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Developmental changes in the expression level of connexin36 in the rat retina
Tamás Kovács-Öller1, Katalin Raics, József Orbán
1Department of Experimental Zoology and Neurobiology, University of Pécs, Pécs, Ifjúság street 6, Hungary.
Insights
Connexin36 (Cx36) gap junctions form in the developing rat retina, with expression and plaque formation increasing from birth to P20. Cx36 plaques show a preference for the ON sublamina and associate with AII amacrine cells, reflecting electrical circuit development.
Area of Science:
- Neuroscience
- Developmental Biology
- Ophthalmology
Background:
- Connexin36 (Cx36) is the primary gap junction protein in the brain and retina.
- Retinal structural development involves significant changes in gap junction formation before functional circuits are established.
Purpose of the Study:
- To investigate the temporal and spatial formation of inner retinal gap junctions by examining Cx36 expression during postnatal development.
- To understand the role of Cx36 in the maturation of retinal electrical synaptic circuitry.
Main Methods:
- Analysis of Cx36 mRNA and protein levels in rat retinas from postnatal day 0 (P0) to P20.
- Immunohistochemical localization of Cx36 plaques in the inner plexiform layer (IPL).
- Colocalization studies with calretinin-positive (CaR(+)) fibers and parvalbumin-positive (PV(+)) AII amacrine cells.
Main Results:
- Cx36 transcript and protein expression continuously increased from P0 to P20.
- Cx36 plaque formation began around P10 in the IPL, with a distinct preference for the ON sublamina.
- Cx36 plaques were found to colocalize with AII amacrine cell dendrites, with specific stratification patterns emerging over time.
Conclusions:
- Cx36 expression and localization in the developing rat IPL follow a specific sequence, mirroring the formation of electrical synaptic circuits.
- The observed Cx36 changes are attributed to the formation of gap junctions between AII amacrine cells and ON cone bipolar cells, and subsequently between AII amacrine cells themselves.
Abstract:
Connexin36 (Cx36) is the major gap junction forming protein in the brain and the retina; thus, alterations in its expression indicate changes in the corresponding circuitry. Many structural changes occur in the early postnatal retina before functional neuronal circuits are finalized, including those that incorporate gap junctions. To reveal the time-lapse formation of inner retinal gap junctions, we examine the developing postnatal rat retina from birth (P0) to young adult age (P20) and follow the expression of Cx36 in the mRNA and protein levels. We found a continuous elevation in the expression of both the Cx36 transcript and protein between P0 and P20 and a somewhat delayed Cx36 plaque formation throughout the inner plexiform layer (IPL) starting at P10. By using tristratificated calretinin positive (CaR(+)) fibers in the IPL as a guide, we detected a clear preference of Cx36 plaques for the ON sublamina from the earliest time of detection. This distributional preference became more pronounced at P15 and P20 due to the emergence and widespread expression of large (>0.1 μm(2)) Cx36 plaques in the ON sublamina. Finally, we showed that parvalbumin-positive (PV(+)) AII amacrine cell dendrites colocalize with Cx36 plaques as early as P10 in strata 3 and 4, whereas colocalizations in stratum 5 became characteristic only around P20. We conclude that Cx36 expression in the rat IPL displays a characteristic succession of changes during retinogenesis reflecting the formation of the underlying electrical synaptic circuitry. In particular, AII cell gap junctions, first formed with ON cone bipolar cells and later with other AII amacrine cells, accounted for the observed Cx36 expressional changes.
