Developmental changes in phospholipase D activity and mRNA levels in rat brain

Differential expression patterns of phospholipase D isoforms 1 and 2 in the mammalian brain and retina

Phosphatidic acid is a key signaling molecule heavily implicated in exocytosis due to its protein-binding partners and propensity to induce negative membrane curvature. One phosphatidic acid-producing enzyme, phospholipase D (PLD), has also been implicated in neurotransmission. Unfortunately, due to the unreliability of reagents, there has been confusion in the literature regarding the expression of PLD isoforms in the mammalian brain which has hampered our understanding of their functional roles in neurons. To address this, we generated epitope-tagged PLD1 and PLD2 knockin mice using CRISPR/Cas9. Using these mice, we show that PLD1 and PLD2 are both localized at synapses by adulthood, with PLD2 expression being considerably higher in glial cells and PLD1 expression predominating in neurons. Interestingly, we observed that only PLD1 is expressed in the mouse retina, where it is found in the synaptic plexiform layers. These data provide critical information regarding the localization and potential role of PLDs in the central nervous system.

Phospholipase D1 Ablation Disrupts Mouse Longitudinal Hippocampal Axis Organization and Functioning

Phosphatidic acid (PA) is a signaling lipid involved in the modulation of synaptic structure and functioning. Based on previous work showing a decreasing PA gradient along the longitudinal axis of the rodent hippocampus, we asked whether the dorsal hippocampus (DH) and the ventral hippocampus (VH) are differentially affected by PA modulation. Here, we show that phospholipase D1 (PLD1) is a major hippocampal PA source, compared to PLD2, and that PLD1 ablation affects predominantly the lipidome of the DH. Moreover, Pld1 knockout (KO) mice show specific deficits in novel object recognition and social interaction and disruption in the DH-VH dendritic arborization differentiation in CA1/CA3 pyramidal neurons. Also, Pld1 KO animals present reduced long-term depression (LTD) induction and reduced GluN2A and SNAP-25 protein levels in the DH. Overall, we observe that PLD1-derived PA reduction leads to differential lipid signatures along the longitudinal hippocampal axis, predominantly affecting DH organization and functioning.

Developmental levels of phospholipase D isozymes in the brain of developing rats

The developmental levels of phospholipase D (PLD) isozymes was examined in the cerebrum and hindbrain of the developing rat to better understand the involvement of PLD in brain development. Western blot analysis of PLD in the cerebrum showed that PLD1, a major PLD isoform in the brain, was detected weakly in the cerebrum at day 17 embryonic stage and its levels gradually increased until postnatal day 35 and remained unaltered thereafter. In the hindbrain, comprising the cerebellum and pons, the peak level of PLD1 was detected at 21 days postnatally and declined progressively thereafter. The level of PLD2 in both the cerebrum and hindbrain was minimal compared to that of PLD1. Based on immunohistochemistry, PLD was detected in some neurons and glial cells in the cerebrum. In the hindbrain, PLD was found in some Purkinje cells and some cells of the molecular layer, as well as glial cells, consistent with the results obtained from Western blot analysis. These findings suggest that PLD may differentially play a role in the course of early development of the brain, with special reference to the cerebrum and hindbrain, in rats.

Effect of aroclor 1248 and two pure PCB congeners on phospholipase D activity in rat renal tubular cell cultures

This paper elucidates the effect of different polychlorinated biphenyls (PCBs) on the phospholipase D (PLD) activity in soluble and particulate fractions of rat renal proximal tubular culture cells. Treatment with Aroclor 1248 (a commercial PCB mixture) caused a marked increase in the activity of PLD in intact renal tubular cells. The PLD activity was increased by Aroclor 1248 in the particulate fraction while the enzyme activity was unaffected in the soluble fraction. This work also shows that PCB 153 (2,2',4,4',5,5'-hexachlorobiphenyl, a di-ortho-substituted nonplanar congener) can increase the activity of PLD only in the particulate fraction. The exposure of cell cultures to PCB 77 (3,3',4,4'-tetrachlorobiphenyl, a non-ortho-substituted planar congener) does not alter PLD activity. These results suggest that PCB effects are structure dependent. Therefore, in order to clarify the molecular mechanism of activation of PLD by PCBs, the contents of immunoreactive PLD were examined by immunoblot analysis. Renal tubular cells expressed a PLD protein of 120 kDa corresponding with the PLD1 mammalian isoform in both the particulate and the soluble fraction. Aroclor 1248, PCB 153, and PCB 77 do not induce changes in the levels of PLD protein. These data indicate that PCBs, particularly nonplanar congeners, increase PLD activity. Moreover, these changes could not be demonstrated in the enzyme content in rat renal tubular cell cultures.

Functions and pathophysiological roles of phospholipase D in the brain

Ten years after the isoforms of mammalian phospholipase D (PLD), PLD1 and 2, were cloned, their roles in the brain remain speculative but several lines of evidence now implicate these enzymes in basic cell functions such as vesicular trafficking as well as in brain development. Many mitogenic factors, including neurotransmitters and growth factors, activate PLD in neurons and astrocytes. Activation of PLD downstream of protein kinase C seems to be a required step for astroglial proliferation. The characteristic disruption of the PLD signaling pathway by ethanol probably contributes to the delay of brain growth in fetal alcohol syndrome. The post-natal increase of PLD activities concurs with synapto- and myelinogenesis in the brain and PLD is apparently involved in neurite formation. In the adult and aging brain, PLD activity has antiapoptotic properties suppressing ceramide formation. Increased PLD activities in acute and chronic neurodegeneration as well as in inflammatory processes are evidently due to astrogliosis and may be associated with protective responses of tissue repair and remodeling. ARF-regulated PLD participates in receptor endocytosis as well as in exocytosis of neurotransmitters where PLD seems to favor vesicle fusion by modifications of the shape and charge of lipid membranes. Finally, PLD activities contribute free choline for the synthesis of acetylcholine in the brain. Novel tools such as RNA interference should help to further elucidate the roles of PLD isoforms in brain physiology and pathology.

Phospholipase D (PLD) gene expression in human neutrophils and HL-60 differentiation

Human neutrophils exhibit a regulated phospholipase D (PLD) activity that can be measured biochemically in vitro. However, the precise expression pattern of PLD isoforms and their specific biological role(s) are not well understood. Neutrophil mRNA is intrinsically difficult to isolate as a result of the extremely high content of lytic enzymes in the cell's lysosomal granules. Reverse transcription coupled to polymerase chain reaction indicated that pure populations of human neutrophils had the CD16b(+)/CD115(-)/CD20(-)/CD3zeta(-)/interleukin-5 receptor alpha(-) phenotype. These cells expressed the following splice variants of the PLD1 isoform: PLD1a, PLD1b, PLD1a2, and PLD1b2. As for the PLD2 isoform, neutrophils expressed the PLD2a but not the PLD2b mRNA variant. The relative amount of PLD1/PLD2 transcripts exists in an approximate 4:1 ratio. The expression of PLD isoforms varies during granulocytic differentiation, as demonstrated in the promyelocytic leukemia HL-60 cell line. Further, the pattern of mRNA expression is dependent on the differentiation-inducing agent, 1.25% dimethyl sulfoxide causes a dramatic increase in PLD2a and PLD1b transcripts, and 300 nM all-trans-retinoic acid induced PLD1a expression. These results demonstrate for the first time that human neutrophils express five PLD transcripts and that the PLD genes undergo qualitative changes in transcription regulation during granulocytic differentiation.

Differential Expression of Phospholipase D Isozymes in the Hippocampus Following Kainic Acid-Induced Seizures

To investigate the pathophysiological role of phospholipase D (PLD)-mediated signaling, changes in the expression of the PLD isozymes PLD1 and PLD2 were investigated in the rat kainic acid (KA) model of human temporal lobe epilepsy. Western blot analysis showed a significant increase in the expression of PLD1 and PLD2 in the postictal hippocampus. PLD1 immunoreactivity increased preferentially in the CA3 and CA1 regions, where pyramidal neurons are susceptible to temporal lobe epilepsy. Experiments employing double immunofluorescence revealed that the cells expressing PLD1 were GFAP-expressing reactive astrocytes. By contrast, PLD2 immunoreactivity increased strikingly in infrapyramidal, but not in suprapyramidal granule cells of the postictal dentate gyrus, fitting well with results of the PLD activity assay. Considering that PLD belongs to a key signaling pathway, this result suggests that changes in granule cell activity in the dentate gyrus after seizures occurs specifically between the supra- and infrapyramidal blades. In addition, enhanced immunoreactivity of PLD2 was observed in the reactive astrocytes of the CA1, CA3, and hilar subregions, but its temporal pattern is different from that of PLD1. Taken together, our results suggest that PLD1 and PLD2 exercise their unique pathophysiological functions in the rat hippocampus after KA-induced seizures.

Retinoic acid-induced differentiation into astrocytes and glutamatergic neurons is associated with expression of functional and activable phospholipase D

Phospholipase D (PLD) activity in mammalian cells has been associated with cell proliferation and differentiation. Here, we investigated the expression of PLD during differentiation of pluripotent embryonal carcinoma cells (P19) into astrocytes and neurons. Retinoic acid (RA)-induced differentiation increased PLD1 and PLD2 mRNA levels and PLD activity that was responsive to phorbol myristate acetate. Various agonists of membrane receptors activated PLD in RA-differentiated cells. Glutamate was a potent activator of PLD in neurons but not in astrocytes, whereas noradrenaline and carbachol increased PLD activity only in astrocytes. P19 neurons but not astrocytes released glutamate in response to a depolarizing stimulus, confirming the glutamatergic phenotype of these neurons. These results indicate upregulation of PLD gene expression associated with RA-induced neural differentiation.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Stability of phospholipase D in primary astrocytes

Induction of expression and proteolytic breakdown of phospholipase D (PLD) isoforms in primary astrocyte cultures have been investigated. Astrocytes express both PLD1 and 2 and are dependent on PLD activity for cell proliferation [K. Kötter, J. Klein, J. Neurochem. 73 (1999) 2517]. Competitive RT-PCR analysis demonstrated a higher level of PLD1 mRNA than PLD2 mRNA (8.9 vs. 0.9amol/microg RNA, respectively). Treatment of astroglial cultures with the phorbol ester, 4beta-phorbol-12beta,13alpha-dibutyrate (0.1 microM), for 24-48h selectively induced PLD1b but not PLD1a or 2 expression as shown by PCR and Western blot; the effect was sensitive to Gö 6976. In cells transiently permeabilized with streptolysin-O, antisense oligonucleotides directed against PLD1 or 2 entered the cytoplasm as shown by immunofluorescence experiments but did not affect astroglial proliferation within 2-6 days. Treatment of the cultures with cycloheximide revealed that PLD1 and 2 proteins had biological half-lives of 2-3 days (PLD2) and 4-6 days (PLD1), respectively. It has been concluded that astroglial PLD1b is up-regulated by phorbol esters via protein kinase C activation. Down-regulation of PLD isoforms is prevented by extended biological half-lives of the PLD proteins.

Differential expression of phospholipase D1 in the developing retina

Expression patterns of phospholipase D1 (PLD1) in the developing rat retina were investigated using immunocytochemistry and Western blot analysis and compared with the expression patterns of glutamine synthetase. PLD1 immunoreactivity appeared first in a few neuroblasts in the middle of the mantle zone of the primitive retina by embryonic (E) day 13. PLD1-immunoreactive primitive ganglion cells were characterized in the ganglion cell layer by E17. Faint immunoreactivity at E17 profiled radially orientated cells and this pattern appeared up to postnatal (P) day 7. In the ganglion cell layer at P3, displaced amacrine cells and ganglion cells were classified. At P5, presumptive horizontal cells and amacrine cells were identified. By P7, a thin outermost layer of newly formed segments of the photoreceptor cells was also PLD1 immunoreactive. PLD1 immunoreactivity at P8 was limited to radial Müller cells and the outer segment layer of the photoreceptor cells, and the expression pattern was conserved to adulthood. Western blot analysis showed relatively high amounts of PLD1 protein at E17 and P3, a decrease at P7, and moderate amounts from P8 onward. Co-expression of PLD1 with glutamine synthetase in the retina appeared first after birth in differentiating neurons and in Müller cells by P8; thereafter the pattern was maintained. The expression pattern of the PLD1 during development of the retina suggests that PLD1 plays important roles in glutamate-associated differentiation of both specific neurons and radial glial cells, and in glutamate-mediated cellular signalling in Müller cells.

Generation of choline for acetylcholine synthesis by phospholipase D isoforms

BACKGROUND

In cholinergic neurons, the hydrolysis of phosphatidylcholine (PC) by a phospholipase D (PLD)-type enzyme generates some of the precursor choline used for the synthesis of the neurotransmitter acetylcholine (ACh). We sought to determine the molecular identity of the relevant PLD using murine basal forebrain cholinergic SN56 cells in which the expression and activity of the two PLD isoforms, PLD1 and PLD2, were experimentally modified. ACh levels were examined in cells incubated in a choline-free medium, to ensure that their ACh was synthesized entirely from intracellular choline.

RESULTS

PLD2, but not PLD1, mRNA and protein were detected in these cells and endogenous PLD activity and ACh synthesis were stimulated by phorbol 12-myristate 13-acetate (PMA). Introduction of a PLD2 antisense oligonucleotide into the cells reduced PLD2 mRNA and protein expression by approximately 30%. The PLD2 antisense oligomer similarly reduced basal- and PMA-stimulated PLD activity and ACh levels. Overexpression of mouse PLD2 by transient transfection increased basal- (by 74%) and PMA-stimulated (by 3.2-fold) PLD activity. Moreover, PLD2 transfection increased ACh levels by 26% in the absence of PMA and by 2.1-fold in the presence of PMA. Overexpression of human PLD1 by transient transfection increased PLD activity by 4.6-fold and ACh synthesis by 2.3-fold in the presence of PMA as compared to controls.

CONCLUSIONS

These data identify PLD2 as the endogenous enzyme that hydrolyzes PC to generate choline for ACh synthesis in cholinergic cells, and indicate that in a model system choline generated by PLD1 may also be used for this purpose.

Metabotropic glutamate receptors stimulate phospholipase D via different pathways in the adult and neonate rat hippocampus

In order to characterize the ontogenetic profile of metabotropic glutamate (mGlu) receptors coupled to phospholipase D (PLD) we examined the effects of selected mGlu agents on PLD activity in immature and adult rat hippocampus. The group I mGlu receptor agonist 3,5-dihydroxyphenylglycine stimulated PLD in immature tissue, but reduced the PLD response evoked by the nonselective mGlu receptor agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate [(1S,3R)-ACPD] in adult hippocampus. (2R,1'S,2'R,3'S)-2-(2'-Carboxy-3'-phenylcyclopropyl) glycine (PCCG-13), a recently characterized selective antagonist of PLD-coupled mGlu receptors, displayed a much greater activity in reducing the PLD response to (1S,3R)-ACPD in adult than in neonate hippocampus. Our results lend support to the hypothesis that glutamatergic activation of PLD in the rat hippocampus is developmentally regulated.

Transient expression of phospholipase D1 in developing rat hippocampus

We investigated the distribution of phospholipase D1 (PLD1) protein in the developing rat hippocampus using an affinity-purified peptide antibody against PLD1. Immunoreactivity for PLD1 was first seen in some scattered cells in the hippocampus at embryonic day 18. At postnatal day 1 (P1), many PLD1 immunoreactive cells were observed in the CA1 and CA3 sectors, subiculum and the hilus of the dentate gyrus. During the first postnatal week, there was an abrupt increase of immunoreactive neurons in the hippocampus, and their number and intensity peaked at P7. During the second postnatal week, there was an abrupt decrease in the number of immunoreactive hippocampal neurons. By P14, no significant labeling was found in the hippocampus. These results corresponded well with those from Western blot analysis, suggesting that PLD1 may regulate the developmental processes of hippocampal neurons.

Modifications in phospholipase D activity and isoform expression occur upon maturation and differentiation in vivo and in vitro in human myeloid cells

Activation of phospholipase D (PLD) occurs in response to various stimuli and results from the activity of two isozymes, hPLD1 and hPLD2. PLD activity appears to be involved in several myeloid cell processes during their development and activation, including proliferation of myeloblasts in the bone marrow and secretion, phagocytosis and NADPH oxidase activation, essential functions of differentiated neutrophils. The present work studies PLD characteristics, activity and both isozyme expression during maturation and differentiation of myeloid cells by using three different systems: leukemic myeloblasts at different stages of maturation, terminally differentiated neutrophils ex vivo and four human myeloid cell lines, NB4, HL-60, PLB 985 and U937, induced to differentiate with alltrans retinoic acid (ATRA), a cyclic adenosine monophosphate (cAMP) analogue or both agents together. HL-60, a bipotential cell line has also been differentiated along the granulocytic pathway with DMSO and the monocytic pathway with 1,25-dihydroxy vitamin D3. In all these systems, PLD activity increases with maturation and differentiation whatever the inducer used and the granulocytic or monocytic pathways. Increase in basal activity which reflects the expression during development of both hPLD1 and hPLD2 appears to be mainly related to the former isozyme expression. Association of PLD characteristic changes with maturation and differentiation was also confirmed using two NB4 clones resistant to these processes. Comparison between PLD characteristics in myeloblasts during maturation and differentiation ex vivo and in vitro in the different cell lines demonstrated that NB4 induced to differentiate with ATRA represents the best model for further studies on the specific roles of each PLD isoform in various functions of differentiated myeloid cells.

Developmental expression of phospholipase D2 mRNA in rat brain

Phospholipase D (PLD) is a ubiquitous enzyme involved in many important cellular functions. Rat brain PLD isoforms have recently been cloned and characterized, but the expression of this gene has not been well studied. We thus examined the developmental expression of PLD2 in postnatal brains by Northern blotting employing a non-radioactive RNA probe. Two PLD2 mRNA transcripts of 3.9 and 10.8 kb were detected in different brain regions and various tissues of the rat. In postnatal brains, the level of PLD2 mRNA transcripts are low 1 day after birth, increase progressively during development, and reach the maximum level in the adult brain. We thus conclude that rat brain PLD2 mRNA is developmentally regulated.

Immunohistochemical localization of phospholipase D1 in rat central nervous system

Phospholipase D (PLD) is one of the intracellular signal transduction enzymes and plays an important role in a variety of cellular functions. We investigated the distribution of PLD isozyme, PLD1 in the rat brain and spinal cord using an immunological approach. Western blot analysis showed the presence of PLD1 protein in all tissues studied, with significantly higher levels in the brainstem and spinal cord, which was correlated with the results obtained from PLD activity assay. Prominent and specific signals of PLD1 were observed in many functionally diverse brain areas, including the olfactory bulb, medial septum-diagonal band complex, cerebral cortex, brainstem, cerebellum, and spinal cord. In the brainstem, the red nucleus, substantia nigra, interpeduncular nucleus, cranial motor nuclei (trigeminal motor, abducent, facial, and hypoglossal), sensory cranial nerve nuclei (spinal trigeminal, vestibular, and cochlear), as well as nuclei of the reticular formation, all showed intense immunoreactivity. Purkinje cells and deep cerebellar nuclei of the cerebellum were also labeled intensely. However, no significant labeling was found in the thalamus, epithalamus, and basal ganglia. Although many of the PLD1 immunoreactive cells were neurons, PLD1 was also expressed in glial cells such as presumed astrocytes and tanycytes. These findings suggest that PLD1 may play an important role in the central nervous system of the adult rat.

Changes in phospholipase D isoform activity and expression in multidrug-resistant human cancer cells

Multidrug resistance (MDR) is a major cause of failure of cancer chemotherapy and is often associated with elevated expression of drug transporters such as P-glycoprotein (P-gp) in the cancer cells. MDR is, however, accompanied by additional biochemical changes including modifications of membrane composition and properties. We have shown that MDR is associated with a massive up-regulation of caveolin expression and an elevated surface density of caveolae. We report that phospholipase D (PLD), a constituent enzyme of caveolae and detergent-insoluble glycolipid-rich membranes (DIGs), is up-regulated in human MDR cancer cells. Lysates of HT-29-MDR human colon adenocarcinoma cells, MCF-7 AdrR human breast adenocarcinoma cells and the corresponding parental drug-sensitive cells, were fractionated on discontinuous sucrose density gradients. PLD activity was found to be enriched in low density fractions that contain DIGs and caveolar membranes, and the activity in these fractions was 4- to 6-fold higher in the MDR cells compared with the parental drug- sensitive cells. Utilizing specific antibodies to PLD1 and PLD2, the distribution of PLD isoforms along the gradient was determined and the PLD localized in DIGs and caveolar membranes has been identified as PLD2. Northern blot analysis of PLD1 and PLD2 mRNA levels has indicated that PLD2 mRNA is elevated in both HT-29-MDR and MCF-7 AdrR cells. PLD1 mRNA levels were either unchanged or reduced in the MDR cells. Finally, in vivo experiments have confirmed previous results showing that activation of PLD by phorbol esters is markedly potentiated in the MDR cells. We conclude that MDR is accompanied by an increase in PLD2 activity in DIGs and caveolar membranes.

Localization of mRNAs for phospholipase D (PLD) type 1 and 2 in the brain of developing and mature rat

Phospholipase D (PLD) is known as one of the key enzymes in the lipid metabolism which produces several second messengers. We demonstrated the localization of the gene expression for PLD1 and PLD2 using in situ hybridization histochemistry in the brain of developing and mature rats. Whereas PLD1 mRNA expression was detected mainly in presumptive oligodendrocytes, PLD2 mRNA expression was detected mainly in presumptive astrocytes. In addition, the gene expression for PLDs were expressed in neuroepithelial cells of the ventricular/ependymal zones and the gene for PLD2 was expressed transiently in early postnatal gray matters, presumptive neurons.

Expression of phospholipase D isoforms in mammalian cells

Two mammalian isoforms of phospholipase D, PLD1 and PLD2, have recently been characterized at the molecular level. Effects of physiologic agonists on PLD activity in intact cells, as characterized in earlier studies, have generally not been attributed to specific PLD isoforms. Recent work has established that expression of PLD1 and PLD2 varies within tissues and between cell lines. A single cell type can express one, both, or neither isoform, although most cells co-express PLD1 and PLD2. Lymphocytes often lack expression of one or both isoforms of PLD. Relative levels of PLD mRNA expression vary considerably between established cell lines. Expression of transcripts for both PLD1 and PLD2 can be regulated at the transcriptional level by growth and differentiation factors in cultured cells. Thus, it is apparent that the known mammalian PLD isoforms are subject to regulation at the transcriptional level. The available data do not conclusively establish whether PLD1 and PLD2 are the only isoforms responsible for agonist-mediated PLD activation. Further studies of the regulation of expression of PLD isoforms should provide insight into the roles of PLD1 and PLD2 in physiologic responses, and may suggest whether additional forms of PLD remain to be characterized.

New gene targets related to schizophrenia and other psychiatric disorders: enzymes, binding proteins and transport proteins involved in phospholipid and fatty acid metabolism

Phospholipids make up about 60% of the brain's dry weight. In spite of this, phospholipid metabolism has received relatively little attention from those seeking genetic factors involved in psychiatric and neurological disorders. However, there is now increasing evidence from many quarters that abnormal phospholipid and related fatty acid metabolism may contribute to illnesses such as schizophrenia, bipolar disorder, depression and attention deficit hyperactivity disorder. To date the possible specific proteins and genes involved have been relatively ill-defined. This paper reviews the main pathways of phospholipid metabolism, emphasizing the roles of phospholipases of the A2 and C series in signal transduction processes. It identifies some likely protein candidates for involvement in psychiatric and neurological disorders. It also reviews the chromosomal locations of regions likely to be involved in these disorders, and relates these to the known locations of genes directly or indirectly involved in phospholipid and fatty acid metabolism.