Biology subjects

Hackett, J. A.

Publications and source records attributed to Hackett, J. A..

7 recordsLinked to original sources

bioRxiv2026

Iterative engineering of a compact Cas9 ortholog for in vivo gene editing via single AAV delivery

The development of compact and efficient CRISPR-Cas systems is crucial for biomedical and therapeutic genome editing, particularly in vivo applications based on viral delivery. Here, we performed a comparative functional screen of seven Cas9 orthologs to systematically evaluate their genome editing activity in mammalian cells. Among these, Cme2--a 1008 amino acid nuclease recognizing a 5'-NAGNGC PAM--emerged as a promising candidate based on its compact size and baseline editing activity. To overcome its limited native efficiency, we employed a dual engineering approach combining sgRNA scaffold optimization and rational protein mutagenesis. The resulting variant, enCme2, exhibits markedly improved editing efficiency across multiple loci in both mouse and human cells while maintaining extremely high specificity and minimal off-target activity. Importantly, the small size of enCme2 permits packaging of the complete system into a single rAAV vector, enabling efficient genome editing/HDR in in vivo tissues and mouse embryos, and facile generation of transgenic models. These results establish enCme2 as a compact, precise, and AAV-compatible genome editing platform with broad applicability for in vivo research and therapeutic approaches, especially where high specificity is desirable.

molecular biology↗

bioRxiv2025

HDAC3 prevents enhancer hyperactivation to enable developmental transitions

Dynamic gene regulation requires precise cooperation between transcription factors and chromatin modifiers at regulatory elements to achieve not only activation or repression, but also appropriate transcript dosage. However, the molecular mechanisms that ensure developmental genes are transcribed at specific levels remain largely unknown. Here, we discover that the epigenetic repressor histone deacetylase 3 (HDAC3), together with co-activators, binds a subset of the most active putative enhancer elements. Using a tunable mouse embryonic stem cell degron system, we uncover that HDAC3 directly prevents enhancer--and consequently gene--overactivation, effectively establishing a molecular "speed limit" for many naive pluripotency and housekeeping genes. Interestingly, we find that both the catalytic and non-catalytic functions of HDAC3 contribute to establishing this physiological transcript dose. Specifically during early development, HDAC3 rather than functioning as a canonical repressor, constrains the activity of highly transcribed genes of the implanting epiblast and ensures timely exit from naive pluripotency in vitro. Altogether, this indicates that a dynamic equilibrium between activators and repressors coexists at highly active enhancer elements in pluripotent stem cells, establishing appropriate transcriptional dosage and rendering them responsive to signaling cues, thereby enabling timely and coordinated developmental progression.

developmental biology↗

bioRxiv2024

Embryonic Signatures of Intergenerational Inheritance across Paternal Environments and Genetic Backgrounds

The paternal preconception environment has been implicated as a modulator of phenotypic traits and disease risk in F1 offspring. However, the prevalence and mechanisms of such intergenerational epigenetic inheritance (IEI) in mammals remain poorly defined. Moreover, the interplay between paternal exposure, genetics, and age on emergent offspring features is unexplored. Here, we measure the quantitative impact of three paternal environments on early embryogenesis across genetic backgrounds. Using in vitro fertilisation (IVF) at scale, we capture batch-robust transcriptomic signatures of IEI with single-blastocyst resolution. Amongst these, paternal gut microbiota dysbiosis is linked with aberrant expression of lineage regulators in blastocysts, particularly affecting extra-embryonic tissues. Conversely, paternal low-protein high-sugar diet associates with subtle preimplantation developmental delay. We further identify gene expression variability as a paternally-induced F1 phenotype, and highlight confounding issues for IEI such as batch-effects and under-sampling. Finally, paternal genetic background and age exert a dominant influence over the inherited environmental signature. This study systematically characterises how paternal conditioning programmes subtle but detectable molecular responses in early embryos, and suggests guiding principles to dissect intergenerational phenomenology.

genomics↗

bioRxiv2022

Systematic Epigenome Editing Captures the Context-dependent Instructive Function of Chromatin Modifications

Chromatin modifications are linked with regulating patterns of gene expression, but their causal role and context-dependent impact on transcription remains unresolved. Here, we develop a modular epigenome editing platform that programmes nine key chromatin modifications - or combinations thereof - to precise loci in living cells. We couple this with single-cell readouts to systematically quantitate the magnitude and heterogeneity of transcriptional responses elicited by each specific chromatin modification. Amongst these, we show installing H3K4me3 at promoters causally instructs transcription activation by hierarchically remodeling the chromatin landscape. We further dissect how DNA sequence motifs influence the transcriptional impact of chromatin marks, identifying switch-like and attenuative effects within distinct cis contexts. Finally, we examine the interplay of combinatorial modifications, revealing co-targeted H3K27me3 and H2AK119ub maximise silencing penetrance across single-cells. Our precision perturbation strategy unveils the causal principles of how chromatin modification(s) influence transcription, and dissects how quantitative responses are calibrated by contextual interactions.

synthetic biology↗

bioRxiv2021

Epigenetic Inheritance is Gated by Naive Pluripotency and Dppa2

Environmental factors can trigger cellular responses that propagate across mitosis or even generations. Perturbations to the epigenome could underpin such acquired changes, however, the extent and contexts in which modified chromatin states confer heritable memory in mammals is unclear. Here we exploit a modular epigenetic editing strategy to establish de novo heterochromatin domains (epialleles) at endogenous loci and track their inheritance in a developmental model. We find that naive pluripotent phases systematically erase ectopic domains of heterochromatin via active mechanisms, which acts as an intergenerational safeguard against transmission of epialleles. Upon lineage specification however, acquired chromatin states can be probabilistically inherited under selectively favourable conditions, including propagation of p53 silencing through in vivo development. Using genome-wide CRISPR screening, we identify the mechanisms that block heritable silencing memory in pluripotent cells, and demonstrate removal of Dppa2 unlocks the potential for epigenetic inheritance uncoupled from DNA sequence. Our study outlines a mechanistic basis for how epigenetic inheritance is restricted in mammals, and reveals genomic- and developmental-contexts in which heritable memory is feasible.

genetics↗

bioRxiv2020

Dppa2/4 Counteract De Novo Methylation to Establish a Permissive Epigenome for Development

Early mammalian development entails genome-wide epigenome remodeling, including DNA methylation erasure and reacquisition, which facilitates developmental competence. To uncover the mechanisms that orchestrate DNA methylation (DNAme) dynamics, we coupled a single-cell ratiometric DNAme reporter with unbiased CRISPR screening in ESC. We identify key genes and regulatory pathways that drive global DNA hypomethylation, and characterise roles for Cop1 and Dusp6. We also identify Dppa2 and Dppa4 as essential safeguards of focal epigenetic states. In their absence, developmental genes and evolutionary-young LINE1 elements, which DPPA2 specifically binds, lose H3K4me3 and gain ectopic de novo DNA methylation in pluripotent cells. Consequently, lineage-associated genes (and LINE1) acquire a repressive epigenetic memory, which renders them incompetent for activation during future lineage-specification. Dppa2/4 thereby sculpt the pluripotent epigenome by facilitating H3K4me3 and bivalency to counteract de novo methylation; a function co-opted by evolutionary young LINE1 to evade epigenetic decommissioning.

genetics↗

bioRxiv2018

Tracing the Transitions from Pluripotency to Germ Cell Fate with CRISPR Screening

Early mammalian development entails a series of cell fate transitions that includes transit through naive pluripotency to post-implantation epiblast. This subsequently gives rise to primordial germ cells (PGC), the founding population of the germline lineage. To investigate the gene regulatory networks that control these critical cell fate decisions, we developed a compound-reporter system to track cellular identity in a model of PGC specification (PGC-like cells; PGCLC), and coupled it with unbiased genome-wide CRISPR screening. This enabled identification of key genes both for exit from pluripotency and for acquisition of PGC fate, with further characterisation revealing a central role for the transcription factors Nr5a2 and Zfp296 in germline ontogeny. Abrogation of these genes results in significantly impaired PGCLC development due to widespread activation (Nr5a2-/-) or inhibition (Zfp296-/-) of WNT pathway components. This leads to aberrant upregulation of the somatic programme or failure to appropriately activate germline genes in PGCLC, respectively, and consequently loss of germ cell identity. Overall our study places Zfp296 and Nr5a2 as key components of an expanded PGC gene regulatory network, and outlines a transferable strategy for identifying critical regulators of complex cell fate transitions.

developmental biology↗