Atypical guanylyl cyclase from the pond snail Lymnaea stagnalis: cloning, sequence analysis and characterization of expression.

Soluble guanylyl cyclases (sGCs) are traditionally recognized as the main molecular receptor for nitric oxide (NO), a gaseous transmitter involved in many functions of the nervous system. Some sGCs are however insensitive to NO and therefore are known as atypical. Although atypical sGCs have been shown to exist in both vertebrate and invertebrate nervous systems, our understanding of their functional role is incomplete. Here we report on the cloning, sequencing and localization of an atypical sGC named Lym-sGCbeta3 from the snail Lymnaea stagnalis. We found that Lym-sGCbeta3 shares a number of structural characteristics with some previously characterized atypical sGCs including the presence of Tyr140 in the regulatory domain. This residue is thought to be of a critical importance in determining sensitivity of atypical sGCs to oxygen. These findings raise the possibility that Lym-sGCbeta3 is an oxygen receptor. The results of our in situ hybridization and RT-PCR experiments support this idea further by showing that Lym-sGCbeta3 is expressed in the osphradium, a peripheral sense organ in which oxygen-sensing neurons are located. Also of interest are our observations that many neurons in Lymnaea CNS co-express conventional and atypical sGC subunits. These data are consistent with a possible dominant negative regulatory role of atypical sGC subunits through the formation of heterodimers exhibiting low enzymatic activity.

Neuronal expression of neural nitric oxide synthase (nNOS) protein is suppressed by an antisense RNA transcribed from an NOS pseudogene.

Here, we show that a nitric oxide synthase (NOS) pseudogene is expressed in the CNS of the snail Lymnaea stagnalis. The pseudo-NOS transcript includes a region of significant antisense homology to a previously reported neuronal NOS (nNOS)-encoding mRNA. This suggested that the pseudo-NOS transcript acts as a natural antisense regulator of nNOS protein synthesis. In support of this, we show that both the nNOS-encoding and the pseudo-NOS transcripts are coexpressed in giant identified neurons (the cerebral giant cells) in the cerebral ganglion. Moreover, reverse transcription-PCR experiments on RNA isolated from the CNS establish that stable RNA-RNA duplex molecules do form between the two transcripts in vivo. Using an in vitro translation assay, we further demonstrate that the antisense region of the pseudogene transcript prevents the translation of nNOS protein from the nNOS-encoding mRNA. By analyzing NOS RNA and nNOS protein expression in two different identified neurons, we find that when both the nNOS-encoding and the pseudo-NOS transcripts are present in the same neuron, nNOS enzyme activity is substantially suppressed. Importantly, these results show that a natural antisense mechanism can mediate the translational control of nNOS expression in the Lymnaea CNS. Our findings also suggest that transcribed pseudogenes are not entirely without purpose and are a potential source of a new class of regulatory gene in the nervous system.

Molecular characterization of NOS in a mollusc: expression in a giant modulatory neuron.

Here we report on the molecular characterization of the first molluscan NOS in the CNS of the pond snail Lymnaea stagnalis. This Lymnaea NOS (Lym-nNOS) which is expressed preferentially in the CNS is most similar to mammalian neuronal NOS but contains tandem repeats of a seven amino acid motif not found in any other known NOS. We have localized Lym-nNOS to the serotonergic cerebral giant cells (CGCs) which modulate synaptic transmission within a neural network that generates feeding behavior. Our results suggest that the CGCs employ both NO and serotonin in the modulation of the central neural network underlying feeding.

[Repetitive sequences of the human genome]. / Povtoriaiushchiesia posledovatel'nosti genoma cheloveka.

A review of literature data on different families of repetitive sequences of human genome is presented. Both tandemly organized (classical satellite DNA, alpha satellite DNA, "minisatellites" etc.) and interspersed repetitive elements are characterized in detail. Special attention is paid to description of human genome mobile elements.

Cloning of Alu-containing cDNAs from human fibroblasts and identification of small Alu+ poly(A)+ RNAs in a variety of human normal and tumor cells.

Two clones have been selected from a human fibroblast cDNA bank. By DNA sequencing the clones were shown to contain Alu elements located near the ends of the cDNA inserts. DNA of the clones was used for Northern blot hybridization analysis of a number of poly(A)-containing RNAs from normal human tissues (brain, stomach, uterus, spleen, fibroblasts) and tumors (neurinoma, glioma, neuroblastoma, liposarcoma, adrenal cortex adenocarcinoma). All RNA samples reveal a heterodisperse distribution of Alu transcripts with discrete bands in the region of 7-12 S RNA. The majority of these small poly(A)+ Alu+ RNAs contain Alu sequences only in one (canonical) orientation with functional signals including the split promoter for RNA polymerase III.

[Sequences containing the Alu elements from a human fibroblast cDNA clone library: nucleotide sequence and expression in various tissues]. / Posledovatel'nosti, soderzhashchie élementy Alu, iz banka klonov kDNK fibroblastov cheloveka: opredelenie nukleotidnoi posledovatel'nosti i ékspressiia v raznykh tkaniakh.

Alu containing cDNA clones were isolated from a human fibroblast cDNA library. The nucleotide sequences of two clones were determined. In both cases Alu repeats appeared to be situated in the regions presumably corresponding to the 3'-end of mRNA. The comparison of the unique sequences of those clones did not show any homology between them. Both cDNA clones contained large open reading frames, extending into the Alu regions. DNA of one clone was used as a probe for Northern blot-hybridization analysis of poly(A)+ cytoplasmic RNA from some normal and tumor human tissues. All RNA samples contained Alu-homologous transcripts, mainly in 7-12S fractions and only in one (canonical) orientation. This orientation contained functional regions including promotor region for RNA-polymerase III.

Synthesis of full-length cDNAs from partially purified human procollagen mRNAs.

Partially purified human procollagen mRNAs have been copied using reverse transcriptase from avian myeloblastosis virus. Under standard conditions, using a high deoxynucleotide concentration, only incomplete cDNAs corresponding to one-fifth to one-half of the template could be synthesized. Addition of a ribonuclease inhibitor from human placenta in the reaction mixture allowed the synthesis of full-length cDNA copies from extremely long procollagen mRNA.