Functional organization of spatial and nonspatial working memory processing within the human lateral frontal cortex

The present study used functional magnetic resonance imaging to demonstrate that performance of visual spatial and visual nonspatial working memory tasks involve the same regions of the lateral prefrontal cortex when all factors unrelated to the type of stimulus material are appropriately controlled. These results provide evidence that spatial and nonspatial working memory may not be mediated, respectively, by mid-dorsolateral and mid-ventrolateral regions of the frontal lobe, as widely assumed, and support the alternative notion that specific regions of the lateral prefrontal cortex make identical executive functional contributions to both spatial and nonspatial working memory.

Complete sequencing of the Fugu WAGR region from WT1 to PAX6: Dramatic compaction and conservation of synteny with human chromosome 11p13

The pufferfish Fugu rubripes has a genome ≈7.5 times smaller than that of mammals but with a similar number of genes. Although conserved synteny has been demonstrated between pufferfish and mammals across some regions of the genome, there is some controversy as to what extent Fugu will be a useful model for the human genome, e.g., [Gilley, J., Armes, N. & Fried, M. (1997) Nature (London) 385, 305–306]. We report extensive conservation of synteny between a 1.5-Mb region of human chromosome 11 and <100 kb of the Fugu genome in three overlapping cosmids. Our findings support the idea that the majority of DNA in the region of human chromosome 11p13 is intergenic. Comparative analysis of three unrelated genes with quite different roles, WT1, RCN1, and PAX6, has revealed differences in their structural evolution. Whereas the human WT1 gene can generate 16 protein isoforms via a combination of alternative splicing, RNA editing, and alternative start site usage, our data predict that Fugu WT1 is capable of generating only two isoforms. This raises the question of the extent to which the evolution of WT1 isoforms is related to the evolution of the mammalian genitourinary system. In addition, this region of the Fugu genome shows a much greater overall compaction than usual but with significant noncoding homology observed at the PAX6 locus, implying that comparative genomics has identified regulatory elements associated with this gene.

Conservation of the Drosophila lateral inhibition pathway in human lung cancer: A hairy-related protein (HES-1) directly represses achaete-scute homolog-1 expression

The achaete-scute genes encode essential transcription factors in normal Drosophila and vertebrate nervous system development. Human achaete-scute homolog-1 (hASH1) is constitutively expressed in a human lung cancer with neuroendocrine (NE) features, small cell lung cancer (SCLC), and is essential for development of the normal pulmonary NE cells that most resemble this neoplasm. Mechanisms regulating achaete-scute homolog expression outside of Drosophila are presently unclear, either in the context of the developing nervous system or in normal or neoplastic cells with NE features. We now provide evidence that the protein hairy-enhancer-of-split-1 (HES-1) acts in a similar manner as its Drosophila homolog, hairy, to transcriptionally repress achaete-scute expression. HES-1 protein is detected at abundant levels in most non-NE human lung cancer cell lines which lack hASH1 but is virtually absent in hASH1-expressing lung cancer cells. Moreover, induction of HES-1 in a SCLC cell line down-regulates endogenous hASH1 gene expression. The repressive effect of HES-1 is directly mediated by binding of the protein to a class C site in the hASH1 promoter. Thus, a key part of the process that determines neural fate in Drosophila is conserved in human lung cancer cells. Furthermore, modulation of this pathway may underlie the constitutive hASH1 expression seen in NE tumors such as SCLC, the most virulent human lung cancer.

Transgenic rats reveal functional conservation of regulatory controls between the Fugu isotocin and rat oxytocin genes

We have asked whether comparative genome analysis and rat transgenesis can be used to identify functional regulatory domains in the gene locus encoding the hypothalamic neuropeptides oxytocin (OT) and vasopressin. Isotocin (IT) and vasotocin (VT) are the teleost homologues of these genes. A contiguous stretch of 46 kb spanning the Fugu IT-VT locus has been sequenced, and nine putative genes were found. Unlike the OT and vasopressin genes, which are closely linked in the mammalian genome in a tail-to-tail orientation, Fugu IT and VT genes are linked head to tail and are separated by five genes. When a cosmid containing the Fugu IT-VT locus was introduced into the rat genome, we found that the Fugu IT gene was specifically expressed in rat hypothalamic oxytocinergic neurons and mimicked the response of the endogenous OT gene to an osmotic stimulus. These data show that cis-acting elements and trans-acting factors mediating the cell-specific and physiological regulation of the OT and IT genes are conserved between mammals and fish. The combination of Fugu genome analysis and transgenesis in a mammal is a powerful tool for identifying and analyzing conserved vertebrate regulatory elements.

Evolutionary conservation of apoptosis mechanisms: Lepidopteran and baculoviral inhibitor of apoptosis proteins are inhibitors of mammalian caspase-9

We cloned a new inhibitor of apoptosis protein (IAP) homolog, SfIAP, from Spodoptera frugiperda Sf-21 cells, a host of insect baculoviruses. SfIAP contains two baculovirus IAP repeat domains followed by a RING domain. SfIAP has striking amino acid sequence similarity with baculoviral IAPs, CpIAP and OpIAP, suggesting that baculoviral IAPs may be host-derived genes. SfIAP and baculoviral CpIAP inhibit Bax but not Fas-induced apoptosis in human cells. Their apoptosis-suppressing activity in mammalian cells requires both baculovirus IAP repeat and RING domains. Further biochemical data suggest that SfIAP and CpIAP are specific inhibitors of mammalian caspase-9, the pinnacle caspase in the mitochondria/cytochrome c pathway for apoptosis, but are not inhibitors of downstream caspase-3 and caspase-7. Thus the mechanisms by which insect and baculoviral IAPs suppress apoptosis may involve inhibition of an insect caspase-9 homologue. Peptides representing the IAP-binding domain of the Drosophila cell death protein Grim abrogated human caspase suppression by SfIAP and CpIAP, implying evolutionary conservation of the functions of IAPs and their inhibitors.

Conservation of the expression and function of apterous orthologs in Drosophila and mammals

The Drosophila apterous (ap) gene encodes a protein of the LIM-homeodomain family. Many transcription factors of this class have been conserved during evolution; however, the functional significance of their structural conservation is generally not known. ap is best known for its fundamental role as a dorsal selector gene required for patterning and growth of the wing, but it also has other important functions required for neuronal fasciculation, fertility, and normal viability. We isolated mouse (mLhx2) and human (hLhx2) ap orthologs, and we used transgenic animals and rescue assays to investigate the conservation of the Ap protein during evolution. We found that the human protein LHX2 is able to regulate correctly ap target genes in the fly, causes the same phenotypes as Ap when ectopically produced, and most importantly rescues ap mutant phenotypes as efficiently as the fly protein. In addition, we found striking similarities in the expression patterns of the Drosophila and murine genes. Both mLhx2 and ap are expressed in the respective nerve cords, eyes, olfactory organs, brain, and limbs. These results demonstrate the conservation of Ap protein function across phyla and argue that aspects of its expression pattern have also been conserved from a common ancestor of insects and vertebrates.

Conservation of early odontogenic signaling pathways in Aves

Teeth have been missing from birds (Aves) for at least 60 million years. However, in the chick oral cavity a rudiment forms that resembles the lamina stage of the mammalian molar tooth germ. We have addressed the molecular basis for this secondary loss of tooth formation in Aves by analyzing in chick embryos the status of molecular pathways known to regulate mouse tooth development. Similar to the mouse dental lamina, expression of Fgf8, Pitx2, Barx1, and Pax9 defines a potential chick odontogenic region. However, the expression of three molecules involved in tooth initiation, Bmp4, Msx1, and Msx2, are absent from the presumptive chick dental lamina. In chick mandibles, exogenous bone morphogenetic protein (BMP) induces Msx expression and together with fibroblast growth factor promotes the development of Sonic hedgehog expressing epithelial structures. Distinct epithelial appendages also were induced when chick mandibular epithelium was recombined with a tissue source of BMPs and fibroblast growth factors, chick skin mesenchyme. These results show that, although latent, the early signaling pathways involved in odontogenesis remain inducible in Aves and suggest that loss of odontogenic Bmp4 expression may be responsible for the early arrest of tooth development in living birds.

Conservation of fibroblast growth factor function in lens regeneration

In urodele amphibians, lens induction during development and regeneration occurs through different pathways. During development, the lens is induced from the mutual interaction of the ectoderm and the optic vesicle, whereas after lentectomy the lens is regenerated through the transdifferentiation of the iris-pigmented epithelial cells. Given the known role of fibroblast growth factors (FGFs) during lens development, we examined whether or not the expression and the effects of exogenous FGF during urodele lens regeneration were conserved. In this paper, we describe expression of FGF-1 and its receptors, FGFR-2 (KGFR and bek variants) and FGFR-3, in newts during lens regeneration. Expression of these genes was readily observed in the dedifferentiating pigmented epithelial cells, and the levels of expression were high in the lens epithelium and the differentiating fibers and lower in the retina. These patterns of expression implied involvement of FGFs in lens regeneration. To further elucidate this function, we examined the effects of exogenous FGF-1 and FGF-4 during lens regeneration. FGF-1 or FGF-4 treatment in lentectomized eyes resulted in the induction of abnormalities reminiscent to the ones induced during lens development in transgenic mice. Effects included transformation of epithelial cells to fiber cells, double lens regeneration, and lenses with abnormal polarity. These results establish that FGF molecules are key factors in fiber differentiation, polarity, and morphogenesis of the lens during regeneration even though the regenerating lens is induced by a different mechanism than in lens development. In this sense, FGF function in lens regeneration and development should be regarded as conserved. Such conservation should help elucidate the mechanisms of lens regeneration in urodeles and its absence in higher vertebrates.

The neural basis of task-switching in working memory: Effects of performance and aging

We studied the performance of young and senior subjects on a well known working memory task, the Operation Span. This is a dual-task in which subjects perform a memory task while simultaneously verifying simple equations. Positron-emission tomography scans were taken during performance. Both young and senior subjects demonstrated a cost in accuracy and latency in the Operation Span compared with performing each component task alone (math verification or memory only). Senior subjects were disproportionately impaired relative to young subjects on the dual-task. When brain activation was examined for senior subjects, we found regions in prefrontal cortex that were active in the dual-task, but not in the component tasks. Similar results were obtained for young subjects who performed relatively poorly on the dual-task; however, for young subjects who performed relatively well in the dual-task, we found no prefrontal regions that were active only in the dual-task. Results are discussed as they relate to the executive component of task switching.

Plant orthologs of p300/CBP: conservation of a core domain in metazoan p300/CBP acetyltransferase-related proteins

p300 and CBP participate as transcriptional coregulators in the execution of a wide spectrum of cellular gene expression programs controlling cell differentiation, growth and homeostasis. Both proteins act together with sequence-specific transcription factors to modify chromatin structure of target genes via their intrinsic acetyltransferase activity directed towards core histones and some transcription factors. So far, p300-related proteins have been described in animals ranging from Drosophila and Caenorhabditis elegans to humans. In this report, we describe p300/CBP-like polypeptides in the plant Arabidopsis thaliana. Interestingly, homology between animal and plant p300/CBP is largely restricted to a C-terminal segment, about 600 amino acids in length, which encompasses acetyltransferase and E1A-binding domains. We have examined whether this conservation in sequence is paralleled by a conservation in function. The same amino acid residues critical for acetyltransferase activity in human p300 are also critical for the function of one of the plant orthologs. Remarkably, plant proteins bind to the adenovirus E1A protein in a manner recapitulating the binding specificity of mammalian p300/CBP. The striking conservation of an extended segment of p300/CBP suggests that it may constitute a functional entity fulfilling functions that may be essential for all metazoan organisms.

Evolutionary conservation of sequence elements controlling cytoplasmic polyadenylylation.

Cytoplasmic polyadenylylation is an evolutionarily conserved mechanism involved in the translational activation of a set of maternal messenger RNAs (mRNAs) during early development. In this report, we show by interspecies injections that Xenopus and mouse use the same regulatory sequences to control cytoplasmic poly(A) addition during meiotic maturation. Similarly, Xenopus and Drosophila embryos exploit functionally conserved signals to regulate polyadenylylation during early post-fertilization development. These experiments demonstrate that the sequence elements that govern cytoplasmic polyadenylylation, and hence one form of translational activation, function across species. We infer that the requisite regulatory sequence elements, and likely the trans-acting components with which they interact, have been conserved since the divergence of vertebrates and arthropods.