Molecular codes for cell type specification in Brn3 retinal ganglion cells

Abstract

Visual information is conveyed from the eye to the brain by distinct types of retinal ganglion cells (RGCs). It is largely unknown how RGCs acquire their defining morphological and physiological features and connect to upstream and downstream synaptic partners. The three Brn3/Pou4f transcription factors (TFs) participate in a combinatorial code for RGC type specification, but their exact molecular roles are still unclear. We use deep sequencing to define () transcriptomes of Brn3a- and/or Brn3b-positive RGCs, () Brn3a- and/or Brn3b-dependent RGC transcripts, and () transcriptomes of retinorecipient areas of the brain at developmental stages relevant for axon guidance, dendrite formation, and synaptogenesis. We reveal a combinatorial code of TFs, cell surface molecules, and determinants of neuronal morphology that is differentially expressed in specific RGC populations and selectively regulated by Brn3a and/or Brn3b. This comprehensive molecular code provides a basis for understanding neuronal cell type specification in RGCs.

Essential Roles of Tbr1 in the Formation and Maintenance of the Orientation-Selective J-RGCs and a Group of OFF-Sustained RGCs in Mouse

“…Intriguingly, we also detected the expression of Tbr1 , a T-brain subfamily gene closely related to Tbr2 , in mouse retinas (Mao et al, 2008, Naiche et al, 2005). A recent paper confirmed the expression of Tbr1 in RGCs (Sajgo et al, 2017). To trace the spatiotemporal expression of Tbr1 during retinogenesis and to study its functions during retinal development, we generated 2 knock-in mouse lines, Tbr1 TauGFP-IRESCreERT2 and Tbr1 mycflox alleles.…”

Differential expression and subcellular localization of Copines in mouse retina

“…To study and compare the expression profile of Copines both embryonically and postnatally, we extracted transcript and gene level expression data for the nine members of the Copine family from our previously reported RNA sequencing data for RGCs, retina and the retino recipient brain areas (Sajgo et al, ; Figure and Supporting Information Figure S1). Briefly, in our previous work, we had purified by immunomagnetic isolation genetically labeled RGCs expressing either Brn3a or Brn3b (Brn3a AP and Brn3b AP RGCs), and compared their RNA expression profile with expression profiles generated from age‐matched (postnatal day 3, P3) whole retina or retinorecipient brain areas.…”

“…Several Copine family members appeared as differentially regulated and/or expressed targets, and preliminary results in tissue culture showed a potential role for Cpne4 in cellular morphology and process extension. For details of the methods used for RNA sequencing, please refer to Sajgo et al ().…”

“…However, the molecules that link the combinatorial Brn3 expression to the activity‐dependent and/or a retrograde signaling pathway‐dependent pruning of dendrites are not known. Brn3a and 3b regulate the expression of several proteins in the mouse retina (Sajgo et al, ). Whether these molecules have a role in dendritic stratification, synapse formation, and axon targeting to the brain by themselves or in conjunction with combinatorial Brn3 expression remains to be explored.…”

Culture Systems of Dissociated Mouse and Human Pluripotent Stem Cell–Derived Retinal Ganglion Cells Purified by Two-Step Immunopanning

“…1 Because the dysfunction and impairment of RGCs in syndromes such as glaucoma and optic neuropathy lead to vision loss, the pathology and etiology of RGC-linked diseases have been investigated widely. For example, glaucoma is the second most common cause of blindness worldwide 2,3 and is characterized by RGC death caused by axonal degeneration.…”