Exclusion of five subunits of cGMP phosphodiesterase in Leber's congenital amaurosis

Translational regulation of the rod photoreceptor cGMP-phosphodiesterase: the role of the 5'- and 3'-untranslated regions

We have established earlier that rod photoreceptor cGMP-phosphodiesterase (PDE6) alpha and beta subunits are equally represented in the retina at the protein level and have similar turnover rates. mRNA quantification revealed five PDE6beta messages for every PDE6alpha transcript pointing at post-transcriptional regulation of PDE6alpha and PDE6beta expression. Indeed, the wild-type PDE6alpha mRNA was translated 5-fold more efficiently than that of PDE6beta. The coding regions of these subunits had a major contribution in this process. Here, we extend our study of translational regulation of PDE6 subunits and present a detailed analysis of the role of PDE6alpha and PDE6beta 5'- and 3'-UTRs (untranslated regions) in this process. We showed that both the short and long PDE6beta 5'-UTRs lead to more efficient protein synthesis than the PDE6alpha 5'-UTR. The 3'-UTRs of PDE6alpha and PDE6beta stimulated translation by approximately 2- and 3-fold, respectively. However, the positive effect of the PDE6alpha or PDE6beta 3'-UTRs was not observed when these regions were placed in constructs containing the 5'-UTR of the corresponding PDE6 subunit. Furthermore, it appears that PDE6alpha 5'- and 3'-UTRs may be involved in a base pairing interaction that reduces the efficiency of protein synthesis. Finally, using progressive deletion analysis of the PDE6alpha 5'-UTR, we have identified several regions that have significant contribution in regulation of protein synthesis. Based on these and earlier published data, it can be stated that an equimolar level of PDE6alpha and PDE6beta synthesized from different amounts of mRNA (ratio of PDE6alpha to PDE6beta mRNA in the retina is 1:5) is achieved as a result of combinatorial effects of 5'-UTRs and coding regions of PDE6alpha and PDE6beta mRNAs on translational regulation.

Targeted gene disruption in the development of mouse models to elucidate the role of receptor guanylyl cyclase signaling pathways in physiological function

The physiological role of receptor guanylyl cyclases (GCs), which transduce a signal via the generation of intracellular cyclic GMP, has been somewhat speculative since there are few specific inhibitors that discriminate among various receptor isoforms. Although the natriuretic peptide receptors have been thought to regulate cardiovascular and renal function, the exact contribution of the receptor subtypes has not been clarified. The normal role of the heat-stable enterotoxin receptor guanylyl cyclase remains undefined, and several orphan members of the family await the identification of ligands as well as function. Targeted gene disruption, familiarly known as gene knockout, has emerged during the past decade as a powerful technique for probing the function of gene products, and has been used to develop animal models of inherited human diseases. We are just beginning to apply gene targeting technology to the guanylyl cyclase receptor family. Reviewed here is the information gained to date from the targeted disruption of several members of the guanylyl cyclase receptor family, their ligands, or effector molecules.