Spatial and temporal expression of AP-1 responsive rod photoreceptor genes and bZIP transcription factors during development of the rat retina.
OBJECTIVE
The promoter region of the rod-specific beta subunit of cGMP PDE (beta-PDE) and opsin genes contains highly conserved cis-acting elements, which include an AP-1 and/or Nrl response element (NRE: An extended AP-1 like sequence). Transactivation of AP-1 or NRE appears necessary to drive expression of these rod-specific genes during adulthood, however, their role during development is relatively unknown. Therefore, we determined the spatial and temporal relationships between rod morphological and functional development, rod-specific gene expression, and expression of the bZIP transcription factors c-fos, junD and Nrl.


METHODS
Retinas from 0-45 day old (PN0-45) dark- and light-adapted Long-Evans rats were used. Morphological development was monitored by light and electron microscopy. Whole retinal trypsin-activated cGMP-PDE activity and rhodopsin content were measured biochemically. The expression of opsin, beta-PDE, c-fos, junD and Nrl mRNAs were determined by Northern blot analysis. The cellular localization of Nrl was examined with in situ hybridization.


RESULTS
The mRNAs for opsin, beta-PDE and c-fos were observed at PN0-2, while cGMP-PDE activity and rhodopsin were detected first at PN5: coincident with rod outer segment development. The developmental pattern of cGMP-PDE activity and rhodopsin accumulation paralleled the expression of beta-PDE and opsin mRNA and all reached their maximal levels by PN45. Nrl expression, for all three transcripts found in the rat retina, was low on PN2 and reached its maximal level at PN14. The c-fos and Nrl expression preceded beta-PDE and opsin mRNA expression by 1-2 days. Nrl expression was detected first in the distal post-mitotic retina at PN5 and then in all nuclear layers during retinal development. Maximal expression shifted from the ganglion cells to the outer nuclear layer as the neural retina matured. In contrast, junD expression was highest at PN0 and declined to a stable level by PN10.


CONCLUSIONS
Colocalization of Nrl and c-Fos suggests that expression of rod-specific genes, which utilize AP-1 or NRE sites in their promoter, could be regulated through the formation of Nrl-Fos dimers. We hypothesize that Nrl and c-Fos play a fundamental role in the initiation and regulation of the rod-specific gene expression in developing and adult rod photoreceptors.
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Department of Biology and Biochemistry, University of Houston, Houston, TX 77204-6052, USA.
Campbell
M L
ML
Srivastava
D
D
Blocker
Y S
YS
Harris
J R
JR
Swaroop
A
A
Fox
D A
DA
D015106:3',5'-Cyclic-GMP Phosphodiesterases / Q000235:genetics / Q000378:metabolism*; D000375:Aging; D000818:Animals; D000831:Animals, Newborn; D015152:Blotting, Northern; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6; D004268:DNA-Binding Proteins / Q000378:metabolism; D003623:Dark Adaptation / Q000235:genetics; D005136:Eye Proteins / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D000071068:Lipocalin-2; D054834:Lipocalins; D008854:Microscopy, Electron; D009363:Neoplasm Proteins; D010727:Phosphoric Diester Hydrolases; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020318:Rats, Long-Evans; D012160:Retina / Q000378:metabolism / Q000502:physiology; D017948:Retinal Rod Photoreceptor Cells / Q000254:growth & development* / Q000378:metabolism* / Q000648:ultrastructure; D012243:Rhodopsin / Q000378:metabolism; D012374:Rod Cell Outer Segment / Q000254:growth & development / Q000378:metabolism / Q000648:ultrastructure; D017299:Rod Opsins / Q000235:genetics
D004268:DNA-Binding Proteins; D005136:Eye Proteins; C097278:Lcn2 protein, rat; D000071068:Lipocalin-2; D054834:Lipocalins; D009363:Neoplasm Proteins; D016760:Proto-Oncogene Proteins c-fos; D016755:Proto-Oncogene Proteins c-jun; D012333:RNA, Messenger; D017299:Rod Opsins; D012243:Rhodopsin; D010727:Phosphoric Diester Hydrolases; D015106:3',5'-Cyclic-GMP Phosphodiesterases; D054707:Cyclic Nucleotide Phosphodiesterases, Type 6