The paracrine effect of exogenous growth hormone alleviates dysmorphogenesis caused by <it>tbx5</it> deficiency in zebrafish (<it>Danio rerio</it>) embryos

<p>Abstract</p> <p>Background</p> <p>Dysmorphogenesis and multiple organ defects are well known in zebrafish (<it>Danio rerio</it>) embryos with T-box transcription factor 5 (<it>tbx5</it>) deficiencies, mimicking human Holt-Oram syndrome.</p> <p>Methods</p> <p>Using an oligonucleotide-based microarray analysis to study the expression of special genes in <it>tbx5</it> morphants, we demonstrated that GH and some GH-related genes were markedly downregulated. Zebrafish embryos microinjected with <it>tbx5</it>-morpholino (MO) antisense RNA and mismatched antisense RNA in the 1-cell stage served as controls, while zebrafish embryos co-injected with exogenous growth hormone (GH) concomitant with <it>tbx5</it>-MO comprised the treatment group.</p> <p>Results</p> <p>The attenuating effects of GH in <it>tbx5</it>-MO knockdown embryos were quantified and observed at 24, 30, 48, 72, and 96 h post-fertilization. Though the understanding of mechanisms involving GH in the <it>tbx5</it> functioning complex is limited, exogenous GH supplied to <it>tbx5</it> knockdown zebrafish embryos is able to enhance the expression of downstream mediators in the GH and insulin-like growth factor (IGF)-1 pathway, including <it>igf1</it>, <it>ghra</it>, and <it>ghrb</it>, and signal transductors (<it>erk1</it>, <it>akt2</it>), and eventually to correct dysmorphogenesis in various organs including the heart and pectoral fins. Supplementary GH also reduced apoptosis as determined by a TUNEL assay and decreased the expression of apoptosis-related genes and proteins (<it>bcl2</it> and <it>bad</it>) according to semiquantitative reverse-transcription polymerase chain reaction and immunohistochemical analysis, respectively, as well as improving cell cycle-related genes (<it>p27</it> and <it>cdk2</it>) and cardiomyogenetic genes (<it>amhc</it>, <it>vmhc</it>, and <it>cmlc2</it>).</p> <p>Conclusions</p> <p>Based on our results, <it>tbx5</it> knockdown causes a pseudo GH deficiency in zebrafish during early embryonic stages, and supplementation of exogenous GH can partially restore dysmorphogenesis, apoptosis, cell growth inhibition, and abnormal cardiomyogenesis in <it>tbx5</it> knockdown zebrafish in a paracrine manner.</p