Molecular underpinnings of photoreceptor transcriptional regulation by CRX and NRL

Two key transcription factors, homeodomain protein CRX and basic leucine zipper protein NRL,
are at the center of gene regulation during photoreceptor differentiation and homeostasis. CRX is
essential for specifying commitment of postmitotic photoreceptor precursors to the development
of photoreceptor cells, whereas NRL determines the rod cell fate. In orchestrating the
transcriptional program of photoreceptor development, CRX and NRL cooperate functionally and
physically via a direct protein-protein interaction. Defects in photoreceptor transcriptional
regulation due to mutations in the genes encoding CRX and NRL cause severe retinal diseases
including retinitis pigmentosa, cone-rod dystrophy, and Leber congenital amaurosis. Despite our
advanced understanding of the biology and transcriptional networks of CRX and NRL,
mechanistic insight into the functions and unique synergy of these transcription factors at the
atomic level is lacking. In the proposed studies, we seek to determine the crystal and solution
structures of the individual DNA-bound complexes of CRX and NRL, as well as the structure of
the ternary CRX/NRL/DNA complex. Although mutations in these TFs have been identified, they
have not been mechanistically linked to regulation of key genes. The mechanistic predictions from
the structures on how disease-causing mutations in CRX and NRL may alter DNA-binding
specificity at cis-regulatory elements will be validated in the follow-up assays, including high-
throughput approaches such as Spec-seq. These studies will enhance our knowledge of the
functions of CRX and NRL, define the molecular nature of their synergy, and allow us to delineate
specific mechanisms whereby mutant CRX and NRL proteins cause retinal diseases. We
hypothesize that ultimately the structures of CRX and NRL complexed with their cis-regulatory
elements will enable targeted design of therapeutics to treat visual disorders via modulation of
transcriptional activities at specific promoters.

Grant Number: 5R01EY034455-04
NIH Institute/Center: NIH
Principal Investigator: Nikolai Artemyev