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1. NUDC is critical for rod photoreceptor function, maintenance, and survival

   https://doi.org/10.1096/fj.202301641RR  

   Garner, Mary Anne; Hubbard, Meredith G; Boitet, Evan R; Hubbard, Seth T; Gade, Anushree; Ying, Guoxin; Jones, Bryan W; Baehr, Wolfgang; Gross, Alecia K (March 2024, The FASEB Journal)

   Abstract NUDC (nucleardistribution proteinC) is a mitotic protein involved in nuclear migration and cytokinesis across species. Considered a cytoplasmic dynein (henceforth dynein) cofactor, NUDC was shown to associate with the dynein motor complex during neuronal migration. NUDC is also expressed in postmitotic vertebrate rod photoreceptors where its function is unknown. Here, we examined the role of NUDC in postmitotic rod photoreceptors by studying the consequences of a conditional NUDC knockout in mouse rods (rNudC^−/−). Loss of NUDC in rods led to complete photoreceptor cell death at 6 weeks of age. By 3 weeks of age, rNudC^−/−function was diminished, and rhodopsin and mitochondria were mislocalized, consistent with dynein inhibition. Levels of outer segment proteins were reduced, but LIS1 (lissencephaly protein 1), a well‐characterized dynein cofactor, was unaffected. Transmission electron microscopy revealed ultrastructural defects within the rods of rNudC^−/−by 3 weeks of age. We investigated whether NUDC interacts with the actin modulator cofilin 1 (CFL1) and found that in rods, CFL1 is localized in close proximity to NUDC. In addition to its potential role in dynein trafficking within rods, loss of NUDC also resulted in increased levels of phosphorylated CFL1 (pCFL1), which would purportedly prevent depolymerization of actin. The absence of NUDC also induced an inflammatory response in Müller glia and microglia across the neural retina by 3 weeks of age. Taken together, our data illustrate the critical role of NUDC in actin cytoskeletal maintenance and dynein‐mediated protein trafficking in a postmitotic rod photoreceptor. 

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2. Proximity labeling reveals interactions necessary to maintain the distinct apical domains of Drosophila photoreceptors

   https://doi.org/10.1242/jcs.262223  

   Sastry, Lalitha; Rylee, Johnathan; Mahato, Simpla; Zelhof, Andrew C (December 2024, Journal of Cell Science)

   ABSTRACT Specialized membrane and cortical protein regions are common features of cells and are utilized to isolate differential cellular functions. In Drosophila photoreceptors, the apical membrane domain is defined by two distinct morphological membranes: the rhabdomere microvilli and the stalk membrane. To define the apical cortical protein complexes, we performed proximity labeling screens utilizing the rhabdomeric-specific protein PIP82 as bait. We found that the PIP82 interactome is enriched in actin-binding and cytoskeleton proteins, as well as proteins for cellular trafficking. Analysis of one target, Bifocal, with PIP82 revealed two independent pathways for localization to the rhabdomeric membrane and an additional mechanism of crosstalk between the protein complexes of the rhabdomeric and stalk membranes. The loss of Bifocal, and enhancement in the PIP82, bifocal double mutant, resulted in the additional distribution of Crumbs, an apical stalk membrane protein, to the lateral basal photoreceptor membrane. This phenotype was recapitulated by the knockdown of the catalytic subunit of Protein phosphatase 1, a known interactor with Bifocal. Taken together, these results expand our understanding of the molecular mechanisms underlying the generation of the two distinct photoreceptor apical domains. 

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3. Neural Circuit Revision in Retinal Remodeling, A Pathoconnectomics Approach

   https://doi.org/10.1101/2024.02.14.580149  

   Pfeiffer, Rebecca L; Dahal, Jeebika; Sigulinsky, Crystal L; Anderson, James R; Barrera, Isabel A; Yang, Jia-Hui; Haddadin, Olivia; Houser, Alexis; Garcia, Jessica C; Jones, Bryan W (February 2024, bioRxiv)

   Abstract The Aii glycinergic amacrine cell (Aii) plays a central role in bridging rod pathways with cone pathways, enabling an increased dynamic range of vision from scotopic to photopic ranges. The Aii integrates scotopic signals via chemical synapses from rod bipolar cells (RodBCs) onto the arboreal processes of Aii ACs, injecting signals into ON-cone bipolar cells (CBbs) via gap junctions with Aiis on the arboreal processes and the waist of the Aii ACs. The CBbs then carry this information to ON and OFF ganglion cell classes. In addition, the Aii is involved in the surround inhibition of OFF cone bipolar cells (CBas) through glycinergic chemical synapses from Aii ACs onto CBas. We have previously shown changes in RodBC connectivity as a consequence of rod photoreceptor degeneration in a pathoconnectome of early retinal degeneration: RPC1. Here, we evaluated the impact of rod photoreceptor degeneration on the connectivity of the Aii to determine the impacts of photoreceptor degeneration on the downstream network of the neural retina and its suitability for integrating therapeutic interventions as rod photoreceptors are lost. Previously, we reported that in early retinal degeneration, prior to photoreceptor cell loss, Rod BCs make pathological gap junctions with Aiis. Here, we further characterize this altered connectivity and additional shifts in both the excitatory drive and gap junctional coupling of Aiis in retinal degeneration, along with discussion of the broader impact of altered connectivity networks. New findings reported here demonstrate that Aiis make additional gap junctions with CBas increasing the number of BC classes that make pathological gap junctional connectivity with Aiis in degenerating retina. In this study, we also report that the Aii, a tertiary retinal neuron alters their synaptic contacts early in photoreceptor degeneration, indicating that rewiring occurs in more distant members of the retinal network earlier in degeneration than was previously predicted. This rewiring impacts retinal processing, presumably acuity, and ultimately its ability to support therapeutics designed to restore image-forming vision. Finally, these Aii alterations may be the cellular network level finding that explains one of the first clinical complaints from human patients with retinal degenerative disease, an inability to adapt back and forth from photopic to scotopic conditions. 

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4. CCSer2 gates dynein activity at the cell periphery

   https://doi.org/10.1083/jcb.202406153  

   Zang, Juliana L; Gibson, Daytan; Zheng, Ann-Marie; Shi, Wanjing; Gillies, John P; Stein, Chris; Drerup, Catherine M; DeSantis, Morgan E (June 2025, Journal of Cell Biology)

   Cytoplasmic dynein-1 (dynein) is a microtubule-associated, minus end–directed motor that traffics hundreds of different cargos. Dynein must discriminate between cargos and traffic them at the appropriate time from the correct cellular region. How dynein’s trafficking activity is regulated in time or cellular space remains poorly understood. Here, we identify CCSer2 as the first known protein to gate dynein activity in the spatial dimension. CCSer2 promotes the migration of developing zebrafish primordium cells, macrophages, and cultured human cells by facilitating the trafficking of cargos that are acted on by peripherally localized dynein. Our data suggest that CCSer2 disfavors the interaction between dynein and its regulator Ndel1 at the cell edge, resulting in localized dynein activation. These findings support a model where the spatial specificity of dynein is achieved by the localization of proteins that trigger Ndel1’s release from dynein. We propose that CCSer2 defines a broader class of proteins that activate dynein in distinct microenvironments via regulating Ndel1–dynein interaction. 

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5. Prostaglandins limit nuclear actin to control nucleolar function during oogenesis

   https://doi.org/10.3389/fcell.2023.1072456  

   Talbot, Danielle E.; Vormezeele, Bailey J.; Kimble, Garrett C.; Wineland, Dylane M.; Kelpsch, Daniel J.; Giedt, Michelle S.; Tootle, Tina L. (February 2023, Frontiers in Cell and Developmental Biology)

   Prostaglandins (PGs), locally acting lipid signals, regulate female reproduction, including oocyte development. However, the cellular mechanisms of PG action remain largely unknown. One cellular target of PG signaling is the nucleolus. Indeed, across organisms, loss of PGs results in misshapen nucleoli, and changes in nucleolar morphology are indicative of altered nucleolar function. A key role of the nucleolus is to transcribe ribosomal RNA (rRNA) to drive ribosomal biogenesis. Here we take advantage of the robust, in vivo system of Drosophila oogenesis to define the roles and downstream mechanisms whereby PGs regulate the nucleolus. We find that the altered nucleolar morphology due to PG loss is not due to reduced rRNA transcription. Instead, loss of PGs results in increased rRNA transcription and overall protein translation. PGs modulate these nucleolar functions by tightly regulating nuclear actin, which is enriched in the nucleolus. Specifically, we find that loss of PGs results in both increased nucleolar actin and changes in its form. Increasing nuclear actin, by either genetic loss of PG signaling or overexpression of nuclear targeted actin (NLS-actin), results in a round nucleolar morphology. Further, loss of PGs, overexpression of NLS-actin or loss of Exportin 6, all manipulations that increase nuclear actin levels, results in increased RNAPI-dependent transcription. Together these data reveal PGs carefully balance the level and forms of nuclear actin to control the level of nucleolar activity required for producing fertilization competent oocytes. 

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