Embryonic Hyperglycemia Delays the Development of Retinal Synapses in a Zebrafish Model

Abstract

Embryonic hyperglycemia negatively impacts retinal development, leading to abnormal visual behavior, altered timing of retinal progenitor differentiation, decreased numbers of retinal ganglion cells and Müller glia, and vascular leakage. Because synaptic disorganization is a prominent feature of many neurological diseases, the goal of the current work was to study the potential impact of hyperglycemia on retinal ribbon synapses during embryonic development. Our approach utilized reverse transcription quantitative PCR (RT-qPCR) and immunofluorescence labeling to compare the transcription of synaptic proteins and their localization in hyperglycemic zebrafish embryos, respectively. Our data revealed that the maturity of synaptic ribbons was compromised in hyperglycemic zebrafish larvae, where altered ribeye expression coincided with the delay in establishing retinal ribbon synapses and an increase in the immature synaptic ribbons. Our results suggested that embryonic hyperglycemia disrupts retinal synapses by altering the development of the synaptic ribbon, which can lead to visual defects. Future studies using zebrafish models of hyperglycemia will allow us to study the underlying mechanisms of retinal synapse development.

The Effects of Aging on Rod Bipolar Cell Ribbon Synapses

“…Based on previous studies, these two subtypes likely comprise (1) the B ON s6L or RRod type of ON-bipolar cells that morphologically resemble the mixed-input (b1 or Mb; (hereafter we call Mb1)) ON-bipolar cells of other teleost fish [41] and (2) the B ON s6 type that contact the cones (named cone-ON) [41,44,45]. Unlike the hexagonal shape of the bipolar cell soma we found in 5 dpf zebrafish larvae [43], we observed a subset of PKCα-labeled bipolar cells from MA and OA zebrafish that exhibited the pear-shaped morphology described for adult Mb1 rod bipolar cells [46]. As expected, these appear to connect to the larger terminals of the Mb1type bipolar cells (Figure 3A, top panel, labeled with white # symbols).…”

“…To determine whether the changes in the number and size of synaptic ribbons observed in single Mb1 bipolar cells from OA zebrafish alter the morphology of the retinal inner plexiform layer (IPL), we double immunostained retinal cryosections from MA and OA zebrafish with fluorescently labeled antibodies specific for ribeye a and for the rod bipolar cell marker protein kinase C (PKCα), as described [41][42][43]. The patterns of PKCα staining in the retinas of MA and OA zebrafish are shown in Figure 3A,B, respectively.…”

The effects of aging on rod bipolar cell ribbon synapses

“…Based on previous studies, these two subtypes likely comprise 1) the BON s6L or RRod type of ON-bipolar cells that morphologically resemble the mixed-input (b1 or Mb; (hereafter we call Mb1) ON-bipolar cells of other teleost fish [41] and 2) the BON s6 type that contact the cones (named cone-ON) [41, 44, 45]. Unlike the hexagonal shape of the bipolar cell soma, we found in 5 dpf zebrafish larvae [43], we observed a subset of PKCα-labeled bipolar cells from MA and OA zebrafish that exhibited the pear-shaped morphology described for adult Mb1 rod bipolar cells [46]. As expected, these appear to connect to the larger terminals of the Mb1-type bipolar cells ( Fig.…”

“…These findings suggest that the bipolar cell terminals of OA fish may compensate for the decreased number of ribbons by increasing the lengths of the individual ribbons. To determine whether the changes in the number and size of synaptic ribbons observed in single Mb1 bipolar cells from OA zebrafish alter the morphology of the retinal inner plexiform layer (IPL), we double immunostained retinal cryosections from MA and OA zebrafish with fluorescently labeled antibodies specific for Ribeye a and for the rod bipolar cell marker protein kinase C (PKCα), as described [41][42][43]. The pa`erns of PKCα staining in the retinas of MA and OA zebrafish are shown in Figures 3A and 3B, respectively.…”