Cloning and characterization of zRICH, a 2',3'-cyclic-nucleotide 3'-phosphodiesterase induced during zebrafish optic nerve regeneration.

We previously reported cloning of cDNAs encoding both components of a protein doublet induced during goldfish optic nerve regeneration. The predicted protein sequences showed significant homology with the mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases (CNPases). CNPases are well-established markers of mammalian myelin; hence, the cDNAs were designated gRICH68 and gRICH70 (for goldfish Regeneration-Induced CNPase Homologues of 68 and 70 kDa). Homologous cDNAs have now been isolated from zebrafish encoding a highly related protein, which we have termed zRICH. RNase protection assays show that zRICH mRNA is induced significantly (fivefold) in optic nerve regenerating zebrafish retinas 7 days following nerve crush. Western blots show a single band in zebrafish brain and retina extracts, with immunoreactivity increasing three-fold in regenerating retinas 21 days postcrush. Immunohistochemical analysis indicated that this increase in zRICH protein expression is localized to the retinal ganglion cell layer in regenerating retina. We have characterized and evaluated the relevance of a conserved beta-ketoacyl synthase motif in zRICH to CNPase activity by means of site-directed mutagenesis. Two residues within the motif, H334 and T336, are critical for enzymatic activity. A cysteine residue within the motif, which corresponds to a critical residue for beta-ketoacyl synthase, does not appear to participate in the phosphodiesterase activity.

gRICH68 and gRICH70 are 2',3'-cyclic-nucleotide 3'-phosphodiesterases induced during goldfish optic nerve regeneration.

Biochemical characterization of changes in gene expression that accompany optic nerve regeneration has led to the identification of proteins that may play key roles in the regeneration process. In this report, a cDNA encoding gRICH70, a novel isoform of the regeneration-induced gRICH68 protein, has been identified and characterized in goldfish. Both gRICH68 and gRICH70 show significant homology (34-36%) to mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases (CNPases), hence the name goldfish regeneration-induced CNPase homolog (gRICH). The predicted 431-amino acid gRICH70 protein is 88% homologous to gRICH68, and the retinal mRNA for gRICH70 is coordinately induced with gRICH68 mRNA during optic nerve regeneration. Enzymatic analysis of recombinant proteins confirms that both gRICH proteins possess CNPase activity. Despite the relatively limited sequence homology, the kinetic constants obtained suggest that both gRICH proteins are at least as efficient as recombinant mouse CNP1 in catalyzing the hydrolysis of 2',3'-cAMP. Immunoprecipitation studies indicate that gRICH proteins are responsible for the majority of the CNPase activity detected in regenerating goldfish retinas. The evidence presented demonstrates that gRICH68 and gRICH70 correspond to a previously described doublet of acidic proteins that are selectively induced in the goldfish retina during optic nerve regeneration. Thus, CNPase enzyme activity is implicated for the first time in the process of nerve regeneration.

Isolation of cDNA clones encoding RICH: a protein induced during goldfish optic nerve regeneration with homology to mammalian 2',3'-cyclic-nucleotide 3'-phosphodiesterases.

Using data derived from peptide sequencing of p68/70, a protein doublet induced during optic nerve regeneration in goldfish, we have isolated cDNAs that encode RICH (regeneration-induced CNPase homolog) from a goldfish regenerating retina cDNA library. The predicted RICH protein comprises 411 amino acids, possesses a pI of 4.48, and shows significant homology to the mammalian myelin marker enzyme 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase; EC 3.1.4.37). The mRNA encoding RICH was demonstrated, by both Northern blot analysis and RNase protection assays, to be induced as much as 8-fold in regenerating goldfish retinas at 20 days after nerve crush. Analysis of total RNA samples from various tissues showed a broad distribution of RICH mRNA, with the highest levels observed in gravid ovary. The data obtained strongly suggest that RICH is identical or very similar to p68/70. The molecular cloning of RICH provides the means for a more detailed analysis of its function in nerve regeneration. Additionally, the homology of RICH and CNPase suggests that further investigation may provide additional insight into the role of these proteins in the nervous system.

Differential expression of mRNAs for protein kinase inhibitor isoforms in mouse brain.

Many neurotransmitters are known to regulate neuronal cell function by means of activation of cAMP-dependent protein kinase (PKA) and phosphorylation of neuronal substrate proteins, including transcription factors and ion channels. Here, we have characterized the gene expression of two isoforms of a protein kinase inhibitor (PKI) specific for PKA in mouse brain by RNase protection and in situ hybridization histochemistry. The studies demonstrate that the PKI alpha isoform is abundant in many regions of the adult mouse brain but particularly in cerebellum, hypothalamus, hippocampus, and cortex. In contrast, PKI beta is present at much lower levels in most brain regions but is found in significant amounts in the cerebellum, as well as in distinct nuclei within the pons, medulla, and hypothalamus. These results are consistent with a regulatory role of endogenous PKI in PKA-mediated signal transduction in brain and suggest differential functions for the two isoforms of PKI within the central nervous system.

Tumorigenic activity of rho genes from Aplysia californica.

rho genes have been found in both lower and higher eucaryotes. They code for proteins of 21 kDa, highly conserved in evolution, which belong to the superfamily of ras GTPases. Among the members of this superfamily there are proteins with a regulatory function, such as ras, and proteins involved in vesicular trafficking, such as the family of rab proteins. We have investigated the putative role of rho proteins from Aplysia californica as transforming GTPases utilizing the wild-type and a Val-14 mutant, equivalent to the oncogenic Val-12 mutation of ras genes found in animal and human tumors. Over-expression of either rho gene was sufficient to confer anchorage- and serum-independent growth. Moreover, when introduced into nude mice, selected clones generated from either gene were able to induce tumors, although those carrying the mutated version were more efficient. Pathological analysis indicated that generated tumors corresponded to well-differentiated fibrosarcomas with distinct and intersecting bundles and spindle cells. By contrast, ras-induced tumors were poorly differentiated fibrosarcomas. Thus, our results indicate that under appropriate conditions rho genes function as oncogenes and may have a role in the regulation of proliferation in fibroblast cells.