Pearring Lab at the University of Michigan

Our laboratory studies the light-sensitive photoreceptor cells of the retina. Light is captured by the outer segment organelle, which is the largest primary cilium in the human body. Importantly, defects associated with ciliary formation, function, and/or trafficking often result in photoreceptor dysfunction or death leading to human blindness.  

We are currently pursuing three main directions. 

Maintaining Photoreceptor Outer Segment Protein Composition 

Wild Type Photoreceptors

Tctn1 KO Photoreceptors

Understanding the underlying mechanisms that establish and maintain the subcellular distribution of membrane proteins remains a central unsolved problem in cell biology. The outer segment ciliary membrane is continuous with the plasma membrane, yet maintains a distinct composition of proteins responsible for capturing light and eliciting an electrical response.  At the base of the cilium is a protein-rich region called the transition zone that is thought to act as a diffusional “gate” to restrict lateral membrane transport between the ciliary and non-ciliary compartments. Loss of the tectonic protein complex that resides within the transition zone results in unsolicited entry of non-resident membrane proteins into the outer segment. We are investigating the structural complexity of the membrane barrier that filters proteins as well as passive and active transport mechanisms that to ensure proper sorting between these two membrane subdomains.

Protein Delivery to the Photoreceptor Outer Segment 

Defects in membrane protein trafficking in photoreceptors underlie many forms of inherited retinal degenerative diseases. Our lab aims to understand the basic mechanisms employed by photoreceptors to ensure polarized delivery of signaling and structural proteins to the light-sensitive outer segment compartment. Current projects include:

Investigating membrane protein targeting and delivery to the light-sensing outer segment compartment of photoreceptors.  The outer segment is a membrane-rich compartment. Resident membrane proteins either encode an outer segment-targeting signal (like the VxPx motif on rhodopsin) or "hitch a ride" with key signaling proteins, like GC-1 with rhodopsin. How does altering targeting signals present in rhodopsin change protein localization?   

How are proteins segregated between the outer segment membrane subdomains: the discs and ciliary plasma membrane?  The light-sensing ability of photoreceptors depends on the localization of different signaling proteins to these specific subdomains. We are exploring the molecular mechanisms guiding the delivery of the cyclic nucleotide-gated channel to the ciliary plasma membrane and how this is similar and/or different from disc-specific protein delivery.

Does membrane protein delivery alter the kinetics of ongoing disc renewal?  80-100 new discs are formed on a daily basis and require a constant influx of membrane material. We aim to understand how the kinetics of ongoing disc renewal are altered when outer segment membrane trafficking is defective. 

Photoreceptor Nuclear Migration During Development

During retinal development, newly postmitotic neurons are born apically and therefore need to migrate varying distances to reach their final retinal layer where they elaborate and make connections. Our recent study found that disrupting Arl3 lipidated trafficking to the cilium during development caused rod nuclei to be mislocalized from the outer retina to the inner retina. Current projects include:

Identifying the molecular signal that is disrupted by aberrant Arl3 activity. Our recent publication found that defects in the Arl3 ciliary gradient disrupt the nuclear translocation of developing rod photoreceptors; however, the molecular mechanism remains unknown.

Examine how defects in nuclear migration affect photoreceptor function and health. Dominant mutations in Arl3 cause various forms of retinal dystrophy. Whether displaced photoreceptors are functional and how the nuclear migration defect impacts overall retina health remains to be determined.

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