Biology subjects

Pannullo, N.

Publications and source records attributed to Pannullo, N..

5 recordsLinked to original sources

bioRxiv2026

Sox8 and Sox9 regulate differentiation and nuclear positioning of retinal Muller glia.

Temporal patterning of retinal progenitor cells governs the sequential generation of retinal cell types, with gliogenesis occurring late in development. Sox8 and Sox9, members of the SoxE transcription factor family, are highly expressed in late-stage retinal progenitor cells and mature Muller glia, yet their functional roles remain incompletely defined. Here we employed gain- and loss-of-function approaches, single-cell multiomic profiling, and injury models to investigate Sox8/9 function. Overexpression of SOX8 and/or SOX9 in early-stage retinal progenitor cells suppressed early-born cell fates and promoted photoreceptor generation, consistent with a role in late-stage temporal identity. Conversely, conditional deletion of Sox8 and/or Sox9 in late-stage progenitors did not impair Muller glia specification, but caused radial displacement of Muller glia nuclei into the outer retina and modest changes in glial gene expression. Loss of Sox8/9 in mature Muller glia modestly increased proliferation post-injury without inducing neurogenic competence. These findings suggest that Sox8/9 are dispensable for gliogenesis and repression of neurogenic competence, but are essential for proper laminar positioning and maturation of retinal Muller glia.

neuroscience↗

bioRxiv2025

Overexpression of Meis factors in late-stage retinal progenitors yields complex effects on temporal patterning and neurogenesis.

The vertebrate retina serves as a model for studying neurogenesis and cell fate specification, with retinal progenitor cells following a tightly regulated temporal sequence to generate distinct cell types. Meis1 and Meis2 are transcription factors implicated in early retinal development, but their role in late-stage RPCs remains poorly understood. Here, we investigate whether Meis1 and Meis2 overexpression in postnatal mouse RPCs can alter temporal identity and induce early-born cell types. Using electroporation and single-cell RNA sequencing, we find that while these factors modestly upregulate early-stage gene regulatory network components, they do not repress late-stage transcription factors or induce early-born retinal cells. Meis1 overexpression reduces proliferation and inhibits neurogenesis, whereas Meis2 overexpression accelerates neurogenic progression without altering fate commitment. Our findings suggest that overexpression of Meis1 and Meis2 modulate largely non-overlapping aspects of temporal identity and neurogenic competence but are insufficient to fully reprogram late-stage progenitors. These results have implications for regenerative strategies aimed at reprogramming retinal cells for therapeutic purposes.

neuroscience↗

bioRxiv2025

Heterochronic transcription factor expression drives cone-dominant retina development in 13-lined ground squirrels.

Evolutionary adaptation to diurnal vision in ground squirrels has led to the development of a cone-dominant retina, in stark contrast to the rod-dominant retinas of most mammals. The molecular mechanisms driving this shift remain largely unexplored. Here, we perform single-cell RNA sequencing (scRNA-Seq) and chromatin accessibility profiling (scATAC-Seq) across developmental retinal neurogenesis in the 13-lined ground squirrel (13LGS) to uncover the regulatory basis of this adaptation. We find that 13LGS cone photoreceptors arise not only from early-stage neurogenic progenitors, as seen in rod-dominant species like mice, but also from late-stage neurogenic progenitors. This extended period of cone generation is driven by a heterochronic shift in transcription factor expression, with cone-promoting factors such as Onecut2, Pou2f1, and Zic3 remaining active in late-stage progenitors, and factors that promote cone differentiation such as Thrb, Rxrg, and Mef2c expressed precociously in late-stage neurogenic progenitors. Functional analyses reveal that Zic3 and Mef2c are sufficient to promote cone and repress rod photoreceptor-specific gene expression, and act through species-specific regulatory elements that drive their expression in late-stage progenitors. These results demonstrate that modifications to gene regulatory networks underlie the development of cone-dominant retinas, and provide insight into mechanisms of sensory adaptation and potential strategies for cone photoreceptor regeneration in vision disorders.

neuroscience↗

bioRxiv2022

Ectopic insert-dependent neuronal expression of GFAP promoter-driven AAV constructs in adult mouse retina.

Direct reprogramming of retinal Muller glia is a promising avenue for replacing photoreceptors and retinal ganglion cells lost to retinal dystrophies. However, questions have recently been raised about the accuracy of studies claiming efficient glia-to-neuron reprogramming in retina that were conducted using GFAP mini promoter-driven adeno-associated virus (AAV) vectors. In this study, we have addressed these questions using GFAP mini promoter-driven AAV constructs to simultaneously overexpress the mCherry reporter and candidate transcription factors predicted to induce glia-to-neuron conversion, in combination with prospective genetic labeling of retinal Muller glia using inducible Cre-dependent GFP reporters. We find that, while control GFAP-mCherry constructs express faithfully in Muller glia, 5 out of 7 transcription factor overexpression constructs tested are predominantly expressed in amacrine and retinal ganglion cells. However, genetic cell lineage analysis shows no evidence for glia-to-neuron conversion. These findings demonstrate strong insert-dependent effects on AAV-based GFAP mini promoter specificity that preclude its use in inferring cell lineage relationships when studying glia-to-neuron conversion in retina.

neuroscience↗

bioRxiv2021

Ptbp1 deletion does not induce glia-to-neuron conversion in adult mouse retina and brain.

Direct reprogramming of glia into neurons is a potentially promising approach for the replacement of neurons lost to injury or neurodegenerative disorders. Knockdown of the polypyrimidine tract-binding protein Ptbp1 has been recently reported to induce efficient conversion of retinal Muller glia and brain astrocytes into functional neurons. However, genetic analysis of Ptbp1 function in adult glia has not been conducted. Here, we use a combination of genetic lineage tracing, scRNA-Seq, and electrophysiological analysis to show that specific deletion of Ptbp1 in adult retinal Muller glia and brain astrocytes does not lead to any detectable level of glia-to-neuron conversion. Only a few changes in gene expression are observed in glia following Ptbp1 deletion, and glial identity is maintained. These findings highlight the importance of using genetic manipulation and lineage tracing methods in studying cell type conversion.

neuroscience↗