No abstract

No abstract

A complete cDNA of a novel zebrafish gene named onecut has been isolated; this gene encodes a protein of 446 amino acids with a Cut domain (73 amino acid residues) and a homeodomain. The Cut domain of zebrafish Onecut is highly similar to those in mammalian hepatocyte nuclear factor-6 and Drosophila Onecut, sharing 90 and 88% amino acid identity, respectively. The expression of zebrafish onecut is restricted to neuronal cells, being first detected in trigeminal ganglia neurons at the end of gastrulation. By the 1-somite stage, onecut expression has begun in primary neurons of the lateral stripes in the neural plate, and appeared in neuronal cells of the medial stripes at the 2-somite stage. By the 4-somite stage, onecut expression expanded to the intermediate stripes and to subsets of neuronal cells in the midbrain and hindbrain. Subsequently, onecut expression intensified in the lateral region of midbrain and hindbrain, yet no onecut-positive cells were seen in the telencephalon. By 24hpf, onecut transcripts remained abundant in the spinal cord but were no longer detectable in differentiated Rohon-Beard sensory neurons. The expression of onecut was greatly increased in the neural mutant mindbomb, while being decreased in narrowminded.

No abstract

During skeletal development, both osteogenic and chondrogenic programs are initiated from multipotent mesenchymal cells, requiring a number of signaling molecules, transcription factors, and downstream effectors to orchestrate the sophisticated process. Col10a1, an important downstream effector gene, has been identified as a marker for maturing chondrocytes in higher vertebrates, such as mammals and birds. In zebrafish, this gene has been shown to be expressed in both osteoblasts and chondrocytes, but no study has reported its role in osteoblast development. To initially delineate the osteogenic program from chondrogenic lineage development, we used the zebrafish col10a1 promoter to establish a transgenic zebrafish expressing a GFP reporter specifically in osteoblast-specific bone structures that do not involve cartilaginous programs. A construct harboring a ~2.2-kb promoter region was found to be sufficient to drive the reporter gene in osteoblast-specific bone structures within the endogenous col10a1 expression domain, confirming that separable cis-acting elements exist for distinct cell type-specific expression of col10a1 during zebrafish skeletal development. The ~2.2-kb col10a1:GFP transgenic zebrafish marking only bone structures derived from osteoblasts will undoubtedly be an invaluable tool for identifying and characterizing molecular events driving osteoblast development in zebrafish, which may further provide a differential mechanism where col10a1 is involved in the development of chondrocytes undergoing maturation in other vertebrate systems.