PRE-1, a cis element sufficient to enhance cone- and rod- specific expression in differentiating zebrafish photoreceptors.
BACKGROUND
Appropriate transcriptional regulation is required for cone photoreceptor development and integrity. To date, only a few cis-regulatory elements that control cone photoreceptor-specific expression have been characterised. The alpha-subunit of cone transducin (TαC) is specifically expressed in cone photoreceptors and is required for colour vision. In order to better understand the molecular genetics controlling the initiation of cone photoreceptor-specific expression in vivo, we have utilised zebrafish to identify cis-regulatory elements in the upstream promoter region of the TαC gene.


RESULTS
A 0.5 kb TαC promoter fragment is sufficient to direct cone-specific expression in transgenic larvae. Within this minimal promoter, we identify photoreceptor regulatory element-1 (PRE-1), a unique 41 bp sequence. PRE-1 specifically binds nuclear factors expressed in ocular tissue. PRE-1 is not required for cone-specific expression directed from a 2.5 kb TαC promoter. However, PRE-1-like sequences, with potential functional redundancy, are located in this 2.5 kb promoter. PRE-1-rho which has the highest sequence and structural homology to PRE-1 is located in the rhodopsin promoter. Surprisingly, PRE-1 and PRE-1-rho are functionally distinct. We demonstrate that PRE-1, but not PRE-1-rho, is sufficient to enhance expression from a heterologous UV cone promoter. PRE-1 is also sufficient to enhance expression from a heterologous rhodopsin promoter without altering its rod photoreceptor specificity. Finally, mutations in consensus E-box and Otx sites prevent PRE-1 from forming complexes with eye nuclear protein and enhancing photoreceptor expression.


CONCLUSIONS
PRE-1 is a novel cis-regulatory module that is sufficient to enhance the initiation of photoreceptor-specific gene expression in differentiating rod and cone photoreceptors.
UCD School of Biomolecular and Biomedical Sciences, UCD Conway Institute, University College Dublin, Dublin, Ireland. brendan.kennedy@ucd.ie
Maria E
ME
Morrissey
Sara
S
Shelton
Susan E
SE
Brockerhoff
James B
JB
Hurley
Breandán N
BN
Kennedy
D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D024721:E-Box Elements / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D007150:Immunohistochemistry; D007814:Larva / Q000235:genetics; D051857:Otx Transcription Factors / Q000235:genetics; D011401:Promoter Regions, Genetic; D050436:Regulatory Elements, Transcriptional / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D017949:Retinal Cone Photoreceptor Cells / Q000378:metabolism*; D017948:Retinal Rod Photoreceptor Cells / Q000378:metabolism*; D012243:Rhodopsin / Q000235:genetics; D015293:Transducin / Q000235:genetics*; D015027:Zebrafish / Q000235:genetics*; D029961:Zebrafish Proteins / Q000235:genetics
D051857:Otx Transcription Factors; D029961:Zebrafish Proteins; C497658:otx1 protein, zebrafish; D012243:Rhodopsin; D015293:Transducin
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