There is a fundamental gap in understanding how circadian (~24-h) clocks regulate development and neuronal activity in the central nervous system (CNS). Continued existence of this gap represents an important problem because, until it is filled, understanding of the mechanisms that link circadian clock malfunction and many behavior disorders will remain largely incomprehensible. Our long-term goal is to better understand how circadian clocks control the activity of neuronal networks in the CNS. We have focused our studies on the retina, a tractable model for the rest of the CNS and a great example of neuronal plasticity on a daily basis. In the retina, most aspects of physiology and function are controlled by circadian clocks, and clock malfunction impinges on information processing and cell viability. Yet, the exact location of the retinal clocks and their control of functional pathwys in both healthy and diseased retinal tissue are still poorly understood. The objective of this project is to determine how circadian clocks within specific retinal cell types control the maturation and/or maintenance of retinal tissue and signal processing during day and night. Our central hypothesis is that the neural retina is a heterogeneous tissue in terms of clock activity; circadian clocks are present in most retinal cell types, and each clock cell type controls specific aspects of retinal development and function through a restricted clock pathway. Our central hypothesis has been formulated on the basis of our own preliminary data and recent publications in the field. The rationale for the proposed research is that by genetically silencing the clock mechanism in specific retinal cell types, we will be able to link specific clock cells to distinct clock pathways associated with retinal development and function. We have developed new genetically modified mouse lines and generated strong preliminary data. We will pursue two Specific Aims: 1) Characterize retinal cell type-specific clock-deficient mouse models; and 2) Identify the circadian clock pathway that controls photoreceptor electrical coupling. Under the first aim, a variety of cellular, molecular and behavioral approaches will be used in a variety of conditional clock-deficient mouse lines already created. Under the second aim, a novel electrophysiological technique-perforated patch clamp recording of single photoreceptors or photoreceptors pairs in mouse retina--will be combined with pharmacological and genetic approaches to reveal a cone-specific clock pathway. The proposed research is significant because it is expected to vertically advance and expand understanding of how circadian clocks control retinal development and function and will provide critical missing information about the clock pathways involved. Ultimately, such knowledge has the potential to increase our understanding of the general rules governing the activity of neuronal circuits in the CNS and of the events leading to their malfunction and behavior disorders.
Completion of this research project will provide a better understanding of the cellular and molecular basis of circadian clocks in the mammalian retina and how these clocks control retinal development and functional pathways. Impairment of circadian rhythmicity in the retina has been linked to photoreceptor cell death, and therefore this study will provide fundamental insights into the mechanisms that underlie retinal diseases, such as retinitis pigmentosa.
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