New insights from the last decade of research in psychiatric genetics: discoveries,challenges and clinical implications

Psychiatric genetics has made substantial progress in the last decade, providing new insights into the genetic etiology of psychiatric disorders, and paving the way for precision psychiatry, in which individual genetic profiles may be used to personalize risk assessment and inform clinical decision-making. Long recognized to be heritable, recent evidence shows that psychiatric disorders are influenced by thousands of genetic variants acting together. Most of these variants are commonly occurring, meaning that every individual has a genetic risk to each psychiatric disorder, from low to high. A series of large-scale genetic studies have discovered an increasing number of common and rare genetic variants robustly associated with major psychiatric disorders. The most convincing biological interpretation of the genetic findings implicates altered synaptic function in autism spectrum disorder and schizophrenia. However, the mechanistic understanding is still incomplete. In line with their extensive clinical and epidemiological overlap, psychiatric disorders appear to exist on genetic continua and share a large degree of genetic risk with one another. This provides further support to the notion that current psychiatric diagnoses do not represent distinct pathogenic entities, which may inform ongoing attempts to reconceptualize psychiatric nosology. Psychiatric disorders also share genetic influences with a range of behavioral and somatic traits and diseases, including brain structures, cognitive function, immunological phenotypes and cardiovascular disease, suggesting shared genetic etiology of potential clinical importance. Current polygenic risk score tools, which predict individual genetic susceptibility to illness, do not yet provide clinically actionable information. However, their precision is likely to improve in the coming years, and they may eventually become part of clinical practice, stressing the need to educate clinicians and patients about their potential use and misuse. This review discusses key recent insights from psychiatric genetics and their possible clinical applications, and suggests future directions.     

Alginate-based solid media for plant tissue culture

Summary A new method for solid medium plant tissue culture based on in situ gelation of alginate is proposed as an alternative to agar-based media. In situ gelation by the use of dispersed CaCO₃ and the slowly hydrolysing acid glucono--lactone (GDL) was the basis for the use of alginate as a gelling agent. Inexpensive alginate-based media can be made in a wide range of pH values. Biological tests of these gels, concerning sterile seed growth and microcalli plating of Brassica napus (cv. Topas) and biomass production of Panax ginseng callus, showed results equal to those achieved with agar-based gels.     

Cyclic adenosine monophosphate acts synergistically with dexamethasone to inhibit the entrance of cultured adult rat hepatocytes into S-phase: with a note on the use of nucleolar and extranucleolar [3H]-thymidine labelling patterns to determine rapid changes in the rate of onset of DNA replication

Analogs of cyclic adenosine monophosphate (cAMP) (N⁶benzoyl cAMP and N⁶monobutyryl cAMP) as well as agents that increased the intracellular level of cAMP (glucagon and isobutylmethylxanthine) inhibited the EGF-stimulated DNA replication of adult rat hepatocytes in primary culture independently of cell density. This inhibition was strongly potentiated by the glucocorticoid dexamethasone. The effect of cAMP (and dexamethasone) was not due to toxicity, because the inhibition was reversible and the cell ultrastructure preserved. cAMP acted by decreasing the rate of transition from G₁- to S-phase, the duration of G₂- and S-phase of the hepatocyte cell cycle being unaffected. DNA replication started in the extranucleolar compartment of the nucleus and ended in the nucleolar compartment as described earlier for cells grown in the absence of cAMP (O.K. Vintermyr and S.O. Døskeland, J. Cell. Physiol., 1987, 132:12-21). The action of cAMP was very rapid: significant inhibition of the transition was noted 2 hr after the addition of glucagon/IBMX and half-maximal inhibition after 4 hours. The determination of extranucleolarly labelled nuclei in cells pulse-labelled with [³H]thymidine allowed precise analysis of rapid changes in the probability of transition from G₁- to S-phase. The extranucleolar labelling index could also be determined in cells continuously exposed to [³H]thymidine.     

Advanced radiogasometric method for the determination of the rates of photorespiratory and respiratory decarboxylations of primary and stored photosynthates under steady-state photosynthesis

An advanced radiogasometric method for the study of plant leaf CO₂ exchange is presented. The method enables determination of the rates of CO₂ fixation, photorespiration and respiration in the light under steady‐state photosynthesis and discrimination between primary and stored photosynthates as substrates of photorespiratory and respiratory decarboxylations. The method is based on the analysis of the time curves of ¹⁴CO₂ evolution from labeled primary and stored photosynthates in leaves previously exposed to ¹⁴CO₂. The molar rates of different decarboxylation reactions are calculated from the initial slopes of the curves taking into account the specific radioactivity of CO₂ fed to leaves and/or evolved from leaves. To estimate the contribution of primary and stored photosynthates, the measurements of ¹⁴CO₂ evolution are performed after feeding plant leaves for different periods with ¹⁴CO₂. Photorespiration and respiration are distinguished on the basis of data obtained from measurements of ¹⁴CO₂ evolution under normal (210 ml l⁻¹) and low (15 ml l⁻¹) concentrations of oxygen. A principally new method for the determination of the rate of intracellular refixation of respiratory CO₂ has been developed. The method is based on the measurements of ¹⁴CO₂ evolution from leaves into the medium of very high concentrations (30 ml l⁻¹) of ¹²CO₂, where the probability of refixation of ¹⁴CO₂ evolved inside the cell is close to zero. The results obtained were comparable with the data derived from parallel refixation measurements by means of gasometric methods. As an example of application, the data on CO₂ exchange in leaves of two contrasting groups of C₃‐species, differing in the ability of starch accumulation, are presented.     

Studies on resilin-like gene products in insects

Putative pro-resilins from 12 Drosophila species are compared with each other and with some pro-resilin-related proteins from other insect species, in an attempt to decide which structural features are likely to be important for the characteristic properties of resilins. The putative pro-resilins from the 12 Drosophila species are very similar; their structures are characterized by a chitin-binding R&R Consensus sequence of type RR-2, surrounded by two repeat-containing regions. The repeat-containing regions are assumed to be responsible for the long-range elasticity characteristic for resilin. Pronounced differences are present between the Drosophila pro-resilins and the resilin-like gene products present in other insect species. It is suggested that gene products, which are predicted both to be cuticular proteins and to possess long-range elasticity, should be classified as either putative pro-resilins or pro-resilin-like proteins. Gene products which are predicted to possess long-range elasticity, but do not contain a chitin-binding region, should not be classified as pro-resilin-like proteins until it has been established that they are cuticular proteins.     

The impact of different water gas levels on cataract formation, muscle and lens free amino acids, and lens antioxidant enzymes and heat shock protein mRNA abundance in smolting Atlantic salmon, Salmo salar L

The present experiment was conducted to examine if freshwater (FW) oxygen and carbon dioxide regimes cause physiological responses that lead to cataract formation in Atlantic salmon (Salmo salar L.) smolt. Duplicate groups of 50 g Atlantic salmon smolts were exposed to three freshwater oxygen saturation regimes (95, 112 or 125% saturation), with or without addition of carbon dioxide (measured 17–18 and 2–3 mg L^− 1, respectively), for six weeks before transfer to seawater (SW). The FW exposure groups were followed up for another six weeks under a common SW regime. Fish were screened for cataract and sampled accordingly, at start, after 6 weeks in FW and after 6 weeks in SW. Increased growth related cataract incidences and severities were recorded in SW, mainly in the groups previously exposed to normoxic and hyperoxic conditions in FW, as compared to the respective groups added carbon dioxide. The concentration of histidine compounds (imidazoles) in muscle and lens tissue, used as quantitative risk markers of cataract, were lower than observed in earlier studies, however, neither were affected by the present water gas regimes in FW nor after follow up in SW. Independently of water oxygenation in FW, muscle free amino acid profiles in salmon groups concomitantly exposed to elevated carbon dioxide indicated use of selected free amino acids for energy purposes. Significantly lower abundance of heat shock protein 70 mRNA and trends towards stepwise reduction of antioxidant enzymes mRNA in the lens from fish exposed to increased water oxygenation were recorded, probably linked to increased growth and/or external stress during smoltification. This represents a first communication on using early molecular markers to express reduced protection of the fish lens against external stress to explain cataract development.     

EBV infection renders B cells resistant to growth inhibition via adenylyl cyclase

Cyclic AMP (cAMP) is an important physiological growth inhibitor of lymphoid cells, and the cAMP/protein kinase A (PKA) pathway is disrupted in several immunological disorders and cancers. Epstein Barr virus (EBV) infection of B lymphocytes is responsible for the development of lymphoproliferative disease as well as certain B-lymphoid malignancies. Here we hypothesized that EBV infection might render B lymphocytes resistant to cAMP/PKA-mediated growth inhibition. To test this, we assessed the growth-inhibitory response of cAMP-elevating compounds such as forskolin and isoproterenol, as well as the PKA activator 8-CPT-cAMP in normal B lymphocytes, EBV-infected B cells and in the EBV-negative B lymphoid cell line Reh. We could demonstrate that EBV infection indeed abolished cAMP-mediated growth inhibition of B cells. The defect was pinpointed to defective adenylyl cyclase (AC) activation by forskolin and isoproterenol, resulting in reduced formation of cAMP and lack of PKA activation and CREB phosphorylation. In contrast, 8-CPT-cAMP which directly activates PKA was able to inhibit EBV-infected B cell growth. The physiological implications of these results were underlined by the observation that the ability of forskolin to inhibit camptothecin-induced apoptosis was abolished in EBV-infected B cells. We conclude that EBV infection of B cells abrogates the activation of AC and thereby cAMP formation, and that this dysfunction renders the cells resistant to growth inhibition via the cAMP/PKA pathway.     

MALS-3 regulates polarity and early neurogenesis in the developing cerebral cortex

Apicobasal polarity plays an important role in regulating asymmetric cell divisions by neural progenitor cells (NPCs) in invertebrates, but the role of polarity in mammalian NPCs is poorly understood. Here, we characterize the function of the PDZ domain protein MALS-3 in the developing cerebral cortex. We find that MALS-3 is localized to the apical domain of NPCs. Mice lacking all three MALS genes fail to localize the polarity proteins PATJ and PALS1 apically in NPCs, whereas the formation and maintenance of adherens junctions appears normal. In the absence of MALS proteins, early NPCs progressed more slowly through the cell cycle, and their daughter cells were more likely to exit the cell cycle and differentiate into neurons. Interestingly, these effects were transient; NPCs recovered normal cell cycle properties during late neurogenesis. Experiments in which MALS-3 was targeted to the entire membrane resulted in a breakdown of apicobasal polarity, loss of adherens junctions, and a slowing of the cell cycle. Our results suggest that MALS-3 plays a role in maintaining apicobasal polarity and is required for normal neurogenesis in the developing cortex.     

Quantitative determination of catecholic degradation products from insect sclerotized cuticles

Acid hydrolysates of cuticle from various insect species were quantitatively analyzed for five catecholic amino acid adducts. Four of the adducts are ketocatechols; in three of them the amino acid moiety, either lysine, glycine or beta-alanine, is connected via its amino group to the alpha-carbon atom of 3,4-dihydroxyacetophenone, in the fourth a tyrosine residue is connected to the same position via its phenolic group. The fifth adduct contains histidine linked via its imidazole-ring to the beta-position of the dopamine sidechain. The three ketocatecholic adducts containing alpha-amino acids were obtained in significant yields from adult cuticles of the locust Schistocerca gregaria, the cockroaches Blaberus craniifer and Periplaneta americana, and the beetles Pachynoda sinuata and Tenebrio molitor, but only in trace amounts from larval and pupal cuticles of T. molitor, pupal cuticles of the moths Manduca sexta and Hyalophora cecropia, and puparia of the blowfly Calliphora vicina. The beta-alanine-containing ketocatechol was not obtained from cuticle of locusts and T. molitor larvae and pupae, but it was present in the hydrolysates of the other cuticles. The beta-histidine-dopamine adduct was obtained from all the cuticles, the highest yield was obtained from adult P. sinuata and the lowest yield was from adult S. gregaria. The beta-histidine-dopamine adduct is derived from the product formed by reaction of p-quinone methides of N-acetyldopamine (NADA) or N-beta-alanyldopamine (NBAD) with histidine residues in the cuticular proteins. The ketocatecholic adducts are assumed to be degradation products of crosslinks formed when oxidized dehydro-NADA reacts with the cuticular proteins. The insect species investigated appear to use both pathways for sclerotization, but to widely differing extents; the dehydro-NADA pathway dominates in cuticles which are exposed to strong deforming forces, such as those of adult locusts and cockroaches, and the p-quinone methide pathway dominates in cuticle of lepidopteran pupae and blowfly puparia, which are not exposed to strong mechanical forces but have to be effectively protected against microbial and fungal attacks.     

Ca2+/calmodulin-dependent protein kinase II is required for microcystin-induced apoptosis.

The potent natural toxins microcystin, nodularin, and okadaic acid act rapidly to induce apoptotic cell death. Here we show that the apoptosis correlates with protein phosphorylation events and can be blocked by protein kinase inhibitors directed against the multifunctional Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). The inhibitors used comprised a battery of cell-permeable protein kinase antagonists and CaMKII-directed peptide inhibitors introduced by microinjection or enforced expression. Furthermore, apoptosis could be induced by enforced expression of active forms of CaMKII but not with inactive CaMKII. It is concluded that the apoptogenic toxins, presumably through their known ability to inhibit serine/threonine protein phosphatases, can cause CaMKII-dependent phosphorylation events leading to cell death.