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Stephen L Johnson

Publications and source records attributed to Stephen L Johnson.

21 records · Page 2Linked to original sources

A genetic, deletion, physical, and human homology map of the long fin region on zebrafish linkage group 2.

Mutation of the gene long fin causes overgrowth of zebrafish fins. Thus, molecular identification of the gene long fin may reveal the mechanisms involved in normal growth control. We have therefore developed genetic and physical maps of the corresponding region on linkage group 2 (LG2). A single deletion allele (lof(jg)(61)) of the long fin gene was also generated. Examination of this deletion for the presence or absence of ESTs independently mapped to LG2 revealed a contiguous deletion of SSLP, STS, and gene-based markers spanning a physical distance of approximately 500 kb, including at least 10 zebrafish genes. Human orthologs of the zebrafish genes in the long fin region were identified and revealed two synteny segments from human chromosome 1 (Hsa1) and Hsa19. Homology searching for additional genes linked to the human orthologs revealed one additional gene in the long fin deletion region. Thus, our development of the genetic, physical, deletion, and human homology maps of the long fin region provides one of the first high-resolution comparisons of a zebrafish region with a homologous human region, and facilitates the molecular identification of the long fin gene.

Animals↗

The evolution of morphological complexity in zebrafish stripes.

The zebrafish pigment stripe pattern is a complex tissue containing iridophores, xanthophores and multiple melanocyte types. Mutational analysis reveals that both ancient and recent gene duplications are involved in the generation or maintenance of the pattern complexity. Receptor tyrosine kinases kit and fms, products of an ancient gene duplication, are required in distinct types of melanocytes and xanthophores. Transcription factors mitfa and mitfb, results of a teleost-specific duplication, partition gene expression and function between different sets of melanocytes. Understanding the roles of these duplicated genes in zebrafish allows us to predict roles for their precursors in ancestral vertebrates.

Animals↗

Mps1 defines a proximal blastemal proliferative compartment essential for zebrafish fin regeneration.

One possible reason why regeneration remains enigmatic is that the dominant organisms used for studying regeneration are not amenable to genetic approaches. We mutagenized zebrafish and screened for temperature-sensitive defects in adult fin regeneration. The nightcap mutant showed a defect in fin regeneration that was first apparent at the onset of regenerative outgrowth. Positional cloning revealed that nightcap encodes the zebrafish orthologue of mps1, a kinase required for the mitotic checkpoint. mps1 expression was specifically induced in the proximal regeneration blastema, a group of cells that normally proliferate intensely during outgrowth. The nightcap mutation caused severe defects in these cells. However, msxb-expressing blastemal cells immediately distal to this proliferative region did not induce mps1 and were retained in mutants. These results indicate that the proximal blastema comprises an essential subpopulation of the fin regenerate defined by the induction and function of Mps1. Furthermore, we show that molecular mechanisms of complex tissue regeneration can now be dissected using zebrafish genetics.

Amino Acid Sequence↗