Interaction between the Transcription Factors Crx and Sp4 Regulates the Expression of Photoreceptor Genes

Abstract

Abstract: : Purpose: Crx is a photoreceptor transcription factor essential for the expression of many rod and cone genes. The Sp family of transcription factors has been implicated in controlling the transcription of a wide-range of genes in various tissues, including the retina. The purpose of this study was to test if Crx was able to physically interact with Sp proteins. Methods: Co-immunoprecipitation assays were used to detect the physical interaction between Crx and Sp4, or Sp1, as well as their truncated mutants, Crx1-107, Crx111-299, Sp4-dZnf and Sp4-Znf. Results: A positive interaction between Crx and Sp4 was detected by co-immunoprecipitation with in vitrotranslated proteins and an antibody against either Crx or Sp4. Further analysis with deleted forms of Crx and Sp4 showed that the DNA binding domain of Crx (homeodomain) and Sp4 (zinc fingers) are necessary and sufficient for mediating the Sp4-Crx interaction. A positive interaction between Crx and Sp1 was also detected using co-immunoprecipitation with the Crx antibody. Conclusions: Both Crx and the Sp family members have been recently implicated in the transcriptional regulation of photoreceptor-specific genes. Crx is able to bind both Sp1 and Sp4 providing the physical basis of their potential functional interactions. Furthermore, it appears that the homeodomain of Crx and the zinc finger domains of Sp1 and Sp4 are critical for this binding. Therefore, interactions between Crx and Sp1 or Sp4 (or both) may be implicated in transcriptional regulation of photoreceptor-specific genes.

Keywords: transcription factors • photoreceptors • gene/expression