Illusory memories: A cognitive neuroscience analysis

Memory illusions and distortions have long been of interest to psychology researchers studying memory, but neuropsychologists and neuroscientists have paid relatively little attention to them. This article attempts to lay the foundation for a cognitive neuroscience analysis of memory illusions and distortions by reviewing relevant evidence from a patient with a right frontal lobe lesion, patients with amnesia produced by damage to the medial temporal lobes, normal aging, and healthy young volunteers studied with functional neuroimaging techniques. Particular attention is paid to the contrasting roles of prefrontal cortex and medial temporal lobe structures in accurate and illusory remembering. Converging evidence suggests that the study of illusory memories can provide a useful tool for delineating the brain processes and systems involved in constructive aspects of remembering.

Morphological innovation and developmental genetics

How do the actions of individual genes contribute to the complex morphologies of animals and plants? How widespread are these genes taxonomically? How many genes are involved in the morphological differences observed between species, and can we identify them? To what extent can empirical data and theory be reconciled? We provide an overview of some recent attempts to answer these questions, answers that have taken us to the threshold of understanding the mechanistic basis and evolutionary factors that underlie morphological innovation.

Imaging neuroscience: Principles or maps?

This article reviews some recent trends in imaging neuroscience. A distinction is made between making maps of functional responses in the brain and discerning the rules or principles that underlie their organization. After considering developments in the characterization of brain imaging data, several examples are presented that highlight the context-sensitive nature of neuronal responses that we measure. These contexts can be endogenous and physiological, reflecting the fact that each cortical area, or neuronal population, expresses its dynamics in the context of interactions with other areas. Conversely, these contexts can be experimental or psychological and can have a profound effect on the regional effects elicited. In this review we consider experimental designs and analytic strategies that go beyond cognitive subtraction and speculate on how functional imaging can be used to address both the details and principles underlying functional integration and specialization in the brain.

Arthropods: Developmental diversity within a (super) phylum

The expression patterns of developmental genes provide new markers that address the homology of body parts and provide clues as to how body plans have evolved. Such markers support the idea that insect wings evolved from limbs but refute the idea that insect and crustacean jaws are fundamentally different in structure. They also confirm that arthropod tagmosis reflects underlying patterns of Hox gene regulation but they do not yet resolve to what extent Hox expression domains may serve to define segment homologies.

Auditory neuroscience: Development, transduction, and integration

Hearing underlies our ability to locate sound sources in the environment, our appreciation of music, and our ability to communicate. Participants in the National Academy of Sciences colloquium on Auditory Neuroscience: Development, Transduction, and Integration presented research results bearing on four key issues in auditory research. How does the complex inner ear develop? How does the cochlea transduce sounds into electrical signals? How does the brain's ability to compute the location of a sound source develop? How does the forebrain analyze complex sounds, particularly species-specific communications? This article provides an introduction to the papers stemming from the meeting.

Developmental and Environmental Effects on the Expression of the C3-C4 Intermediate Phenotype in Moricandia arvensis1

Cellular anatomy and expression of glycine decarboxylase (GDC) protein were studied during leaf development of the C3-C4 intermediate species Moricandia arvensis. Leaf anatomy was initially C3-like and the number and profile area of mitochondria in the bundle-sheath cells were the same as those in adjacent mesophyll cells. Between a leaf length of 6 and 12 mm there was a bundle-sheath-specific, 4-fold increase in the number of mitochondrial profiles, followed by a doubling of their individual profile areas as the leaves expanded further. Subunits of GDC were present in whole-leaf extracts before the anatomical development of bundle-sheath cells. Whereas the GDC H-protein content of leaves increased steadily throughout development, the increase in GDC P-protein was synchronous with the development of mitochondria in the bundle sheath. The P-protein was confined to bundle-sheath mitochondria throughout leaf development, and its content in individual mitochondria increased before the anatomical development of the bundle sheath. Anatomical and biochemical attributes of the C3-C4 character were present in the cotyledons and sepals but not in other photosynthetic organs/tissues. In leaves and cotyledons that developed in the dark, the expression of the P-protein and the organellar development were reduced but the bundle-sheath cell specificity was retained.

Developmental Regulation of Intercellular Protein Trafficking through Plasmodesmata in Tobacco Leaf Epidermis1

Plasmodesmata mediate direct cell-to-cell communication in plants. One of their significant features is that primary plasmodesmata formed at the time of cytokinesis often undergo structural modifications, by the de novo addition of cytoplasmic strands across cell walls, to become complex secondary plasmodesmata during plant development. Whether such modifications allow plasmodesmata to gain special transport functions has been an outstanding issue in plant biology. Here we present data showing that the cucumber mosaic virus 3a movement protein (MP):green fluorescent protein (GFP) fusion was not targeted to primary plasmodesmata in the epidermis of young or mature leaves in transgenic tobacco (Nicotiana tabacum) plants constitutively expressing the 3a:GFP fusion gene. Furthermore, the cucumber mosaic virus 3a MP:GFP fusion protein produced in planta by biolistic bombardment of the 3a:GFP fusion gene did not traffic between cells interconnected by primary plasmodesmata in the epidermis of a young leaf. In contrast, the 3a MP:GFP was targeted to complex secondary plasmodesmata and trafficked from cell to cell when a leaf reached a certain developmental stage. These data provide the first experimental evidence, to our knowledge, that primary and complex secondary plasmodesmata have different protein-trafficking functions and suggest that complex secondary plasmodesmata may be formed to traffic specific macromolecules that are important for certain stages of leaf development.

Developmental and Light Regulation of Desacetoxyvindoline 4-Hydroxylase in Catharanthus roseus (L.) G. Don.1 : Evidence of a Multilevel Regulatory Mechanism

The expression of desacetoxyvindoline 4-hydroxylase (D4H), which catalyzes the second to the last reaction in vindoline biosynthesis in Catharanthus roseus, appears to be under complex, multilevel developmental and light regulation. Developmental studies with etiolated and light-treated seedlings suggested that although light had variable effects on the levels of d4h transcripts, those of D4H protein and enzyme activity could be increased, depending on seedling development, up to 9- and 8-fold, respectively, compared with etiolated seedlings. However, light treatment of etiolated seedlings could stop and reverse the decline of d4h transcripts at later stages of seedling development. Repeated exposure of seedlings to light was also required to maintain the full spectrum of enzyme activity observed during seedling development. Further studies showed that a photoreversible phytochrome appeared to be involved in the activation of D4H, since red-light treatment of etiolated seedlings increased the detectable levels of d4h transcripts, D4H protein, and D4H enzyme activity, whereas far-red-light treatment completely reversed this process. Additional studies also confirmed that different major isoforms of D4H protein exist in etiolated (isoelectric point, 4.7) and light-grown (isoelectric point, 4.6) seedlings, suggesting that a component of the light-mediated activation of D4H may involve an undetermined posttranslational modification. The biological reasons for this complex control of vindoline biosynthesis may be related to the need to produce structures that could sequester away from cellular activities the cytotoxic vinblastine and vincristine dimers that are derived partially from vindoline.

Developmental Expression and Substrate Specificities of Alfalfa Caffeic Acid 3-O-Methyltransferase and Caffeoyl Coenzyme A 3-O-Methyltransferase in Relation to Lignification1

The biosynthesis of monolignols can potentially occur via two parallel pathways involving free acids or their coenzyme A (CoA) esters. Caffeic acid 3-O-methyltransferase (COMT) and caffeoyl CoA 3-O-methyltransferase (CCOMT) catalyze functionally identical reactions in these two pathways, resulting in the formation of mono- or dimethoxylated lignin precursors. The activities of the two enzymes increase from the first to the sixth internode in stems of alfalfa (Medicago sativa L.), preceding the deposition of lignin. Alfalfa CCOMT is highly similar at the amino acid sequence level to the CCOMT from parsley, although it contains a six-amino acid insertion near the N terminus. Transcripts encoding both COMT and CCOMT are primarily localized to vascular tissue in alfalfa stems. Alfalfa CCOMT expressed in Escherichia coli catalyzes O-methylation of caffeoyl and 5-hydroxyferuloyl CoA, with preference for caffeoyl CoA. It has low activity against the free acids. COMT expressed in E. coli is active against both caffeic and 5-hydroxyferulic acids, with preference for the latter compound. Surprisingly, very little extractable O-methyltransferase activity versus 5-hydroxyferuloyl CoA is present in alfalfa stem internodes, in which relative O-methyltransferase activity against 5-hy-droxyferulic acid increases with increasing maturity, correlating with increased lignin methoxyl content.

Implications of a Developmental-Stage-Dependent Thylakoid-Bound Protease in the Stabilization of the Light-Harvesting Pigment-Protein Complex Serving Photosystem II during Thylakoid Biogenesis in Red Kidney Bean1

Intact etioplasts of bean (Phaseolus vulgaris) plants exhibit proteolytic activity against the exogenously added apoprotein of the light-harvesting pigment-protein complex serving photosystem II (LHCII) that increases as etiolation is prolonged. The activity increases in the membrane fraction but not in the stroma, where it remains low and constant and is mainly directed against LHCII and protochlorophyllide oxidoreductase. The thylakoid proteolytic activity, which is low in etioplasts of 6-d-old etiolated plants, increases in plants pretreated with a pulse of light or exposed to intermittent-light (ImL) cycles, but decreases during prolonged exposure to continuous light, coincident with chlorophyll (Chl) accumulation. To distinguish between the control of Chl and/or development on proteolytic activity, we used plants exposed to ImL cycles of varying dark-phase durations. In ImL plants exposed to an equal number of ImL cycles with short or long dark intervals (i.e. equal Chl accumulation but different developmental stage) proteolytic activity increased with the duration of the dark phase. In plants exposed to ImL for equal durations to such light-dark cycles (i.e. different Chl accumulation but same developmental stage) the proteolytic activity was similar. These results suggest that the protease, which is free to act under limited Chl accumulation, is dependent on the developmental stage of the chloroplast, and give a clue as to why plants in ImL with short dark intervals contain LHCII, whereas those with long dark intervals possess only photosystem-unit cores and lack LHCII.

Three Drought-Responsive Members of the Nonspecific Lipid-Transfer Protein Gene Family in Lycopersicon pennellii Show Different Developmental Patterns of Expression1

Genomic clones of two nonspecific lipid-transfer protein genes from a drought-tolerant wild species of tomato (Lycopersicon pennellii Corr.) were isolated using as a probe a drought- and abscisic acid (ABA)-induced cDNA clone (pLE16) from cultivated tomato (Lycopersicon esculentum Mill.). Both genes (LpLtp1 and LpLtp2) were sequenced and their corresponding mRNAs were characterized; they are both interrupted by a single intron at identical positions and predict basic proteins of 114 amino acid residues. Genomic Southern data indicated that these genes are members of a small gene family in Lycopersicon spp. The 3′-untranslated regions from LpLtp1 and LpLtp2, as well as a polymerase chain reaction-amplified 3′-untranslated region from pLE16 (cross-hybridizing to a third gene in L. pennellii, namely LpLtp3), were used as gene-specific probes to describe expression in L. pennellii through northern-blot analyses. All LpLtp genes were exclusively expressed in the aerial tissues of the plant and all were drought and ABA inducible. Each gene had a different pattern of expression in fruit, and LpLtp1 and LpLtp2, unlike LpLtp3, were both primarily developmentally regulated in leaf tissue. Putative ABA-responsive elements were found in the proximal promoter regions of LpLtp1 and LpLtp2.

Analysis of Cell Division and Elongation Underlying the Developmental Acceleration of Root Growth in Arabidopsis thaliana1

To investigate the relation between cell division and expansion in the regulation of organ growth rate, we used Arabidopsis thaliana primary roots grown vertically at 20°C with an elongation rate that increased steadily during the first 14 d after germination. We measured spatial profiles of longitudinal velocity and cell length and calculated parameters of cell expansion and division, including rates of local cell production (cells mm−1 h−1) and cell division (cells cell−1 h−1). Data were obtained for the root cortex and also for the two types of epidermal cell, trichoblasts and atrichoblasts. Accelerating root elongation was caused by an increasingly longer growth zone, while maximal strain rates remained unchanged. The enlargement of the growth zone and, hence, the accelerating root elongation rate, were accompanied by a nearly proportionally increased cell production. This increased production was caused by increasingly numerous dividing cells, whereas their rates of division remained approximately constant. Additionally, the spatial profile of cell division rate was essentially constant. The meristem was longer than generally assumed, extending well into the region where cells elongated rapidly. In the two epidermal cell types, meristem length and cell division rate were both very similar to that of cortical cells, and differences in cell length between the two epidermal cell types originated at the apex of the meristem. These results highlight the importance of controlling the number of dividing cells, both to generate tissues with different cell lengths and to regulate the rate of organ enlargement.