Sequence and expression of the rat prodynorphin gene

Translational control of germ cell-expressed mRNA imposed by alternative splicing: opioid peptide gene expression in rat testis

The three genes encoding the opioid peptide precursors (prodynorphin, proenkephalin, and proopiomelanocortin) are expressed in the rat testis. The sizes of the three opioid mRNAs in the testis differ from the sizes of the corresponding mRNAs in other rat tissues in which these genes are expressed. The smaller testicular proopiomelanocortin mRNA has previously been demonstrated to arise from alternative transcriptional initiation. In the present study, we found that the smaller testicular prodynorphin mRNA, expressed in Sertoli cells, results from alternative mRNA processing. Exon 2, which makes up 5' untranslated sequence, is removed from the mature transcript. Polysome analysis of brain and testis RNA indicates that the alteration of the prodynorphin leader sequence in the testis-specific transcript does not affect the efficiency of translation of this mRNA. The larger testicular proenkephalin transcript, expressed in developing germ cells, also results from alternative mRNA processing. Alternative acceptor site usage in the splicing of intron A results in a germ cell-specific proenkephalin transcript with a 491-nucleotide 5' untranslated leader sequence preceding the preproenkephalin-coding sequence. Polysome analysis indicates that this germ cell-specific proenkephalin mRNA is not efficiently translated. Mechanisms by which alternative mRNA splicing may serve to confer translational regulation upon the testicular proenkephalin transcript are discussed.

Prodynorphin peptide distribution in the forebrain of the Syrian hamster and rat: a comparative study with antisera against dynorphin A, dynorphin B, and the C-terminus of the prodynorphin precursor molecule

The neuroanatomical distribution of the prodynorphin precursor molecule in the forebrain of the male Syrian hamster (Mesocricetus auratus) has been studied with a novel antiserum directed against the C-terminus of the leumorphin [dynorphin B (1-29)] peptide product. C-peptide staining in sections from colchicine-treated hamsters is compared to staining in sections from untreated animals. In addition, the pattern of C-peptide immunostaining in hamster brain is compared to that in the rat brain. Finally, the C-peptide immunolabeling patterns in hamsters and rats are compared to those obtained with antisera to dynorphin A (1-17) and dynorphin B (1-13). Areas of heaviest prodynorphin immunoreactivity in the hamster include the hippocampal formation, lateral septum, bed nucleus of the stria terminalis, medial preoptic area, medial and central amygdaloid nuclei, ventral pallidum, substantia nigra, and numerous hypothalamic nuclei. Although this C-peptide staining pattern is similar to dynorphin staining reported previously in the rat, several species differences are apparent. Whereas moderate dentate gyrus granule cell staining and no CA4 cell staining have been reported in the rat hippocampal formation, intense immunostaining in the dentate gyrus and CA4 cell labeling are observed in the hamster. In addition, the medial preoptic area, bed nucleus of the stria terminalis, and medial nucleus of the amygdala stain lightly for prodynorphin-containing fibers and cells in the rat, compared to heavy cell and fiber staining in the hamster in all three of these regions. In the rat there is no differential staining between tissues processed with the C-peptide, dynorphin A, and dynorphin B antisera, but numerous areas of the hamster brain show striking differences. In most hamster brain areas containing prodynorphin peptides, the C-peptide antiserum immunolabels more cells and fibers than the dynorphin B antiserum, which in turn labels more cells and fibers than dynorphin A antiserum. However, exceptions to this hierarchy of staining intensity are found in the lateral hypothalamus, substantia nigra, arcuate nucleus, and habenula. The differences in staining patterns between rat and hamster are greatest when C-peptide antiserum is used; apparent species differences are present, though less pronounced, in dynorphin B- and dynorphin A-immunostained material.

Expression and Post-Translational Processing of Preprodynorphin in the Rat Anterior Pituitary Cell Line, GH4C1

Abstract A recombinant plasmid containing the rat preprodynorphin cDNA was introduced into the rat anterior pituitary cell line, GH4C1. These cells normally express growth hormone and prolactin but not prodynorphin. Stable transformants were isolated and analyzed for the expression and processing of prodynorphin. Chromatographic analyses demonstrated that the prodynorphin was incompletely processed in GH4C1 cells. Analyses of the peptides by specific radioimmunoassays to chemically synthesized peptides showed that the cells have the ability to process both at dibasic and monobasic cleavage sites. The release of prodynorphin-derived peptides paralleled that of prolactin upon stimulation with thyrotropin-releasing hormone, forskolin or carbachol suggesting that the prodynorphin-derived peptides and prolactin are sequestered in similar physiologically responsive compartments. These data suggest that the GH4C1 cells incompletely process prodynorphin. The processing in GH4C1 cells occurs both at monobasic and dibasic cleavage sites.

Translational control of germ cell-expressed mRNA imposed by alternative splicing: opioid peptide gene expression in rat testis

The three genes encoding the opioid peptide precursors (prodynorphin, proenkephalin, and proopiomelanocortin) are expressed in the rat testis. The sizes of the three opioid mRNAs in the testis differ from the sizes of the corresponding mRNAs in other rat tissues in which these genes are expressed. The smaller testicular proopiomelanocortin mRNA has previously been demonstrated to arise from alternative transcriptional initiation. In the present study, we found that the smaller testicular prodynorphin mRNA, expressed in Sertoli cells, results from alternative mRNA processing. Exon 2, which makes up 5' untranslated sequence, is removed from the mature transcript. Polysome analysis of brain and testis RNA indicates that the alteration of the prodynorphin leader sequence in the testis-specific transcript does not affect the efficiency of translation of this mRNA. The larger testicular proenkephalin transcript, expressed in developing germ cells, also results from alternative mRNA processing. Alternative acceptor site usage in the splicing of intron A results in a germ cell-specific proenkephalin transcript with a 491-nucleotide 5' untranslated leader sequence preceding the preproenkephalin-coding sequence. Polysome analysis indicates that this germ cell-specific proenkephalin mRNA is not efficiently translated. Mechanisms by which alternative mRNA splicing may serve to confer translational regulation upon the testicular proenkephalin transcript are discussed.

Elevated dynorphin in the hippocampal formation of aged rats: relation to cognitive impairment on a spatial learning task

Radioimmunoassay revealed increased dynorphin A(1-8)-like immunoreactivity [dynA(1-8)LI] in the aged rat brain. Among a number of brain regions examined, an age-related dynA(1-8)LI elevation was found only in the hippocampal formation and frontal cortex. Moreover, the increase in dynA(1-8)LI in the aged hippocampus was associated with a decline in spatial learning ability: dynA(1-8)LI distinguished aged rats that were behaviorally impaired from aged cohorts that learned the spatial task as rapidly as younger animals. Northern blot hybridization using a 32P-labeled complementary RNA probe encoding rat prodynorphin indicated that the abundance of prodynorphin mRNA was also significantly increased in the hippocampal formation of aged rats with identified spatial learning impairments.

Localization of striatal opioid gene expression, and its modulation by the mesostriatal dopamine pathway: an in situ hybridization study

In situ hybridization was used to study the macroscopic distribution and regulatory control of proenkephalin mRNA and prodynorphin mRNA in rat striatum. While proenkephalin mRNA was widely distributed throughout the striatum, levels of prodynorphin mRNA were highest in the medial and ventral portions of the striatum. Furthermore, in contrast to the results for proenkephalin mRNA, the levels of prodynorphin mRNA appeared higher in the nucleus accumbens than in the striatum. The mesostriatal dopaminergic pathway was destroyed by discrete, unilateral injection of 6-hydroxy-dopamine (6-OHDA) into either the substantia nigra or the neighboring ventral tegmental area (VTA). Lesions of the substantia nigra caused a dramatic ipsilateral increase in the hybridization signal for proenkephalin mRNA, but no change was observed in the hybridization signal for prodynorphin mRNA. Similar effects were seen with VTA lesions. Since destruction of the mesostriatal dopamine system elevates the levels of proenkephalin mRNA, but not of prodynorphin mRNA, in the striatal target neurons, it appears that the mesostriatal pathway exerts a tonic and selective suppression of striatal proenkephalin gene expression at the mRNA level.

Characterization of cysteine proteases functioning in degradation of dynorphin in neuroblastoma cells: evidence for the presence of a novel enzyme with strict specificity toward paired basic residues

Two dynorphin-degrading cysteine proteases, I and II, were extracted with Triton X-100 from neuroblastoma cell membrane, isolated from accompanying dynorphin-degrading trypsin-like enzyme by affinity chromatography on columns of soybean trypsin inhibitor-immobilized Sepharose and p-mercuribenzoate-Sepharose, and separated by ion-exchange chromatography on diethylaminoethyl (DEAE)-cellulose and TSK gel DEAE-5PW columns. Cysteine protease II was purified further by hydroxyapatite chromatography and gel filtration. The molecular weights of cysteine proteases I and II were estimated to be 100,000 and 70,000, respectively, by gel filtration. Both of the enzymes, were inhibited by p-chloromercuribenzoate, N-ethylmaleimide, and high-molecular-weight kininogen, but not or only slightly inhibited by diisopropylphosphorofluoridate, antipain, leupeptin, E-64, calpain inhibitor, and phosphoramidon. Cysteine protease I cleaved dynorphin(1-17) at the Arg6-Arg7 bond with the optimum pH of 8.0, whereas II cleaved dynorphin(1-17) at the Lys11-Leu12 bond and the Leu12-Lys13 bond with the optimum pH values of 8.0 and 6.0, respectively. These bonds corresponded to those that had been proposed as the initial sites of degradation by neuroblastoma cell membrane. Cysteine protease I was further found to show strict specificity toward the Arg-Arg doublet, when susceptibilities of various peptides containing paired basic residues were examined as substrates for the enzyme.

Expression of preproenkephalin mRNA by cultured astrocytes and neurons

Expression of preproenkephalin mRNA by developing glia and neurons was examined in cultures of embryonic and neonatal rat brain. Cultured glia from specific regions of embryonic day 17 and neonatal day 1 rat brain were identified as astrocytes on the basis of both morphology and expression of immunoreactivity for glial fibrillary acidic protein. The level of preproenkephalin mRNA in cultured neonatal hypothalamic astrocytes was comparable to levels present in cultured embryonic striatal and hypothalamic neurons. Levels of the mRNA were significantly higher in astrocytes derived from neonatal hypothalamus compared to astrocytes derived from other areas of the brain. Thus, there is heterogeneity among astrocytes with respect to preproenkephalin expression. Levels of preproenkephalin mRNA in cultured neonatal striatal astrocytes were only one-third as high as levels in embryonic striatal astrocytes; this observation suggests that glial expression of the gene may be down-regulated during development. Although cultured hypothalamic neurons contained substantial levels of prodynorphin mRNA, levels of this mRNA were not detectable in cultured astrocytes from any brain region or in cultured striatal neurons. Thus, glia do not express all opioid peptide genes during development. These observations suggest that expression of the preproenkephalin gene by astrocytes may play a role in development of the brain.

Opioid peptide gene expression in rat trigeminal nucleus caudalis neurons: normal distribution and effects of trigeminal deafferentation

Preproenkephalin (preproenkephalin A) and preprodynorphin (preproenkephalin B) are the opioid peptide genes expressed in neurons of the nucleus caudalis of the trigeminal nuclear complex. We have used recently developed techniques for quantitative in situ hybridization to identify the neurons in laminae I and II of the nucleus caudalis that display the mRNA products of each of these genes. The specificity of these hybridization patterns is supported by several biochemical features, and by qualitative and quantitative parallels with previous immunohistochemical results. In animals killed 4 days after unilateral lesions of the trigeminal ganglion, neuronal expression of both preproenkephalin and preprodynorphin is altered in the nucleus caudalis. Decreases in preproenkephalin mRNA are due to a decline in the number of neurons that appear to express this gene. Conversely, preprodynorphin mRNA increases by adding a significant population of expressing neurons. These deafferentation-induced changes in gene expression may provide clues to the role of primary afferent information in modulating the functions of nucleus caudalis neurons containing opioid peptides.

Electrical stimulation in vivo increases the expression of proenkephalin mRNA and decreases the expression of prodynorphin mRNA in rat hippocampal granule cells

In situ hybridization histochemistry in combination with RNA blot techniques was used to study the regulation of opioid gene expression in rat hippocampus. By use of a prodynorphin cDNA probe, a strong hybridization signal was identified in the granule cell layer of the hippocampus. However, experiments using a proenkephalin cDNA probe revealed that the content of proenkephalin mRNA was considerably lower than that of prodynorphin mRNA. Following five brief trains of high-frequency electrical stimulation to the dentate gyrus, the proenkephalin mRNA content of the granule cells, measured 22 hr later, was substantially increased on the stimulated side. In contrast, levels of prodynorphin mRNA were markedly decreased ipsilateral to the stimulation site. These results were confirmed by RNA blot analysis of extracted mRNA. The decrease in prodynorphin mRNA content first became apparent between 4 and 7 hr after the end of stimulation. Distinct mechanisms, therefore, regulate the expression of proenkephalin mRNA and prodynorphin mRNA in rat hippocampus.

Paracrine factors in adult rat testis gonadotrophin control of opioids and LHRH like peptide

A paracrine regulation involves agents which are produced by one cell type and act on an other one within an organ. In rodent testis, local control mechanisms modulate the actions of the gonadotrophins according to local requirements. Two groups of peptides-opioids and testicular LHRH are defined as paracrine factors and in vivo they are both modified by HCG. In vitro, after HCG exposure, we first localized an opioid like material in Sertoli cells cytoplasma by immunohistochemistry. This material is detected in freeze dried homologous culture media using a dot immunobinding technique. With a longer HCG exposure, an LHRH like material is then visualized in the basal compartment of the Sertoli cells and it is detected in freeze dried homologous culture media by the same technical procedure than for opioid material. By adding synthetic enkephalins to culture medium, we obtain the same results as with the endogenous opioid material, excreted after HCG addition. If naloxone a potent opiate antagonist, is added to the culture medium previously to HCG or enkephalins, the Sertoli cells cytoplasma are no more immunoreactives with the anti-enkephalin serum and no LHRH material is neither visualized by immunohistochemical technique neither detected in culture media. We conclude that testicular opioids, synthetized by the Leydig cells and which have specific Sertoli cells receptors are one Leydig-Sertoli paracrine communication factor. One way of response to their receptor fixation is the synthesis and excretion by Sertoli cells of testicular LHRH. This one is known to act on Leydig cells via specific receptors and it is one Sertoli-Leydig cells paracrine communication factor.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of opioid genes in bovine seminal vesicles

In seminal vesicles, the organ producing most of seminal plasma in the bovine species, the pro-opiomelanocortin and the proenkephalin genes are transcribed and translated, and their translation products processed into opioid peptides, which are secreted into the seminal plasma. By using a micro-organ preparation of seminal vesicles we found that, after 20 h of incubation with labelled methionine, a multiplicity of opioids was produced. Among these, [Met]enkephalin and beta-endorphin were positively identified, whereas in the newly formed secretion only [Met]enkephalin was detected. This may be correlated to the finding that the concentration of beta-endorphin in an extract of seminal plasma was one order of magnitude lower than that of [Leu]enkephalin and [Met]enkephalin. These findings expand the picture of the presence of opioid peptides in the male reproductive tract, indicating that they should have a role(s) in the physiology of reproduction, not only in the hypothalamus-pituitary-gonadal axis, determining the reproductive potential, but also in the so-termed sex accessory glands, determining the actual events leading to reproduction. To our knowledge this is also the first case studied of opioid peptides produced as exocrine hormones.

Chromosomal localization of the human proenkephalin and prodynorphin genes

DNA probes derived from rat and human proenkephalin and prodynorphin genes have been used to localize these two opiate neuropeptide genes on human chromosomes. Hybridization of probes to Southern blots made with DNAs from a rodent-human somatic-cell hybrid panel indicates localization of proenkephalin to human chromosome 8 and of prodynorphin to human chromosome 20. In situ hybridization to metaphase chromosomes confirms these assignments and indicates regional localizations of proenkephalin to 8q23-q24 and of prodynorphin to 20p12-pter. A human genomic prodynorphin clone reveals a frequent two-allele TaqI polymorphism.

In situ hybridization histochemistry and immunocytochemistry reveal an increase in spinal dynorphin biosynthesis in a rat model of peripheral inflammation and hyperalgesia

Dynorphin, an opioid peptide, is thought to play an important role in the modulation of nociceptive neural circuits at the level of the spinal cord. In a model of peripheral inflammation and hyperalgesia, an oligodeoxyribonucleotide probe complementary to a portion of preprodynorphin mRNA and antisera to dynorphin A-(1-8) were used to localize changes in dynorphin mRNA and peptide to individual spinal cord neurons. Intraplantar injection in rats of complete Freund's adjuvant resulted in edema and hyperalgesia to radiant heat stimulation of the injected hind paw that reached a peak at 4 days. At the same time, in situ hybridization histochemistry and immunocytochemistry identified an increase in transcription of preprodynorphin mRNA that was paralleled by an increase in dynorphin peptide. These changes were seen in spinal neurons in the medial two-thirds of laminae I and II and in laminae V and VI of lumbar segments receiving innervation from the inflamed paw. Since neurons demonstrating the increase in dynorphin biosynthesis are located in both the superficial and deep dorsal horn laminae, our data provide evidence for opioid modulation of nociceptive neural circuits in these two distinct spinal locations.

Vasopressin, oxytocin, dynorphin, enkephalin and corticotrophin-releasing factor mRNA stimulation in the rat

1. Cryostat sections were cut through the hypothalamus of rats which had been given a 2% (w/v) NaCl solution to drink for up to 12 days. 2. In situ hybridization histochemistry was performed on these sections using synthetic oligonucleotide probes against part of the precursor sequence for vasopressin, oxytocin, dynorphin, enkephalin and corticotrophin-releasing factor (CRF). 3. Drinking 2% NaCl solution resulted in a progressive increase of vasopressin, oxytocin and dynorphin mRNAs hybridized in the magnocellular neurones of the supraoptic (s.o.) and paraventricular (p.v.) nuclei. No enkephalin mRNA was detected in the magnocellular areas of the control animals although small quantities of probe did hybridize after 12 days of salt loading and after the stress of I.P. hypertonic saline. 4. Ten-day-lactating female rats were also studied. They had a very marked increase in oxytocin mRNA with smaller increases of vasopressin and dynorphin mRNAs. No detectable enkephalin mRNA was hybridized in the magnocellular s.o. or p.v. nuclei and CRF mRNA was unchanged in both the s.o. nucleus and the p.v. nucleus.

The rat corticotropin-releasing hormone gene

In this paper we have described the isolation and characterization of the rat corticotropin releasing hormone gene. Nucleotide sequence comparisons with the human CRH gene have demonstrated several interesting regions of homology and suggest that the gene was highly conserved through evolution. Additionally we have demonstrated the tissue-specific expression of the rat CRH gene. The regional distribution of expression parallels previously documented immunocytochemical demonstrations and supports the hypothesis that CRH peptides have multiple roles in different tissues. In the peripheral tissues that express CRH mRNA it will be very interesting to document the specific cell type of synthesis by using combined immunocytochemical and in situ histochemical techniques. Additionally we have described initial studies using gene transfer techniques to examine the cAMP responsiveness of the rat CRH gene. We are presently constructing other fusion genes (CRHCAT plasmids) in order to more carefully localize the DNA sequence in the rat CRH gene which mediates this effect, and compare it to the previously reported cAMP-responsive "consensus sequence." Similarly, we also plan to utilize the CRHCAT constructs to examine regulation of the rat CRH gene by glucocorticoids and several other hormone-mediated regulatory pathways. Through these CAT fusion studies we hope to gain a better understanding of the role of certain conserved sequences in the 5' flanking DNA for transcriptional control of the rat (and human) CRH genes.

The next frontier in the molecular biology of the opioid system. The opioid receptors

The analgesic and euphoric properties of some plant alkaloids such as morphine have been known and exploited for centuries. In contrast, only during the last twenty years have we begun to unravel the molecular basis by which opiates exert their effects, mechanisms important to our general understanding of the nervous system. The analgesic response to opiates is the result of a cascade of biochemical events that are triggered by the interaction of the opiate with specific macromolecular components found on the membranes of nervous system tissues, the opioid receptors. The endogenous ligands of these receptors are small peptides, the opioid peptides. Although much has been learned about the structures and the mode of synthesis of the opioid peptides, little is understood about the structure of their receptors. The application of molecular genetic techniques was of great importance to the studies of the opioid peptides. It is now expected that this same technology will unravel the physical mysteries of the opioid receptors.

Localization of preproenkephalin mRNA in the rat brain and spinal cord by in situ hybridization

To determine the localization in rat brain and spinal cord of individual neurons that contain the messenger RNA coding for the opioid peptide precursor preproenkephalin, we performed in situ hybridization with a tritiated cDNA probe complementary to a protion of preproenkephalin mRNA. We observed autoradiographic signal over the cytoplasm of neurons of many regions of the central nervous system. Several types of controls indicated specificity of the labeling. Neurons containing preproenkephalin mRNA were found in the piriform cortex, ventral tenia tecta, several regions of the neocortex, nucleus accumbens, olfactory tubercle, caudate-putamen, lateral septum, bed nucleus of the stria terminalis, diagonal band of Broca, preoptic area, amygdala (especially central nucleus, with fewer labeled neurons in all other nuclei), hippocampal formation, anterior hypothalamic nucleus, perifornical region, lateral hypothalamus, paraventricular nucleus, dorsomedial and ventromedial hypothalamic nuclei, arcuate nucleus, dorsal and ventral premamillary nuclei, medial mamillary nucleus, lateral geniculate nucleus, zona incerta, periaqueductal gray, midbrain reticular formation, ventral tegmental area of Tsai, inferior colliculus, dorsal and ventral tegmental nuclei of Gudden, dorsal and ventral parabrachial nuclei, pontine and medullary reticular formation, several portions of the raphe nuclei, nucleus of the solitary tract, nucleus of the spinal trigeminal tract (especially substantia gelatinosa), ventral and dorsal cochlear nuclei, medial and spinal vestibular nuclei, cuneate and external cuneate nuclei, gracile nucleus, superior olive, nucleus of the trapezoid body, some deep cerebellar nuclei, Golgi neurons in the cerebellum, and most laminae of the spinal cord. In most of these brain regions, the present results indicate that many more neurons contain preproenkephalin mRNA than have been appreciated previously on the basis of immunocytochemistry.

Proenkephalin B messenger RNA in porcine tissues: characterization, quantification, and correlation with opioid peptides

Concentrations of proenkephalin B (PENK B) mRNA in porcine brain, pituitary, spinal cord, and peripheral tissues were measured using RNA blotting and solution hybridization. A single hybridizing species of approximately 2,800 bases in size was present in the CNS, with the highest concentration in the caudate nucleus, followed by hypothalamus and hippocampus. The abundance of PENK B mRNA ranged from 22 pg/micrograms of poly(A)-rich RNA in caudate nucleus to less than 0.1 pg/microgram in cerebellum. Concentrations of immunoreactive PENK B-derived peptides showed a similar distribution, with the exception of the hypothalamus, which had lower PENK B mRNA levels than expected from peptide concentrations. PENK B mRNA of the same size as in the brain was also found in the anterior lobe of the pituitary and in the heart ventricle, whereas in intestine, lung, and kidney, smaller mRNA species of 1,800 bases became apparent by RNA blot analysis. An intermediate size of 2,200 bases was found in heart atrium. As revealed by S1 mapping, however, these smaller mRNAs are not completely homologous with PENK B mRNA, but rather may represent closely related mRNAs from a different gene(s).

Mesencephalic dopamine neurons regulate the expression of neuropeptide mRNAs in the rat forebrain

We used in situ hybridization histochemistry with synthetic oligodeoxyribonucleotide probes to identify cells that synthesize mRNAs encoding tyrosine hydroxylase in the mesencephalon and substance P, enkephalin, and dynorphin in the rat forebrain. Dopaminergic cells in the mesencephalon project to the forebrain and influence neuropeptide levels. We examined the effect of unilateral 6-hydroxydopamine lesions (which eliminated tyrosine hydroxylase mRNA-containing cells in the mesencephalon) on substance P, enkephalin, and dynorphin mRNA levels. Substance P mRNA levels were depressed, whereas enkephalin mRNA levels were elevated in consecutive sections from striatal areas in all animals. The effects of the lesions on dynorphin mRNA levels were less robust, and considerable variation between animals was observed. Changes were evident in the levels of message in individual cells but not in the numbers of labeled cells. These effects were not uniform throughout the dopamine-innervated areas, suggesting degrees of control not apparent with RNA blot-hybridization or dot-blot analyses.

Expression of proenkephalin messenger RNA by mouse spermatogenic cells

The presence of proenkephalin mRNA in germ cells purified from adult mouse testis were examined using RNA gel- and dot-blot analyses. Both pachytene spermatocytes and round spermatids were shown to contain concentrations of this transcript that are 2- to 3-fold greater than that found for whole mouse testis, on a per microgram of polyadenylylated RNA basis. The detection of proenkephalin mRNA in purified spermatocytes and spermatids could not be accounted for by contamination by either Leydig or Sertoli cells. No proenkephalin mRNA was detectable in extracts of mature sperm. These data suggest that developing germ cells may be a major site of proenkephalin synthesis in the adult testis and that proenkephalin-derived peptides may function as germ cell-associated hormones or autocrine/paracrine factors.

In situ hybridization histochemistry with synthetic oligonucleotides: strategies and methods

In situ hybridization histochemistry is a useful method for localizing specific mRNA and studying the regulation of gene expression in an anatomical context. Previously, classical recombinant DNA and microbiological techniques have been required to identify and nick-translate the cloned DNAs necessary for in situ hybridization experiments. These requirements can be circumvented by the use of synthetic oligonucleotides complementary to the mRNA of interest. Compared to cloned cDNA probes, oligonucleotides are easy to manufacture, penetrate tissue much more easily, can be made to correspond to a sequence at any point in a known cDNA structure, and allow for the design of more precise controls for in situ studies. We describe a number of considerations in oligonucleotide probe design, including unique probe design from cDNA sequences and mixed probe design from protein primary structure data. The issues of species specificity, G-C content, probe length, tissue-specific mRNA expression, repeated sequences, non-coding region specific probes, and gene family homologies are discussed in an in situ hybridization context. Alternative strategies for mixed probe design are also considered. Information on the synthesis, purification, and sequence confirmation of oligonucleotides is then presented, followed by methods for labeling and using these probes for in situ hybridization histochemistry. The special considerations of specificity controls are addressed, including combined in situ hybridization histochemistry and immunocytochemistry, competition studies, the use of multiple hybridization probes, Tm studies, and Northern analysis of extracted RNA. The current and future directions of research with this technique are considered, with emphasis on the need to improve quantitation in order to facilitate the study of gene expression and regulation at the single cell level.