Analysis of brain and pituitary RNA metabolism: a review of recent methodologies

Cloning and expression analysis of the chicken DEAD box gene DDX1

DEAD box proteins are putative RNA unwinding proteins found in organisms ranging from mammals to bacteria. While some DEAD box genes expressed in higher eukaryotes are ubiquitous, others have distribution profiles that suggest a cell-, tissue-, or developmental-specific role. The DEAD box gene, DDX1, was identified by differential screening of a subtracted retinoblastoma cDNA library. A limited survey of human fetal tissues indicated that DDX1 mRNA has a widespread distribution but is not uniformly expressed in all tissues. To further document the spatial and temporal distribution of DDX1 during embryonic development, we cloned the chicken DDX1 cDNA. The predicted amino acid sequence of chicken DDX1 was 93% identical to that of human DDX1. All DEAD box motifs, as well as a SPRY domain, were present in chicken DDX1. Northern and Western blot analyses showed highest levels of DDX1 at early stages of development. Tissue maturation was generally accompanied by a decrease in expression, although DDX1 levels remained elevated in late embryonic retina and brain. In situ hybridization of retinal tissue sections revealed widespread distribution of DDX1 mRNA at early developmental stages with preferential expression in amacrine and ganglion cells of the differentiated tissue. Preferential expression of DDX1 was also observed in specific areas of the brain in older embryos, such as the external granule layer of the cerebellum. These results suggest a specific role for DDX1 in subsets of differentiated cells as well as a more general role in undifferentiated cells.

Detection of lamprin mRNA in the anadromous sea lamprey using in situ hybridization

An optimal in situ hybridization protocol is described for the detection of gene expression of a structural protein unique to lampreys, lamprin, in the cartilages of prolarval, metamorphic and adult sea lamprey, Petromyzon marinus. A 156 bp antisense RNA probe labeled with (35)S-UTP was transcribed in vitro from a recombinant plasmid containing a cDNA insert homologous to the largest (1.8 kb) of three known mRNAs for the lamprin gene and hybridized to 6 mu m paraffin sections. Optimal signal to noise ratio was achieved by fixing tissues 30 min in 4% paraformaldehyde and prehybridizing with a probe incorporating a nonradioactive S-UTP. Strong signals were visualized in all cartilaginous elements of the lamprey neurocranium; however, lamprin mRNA transcripts were not detected in branchial and pericardial cartilages suggesting differential expression of the lamprin gene. No signals were observed in tissue sections that had been treated with RNase A prior to hybridization or in sections hybridized with sense RNA probes. This technique has great potential for use in studies of the spatial and temporal distribution of cartilaginous components during developmental stages of lampreys.

Corticosteroid modulation of hippocampal potentials: increased effect with aging

Adrenal steroids bind specifically to hippocampal neurons under normal conditions and may contribute to hippocampal cell loss during aging, but little is known about the neurophysiological mechanisms by which they may change hippocampal cell functions. In the present studies, adrenal steroids have been shown to modulate a well-defined membrane conductance in hippocampal pyramidal cells. The calcium-dependent slow afterhyperpolarization is reduced in hippocampal slices from adrenalectomized rats, and it is increased after in vivo or in vitro administration of the adrenal steroid, corticosterone. Calcium action potentials are also reduced in adrenalectomized animals, indicating that the primary effect of corticosteroids may be on calcium conductance. The afterhyperpolarization component reduced by adrenalectomy is greater in aged rats than in young rats, suggesting that, with aging, there is an increased effect of corticosteroids on some calcium-mediated brain processes. Because elevated concentrations of intracellular calcium can be cytotoxic, these observations may increase the understanding of glucocorticoid involvement in brain aging as well as of the normal functions of these steroids in the brain.

Molecular genetics and human disease. Implications for modern psychiatric research and practice

Techniques of molecular genetics, including recombinant-DNA technology, are likely to have a key role in modern psychiatric research and practice. This article reviews some methods of DNA analysis and their applications to clinical science: specifically, how these methods can be used to localise, identify, isolate, and clone clinically important genes, and how this should enable us to elucidate the molecular pathology of most inherited (psychiatric) disorders. The implications of these developments for prevention and treatment of genetic disease are discussed.

Complexity of nuclear and polysomal RNA from squid optic lobe and gill

The sequence complexity of nuclear and polysomal RNA from squid optic lobe and gill was measured by RNA-driven hybridization reactions with single-copy [3H]DNA. At saturation, brain nuclear and polysomal RNAs were complementary to 22.8 and 7.9% of the DNA probe, respectively. Assuming asymmetric transcription, the complexity of nuclear and polysomal RNA was equivalent to 2.5 X 10(8) and 8.8 X 10(7) nucleotides, respectively. Approximately 80-85% of the sequence complexity of brain total polysomal RNA was found in the polyadenylated RNA fraction. In contrast to these findings, nuclear and polysomal RNAs from gill hybridized to 9.1 and 2.9%, respectively, of the single-copy DNA, values that were 2.5-fold lower than those obtained in the CNS. Taken together, the results focus attention on the striking diversity of gene expression in the squid CNS and extend to the cephalopod mollusks the observation that nervous tissue expresses significantly more genetic information than other somatic tissues or organs.

In situ hybridization histochemistry for the analysis of gene expression in the endocrine and central nervous system tissues: a 3-year experience

We report our experience in development of the in situ hybridization (ISH) procedure to detect messenger RNAs (mRNAs) coding for various molecules involved in endocrine glands and central nervous system activity, including mRNAs coding for endorphin precursors [preproenkephalin A (PPA), pro-opiocortin (POMC)], vasopressin, and transferrin. Various conditions of fixation and handling of the tissues were tested to establish optimal parameters for mRNA detection. Double-stranded DNA probes labeled by nick translation, synthetic oligonucleotides labeled at their 5' end, as well as single-stranded RNA probes were used, after incorporation of 32P- or 35S-labeled nucleotides. Specific requirements for efficient and reproducible ISH investigations are discussed. Cells expressing the PPA gene in the adrenal medulla and in the brain were detected by ISH. The results show that ISH is as sensitive as immunohistochemistry in detecting peptide-producing cells in the adrenal and that it allows detection of PPA cell bodies in brain in conditions in which they are inconstantly detected by immunohistochemistry. Unilateral destruction of substantia nigra provokes a dramatic decrease in the number of neurons expressing the PPA gene in the contralateral striatum. Cells expressing the POMC gene were detected in the pituitary of various species including man and in the rat arcuate nucleus. Neurons containing vasopressin mRNA were visualized in the supraoptic paraventricular and suprachiasmatic nucleus of the adult rat by using a synthetic oligonucleotide probe. Transferrin gene expression was shown in the central nervous system of the rat brain in two cell populations, the oligodendrocytes and the epithelial cells of the choroid plexus, by demonstration of simultaneous presence in them of transferrin immunoreactivity together with transferrin mRNA. These results show that the ISH procedure is a technique that can be routinely used to investigate gene transcription anatomically in complex heterocellular tissues such as the endocrine glands and the nervous system.

Diversity of gene expression in goldfish brain

The sequence complexity of nuclear and polysomal RNA from goldfish brain and kidney was measured by RNA-driven hybridization reactions with single-copy [3H]DNA. At saturation, brain nuclear and polysomal RNA were complementary to 23.2 and 6.7% of the DNA probe, respectively. In contrast to these findings, nuclear and polysomal RNA from kidney hybridized to 16.1 and 3.1% of the single-copy DNA, values that were significantly lower than that obtained in the CNS. Taken together, the results focus attention on the striking diversity of gene expression in goldfish brain and extend to lower vertebrates the observation that nervous tissue expresses significantly more genetic information than other somatic tissues or organs.

Nuclear RNA metabolism in rat hippocampal slices incubated in vitro

Rat hippocampal slices were incubated with [3H]uridine in vitro to analyze the metabolism of nuclear RNA and the RNA precursor fractions. Labeling of total nuclear RNA was linear for 4 h of incubation and proportional to the concentration of labeled uridine in the incubation medium. Addition of 3.5 X 10(-8) M corticosterone to the incubation medium produced an enhancement of nuclear RNA labeling with no significant effect on the labeling of the RNA precursor fraction. Progesterone and dexamethasone, at the same concentration, had no effect on either variable. Labeling of RNA by cerebellar slices under the same conditions was approximately one-half the value obtained using hippocampal slices and the cerebellar RNA precursor fraction accumulated only 65% of the radioactivity from [3H]uridine found in the hippocampal pool. Corticosterone had no effect on the labeling of total nuclear RNA in cerebellar slices. Nuclear poly(A)-containing RNA constituted 19% of the total labeled nuclear RNA in these incubations, as estimated by oligo (dT)-cellulose chromatography. Cordycepin (3'-deoxyadenosine) at a concentration of 25 micrograms/ml inhibited to some extent the labeling of total nuclear RNA and the RNA precursor fraction, but preferentially diminished the amount of labeled RNA bound to oligo (dT)-cellulose. Corticosterone increased the amount of [3H]RNA which bound to oligo (dT)-cellulose, while progesterone had no effect. These results show that hippocampal slices maintained in vitro, can be used to analyze nuclear RNA metabolism, one positive regulator of which in the rat hippocampus is the adrenal steroid, corticosterone.

Alteration of hippocampal B50 phosphorylation after adrenalectomy

Adrenalectomy alters endogenous phosphorylation of the presynaptic protein, B50, in the hippocampus. Three and four days following adrenalectomy decreases are seen, relative to control values, in the in vitro phosphorylation of B50 when a synaptic plasma membrane fraction from the hippocampus is incubated with [gamma-32P]ATP. At four days post-adrenalectomy, the percent decrease in B50 phosphorylation is -49.8 +/- 6.8%. No alteration is seen in the level of B50 phosphorylation when comparing hippocampal membrane preparations from sham-operated and intact animals. Fourteen days following adrenalectomy, hippocampal B50 phosphorylation was restored to normal levels. Hypophysectomy did not alter the degree of in vitro B50 phosphorylation, but the effect of adrenalectomy occurred in hypophysectomized rats. Following adrenalectomy, no differences are seen in the phosphorylation of any hippocampal cytosolic proteins. Changes in B50 phosphorylation seen in hypothalamic synaptic plasma membranes are likely due to the effects of sham-operation. The results indicate that a transient neurochemical or neuroendocrine event following adrenalectomy modulates in vivo the degree of B50 phosphorylation in hippocampal synaptic membranes.