Biology subjects

Packer, J.

Publications and source records attributed to Packer, J..

5 recordsLinked to original sources

bioRxiv2026

Inverse relationship between mitochondrial and non-coding nuclear DNA content in free-living kinetoplastids

The evolution of genome size and eukaryotic genome organisation has puzzled evolutionary biologists for decades. Are differences in DNA content and protein-coding capacity of eukaryotic genomes a result of natural selection, or neutral processes? If they were shaped by natural selection, which features might be connected with these differences: cell volume, ecological strategy, availability of nutrients, etc.? Kinetoplastids are protists with compact nuclear genomes that almost entirely lack introns, but whose mitochondrial DNA content (kDNA) can rival that of their nuclei. We hypothesised that the reduction in non-protein coding nuclear DNA content during the evolution of kinetoplastids is connected with an increase in kDNA content: species with larger fractions of total cellular DNA that is allocated to kDNA will have concomitantly smaller fractions of non-coding DNA in the nuclear genome. We developed a framework for estimation of DNA content in both the mitochondria and nuclei from quantitative fluorescence microscopy data, and inferred the fraction of non-coding DNA in nuclear genomes based on the combination of transcriptomic and fluorescence imaging data. Across 10 genetically distant isolates from diverse free-living kinetoplastid lineages, there is indeed a trend towards a lower proportion of non-protein-coding nuclear DNA when kDNA proportion is higher relative to the total DNA in the cell. This observation is consistent with the hypothesis that in free-living kinetoplastids, mitochondrial and nuclear genomes might co-evolve in terms of their DNA content. This finding raises the possibility that natural selection acts on genome size evolution in kinetoplastids, and contributes evidence and methodology to address this question more broadly in eukaryotes.

evolutionary biology↗

bioRxiv2023

Atypical Protein Kinase C Promotes its own Asymmetric Localisation by Phosphorylating Cdc42 in Polarising Cells

Atypical protein kinase C (aPKC) is a major regulator of cell polarity. Acting in conjunction with Par6, Par3 and the small GTPase Cdc42, aPKC becomes asymmetrically localised and drives the polarisation of cells. aPKC activity is crucial for its own asymmetric localisation, suggesting a hitherto unknown feedback mechanism contributing to polarisation. Here we show in the C. elegans zygote that the feedback relies on aPKC phosphorylation of Cdc42 at serine 71. The turnover of CDC-42 phosphorylation ensures optimal aPKC asymmetry and activity throughout polarisation by tuning Par6/aPKC association with Par3 and Cdc42. Moreover, turnover of Cdc42 phosphorylation regulates actomyosin cortex dynamics that are known to drive aPKC asymmetry. Given the widespread role of aPKC and Cdc42 in cell polarity, this form of self-regulation of aPKC may be vital for the robust control of polarisation in many cell types. Key findings/graphical abstract- Phosphorylation of CDC-42 by aPKC accelerates aPKC dissociation from CDC-42, limiting aPKC activity - CDC-42/aPKC dissociation promotes aPKC association with PAR-3 and, thereby, aPKC asymmetry due to actomyosin flow - Cycling of CDC-42 phosphorylation fuels the exchange of aPKC between anteriorly transported PAR-3 and aPKC-active CDC-42 complexes - Turnover of CDC-42 phosphorylation alternates its association with effectors, aPKC and MRCK-1, ensuring proper actomyosin dynamics O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=136 SRC="FIGDIR/small/563985v2_ufig1.gif" ALT="Figure 1"> View larger version (43K): org.highwire.dtl.DTLVardef@e0ec65org.highwire.dtl.DTLVardef@c00b8dorg.highwire.dtl.DTLVardef@36565dorg.highwire.dtl.DTLVardef@160149a_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

bioRxiv2019

Thyroid hormone regulates distinct paths to maturation in pigment cell lineages

Circulating endocrine factors are critical for orchestrating complex developmental processes during the generation of adult form. One such factor, thyroid hormone, regulates diverse cellular processes during post-embryonic development and can drive disparate morphological outcomes through mechanisms that remain essentially unknown. We sought to define how thyroid hormone elicits opposite responses in the abundance of two pigment cell classes during development of the zebrafish adult pigment pattern. By profiling individual transcriptomes from thousands of neural crest derived cells, including pigment cells, we reconstructed developmental trajectories and identified lineage-specific changes in response to thyroid hormone. Our findings show that thyroid hormone and its receptors regulate distinct events of cellular maturation across lineages, and illustrate how a single, global factor integrates seemingly divergent morphogenetic outcomes across developmental time.

developmental biology↗

bioRxiv2018

On the design of CRISPR-based single cell molecular screens

Several groups recently reported coupling CRISPR/Cas9 perturbations and single cell RNA-seq as a potentially powerful approach for forward genetics. Here we demonstrate that vector designs for such screens that rely on cis linkage of guides and distally located barcodes suffer from swapping of intended guide-barcode associations at rates approaching 50% due to template switching during lentivirus production, greatly reducing sensitivity. We optimize a published strategy, CROP-seq, that instead uses a Pol II transcribed copy of the sgRNA sequence itself, doubling the rate at which guides are assigned to cells to 94%. We confirm this strategy performs robustly and further explore experimental best practices for CRISPR/Cas9-based single cell molecular screens.

genomics↗

bioRxiv2017

Chromatin accessibility dynamics of myogenesis at single cell resolution

Over a million DNA regulatory elements have been cataloged in the human genome, but linking these elements to the genes that they regulate remains challenging. We introduce Cicero, a statistical method that connects regulatory elements to target genes using single cell chromatin accessibility data. We apply Cicero to investigate how thousands of dynamically accessible elements orchestrate gene regulation in differentiating myoblasts. Groups of co-accessible regulatory elements linked by Cicero meet criteria of \"chromatin hubs\", in that they are physically proximal, interact with a common set of transcription factors, and undergo coordinated changes in histone marks that are predictive of gene expression. Pseudotemporal analysis revealed a subset of elements bound by MYOD in myoblasts that exhibit early opening, potentially serving as the initial sites of recruitment of chromatin remodeling and histone-modifying enzymes. The methodological framework described here constitutes a powerful new approach for elucidating the architecture, grammar and mechanisms of cis-regulation on a genome-wide basis.

genomics↗