Much of the protein encoding portion of the genome is expressed in the mammalian brain. Hence, it may be expected that a large number of brain-restricted proteins are to be found. Most of these proteins are probably low in abundance as most brain-specific mRNAs are rare copy species. However, a variety of molecular cloning approaches provide the amplification required to identify and characterize individual, low abundance proteins. Alignment of rare copy mRNAs with their respective proteins is an important step in establishing the functional significance of rare copy mRNAs. Many brain mRNAs appear during the course of postnatal development. It is suggested that some of these late mRNAs encode for proteins involved in the last major developmental phase of the brain, namely, establishment of connectivity. Most of the postnatal brain mRNAs lack a 3′,-poly(A) tract and appear to be transcriptionally regulated. Some mRNAs are apparently bimorphic with respect to the presence or absence of poly(A) tracts. The coupling of molecular genetics with anatomy and cytology should provide a powerful new approach toward gaining an understanding of brain function in the context of specialized cell populations. Proteins, such as receptors and components of synaptic membranes, are attractive targets for investigation.

International Journal of Developmental NeuroscienceVolume 1, Issue 3 p. 193-193 Symposium 1 Activation of genes during postnatal development of the brain W.E. Hahn, W.E. Hahn University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this authorN. Chaudhari, N. Chaudhari University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this authorL. Beck, L. Beck University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this author W.E. Hahn, W.E. Hahn University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this authorN. Chaudhari, N. Chaudhari University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this authorL. Beck, L. Beck University of Colorado School of Medicine, Department of Anatomy, 4200 E. 9th Ave., Denver, Colorado, 80262 U.S.A.Search for more papers by this author First published: 1983 https://doi.org/10.1016/0736-5748(83)90216-2AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume1, Issue31983Pages 193-193 RelatedInformation

The size distribution of labeled hnRNA and mRNA from Hela cells and mouse Ehrlich ascites cells has been analyzed by gel electrophoresis in the presence of the denaturing agent CH 3 HgOH. Up to 43% of the mass of total hnRNA consisted of molecules at least 28 kilobases in size, provided this RNA had been extracted under conditions minimizing degradation. Ten to sixteen percent of the mass of polyadenylated hnRNA consisted of molecules larger than 13 kilobases, although the average molecular weight was less than that of total hnRNA. In comparison, more than 90% of the mass of labeled mRNA (total or polyadenylated) consisted of molecules smaller than 5.5 kilobases. A linear relationship was observed between appropriate functions of molecular weight and mobility for RNA molecules up to at least 13 kilobases in size, provided a low gel concentration and voltage gradient were employed. Increasing these parameters resulted in anomalously fast migration of large RNA molecules. Electrophoretic profiles were not significantly altered when the amount of poly(A) hnRNA was increased from about 1 to 50 μg per cylindrical gel. Thus CH 3 HgOH-agarose gel electrophoresis can be used preparatively for the fractionation of hnRNA. Aggregates containing labeled mRNA (formed in vitro in the presence of excess nuclear RNA) were dissociated by CH 3 HgOH. Partial degradation of high molecular weight RNA was observed after prolonged exposure to CH 3 HgOH.

Polyadenylylated heterogeneous nuclear RNA [poly(A)-hnRNA] from mouse brain was subjected to electrophoresis in agarose gels containing CH3HgOH, and molecules larger than 8 kilobases or 13 kilobases were recovered. cDNA was then transcribed from polyadenylylated RNA fragments cleaved from these large molecules. The resulting cDNA hybridized almost to completion with poly(A)-mRNA isolated from mouse brain polysomes. From the hybridization kinetics of this cDNA with its template RNA, it was estimated that the sequence complexity of the 3'-proximal sequences (of the same average size as mRNA) of the greater than 8 kilobase poly(A)-hnRNA was about 57,000 kilobases. The sequence complexity of poly(A)-mRNA, estimated from the template-driven hybridization kinetics of its respective cDNA, was about 110,000 kilobases. It is concluded that most, if not all, of the 3'-proximal sequences of large poly(A)-hnRNA molecules are homologous with mRNA in the mouse brain and that at least 40,000 different mRNA sequences (or portions of mRNA sequences) are represented in the 3'-proximal sequences of greater than 8 kilobase poly(A)-hnRNA.

DNA-RNA hybridization experiments show that essentially all of the genomic information is transcribed. High, intermediate, and rare abundance classes of messenger RNA (mRNA) are present, and their estimated complexities are equal to about 240, 1300, and 700 average-sized mRNA species, respectively. The high abundance mRNA species are present, on average, two to three copies per cell and constitute about 95 percent of the mRNA mass. Intermediate abundance mRNA species are present, on average, about once per 35 cells. The relative abundance and complexity of these mRNA classes correspond well with previous respective measurements on protein. Rare RNA species are thought to represent maximally repressed genes. Analysis of RNA synthesized in vitro by isolated nucleoids (chromosomes) suggests that sense and nonsense sequences are extensively interspersed on a given strand of the DNA.

Severe degradation of high molecular weight RNA was shown to occur during incubation with commercially purified DNase. Most of the RNase activity could be removed by passage of the DNase through a column of agarose-coupled amino phenylphosphoryl-uridine-2' (3')-phosphate. Incubation with the treated DNase caused only minimal alteration of the sedimentation pattern of high molecular weight nuclear RNA, determined under partially denturing conditions. No impairment of DNase activity was detected.

It is evident that the bulbar EEG is a complex response which can be influenced by several methodological and stimulant variables. What EEG patterns tell us about actual behavior remains obscure. The bulbar EEG which is evoked by homestream water is not necessarily a reflection of olfactory memory. The evoked bulbar EEG also does not necessarily demonstrate the salmon has distinguished the home-water from another water in terms of migrational orientation. Despite lack of absolute specificity, a correlation between bulbar EEG and actual behavioral performance has been observed even though some non-home waters evoke responses similar to that of the home water. In general it has been found that the home water response can be distinguished from the response to other natural waters. Failure to obtain complete specificity may be due to a variety of variables which have been alluded to earlier in this section. Thus considering that the evoked EEG is a reflection of the integration of a diverse afferent input, further electrical and computer analyses may eventually permit the decoding of the EEG in terms of behavior. However, if the EEG proves to be more a quantitative rather than qualitative reflection of brain activity, relating EEG to behavior will prove to be of limited value. Since afferent responses in the olfactory bulb are influenced by impulses from higher brain centers, studies on centrifugal aspects during olfactory stimulation may be useful in gaining some qualitative understanding of the home water evoked EEG of the olfactory bulb.

Nonspecific types of binding occur when oligo(dT)-cellulose is used to analyze or prepare poly(A)RNA. First, nonpolyadenylated nucleic acids bind and are eluted under conditions used to elute poly(A)RNA. Second, "tight" nonspecific binding occurs in which poly(A)RNA fails to elute under conditions which dissociate A-T bonds. Hydrolysis is required to remove tightly bound RNA. Oligo(dT)-cellulose has a low capacity for both these types of binding, and can be readily preempted with a heterologous RNA e.g., bacterial. Third, indirect nonspecific binding can also occur. rRNA aggregates with poly(A)RNA and thus can bind indirectly to oligo(dT)-cellulose. After these aggregates are disrupted by treatment with DMSO and heat, poly(A)mRNA free of rRNA can be isolated. Efficient recovery of poly(A)hnRNA from total nuclear RNA is accomplished using oligo(dT)-cellulose if the RNA is first subjected to conditions which disrupt aggregates and reduce secondary structure. Ninety-five to ninety-eight per cent of the purified poly(A)hnRNA and poly(A)mRNA rebinds to oligo(dT)-cellulose.

The complexity of nuclear RNA, poly(A)hnRNA, poly(A)mRNA, and total poly(A)RNA from mouse brain has been measured by saturation hybridization with nonrepeated DNA. These DNA populations were complementary, respectively, to 21, 13.5, 3.8, and 13.3% of the DNA. From the RNA Cot required to achieve half-sturation, it was estimated that about 2.5–3% of the mass of total nuclear RNA constituted most of the complexity. Similarly, complexity driver molecules constituted 6–7% of the mass of the poly(A)hnRNA. 75–80% of the poly(A)mRNA diversity is contained in an estimated 4–5% of the mass of this mRNA. Poly(A)hnRNA constituted about 20% of the mass of nuclear RNA and was comprised of molecules which sedimented in DMSO-sucrose gradients largely between 16S and 60S. The number average size of poly(A)hnRNA determined by sedimentation, electron microscopy, or poly(A) content was 4200–4800 nucleotides. Poly(A)mRNA constituted about 2% of the total polysomal RNA, and the number average size was 1100–1400 nucleotides. The complexity of whole cell poly(A)RNA, which contains both poly(A)hnRNA and poly(A)mRNA populations, was the same as poly(A)hnRNA. This implies that cytoplasmic polyadenylation does not occur to any apparent qualitative extent and that poly(A)mRNA is a subset of the poly(A)hnRNA population. The complexity of poly(A)hnRNA and poly(A)mRNA in kilobases was 5 × 105 and 1.4 × 105, respectively. DNA which hybridized with poly(A)mRNA renatures in the presence of excess total DNA at the same rate as nonrepetitive tracer DNA. Hence saturation values are due to hybridization with nonrepeated DNA and are therefore a direct measure of the sequence complexity of poly(A)mRNA. These results indicate that the nonrepeated sequence complexity of the poly(A)mRNA population is equal to about one fourth that observed for poly(A)hnRNA.

Under normal conditions of DNA renaturation, about 60 percent of mouse DNA fragments renature at a rate consistent with their being present only once per sperm. These nonrepeated sequences (also called single-copy or unique) may be used in RNA-DNA hybridization experiments to provide quantitative estimates of RNA diversity. About 10 percent of the mouse single-copy sequences are transcribed in mouse brain tissue. Estimates of about 3 percent were obtained for mouse liver and kidney RNA's. If only one of the complementary DNA strands is transcribed, this hybridization value implies that the equivalent of at least 300,000 different sequences of 1000 nucleotides are expressed in mouse brain tissue. It is suggested that the large amount of DNA in mammals is functionally important, and that a substantial proportion of the genome is expressed in the brain.