Single cell transcriptomics reveals early photoreceptor states, cell-specific transcript isoforms, and cancer-predisposing features.

Human cone photoreceptors differ from rods and serve as the retinoblastoma cell-of-origin. Here, we used deep full-length single-cell RNA-sequencing to distinguish post-mitotic cone and rod developmental states and cone-specific features that contribute to retinoblastomagenesis. The analyses revealed early post-mitotic cone- and rod-directed populations characterized by higher THRB or NRL regulon activities, an immature photoreceptor precursor population with concurrent cone and rod gene and regulon expression, and distinct early and late cone and rod maturation states distinguished by maturation-associated declines in RAX regulon activity. Unexpectedly, both L/M cone and rod precursors co-expressed NRL and THRB RNAs, yet they differentially expressed functionally antagonistic NRL isoforms and prematurely terminated THRB transcripts. Early L/M cone precursors exhibited successive expression of lncRNAs along with MYCN, which composed the seventh most L/M-cone-specific regulon, and SYK, which contributed to the early cone precursors' proliferative response to RB1 loss. These findings reveal previously unrecognized photoreceptor precursor states and a role for early cone-precursor-intrinsic SYK expression in retinoblastoma initiation.

Initiation of retinopathy of prematurity screening examinations in extremely premature infants.

PURPOSE: To determine whether extremely premature infants require screening for retinopathy of prematurity (ROP) if <31 weeks' postmenstrual age (PMA). METHODS: The medical records of infants born in community hospital settings at <31 weeks' gestational age (GA) were reviewed retrospectively. Prevalence and progression of ROP in infants born at <24 weeks' GA were compared with infants born at 24-30 weeks' GA. RESULTS: A total of 2,061 records were reviewed: 1,969 infants were born at 24-30 weeks' GA; 92, at <24 weeks. Infants born <24 weeks' GA were more likely to develop pre-plus and plus disease or require treatment than infants born 24-30 weeks' GA (P < 0.0001) and did so earlier (P = 0.0001). Eight infants developed pre-plus or greater ROP <31 weeks' PMA; 6 were born <24 weeks' GA. Three infants developed plus disease or required treatment <31 weeks' PMA, the earliest at 27 and 3/7 weeks. CONCLUSIONS: Clinicians should consider initiating ROP screening examinations before 31 weeks' PMA, particularly for infants born <24 weeks' GA and those with lower birth weights.

Non-canonical Wnt pathway expression in the developing mouse and human retina.

The non-canonical Wnt pathway is an evolutionarily conserved pathway essential for tissue patterning and development across species and tissues. In mammals, this pathway plays a role in neuronal migration, dendritogenesis, axon growth, and synapse formation. However, its role in development and synaptogenesis of the human retina remains less established. In order to address this knowledge gap, we analyzed publicly available single-cell RNA sequencing (scRNAseq) datasets for mouse retina, human retina, and human retinal organoids over multiple developmental time points during outer retinal maturation. We identified ligands, receptors, and mediator genes with a putative role in retinal development, including those with novel or species-specific expression, and validated this expression using fluorescence in situ hybridization (FISH). By quantifying outer nuclear layer (ONL) versus inner nuclear layer (INL) expression, we provide evidence for the differential expression of certain non-canonical Wnt signaling components in the developing mouse and human retina during outer plexiform layer (OPL) development. Importantly, we identified distinct expression patterns of mouse and human FZD3 and WNT10A, as well as previously undescribed expression, such as for mouse Wnt2b in Chat+ starburst amacrine cells. Human retinal organoids largely recapitulated the human non-canonical Wnt pathway expression. Together, this work provides the basis for further study of non-canonical Wnt signaling in mouse and human retinal development and synaptogenesis.