Gene expression of Spag6 in chick central nervous system.

Using a differential display method, we identified sperm-associated antigen 6 (Spag6) as a gene with a dynamic expression profile within the chick embryonic spinal cord. The expression of Spag6 gradually decreased along with spinal cord development. Spag6 expression was detected adjacent to the ventricular zone of the spinal cord at embryonic day (E) 4. At E6, Spag6 was apparent in the ventral ventricular zone adjacent to floor plate and the surrounding region close to the ventricular zone, with additional weak expression at the adjacent region to the ventral horn. At E10, the Spag6 mRNA can be detected slightly in the ventral ventricular zone and surrounding region of dorsal ventricular zone. In the E6 hindbrain, Spag6 was detected in the roof, the ventricular zone adjacent to floor plate and the surrounding regions of the ventricular zones. In the E6 caudal diencephalon, Spag6 expression was detected adjacent to the ventricular zone. As Spag6 was expressed in areas containing ependymal progenitor cells and in the borders of undifferentiated regions, Spag6 may be involved in the development of ependymal cells and in the differentiation process of neuronal cells in chick neural organs.

Identification of synergistic signals initiating inner ear development.

Tissue manipulation experiments in amphibians more than 50 years ago showed that induction of the inner ear requires two signals: a mesodermal signal followed by a neural signal. However, the molecules mediating this process have remained elusive. We present evidence for mesodermal initiation of otic development in higher vertebrates and show that the mesoderm can direct terminal differentiation of the inner ear in rostral ectoderm. Furthermore, we demonstrate the synergistic interactions of the extracellular polypeptide ligands FGF-19 and Wnt-8c as mediators of mesodermal and neural signals, respectively, initiating inner ear development.

Cloning and expression of the Wnt antagonists Sfrp-2 and Frzb during chick development.

The Wnt genes are known to play fundamental roles during patterning and development of a number of embryonic structures. Receptors for Wnts are members of the Frizzled family of proteins containing a cysteine-rich domain (CRD) that binds the Wnt protein. Recently several secreted frizzled-related proteins (Sfrps) that also contain a CRD have been identified and some of these can both bind and antagonise Wnt proteins. In this paper we report the expression patterns of the chick homologues of Frzb, a known Wnt antagonist, and Sfrp-2. Both genes are expressed in areas where Wnts are known to play a role in development, including the neural tube, myotome, cartilage, and sites of epithelial-mesenchymal interactions. Initially, Sfrp-2 and Frzb are expressed in overlapping areas in the neural plate and neural tube, whereas later, they have distinct patterns. In particular Sfrp-2 is associated with myogenesis while Frzb is associated with chondrogenesis, suggesting that they play different roles during development. Finally, we have used the early Xenopus embryo as an in vivo assay to show that Sfrp-2, like Frzb, is a Wnt antagonist. These results suggest that Sfrp-2 and Frzb may function in the developing embryo by modulating Wnt signalling.