RNA sequence complexity in central nervous system development and plasticity

Biocultural orchestration of developmental plasticity across levels: the interplay of biology and culture in shaping the mind and behavior across the life span

The author reviews reemerging coconstructive conceptions of development and recent empirical findings of developmental plasticity at different levels spanning several fields of developmental and life sciences. A cross-level dynamic biocultural coconstructive framework is endorsed to understand cognitive and behavioral development across the life span. This framework integrates main conceptions of earlier views into a unifying frame, viewing the dynamics of life span development as occurring simultaneously within different time scales (i.e., moment-to-moment microgenesis, life span ontogeny, and human phylogeny) and encompassing multiple levels (i.e., neurobiological, cognitive, behavioral, and sociocultural). Viewed through this metatheoretical framework, new insights of potential interfaces for reciprocal cultural and experiential influences to be integrated with behavioral genetics and cognitive neuroscience research can be more easily prescribed.

Gene-trapping to identify and analyze genes expressed in the mouse hippocampus

Mice harboring random gene-trap insertions of a lacZ (beta-galactosidase)-neomycin resistance fusion cassette (beta-geo) were analyzed for expression in the hippocampus. In 4 of 15 lines reporter gene activity was observed in the hippocampal formation. In the obn line, enzyme activity was detected in the CA1-3 hippocampal subfields, in hpk expression was restricted to CA1, but in both lines reporter activity was also present in other brain regions. In the third line, kin, reporter activity was robustly expressed throughout the stratum pyrimidale of CA1-3, with only low-level expression elsewhere. The final line (glnC) displayed ubiquitous expression of the reporter and was not analyzed further. Fusion transcripts for the first three lines were characterized; all encode polypeptides with features of membrane-associated signalling proteins. The obn fusion identified a human cDNA (B2-1) encoding a pleckstrin homology (PH) domain, while hpk sequences matched the Epstein-Barr Virus (EBV) inducible G-protein coupled receptor, EBI-1. kin identified an alternative form of the abl-related nonreceptor tyrosine kinase c-arg. Electrophysiological studies on mice homozygous for the insertions revealed normal synaptic transmission, paired pulse facilitation and paired-pulse depression at Schaffer collateral-commissural CA1 synapses, and normal long-term potentiation (LTP) in obn and kin. hpk mice displayed an increase in hippocampal CA1 long-term potentiation (LTP), suggesting a role for this receptor in synaptic plasticity.

Gene expression in cells of the central nervous system

This review summarized a part of our studies over a long period of time, relating them to the literature on the same topics. We aimed our research toward an understanding of the genetic origin of brain specific proteins, identified by B. W. Moore and of the high complexity of the nucleotide sequence of brain mRNA, originally investigated by W. E. Hahn, but have not completely achieved the projected goal. According to our studies, the reason for the high complexity in the RNA of brain nuclei might be the high complexity in neuronal nuclear RNA as described in the Introduction. Although one possible explanation is that it results from the summation of RNA complexities of several neuronal types, our saturation hybridization study with RNA from the isolated nuclei of granule cells showed an equally high sequence complexity as that of brain. It is likely that this type of neuron also contains numerous rare proteins and peptides, perhaps as many as 20,000 species which were not detectable even by two-dimensional PAGE. I was possible to gain insight into the reasons for the high sequence complexity of brain RNA by cloning the cDNA and genomic DNA of the brain-specific proteins as described in the previous sections. These data provided evidence for the long 3'-noncoding regions in the cDNA of the brain-specific proteins which caused the mRNA of brain to be larger than that from other tissues. During isolation of such large mRNAs, a molecule might be split into a 3'-poly(A)+RNA and 5'-poly(A)-RNA. In the studies on genomic DNA, genes with multiple transcription initiation sites were found in brain, such as CCK, CNP and MAG, in addition to NSE which was a housekeeping gene, and this may contribute to the high sequence complexity of brain RNA. Our studies also indicated the presence of genes with alternative splicing in brain, such as those for CNP, MAG and NGF, suggesting a further basis for greater RNA nucleotide sequence complexity. It is noteworthy that alternative splicing of the genes for MBP and PLP also produced multiple mRNAs. Such a mechanism may be a general characteristic of the genes for the myelin-specific proteins produced by oligodendrocytes. In considering the high nucleotide sequence complexity, it is interesting that MAG and S-100 beta genes etc. possess two additional sites for poly(A).(ABSTRACT TRUNCATED AT 400 WORDS)

Forebrain-enriched RNAs of the canary: a population analysis using hybridization kinetics

Canaries and other songbirds offer unique advantages for analyzing the relationship between specific gene regulation and neural plasticity. To establish a quantitative profile of the population of RNAs potentially involved in this regulation, we analyzed the solution hybridization kinetics of canary forebrain cytoplasmic polyadenylated RNA. Hybridization of forebrain cDNA to forebrain RNA provides evidence for RNA species at individual concentrations ranging from less than 10(-6) to about 10(-3) (by fractional mass). Cross-hybridization to RNA from the rest of the brain, together with other studies, defines a subpopulation of about 5000 rare RNAs that are enriched in the forebrain compared to the rest of the brain. Some of these forebrain-enriched RNAs are likely to play a role in regulating the neural plasticity characteristic of the canary forebrain.

Probes for rare mRNAs reveal distributed cell subsets in canary brain

cDNA clones of 7 low-abundance canary brain RNAs hybridize in situ to different subsets of brain cells. Although these cell sets are distinct, they are dispersed in a variety of brain regions with overlapping anatomical distributions. These cDNA clones were initially selected by their relative hybridization to forebrain and rest-of-brain RNAs and represent a sampling of a much larger population of differentially expressed RNAs present at individual concentrations of 10(-7) to 10(-4) as a fraction of polyadenylated RNA mass. Our results suggest the existence of several thousand low-abundance brain mRNAs likely to be distributed in diverse and overlapping brain cell subsets. Furthermore, our experiments define a simple and general strategy for producing and analyzing molecular probes for subsets of brain cells and provide an initial set of useful reagents for further study of brain organization and development.