb by the surface ectoderm.The limbs of tetrapods form as mesenchymal protrusions of the somatic lateral plate mesoderm covered by an ectodermal sheath. The cartilaginous anlagen of the limb skeletal elements form from the centralmost region of the limb mesenchyme in a process called chondrogenesis (reviewed in [1]). Chondrogenesis starts by enhanced proliferation of the central limb mesenchyme, which leads to local mesenchymal condensations. One of the earliest markers of these presumptive chondrocytes is the SRY-related transcription factor Sox9 [2-4]. Subsequently, Sox9 - positive chondroprogenitor cells produce cartilage-specific extracellular matrix (ECM) components like Aggrecan and Collagen II and undergo terminal differentiation into chondrocytes. Later in development, the cartilaginous matrices of the skeletal elements become vascularized and undergo ossification.Interaction of limb mesenchyme and ectoderm is important in the
%U http://www.biomedcentral.com/1471-213X/10/32