Retinal Circuit Development & Genetics

National Eye Institute

Investigators

Linked publications, trials & patents

Abstract

This year I have focused on completing several previously initiated studies. 1) Development of RGC types. Our study regarding the genetic interaction between the Ret Neurotrophin receptor and the transcription factor Brn3a has been revised and is under peer review. We had uncovered that mosaic gene dosage manipulation of the transcription factor Brn3a/Pou4f1 in neurotrophic receptor Ret heterozygote RGCs results in altered cell fate decisions and/or morphological dendritic defects. Specific RGC types are lost if Brn3a is ablated during embryogenesis and only mildly affected by postnatal Brn3a ablation. Sparse but not complete Brn3a heterozygosity combined with complete Ret heterozygosity has striking effects on RGC type distribution. Brn3a only mildly modulates Ret transcription, while Ret knockouts exhibit normal Brn3a and Brn3b expression. We now found that Brn3a loss of function significantly affects distribution of Ret co-receptors GFR1-3, and neurotrophin receptors TrkA and TrkC in RGCs. Based on these observations, we propose that Brn3a and Ret converge onto developmental pathways that control RGC type specification, potentially through a competitive mechanism requiring signaling from the surrounding tissue. (Muzyka 2020, BioRxiv preprint, manuscript resubmitted, in revision). Our new Brn3c-Cre allele is fully characterized and paper is published (Parmhans 2021). Besides a complete anatomic and physiologic description of Brn3c+ RGCs, we also characterized a very interesting new RGC projection to the Rheticular Thalamic Nucleus, a relay/feedback visual nucleus that was not known to receive retinal input. We also surveyed the brain nuclei that express Brn3c. In addition we have generated novel genetic tools for further novel or recently described RGC markers that are regulated by Brn3a. This year, two of our collaborations with regard to transcriptional regulation of RGC type specification were published. In a collaboration with the retina circuits groups of Drs. Chen, Massey and Mao in Houston, we helped characterize Tbr2+ RGCs. A large subset of these are ipRGCs, expressing Melanopsin and projecting to Suprachiasmatic Nucleus and Olivary pretectal nucleus. However, a second subset co-express Brn3a and have small dense dendritic arbors. Finally, some widefield amacrine cells are also Tbr2 positive (CK Chen et al 2021). In addition, a multi-group collaboration lead by Justin Brodie-Kommit in Dr. Samer Hattars group published the interesting observation that Atoh7, a master regulator of RGC cell fate is dispensible for expression of Brn3a and Isl1, and to a lesser degree Brn3b, when apoptosis is inhibited by blocking the Bax pathway. Indeed a population of RGC-like cells survives in Atoh7KO/KO Bax KO/KO mutant retinas, however their axons are unable to navigate the optic nerve and remain trapped in the retina (Brodie-Kommit 2021). Our characterization of molecular interactions for Copine4, and implications for its function in RGC development is now submitted and published on BioRxiv. We found a rather broad set of interactors, by mass spectrometry of Copine4 interactors pulled down from retina lysates and yeast two-hybrid screening, indicating that Copine4 could be involved in mediating mebrane cytoskeleton interactions in both cell membrane protrusions and intracellular vesicular traffic. (Goel 2021, BioRxiv). 2) RGC function Our study regarding visually evoked defense responses in mouse lines missing specific RGC subpopulation is now published (Lees 2020). We discovered that retinal or global loss of Brn3b selectively ablates the fleeing response to looming stimuli while leaving the freeze response intact. In contrast, freezing responses to sweeping stimuli are significantly affected. Genetic manipulations removing three RGC subpopulations (Brn3a+ betta RGCs, Opn4+Brn3b+, and Brn3c+Brn3b+ RGCs) result in milder phenocopies of Brn3b knockout response deficits. These findings show that flight and freezing responses to distinct visual cues are mediated by circuits that can already be separated at the level of the retina, potentially by enlisting dedicated RGC types. 3) Transcriptional control of other somatosensory projection neurons. We had previously reported that Brn3c is expressed in subclasses of nociceptors. A group led by J. de Nooij, now characterized, with our assistance, the existence of a population of Brn3c+ proprioceptors. This long term collaborations is now published (Oliver 2021). 4) This year we made great progress in understanding the role of RGC-32, a cell cycle regulator activated in response to inflammatory signals in a variety of cells. In collaboration with Dr. Rus, with which I had cloned the gene some 23 years ago, we now showed that RGC-32 modulates astrocyte responses to TGF-betta, with a direct impact on the outcome of EAE, a mouse model for multiple sclerosis. Two papers published (Tatomir 2021a, b). We have initiated the characterization of RGC-32 in autoimmune ophthalmologic disorders. The papers that are already published are in the regular bibliography, while Preprints, or accepted papers not captured in the report, are indicated in the list below. 1: Muzyka, VV, Badea TC. Genetic Interplay Between Transcription Factor Pou4f1/Brn3a and Neurotrophin Receptor Ret In Retinal Ganglion Cell Type Specification. bioRxiv , no. (2020): 2020.03.23.004242. doi: 10.1101/2020.03.23.004242. 2: Liu S, Aldinger KA, Cheng CV, Kiyama T, Dave M, McNamara HK, Caraffi SG, Ivanovski I, Errichiello E, Zweier C, Zuffardi O, Schneider M, Papavasiliou AS, Perry MS, Cho MT, Weber A, Swale A, Badea TC, Mao C-A, Garavelli L, Dobyns WB, and Reinberg D. (2021) NRF1 Association with AUTS2-Polycomb Mediates Specific Gene Activation in the Brain. bioRxiv , (2021): doi: 10.1101/2021.03.30.437620 3: Goel M, Aponte AM, Wistow G, Badea TC. (2021) Molecular studies into Copine-4 function in Retinal Ganglion Cells, bioRxiv , under Review. 4: Tatomir A, Beltrand A, Nguyen V, Courneya, JP, Boodhoo D, Cudrici C, Muresanu DF, Rus V, Badea TC, Rus H (2021) RGC-32 acts as a hub to regulate the transcriptomic changes associated with astrocyte development and reactive astrocytosis. Frontiers in Immunology Aug 01, doi: 10.3389/fimmu.2021.705308