Loss of <i>tbx5a</i> in adult zebrafish leads to severe regeneration defects.

<p>Top, experimental outline. Bottom, sections of zebrafish hearts stained by Picro-Mallory stain. <b>A-G.</b> Hearts of zebrafish (n = 7) homozygous for the reverted <i>tbx5a</i> allele, and heterozygous for <i>tnnt2</i>:<i>CreERT2</i>, treated with ethanol (solvent for 4-HT). <b>H, I.</b> Hearts of zebrafish (n = 2) heterozygous for the reverted <i>tbx5a</i> allele, and heterozygous for <i>tnnt2</i>:<i>CreERT2</i>, treated with 4-HT. <b>J-Q.</b> Hearts of zebrafish (n = 8) homozygous for the reverted <i>tbx5a</i> allele, and heterozygous for <i>tnnt2</i>:<i>CreERT2</i>, treated with 4-HT.</p

Analysis of a conditional gene trap reveals that <i>tbx5a</i> is required for heart regeneration in zebrafish

<div><p>The ability to conditionally inactivate genes is instrumental for fine genetic analysis of all biological processes, but is especially important for studies of biological events, such as regeneration, which occur late in ontogenesis or in adult life. We have constructed and tested a fully conditional gene trap vector, and used it to inactivate <i>tbx5a</i> in the cardiomyocytes of larval and adult zebrafish. We observe that loss of <i>tbx5a</i> function significantly impairs the ability of zebrafish hearts to regenerate after ventricular resection, indicating that Tbx5a plays an essential role in the transcriptional program of heart regeneration.</p></div

Tol2-based On/Off/On (“Switchblade”, GBT-S1/S8) vectors for insertional mutagenesis and characterized gene trap lines.

<p><b>A.</b> Diagram of the vector and conditional regulation. The gene trap cassette is flanked by lox71, FRT-10, FRT+10 and lox66 sites. Components responsible for high degree of mutagenicity are shown in red. SA, carp beta actin splice acceptor, ^Gal-VP16, AUG-less Gal4-VP16, zp(A), zebrafish beta actin 3’ UTR and transcriptional termination sequences, cry, <i>X</i>. <i>laevis</i> gamma crystalline promoter, p(A), SV40 poly(A). The gene trap cassette is identical to that used in GBT-B1 gene trap vector (Balciuniene et al., 2013). Expression Flp recombinase will result in inversion of the gene trap cassette and one wild type (FRT) and one double mutant, inactive (FRT+10/-10, two red dots) site. Expression of the Cre recombinase will result in second inversion of the cassette conditionally mutating the gene. <b>B.</b> GBT-S1 and GBT-S8 gene trap lines. First column, gene trap line. Second column, sequence adjacent to the 3’ end of the gene trap integration. The capital CTG are the last three nucleotides of Tol2. Third column, location of the gene trap integration on the GRCz10 zebrafish genome assembly. Fourth column, insertionally mutated gene (IMG). Fifth column, sequence of the IMG-Gal4-VP16 fusion protein, IMG sequence is highlighted in aqua, Gal4 sequence is highlighted in magenta. The “linker” sequence is encoded by the linker between splice acceptor and Gal4 in GBT-S1 and GBT-S8. <b>C.</b> Diagram of gene trap loci. Gene trap integration site is shown as a triangle, with mutated gene’s exons depicted as squares: grey for non-coding, black for 5’ of integration site and white for 3’ of integration site. <b>D.</b> Assessment of transcript levels by quantitative RT-PCR. Three non-phenotypic lines were chosen for analysis. Quantitative RT PCR was performed on pools of RNA from wild type and homozygous mutant 5 dpf embryos, and normalized to beta actin. Error bars represent standard deviation.</p

Cardiomyocytes heterozygous for <i>tbx5a</i>^<i>tpl58</i> contribute to the adult heart but lead to impaired regeneration.

<p>Top, experimental outline. <b>A-F.</b> <i>Representative</i> images of adjacent sections (A and B, C and D, E and F) of hearts (n = 7) stained for DAPI (A, C, E) and by Pico-Mallory stain (B, D, F).</p

Analysis of a conditional gene trap reveals that <i>tbx5a</i> is required for heart regeneration in zebrafish - Fig 2

<p><b><i>tbx5a</i>^<i>tpl58</i> mutant phenotypes. A-D.</b> Larvae heterozygous for <i>tbx5a</i>^<i>tpl58</i> gene trap allele display severe but variable fin defects at 5 days post fertilization. Compared to wild type siblings (a), heterozygous mutants display bilaterally equal fin truncation (b), or unequal fin truncation with left (c) or right (d) pectoral fin more severely affected. <b>E.</b> Gene trap homozygotes display a phenotype similar to the more severe version of <i>heartstrings</i> phenotype described previously (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0197293#pone.0197293.g001" target="_blank">Fig 1D and 1E</a> in Garrity <i>et al</i>., 2002). <b>F-H.</b> All adults heterozygous for the gene trap had hearts with enlarged atria and mis-shapen (blunt) ventricles (n = 13). <i>a</i>, atrium, <i>v</i>, ventricle, <i>ba</i>, <i>bulbus arteriosus</i>.</p