Transcriptomic analysis of the zebrafish inner ear points to growth hormone mediated regeneration following acoustic trauma.

BACKGROUND: Unlike mammals, teleost fishes are capable of regenerating sensory inner ear hair cells that have been lost following acoustic or ototoxic trauma. Previous work indicated that immediately following sound exposure, zebrafish saccules exhibit significant hair cell loss that recovers to pre-treatment levels within 14 days. Following acoustic trauma in the zebrafish inner ear, we used microarray analysis to identify genes involved in inner ear repair following acoustic exposure. Additionally, we investigated the effect of growth hormone (GH) on cell proliferation in control zebrafish utricles and saccules, since GH was significantly up-regulated following acoustic trauma. RESULTS: Microarray analysis, validated with the aid of quantitative real-time PCR, revealed several genes that were highly regulated during the process of regeneration in the zebrafish inner ear. Genes that had fold changes of ≥ 1.4 and P -values ≤ 0.05 were considered significantly regulated and were used for subsequent analysis. Categories of biological function that were significantly regulated included cancer, cellular growth and proliferation, and inflammation. Of particular significance, a greater than 64-fold increase in growth hormone (gh1) transcripts occurred, peaking at 2 days post-sound exposure (dpse) and decreasing to approximately 5.5-fold by 4 dpse. Pathway Analysis software was used to reveal networks of regulated genes and showed how GH affected these networks. Subsequent experiments showed that intraperitoneal injection of salmon growth hormone significantly increased cell proliferation in the zebrafish inner ear. Many other gene transcripts were also differentially regulated, including heavy and light chain myosin transcripts, both of which were down-regulated following sound exposure, and major histocompatability class I and II genes, several of which were significantly regulated on 2 dpse. CONCLUSIONS: Transcripts for GH, MHC Class I and II genes, and heavy- and light-chain myosins, as well as many others genes, were differentially regulated in the zebrafish inner ear following overexposure to sound. GH injection increased cell proliferation in the inner ear of non-sound-exposed zebrafish, suggesting that GH could play an important role in sensory hair cell regeneration in the teleost ear.

Transplantation and in vivo imaging of multilineage engraftment in zebrafish bloodless mutants.

The zebrafish is firmly established as a genetic model for the study of vertebrate blood development. Here we have characterized the blood-forming system of adult zebrafish. Each major blood lineage can be isolated by flow cytometry, and with these lineal profiles, defects in zebrafish blood mutants can be quantified. We developed hematopoietic cell transplantation to study cell autonomy of mutant gene function and to establish a hematopoietic stem cell assay. Hematopoietic cell transplantation can rescue multilineage hematopoiesis in embryonic lethal gata1-/- mutants for over 6 months. Direct visualization of fluorescent donor cells in embryonic recipients allows engraftment and homing events to be imaged in real time. These results provide a cellular context in which to study the genetics of hematopoiesis.

Isolation of the B3 transcription factor of the Xenopus TFIIIA gene.

The selective expression of the Xenopus TFIIIA gene in immature oocytes is principally regulated by a single 5'-flanking DNA sequence element, termed element 3 (i.e. E3). We describe the isolation and characterization of a cDNA for a protein present in immature Xenopus ooctyes, termed B3.65, which appears to bind to and activate E3-mediated expression. The approximate molecular weight of the E3 binding protein(s) was determined by ultraviolet light cross-linking analysis. B3.65, a protein of the appropriate molecular weight, was purified biochemically from immature Xenopus ooctye extracts by affinity chromatography. Antiserum to purified B3.65 super-shifted the E3 activator complex. In addition, B3.65 mRNA was found to be highly enriched in immature oocytes. All of these data are consistent with B3.65 either being the E3 activator, or antigenically related to the specific activator required for XenopusTFIIIA gene transcription. B3.65 is a member of the K-homologous (KH) domain family of proteins, with almost absolute identity to Xenopus Vg1 RBP/VERA (97%) and significant similarity to human koc (82%). The koc mRNA is over-expressed in human pancreatic cancer tissues, and B3.65 mRNA was detected in Xenopus pancreas and kidney. Interestingly, KH proteins, like Vg1RBP/VERA, are most commonly associated with RNA metabolism, in their capacity to regulate RNA localization, stability, and translation. Our results suggest that B3.65 is a key regulator of both RNA- and DNA metabolism.