Biology subjects

Balciunas, D.

Publications and source records attributed to Balciunas, D..

7 recordsLinked to original sources

bioRxiv2025

Epicardial Tcf21 facilitates cardiomyocyte dedifferentiation and heart regeneration in zebrafish

Unlike mammals, zebrafish (Danio rerio) are able to regenerate their hearts after injury, making them an excellent model organism for studying the molecular mechanisms underlying heart regeneration. Epicardium, the outermost layer of the heart, is an essential player in this process. Injury-induced epicardium activation, characterized by the expression of embryonic epicardial marker genes including tcf21 supports cardiac regeneration by providing various cell types and releasing paracrine signals that promote the restoration of damaged tissue. However, the molecular mechanisms involved in this process are insufficiently understood. In this study, we describe a conditional tcf21flox allele and use it to investigate the role of Tcf21 in heart regeneration. By employing 4-hydroxytamoxifen inducible CreERT2 recombinase, we eliminated tcf21 expression in adult fish. Our findings indicate that loss of this transcription factor reduces the presence of dedifferentiated cardiomyocytes in the injury area and impairs heart regeneration. This work provides new insights into the molecular basis of the epicardial response to heart injury and its role in guiding heart regeneration.

developmental biology↗

bioRxiv2024

Highly efficient tamoxifen-inducible Cre recombination in embryonic, larval and adult zebrafish

We have generated transgenic lines containing zebrafish-optimized CreERT2 recombinase under the control of a recombinant ubbR promoter consisting of the zebrafish ubiquitin promoter supplemented with an intronic enhancer from the carp beta-actin2 gene. These lines enable highly efficient tamoxifen-inducible recombination in embryonic, larval and adult zebrafish. AbstractThe ability to inactivate gene function in an adult organism is essential for studies of biological processes such as regeneration and behavior. This is best achieved by engineering an allele which could be conditionally inactivated using Cre recombinase and subsequently inactivating gene function using a drug-inducible Cre recombinase. Several recent studies clearly demonstrate feasibility of engineering such conditional alleles in zebrafish. Meanwhile, achieving sufficient degree of recombination to induce complete loss of function has remained a major limitation. Herein we address this limitation by engineering a recombinant ubiquitin promoter ubbR consisting of the zebrafish ubiquitin promoter supplemented with an intronic enhancer from the carp beta-actin2 gene. Using phiC31-mediated targeted integration, we demonstrate that ubbR clearly outperforms both parental promoters as well as currently available ubiquitous CreERT2 driver lines at all embryonic and larval stages tested. Furthermore, the ubbR:CreERT2driver line we generated enables near-complete inactivation of floxed alleles in adult zebrafish hearts. Finally, we demonstrate that our ubbRpromoter retains high activity when integrated at other genomic loci, making it uniquely suitable for robust expression of transgenes at all stages of zebrafish ontogenesis. HighlightsO_LIUsed targeted integration to directly compare different CreERT2 drivers C_LIO_LIGenerated a ubiquitous ubbR:CreERT2 driver line capable of near-complete inactivation of floxed genes in adult zebrafish hearts C_LIO_LIDemonstrated that the recombinant ubbR promoter is suitable for robust transgene expression when integrated at different genomic loci C_LI

developmental biology↗

bioRxiv2024

EpicTope: narrating protein sequence features to identify non-disruptive epitope tagging sites

Epitope tagging is a valuable technique enabling the in vivo identification, tracking, and purification of proteins. We developed a tool, EpicTope, to facilitate this method by identifying amino acid positions most suitable for epitope insertion. Our method uses a scoring function that considers protein sequence secondary and tertiary structural features, solvent accessibility, and disordered binding regions to determine locations least disruptive to the proteins function. We validated our approach on the zebrafish Smad5 and Hdac1 proteins. We show that multiple predicted internally tagged Smad5 proteins rescue zebrafish smad5 mutant embryos, while the N- and C-terminal tagged variants do not, as predicted. Similarly, we found that optimally-predicted internal and C-terminal Hdac1 tags rescued hdac1 mutant embryos, while a less-optimal N-terminal tag did not. We further show that these functionally tagged Smad5 and Hdac1 proteins are accessible to antibodies in wholemount zebrafish embryo immunohistochemistry, by western blot, and by immunoprecipitation from embryo extracts. Our work demonstrates that EpicTope is an accessible and effective tool for designing epitope tag insertion sites.

developmental biology↗

bioRxiv2023

Rapid generation of single-insertion transgenics by Tol2 transposition in zebrafish

The Tol2 transposable element is the most widely used transgenesis tool in zebrafish. However, its high activity almost always leads to multiple unlinked integrations of the transgenic cassette in F1 fish. Each of these transgenes is susceptible to position effects from surrounding regulatory landscape, which can lead to altered expression and, consequently, activity. Scientists therefore must strike a balance between the need to maximize reproducibility by establishing single-insertion transgenic lines and the need to complete experiments within a reasonable timeframe. In this article, we introduce a simple competitive dilution strategy for rapid generation of single-insertion transgenics. By using cry:BFP reporter plasmid as a competitor, we achieved a nearly fourfold reduction in the number of the transgene of interest (TgOI) integrations while simultaneously increasing the proportion of single-insertion F1 generation transgenics to over 50%. We also observed variations in TgOI expression among independent single-insertion transgenics, highlighting that the commonly used ubiquitous ubb promoter is susceptible to position effects. Wide application of our competitive dilution strategy will save time, reduce animal usage, and improve reproducibility of zebrafish research. SummaryCompetitive dilution of Tol2 transgenesis vectors facilitates isolation of single-insertion transgenic zebrafish lines in the F1 generation, reducing animal usage, improving reproducibility, and saving time.

developmental biology↗

bioRxiv2020

Deletion of MOrpholino Binding Sites (DeMOBS) to Assess Specificity of Morphant Phenotypes

Two complimentary approaches are widely used to study gene function in zebrafish: induction of genetic mutations, usually using targeted nucleases such as CRISPR/Cas9, and suppression of gene expression, typically using Morpholino oligomers. Neither method is perfect. Morpholinos (MOs) sometimes produce off-target or toxicity-related effects that can be mistaken for true phenotypes. Conversely, genetic mutants can be subject to compensation, or may fail to yield a null phenotype due to leakiness. When discrepancy between mutant and morpholino-induced (morphant) phenotypes is observed, experimental validation of such phenotypes becomes very labor intensive. We have developed a simple genetic method to differentiate between genuine morphant phenotypes and those produced due to off-target effects. We speculated that indels within 5 untranslated regions would be unlikely to have a significant negative effect on gene expression. Mutations induced within a MO target site would result in a Morpholino-refractive allele thus suppressing true MO phenotypes whilst non-specific phenotypes would remain. We tested this hypothesis on one gene with an exclusively zygotic function, tbx5a, and one gene with strong maternal effect, ctnnb2. We found that indels within the Morpholino binding site are indeed able to suppress both zygotic and maternal morphant phenotypes. We also observed that the ability of such indels to suppress Morpholino phenotypes does depend on the size and the location of the deletion. Nonetheless, mutating the morpholino binding sites in both maternal and zygotic genes can ascertain the specificity of morphant phenotypes.

developmental biology↗

bioRxiv2019

The Vertebrate Codex Gene Breaking Protein Trap Library For Genomic Discovery and Disease Modeling Applications

The zebrafish is a powerful model to explore the molecular genetics and expression of the vertebrate genome. The gene break transposon (GBT) is a unique insertional mutagen that reports the expression of the tagged member of the proteome while generating Cre-revertible genetic alleles. This 1000+ locus collection represents novel codex expression data from the illuminated mRFP protein trap, with 36% and 87% of the cloned lines showcasing to our knowledge the first described expression of these genes at day 2 and day 4 of development, respectively. Analyses of 183 molecularly characterized loci indicate a rich mix of genes involved in diverse cellular processes from cell signaling to DNA repair. The mutagenicity of the GBT cassette is very high as assessed using both forward and reverse genetic approaches. Sampling over 150 lines for visible phenotypes after 5dpf shows a similar rate of discovery of embryonic phenotypes as ENU and retroviral mutagenesis. Furthermore, five cloned insertions were in loci with previously described phenotypes; embryos homozygous for each of the corresponding GBT alleles displayed strong loss of function phenotypes comparable to published mutants using other mutagenesis strategies (ryr1b, fras1, tnnt2a, edar and hmcn1). Using molecular assessment after positional cloning, to date nearly all alleles cause at least a 99+% knockdown of the tagged gene. Interestingly, over 35% of the cloned loci represent 68 mutants in zebrafish orthologs of human disease loci, including nervous, cardiovascular, endocrine, digestive, musculoskeletal, immune and integument systems. The GBT protein trapping system enabled the construction of a comprehensive protein codex including novel expression annotation, identifying new functional roles of the vertebrate genome and generating a diverse collection of potential models of human disease.

genomics↗

bioRxiv2018

GeneWeld: a method for efficient targeted integration directed by short homology

Choices for genome engineering and integration involve high efficiency with little or no target specificity or high specificity with low activity. Here, we describe a targeted integration strategy, called GeneWeld, and a vector series for gene tagging, pGTag (plasmids for Gene Tagging), which promote highly efficient and precise targeted integration in zebrafish embryos, pig fibroblasts, and human cells utilizing the CRISPR/Cas9 system. Our work demonstrates that in vivo targeting of a genomic locus of interest with CRISPR/Cas9 and a donor vector containing as little as 24 to 48 base pairs of homology directs precise and efficient knock-in when the homology arms are exposed with a double strand break in vivo. Our results suggest that the length of homology is not important in the design of knock-in vectors but rather how the homology is presented to a double strand break in the genome. Given our results targeting multiple loci in different species, we expect the accompanying protocols, vectors, and web interface for homology arm design to help streamline gene targeting and applications in CRISPR and TALEN compatible systems.

genetics↗