Biology subjects

Carroll, J.

Publications and source records attributed to Carroll, J..

At least 19 recordsLinked to original sources

bioRxiv2026

A Humanized Mouse Model of DRPLA Recapitulates Epilepsy and Demonstrates Antisense Oligonucleotide-Mediated Disease Modification

Dentatorubral-pallidoluysian atrophy (DRPLA) is an ultra-rare progressive myoclonus epilepsy caused by a glutamine-coding CAG repeat expansion in atrophin-1 (ATN1). Mutant ATN1 (mATN1) expression results in symptoms that inversely correlate to CAG-expansion size: young-onset cases have the most CAG repeats and developmental delay, high-frequency treatment-resistant seizures, and early mortality. We sought to characterize the seizure susceptibility of a fully humanized ATN1 mouse expressing human mATN1 with 112 CAG repeats to then assess therapeutic antisense oligonucleotide (ASO) intervention on seizure-related outcomes. Atn1Q112/+ or wild-type (WT) mice were treated with investigational ASO targeting human, CAG-expanded, ATN1 or saline (P2 and then again at 4 weeks-old) before acute seizure testing, ataxia profiling, and chronic in vivo video-EEG recording for spontaneous seizures up to 8 weeks-old. Saline-treated Atn1Q112/+ mice were more seizure prone with early death. However, ASO administration to Atn1Q112/+ mice normalized seizure threshold, decreased ataxia, and protected against early death. Atn1Q112/+ mice exhibited spontaneous behavioral seizures recorded over 2 weeks, which were absent in ASO-treated Atn1Q112/+ and WT mice, with a specific mATN1 expression-driven decrease in delta and theta EEG frequencies. Atn1Q112/+ mice are highly seizure prone, validating this model for DRPLA epilepsy. ATN1 represents a novel epilepsy-related risk factor for therapeutic investigation.

neuroscience↗

bioRxiv2026

Staphylococcus aureus GpsB, Stk, and VraSR form a cell wall surveillance network to maintain cell envelope integrity and mediate antibiotic resistance

Antibiotic resistance is an alarming threat to public health worldwide. Specifically, drug-resistant Staphylococcus aureus remains a major contributor to global mortality. Therefore, in-depth understanding of antibiotic resistance mechanisms is urgently needed to inform alternative therapeutic strategies. We previously showed that GpsB is a critical regulator of cell wall synthesis in S. aureus. GpsB executes its regulatory role via protein-protein interactions. Yet, how GpsB function is modulated in this organism has remained unclear. Intriguingly, a prior proteomics report indicated that GpsB is phosphorylated at six different residues by the sole serine/threonine kinase Stk. Hence, we explored the physiological significance of GpsB phosphorylation. We identify three phosphosites that are each independently sufficient to drive GpsB phosphoregulation, which likely alters its partner preference. We find that cells lacking gpsB exhibit heightened fosfomycin sensitivity, and that this is exacerbated by stk deletion. Our findings reveal that GpsB collaborates with Stk and the VraSR cell wall stress response system to coordinate the demand-driven availability of cell wall precursors. Collectively, this report establishes GpsB as a pivotal peptidoglycan supply chain sentinel that together with Stk and VraSR forms an integrated cell wall stress monitoring network that maintains cell envelope homeostasis and aids in antibiotic resistance.

microbiology↗

bioRxiv2026

Optoretinography in R9AP-bradyopsia reveals the essential role of G-protein signaling in the human cone elongation response

Human cone and rod outer segments exhibit a rapid shrinkage followed by a slower elongation in response to light, forming the basis of the optoretinogram. The molecular basis of this optical assay of photoreceptor function remains incompletely understood. In mouse rods, the elongation response requires transducin, the G-protein -subunit activated in the initial amplifying step of the phototransduction cascade. Here, we measured human cone outer segment responses in subjects with bradyopsia arising from a triple-deletion mutation in R9AP, the anchor and transport protein for the GTPase-activating protein (GAP) RGS9. Immunoprecipitation showed that the mutant R9AP has greatly reduced affinity for RGS9, predictably reducing the level of RGS9 in the outer segment. The bradyopsia subjects elongation responses had normal activation kinetics, amplitude and photosensitivity, but markedly slowed recovery. These results indicate that normal levels of RGS9 are required for deactivation of the cone elongation response, situating the underlying molecular mechanism within the G-protein cascade at or prior to formation of the GAP complex. The recovery of the cone elongation response, measured in a paired-flash paradigm for stimuli isomerizing up to 75% of opsin, revealed that elongation requires a substrate that is depleted and recovers in a bleach-dependent manner. In particular, recovery from the highest bleaching exposure (75%) tracked the time course of cone opsin regeneration, implying that unregenerated cone opsin produces "dark light", known in rods to arise from constitutive activation of G-protein. Taken together, the results from controls and bradyopsia identify the inactive (GDP-bound) transducin complex as the essential substrate for the human cone elongation response. Suppression of the elongation response in the paired-flash paradigm further revealed the complete profile of the initial fast cone outer segment shrinkage response and reinforced its origin in opsin structural changes. Overall, these results identify key mechanistic elements of the optoretinogram and enable its use as a molecularly interpretable, non- invasive assay of cone function in disease and therapeutic response.

neuroscience↗

bioRxiv2026

Observing concurrent subcellular dynamics in large living tissues

An outstanding question in eukaryotic biology is the mechanistic connection between events occurring at (sub)cellular levels (time scales of milliseconds to minutes) to those at the tissue levels (tens of minutes to months). Deciphering such mechanisms requires imaging approaches capable of simultaneously achieving high spatial and temporal resolutions for large samples over long periods of time. Here, we demonstrate Airy beam-based light sheet microscopy of organelles in tens to hundreds of cells in a few hundred micrometre-wide tissue environments. We achieve a typical resolution of 320 nm over 266 x 266 x 100 m3 volumes at a temporal rate of 0.05 Hz, typically with generally used fluorophores such as Green Fluorescent Protein, over extended periods of time that allow tracking of organelle and protein dynamics. We validated our approach across different length and time scales by imaging mitochondria and endosome dynamics in very large fields of view in zebrafish tissue, molecular assemblies of myosin as gastrulation proceeds in Drosophila embryos, 3D mitochondrial streaming in mouse oocytes, pressure-driven motility and protrusions in amoebae, mitochondrial dynamics in cancer spheroids, 5 -colour fast imaging in iBlastoids, and endosomal dynamics in single cells. Through these model systems, we demonstrate the versatility of Airy beam light sheet microscopy to image large tissues at unprecedented high resolution; to capture dynamics in photosensitive, delicate samples; and to screen 3D samples. We anticipate that our Airy beam-based approach will represent a pivotal advance in cellular biology--especially developmental biology--as it provides, for the first time, true subcellular resolution over large imaging volumes with high temporal resolution.

developmental biology↗

bioRxiv2026

Chromatin- and actin-mediated mitochondrial streaming leads to patterning of mitochondrial distribution in oocytes

Mitochondria are highly dynamic organelles, and their spatiotemporal organization is strictly regulated. While it has long been recognized that mitochondria in ovulated oocytes are concentrated in the spindle hemisphere, the mechanism remains unknown. Through live cell imaging and modelling, we have discovered three features of mitochondrial dynamics in the ooplasm: (i) actin-driven cortical mitochondrial streaming is delimited to the boundary of the polarized spindle hemisphere; (ii) distinct from bulk cytoplasmic streaming, mitochondrial streaming occurs bilaterally and perpendicular to the long axis of the MII spindle and, (iii) mitochondria movement from the cytoplasm to the polarized cortex is via MYO19-mediated chromatin-associated channel around the spindle midzone. This directionality in mitochondrial streaming patterns the ooplasm of the spindle cortex, creating mitochondria-rich and mitochondria-poor regions. These features explain the establishment of the polar gradient of mitochondria in MII oocytes and may provide new insight into the spatiotemporal organization of mitochondria in cells.

cell biology↗

bioRxiv2025

Comparative ASCL1 interactome analysis reveals CDK2-Cyclin A2 as suppressors of differentiation in MYCN-amplified neuroblastoma

Neuroblastoma is a heterogeneous paediatric cancer arising from developmentally arrested neuronal precursors, where restoring differentiation offers therapeutic promise. ASCL1, a pro-neural transcription factor, is widely expressed in neuroblastoma and can drive either proliferation or differentiation depending on the cellular context. Here, we show that distinct MYCN-amplified neuroblastoma cell lines exhibit differing cell cycle and differentiation responses to ASCL1 overexpression. By comparing genome-wide ASCL1 chromatin binding, transcriptional changes, and protein-protein interactions, we found that ASCL1 binds more extensively to neuronal proteins in a cell line that is more susceptible to ASCL1-driven differentiation, but associates with cell cycle regulators in less responsive cells. We show that CDK2-Cyclin A2 bind ASCL1 in less responsive cells, with CDK-mediated phosphorylation of ASCL1 limiting the ability of ASCL1 to drive differentiation. Our study reveals that context-dependent interactions of ASCL1 with protein partners on the chromatin control its ability to re-engage a differentiation program in neuroblastoma.

cancer biology↗

bioRxiv2025

JAK2 signalling to HNRNPA1 represses retrotransposon activity in haematopoietic stem cells

Retrotransposon expression must be tightly controlled, particularly in long-lived multipotent stem cells, to prevent deleterious consequences including insertional mutations. Several mechanisms are known to repress retrotransposon transcription during development which are generally thought to persist thereafter. However, integration of retrotransposable elements into host genomes has also provided a major source of genetic variation across evolution. This has generated many sequences that have acquired advantageous host functions, but little is known about retrotransposon expression and mobility in adult stem cells or about how these processes might be dynamically regulated. Here we describe the landscape of somatic retrotransposition in haematopoietic stem cells and identify a previously unrecognised pathway which links cytokine signalling, RNA-modulating HNRNP complexes and repression of retrotransposon activity. Activation of JAK2, by thrombopoietin or gain-of-function JAK2 mutations, triggers tyrosine phosphorylation of HNRNPA1 that represses expression of ERVs, LINEs and SINEs and reduces insertional mutagenesis. This pathway coordinates retrotransposon activity with cellular context and state and provides a mechanism for protecting the haematopoietic stem cell genome.

cell biology↗

bioRxiv2024

Redox-dependent binding and conformational equilibria govern the fluorescence decay of NAD(P)H in living cells

When probed using fluorescence lifetime imaging microscopy (FLIM), the emission from reduced nicotinamide adenine dinucleotide (NADH) and its phosphorylated form NADPH have shown promise as sensitive intrinsic reporters of metabolism in living systems. However, an incomplete understanding of the biochemical processes controlling their fluorescence decay makes it difficult to draw unambiguous conclusions from NAD(P)H FLIM data. Here we utilised time-resolved fluorescence anisotropy imaging to identify multiple enzyme binding configurations in live cells associated with lifetimes both longer and shorter than unbound NAD(P)H. FLIM, combined with mathematical and computational modelling, revealed that the redox states of the NAD and NADP pools control the steady-state equilibrium of binding configurations, which in-turn determines the observed fluorescence decay. This knowledge will be foundational to developing the accurate interpretation of NAD(P)H FLIM.

biochemistry↗

bioRxiv2024

EstroGene2.0: A multi-omic database of response to estrogens, ER-modulators, and resistance to endocrine therapies in breast cancer

Endocrine therapies targeting the estrogen receptor (ER/ESR1) are the cornerstone to treat ER-positive breast cancers patients, but resistance often limits their effectiveness. Understanding the molecular mechanisms is thus key to optimize the existing drugs and to develop new ER-modulators. Notable progress has been made although the fragmented way data is reported has reduced their potential impact. Here, we introduce EstroGene2.0, an expanded database of its precursor 1.0 version. EstroGene2.0 focusses on response and resistance to endocrine therapies in breast cancer models. Incorporating multi-omic profiling of 361 experiments from 212 studies across 28 cell lines, a user-friendly browser offers comprehensive data visualization and metadata mining capabilities (https://estrogeneii.web.app/). Taking advantage of the harmonized data collection, our follow-up meta-analysis revealed substantial diversity in response to different classes of ER-modulators including SERMs, SERDs, SERCA and LDD/PROTAC. Notably, endocrine resistant models exhibit a spectrum of transcriptomic alterations including a contra-directional shift in ER and interferon signaling, which is recapitulated clinically. Furthermore, dissecting multiple ESR1-mutant cell models revealed the different clinical relevance of genome-edited versus ectopic overexpression model engineering and identified high-confidence mutant-ER targets, such as NPY1R. These examples demonstrate how EstroGene2.0 helps investigate breast cancers response to endocrine therapies and explore resistance mechanisms.

cancer biology↗

bioRxiv2024

Redistribution of fragmented mitochondria ensure symmetric organelle partitioning and faithful chromosome segregation in mitotic mouse zygotes

In cleavage-stage embryos, preexisting organelles partition evenly into daughter blastomeres without significant cell growth after symmetric cell division. The presence of mitochondrial DNA within mitochondria and its restricted replication during preimplantation development makes their inheritance particularly important. While chromosomes are precisely segregated by the mitotic spindle, the mechanisms controlling mitochondrial partitioning remain poorly understood. In this study, we investigate the mechanism by which Dynamin-related protein 1 (Drp1) controls the mitochondrial redistribution and partitioning during embryonic cleavage. Depletion of Drp1 in mouse zygotes causes marked mitochondrial aggregation, and the majority of embryos arrest at the 2-cell stage. Clumped mitochondria are located in the center of mitotic Drp1-depleted zygotes with less uniform distribution, thereby preventing their symmetric partitioning. Asymmetric mitochondrial inheritance is accompanied by functionally inequivalent blastomeres with biased ATP and endoplasmic reticulum Ca2+ levels. We also find that marked mitochondrial centration in Drp1-depleted zygotes prevents the assembly of parental chromosomes, resulting in chromosome segregation defects and binucleation. Thus, mitochondrial fragmentation mediated by Drp1 ensure proper organelle positioning and partitioning into functional daughters during the first embryonic cleavage. Impact statementDepletion of Dynamin-related protein 1, a key regulator of mitochondrial fission, in mouse zygotes impair symmetric organelle partitioning and chromosome segregation leading to early developmental arrest.

developmental biology↗

bioRxiv2024

BOLD Contrast Response Characteristics of Aberrant Voxels with Bilateral Visual Population Receptive Fields in Human Albinism

Albinism is an inherited disorder characterized by disrupted melanin production in the eye, and often in the skin and hair. This retinal hypopigmentation is accompanied by pathological decussation of many temporal retinal afferents at the optic chiasm during development, ultimately resulting in partially superimposed representations of opposite visual hemifields in each cortical hemisphere. Within these aberrant regions of hemifield overlap, individual voxels have been shown to have bilateral, dual population receptive fields (pRFs) responding to roughly mirror-image locations across the vertical meridian. Nonetheless, how these two conflicting inputs combine to determine a voxels response to image contrast is still unknown. To address this, we stimulated the right and left hemifields with separately controlled sinusoidal gratings, each having a variety of contrasts (0, 8, 20, 45, 100%), and extracted voxel-wise BOLD response amplitudes to each contrast combination in visual areas V1-V3. We then compared voxels responses to each hemifield stimulated individually with conditions when both hemifields were stimulated simultaneously. We hypothesized that simultaneous stimulation of the two pRF components will result in either a suppressive or facilitative interaction. However, we found that BOLD responses to simultaneous stimulation appeared to reflect simple summation of the neural activity from the individual hemifield conditions. This suggests that the superimposed opposite hemifield representations do not interact. Thus, dual pRFs in albinism likely reflect two co-localized, but functionally independent populations of neurons each of which respond to a single hemifield. This finding is commensurate with psychophysical studies which have shown no clear perceptual interaction between opposite visual hemifields in human albinism.

neuroscience↗

bioRxiv2023

Identification of conserved gene expression programs activated in multiple modes of torpor across vertebrate clades.

Torpor encompasses adaptations to diverse extreme environmental stressors such as hibernation, aestivation, brumation, and daily torpor. Here we introduce StrokeofGenus, an analytic pipeline that identifies distinct transcriptomic states and conservation of gene expression patterns across studies, tissues, and species. We use StrokeofGenus to study multiple and diverse forms of torpor from publicly available RNA-seq datasets that span eight species and two classes. We identify three transcriptionally distinct states during the cycle of heterothermia: euthermia, torpor, and interbout arousal. We also identify torpor-specific gene expression patterns that are conserved both across tissues and between species with over three hundred million years of evolutionary divergence. We further demonstrate the general conservation of gene expression patterns in multiple forms of torpor, implying a common evolutionary origin for this process. Although here we apply StrokeofGenus to analysis of torpor, it can be used to interrogate any other complex physiological processes defined by transient transcriptomic states. HIGHLIGHTSO_LIStrokeofGenus integrates orthologue annotation, non-negative matrix factorization, and transfer learning for cross-species analysis. C_LIO_LIStrokeofGenus identifies conserved topor-related gene expression patterns across divergent species and cell types. C_LIO_LIHeterothermia has three distinct transcriptomic states. C_LIO_LITorpor-specific gene expression patterns are conserved between species and forms of torpor. C_LI

physiology↗

bioRxiv2023

Fertility is compromised after oocyte-specific deletion of Katanin A-subunit, Katna1, but not Katnal1

Katanins are microtubule severing enzymes that play roles in shaping diverse microtubule-based structures during all cell cycle stages. To address the role of katanin A-subunits in mammalian oocytes, we have used the Zp3-CreLox approach to specifically delete katanin A1 (Katna1) and katanin A-like 1 (Katnal1) from the start of oocyte growth in mice. Here, we show that Katnal1 is not required for normal female fertility, but that deletion of Katna1 causes a 50% decrease in fertility. Further investigation in Katna1-/- oocytes revealed no effect on MI spindle morphology but a significant effect on the morphology of MII spindles. This was accompanied by a decreased rate of fertilisation. Resultant Katna1+/- heterozygous embryos that reached the 2-cell stage developed at normal rates to the blastocyst stage. Diploid homozygous parthenotes derived from Katna1-/- oocytes revealed a reduced rate of blastocyst formation, decreased cell number and increased nuclear size. The ability of the paternal allele to rescue preimplantation development suggests the origin of the decrease in the fertility of conditional Katna1-/- mice lies in abnormalities arising in the egg to embryo transition prior to embryonic genome activation.

developmental biology↗

bioRxiv2023

TRIB1 modulates transcriptional programming in breast cancer cells to regulate cell proliferation

The pseudokinase Tribbles Homolog 1 (TRIB1) is a known driver of tumorigenesis in acute myeloid leukemia and is encoded upstream of the oncogene MYC at the 8q24 locus. We observed that TRIB1/MYC co-amplification is associated with decreased relapse-free and overall survival in breast cancer patients, but the role of TRIB1 in this disease has not been well characterized. TRIB1 knockdown in multiple breast cancer cell lines inhibited cell proliferation and suppressed MYC expression, implicating TRIB1 in breast cancer cell proliferation. Transcriptomic and cell cycle analysis revealed cell cycle regulation as the likely mechanism through which TRIB1 influences breast cancer cell proliferation. TRIB1 knockdown also resulted in significant changes in both estrogen receptor (ER) and {beta}-catenin associated transcription. Interrogating the TRIB1 interactome in breast cancer cells by qPLEX-RIME reinforced the known association between TRIB1 and ubiquitination, while revealing a range of previously undescribed TRIB1 associated factors. Further analysis of the association between TRIB1, {beta}-catenin and FERMT2 suggests TRIB1 may regulate {beta}-catenin activity by controlling the levels of both {beta}-catenin, and its co-factor FERMT2. Together, these results suggest that coregulation of {beta}-catenin and ER-driven transcription by TRIB1, facilitates regulation of MYC expression and breast cancer cell proliferation. SignificanceThe pseudokinase TRIB1 is frequently co-amplified in breast cancers with the potent oncogene MYC, although the functional consequences of this event are not well understood. This study demonstrates TRIB1 is a regulator of cell cycle progression and MYC expression in breast cancer cells. It also profiles TRIB1-associated proteins in breast cancer cells, demonstrating conservation of TRIB1s canonical interaction with COP1 and reveals associations with members of the wider ubiquitination machinery, a range of transcriptional regulators and chromatin remodelers. The data presented provide insight into the function of TRIB1 in breast cancer and the role of TRIB1 in transcriptional regulation.

cancer biology↗

bioRxiv2023

EstroGene database reveals diverse temporal, context-dependent and directional estrogen receptor regulomes in breast cancer

As one of the most successful cancer therapeutic targets, estrogen receptor- (ER/ESR1) has been extensively studied in decade-long. Sequencing technological advances have enabled genome-wide analysis of ER action. However, reproducibility is limited by different experimental design. Here, we established the EstroGene database through centralizing 246 experiments from 136 transcriptomic, cistromic and epigenetic datasets focusing on estradiol-treated ER activation across 19 breast cancer cell lines. We generated a user-friendly browser (https://estrogene.org/) for data visualization and gene inquiry under user-defined experimental conditions and statistical thresholds. Notably, documentation-based meta-analysis revealed a considerable lack of experimental details. Comparison of independent RNA-seq or ER ChIP-seq data with the same design showed large variability and only strong effects could be consistently detected. We defined temporal estrogen response metasignatures and showed the association with specific transcriptional factors, chromatin accessibility and ER heterogeneity. Unexpectedly, harmonizing 146 transcriptomic analyses uncovered a subset of E2-bidirectionally regulated genes, which linked to immune surveillance in the clinical setting. Furthermore, we defined context dependent E2 response programs in MCF7 and T47D cell lines, the two most frequently used models in the field. Collectively, the EstroGene database provides an informative resource to the cancer research community and reveals a diverse mode of ER signaling.

cancer biology↗

bioRxiv2022

Transient Polycomb activity represses developmental genes in growing oocytes.

BackgroundNon-genetic disease inheritance and offspring phenotype is substantially influenced by germline epigenetic programming, including genomic imprinting. Loss of Polycomb Repressive Complex 2 (PRC2) function in oocytes causes non-genetically inherited effects on offspring, including embryonic growth restriction followed by post-natal offspring overgrowth. While PRC2 dependent non-canonical imprinting is likely to contribute, less is known about germline epigenetic programming of non-imprinted genes during oocyte growth. In addition, de novo germline mutations in genes encoding PRC2 lead to overgrowth syndromes in human patients, but the extent to which PRC2 activity is conserved in human oocytes is poorly understood. ResultsIn this study we identify a discrete period of early oocyte growth during which PRC2 is expressed in mouse growing oocytes. Deletion of Eed during this window led to the de-repression of 343 genes. A high proportion of these were developmental regulators, and the vast majority were not imprinted genes. Many of the de-repressed genes were also marked by the PRC2-dependent epigenetic modification histone 3 lysine 27 trimethylation (H3K27me3) in primary-secondary mouse oocytes, at a time concurrent with PRC2 expression. In addition, we found H3K27me3 was also enriched on many of these genes by the germinal vesicle (GV) stage in human oocytes, strongly indicating that this PRC2 function is conserved in the human germline. However, while the 343 genes were de-repressed in mouse oocytes lacking EED, they were not de-repressed in pre-implantation embryos and lost H3K27me3 during pre-implantation development. This implies that H3K27me3 is a transient feature that represses a wide range of genes in oocytes. ConclusionsTogether, these data indicate that EED has spatially and temporally distinct functions in the female germline to repress a wide range of developmentally important genes, and that this activity is conserved in the mouse and human germlines.

developmental biology↗

bioRxiv2022

Di-valent siRNA Mediated Silencing of MSH3 Blocks Somatic Repeat Expansion in Mouse Models of Huntington's Disease

Huntingtons Disease (HD) is a severe neurodegenerative disorder caused by expansion of the CAG trinucleotide repeat tract in the huntingtin gene. Inheritance of expanded CAG repeats is needed for HD manifestation, but further somatic expansion of the repeat tract in non-dividing cells, particularly striatal neurons, hastens disease onset. Called somatic repeat expansion, this process is mediated by the mismatch repair (MMR) pathway. Among MMR components identified as modifiers of HD onset, MutS Homolog 3 (MSH3) has emerged as a potentially safe and effective target for therapeutic intervention. Here, we identify fully chemically modified short interfering RNA (siRNA) that robustly silence MSH3 in vitro and in vivo. When synthesized in a di-valent scaffold, siRNA-mediated silencing of MSH3 effectively blocked CAG repeat expansion in striatum of two HD mouse models without impacting tumor-associated microsatellite instability. Our findings establish a novel paradigm for treating patients with HD and other repeat expansion diseases. One Sentence SummarySilencing MSH3 in the CNS of two models of Huntingtons disease using di-valent siRNA blocks disease-accelerating somatic expansion of CAG repeats.

molecular biology↗

bioRxiv2021

Analysis of Rod/Cone Gap Junctions from the Reconstruction of Mouse Photoreceptor Terminals

Using serial blockface-scanning electron microscopy (SBF-SEM) and focused ion beam-scanning electron microscopy (FIB-SEM), combined with confocal microscopy for the gap junction protein Cx36, we reconstructed mouse photoreceptor terminals and located the gap junctions between them. An exuberant spray of fine telodendria extends from each cone pedicle (including blue cones) to contact 40-50 nearby rod spherules where Cx36 clusters were located, close to the mouth of the synaptic opening. There were approximately 50 Cx36 clusters per cone pedicle and 2-3 per rod spherule. We were unable to detect rod/rod or cone/cone coupling. Thus, rod/cone coupling accounts for nearly all gap junctions between photoreceptors. Our calculations suggest a mean of 82 Cx36 channels between a rod/cone pair of which 25% are open at rest. Rod/cone gap junctions are modulated by dopamine. Comparing our morphological calculations of maximum coupling to previous physiological results suggests that dopamine antagonists can drive rod/cone gap junctions to a surprisingly high open probability, approaching 100%.

neuroscience↗