Biology subjects

Chiavacci, E.

Publications and source records attributed to Chiavacci, E..

7 recordsLinked to original sources

bioRxiv2025

Resilience to cardiac aging in Greenland shark Somniosus microcephalus

The Greenland shark (Somniosus microcephalus), with a lifespan exceeding 400 years, represents a unique model for studying vertebrate longevity. Here, we characterize its cardiac aging profile and compare it with two other species: the deep-sea shark Etmopterus spinax and the short-lived teleost Nothobranchius furzeri. Histological analysis revealed extensive interstitial and perivascular fibrosis throughout the ventricular myocardium of S. microcephalus, affecting both compact and spongy layers of both sexes. This fibrotic pattern was absent in E. spinax and N. furzeri, suggesting it is a specific feature of S. microcephalus. We also observed extreme lipofuscin accumulation within cardiomyocytes of S. microcephalus, which correlates at the ultrastructural level with abundance of damaged mitochondria and the presence of strikingly enlarged lysosomes filled with electrondense material of likely mitochondrial origin. Additionally, in the myocardium of S. microcephalus we found abundant deposition of the oxidative stress marker 3-nitrotyrosine. Remarkably, despite showing multiple canonical markers of aging such as fibrosis, lipofuscin accumulation, and oxidative damage, S. microcephalus individuals appeared healthy and physiologically uncompromised at the time of capture. These findings suggest that S. microcephalus has evolved resilience to molecular and tissue-level aging hallmarks, supporting sustained cardiac function over centuries and offering new insights into the mechanisms of extreme vertebrate longevity.

cell biology↗

bioRxiv2023

TAR Syndrome-associated Rbm8a deficiency causes hematopoietic defects and attenuates Wnt/PCP signaling

Defects in blood development frequently occur among syndromic congenital anomalies. Thrombocytopenia-Absent Radius (TAR) syndrome is a rare congenital condition with reduced platelets (hypomegakaryocytic thrombocytopenia) and forelimb anomalies, concurrent with more variable heart and kidney defects. TAR syndrome associates with hypomorphic gene function for RBM8A/Y14 that encodes a component of the exon junction complex involved in mRNA splicing, transport, and nonsense-mediated decay. How perturbing a general mRNA-processing factor causes the selective TAR Syndrome phenotypes remains unknown. Here, we connect zebrafish rbm8a perturbation to early hematopoietic defects via attenuated non-canonical Wnt/Planar Cell Polarity (PCP) signaling that controls developmental cell re-arrangements. In hypomorphic rbm8a zebrafish, we observe a significant reduction of cd41-positive thrombocytes. rbm8a-mutant zebrafish embryos accumulate mRNAs with individual retained introns, a hallmark of defective nonsense-mediated decay; affected mRNAs include transcripts for non-canonical Wnt/PCP pathway components. We establish that rbm8a-mutant embryos show convergent extension defects and that reduced rbm8a function interacts with perturbations in non-canonical Wnt/PCP pathway genes wnt5b, wnt11f2, fzd7a, and vangl2. Using live-imaging, we found reduced rbm8a function impairs the architecture of the lateral plate mesoderm (LPM) that forms hematopoietic, cardiovascular, kidney, and forelimb skeleton progenitors as affected in TAR Syndrome. Both mutants for rbm8a and for the PCP gene vangl2 feature impaired expression of early hematopoietic/endothelial genes including runx1 and the megakaryocyte regulator gfi1aa. Together, our data propose aberrant LPM patterning and hematopoietic defects as consequence of attenuated non-canonical Wnt/PCP signaling upon reduced rbm8a function. These results also link TAR Syndrome to a potential LPM origin and a developmental mechanism. HIGHLIGHTSO_LIZebrafish mutants for the TAR Syndrome gene rbm8a show thrombocyte reduction C_LIO_LIAttenuated Rbm8a function results in retained introns in mRNAs encoding PCP components C_LIO_LIEarly PCP defects result in lateral plate mesoderm anomalies and hematopoietic defects C_LIO_LIPCP anomalies selectively impact cell fate patterning C_LI

developmental biology↗

bioRxiv2018

Cre/lox-controlled spatio-temporal perturbation of FGF signaling in zebrafish

Fibroblast Growth Factor (FGF) signaling guides multiple developmental processes including body axis formation and specific cell fate patterning. In zebrafish, genetic mutants and chemical perturbations affecting FGF signaling have uncovered key developmental processes; however, these approaches cause embryo-wide FGF signaling perturbations, rendering assessment of cell-autonomous versus non-autonomous requirements for FGF signaling in individual processes difficult. Here, we created the novel transgenic line fgfr1-dn-cargo, encoding dominant-negative Fgfr1 with fluorescent tag under combined Cre/lox and heatshock control to provide spatio-temporal perturbation of FGF signaling. Validating efficient perturbation of FGF signaling by fgfr1-dn-cargo primed with ubiquitous CreERT2, we established that primed, heatshock-induced fgfr1-dn-cargo behaves akin to pulsed treatment with the FGFR inhibitor SU5402. Priming fgfr1-dn-cargo with CreERT2 in the lateral plate mesoderm, we observed selective cardiac and pectoral fin phenotypes without drastic impact on overall embryo patterning. Harnessing lateral plate mesoderm-specific FGF inhibition, we recapitulated the cell-autonomous and temporal requirement for FGF signaling in pectoral fin outgrow, as previously hypothesized from pan-embryonic FGF inhibition. Altogether, our results establish fgfr1-dn-cargo as a genetic tool to define the spatio-temporal requirements for FGF signaling in zebrafish.

developmental biology↗

bioRxiv2018

A conserved regulatory program drives emergence of the lateral plate mesoderm

Cardiovascular lineages develop together with kidney, smooth muscle, and limb connective tissue progenitors from the lateral plate mesoderm (LPM). How the LPM initially emerges and how its downstream fates are molecularly interconnected remain unknown. Here, we isolated a pan-LPM enhancer in the zebrafish draculin (drl) gene that provides specific LPM reporter activity from early gastrulation. In toto live imaging and lineage tracing of drl-based reporters captured the dynamic LPM emergence as lineage-restricted mesendoderm field. The drl pan-LPM enhancer responds to the transcription factors EomesoderminA, FoxH1, and MixL1 that combined with Smad activity drive LPM emergence. We uncovered specific drl reporter activity in LPM-corresponding territories of several chordates including chicken, axolotl, lamprey, Ciona, and amphioxus, revealing a universal upstream LPM program. Altogether, our work provides a mechanistic framework for LPM emergence as defined progenitor field, possibly representing an ancient mesodermal cell state that predates the primordial vertebrate embryo.

developmental biology↗

bioRxiv2018

Mutations in Bcl9 and Pygo genes cause congenital heart defects by tissue-specific perturbation of Wnt/β-catenin signaling

Genetic alterations in human BCL9 genes have repeatedly been found in congenital heart disease (CHD) with as-of-yet unclear causality. BCL9 proteins and their Pygopus (Pygo) co-factors can participate in canonical Wnt signaling via binding to {beta}-catenin. Nonetheless, their contributions to vertebrate heart development remain uncharted. Here, combining zebrafish and mouse genetics, we document tissue-specific functions in canonical Wnt signaling for BCL9 and Pygo proteins during heart development. In a CRISPR-Cas9-based genotype-phenotype association screen, we uncovered that zebrafish mutants for bcl9 and pygo genes largely retain {beta}-catenin activity, yet develop cardiac malformations. In mouse, both systemic and lineage-specific loss of the Pygo-BCL9-{beta}-catenin complex caused heart defects with outflow tract malformations, aberrant cardiac septation and valve formation, and compact myocardium hypoplasia. Mechanistically, these phenotypes coincide with transcriptional deregulation during heart patterning, and Pygo2 associates with {beta}-catenin at cis-regulatory regions of cardiac genes. Taken together, our results establish BCL9 and Pygo as tissue-specific {beta}-catenin co-factors during vertebrate heart development. Our results further implicate alterations in BCL9 and BCL9L in human CHDs as possibly causative.

genetics↗

bioRxiv2017

Highly efficient DNA-free gene disruption in the agricultural pest Ceratitis capitata by CRISPR-Cas9 RNPs

The Mediterranean fruitfly Ceratitis capitata (medfly) is an invasive agricultural pest of high economical impact and has become an emerging model for developing new genetic control strategies as alternative to insecticides. Here, we report the successful adaptation of CRISPR-Cas9-based gene disruption in the medfly by injecting in vitro pre-assembled, solubilized Cas9 ribonucleoprotein complexes (RNPs) loaded with gene-specific sgRNAs into early embryos. When targeting the eye pigmentation gene white eye (we), we observed a high rate of somatic mosaicism in surviving G0 adults. Germline transmission of mutated we alleles by G0 animals was on average above 70%, with individual cases achieving a transmission rate of nearly 100%. We further recovered large deletions in the we gene when two sites were simultaneously targeted by two sgRNAs. CRISPR-Cas9 targeting of the Ceratitis ortholog of the Drosophila segmentation paired gene (Ccprd) caused segmental malformations in late embryos and in hatched larvae. Mutant phenotypes correlate with repair by non-homologous end joining (NHEJ) lesions in the two targeted genes. This simple and highly effective Cas9 RNP-based gene editing to introduce mutations in Ceratitis capitata will significantly advance the design and development of new effective strategies for pest control management.

genetics↗

bioRxiv2017

Early frameshift alleles of zebrafish tbx5a that fail to develop the heartstrings phenotype

Tbx5 is a key transcription factor for vertebrate heart and forelimb development that causes Holt-Oram syndrome when mutated in humans. The classic zebrafish mutant for tbx5a named heartstrings (hst) features recessive absence of pectoral fins and a spectrum of heart defects, most-prominently featuring the name-giving stretched heart tube. The mutation of the hst allele is a stop codon that is predicted to result in a truncated Tbx5a protein that might feature residual activity. Here, using CRISPR-Cas9 mutagenesis, we generated zebrafish strains for two new tbx5a frameshift alleles in the first coding exon: tbx5a c.21_25del and tbx5a c.22_31del, abbreviated as tbx5a{Delta}5 and tbx5a{Delta}10. Homozygous and trans-heterozygous combinations of these new tbx5a alleles cause fully penetrant loss of pectoral fins and heart defects including changes in cardiac marker expression akin to hst mutants. Nonetheless, distinct from hst mutants, homozygous and trans-heterozygous combinations of these tbx5a frameshift mutants do not readily manifest the stretched hst heart phenotype. Our observation points out the importance and value of comparing phenotypes from different classes of mutant alleles per gene.

developmental biology↗