Transient receptor potential melastatin (TRPM) channels mediate clozapine-induced phenotypes in Caenorhabditis elegans

Dendrite morphogenesis in Caenorhabditis elegans

Since the days of Ramón y Cajal, the vast diversity of neuronal and particularly dendrite morphology has been used to catalog neurons into different classes. Dendrite morphology varies greatly and reflects the different functions performed by different types of neurons. Significant progress has been made in our understanding of how dendrites form and the molecular factors and forces that shape these often elaborately sculpted structures. Here, we review work in the nematode Caenorhabditis elegans that has shed light on the developmental mechanisms that mediate dendrite morphogenesis with a focus on studies investigating ciliated sensory neurons and the highly elaborated dendritic trees of somatosensory neurons. These studies, which combine time-lapse imaging, genetics, and biochemistry, reveal an intricate network of factors that function both intrinsically in dendrites and extrinsically from surrounding tissues. Therefore, dendrite morphogenesis is the result of multiple tissue interactions, which ultimately determine the shape of dendritic arbors.

Pharming for Genes in Neurotransmission: Combining Chemical and Genetic Approaches in Caenorhabditis elegans

Synaptic transmission is central to nervous system function. Chemical and genetic screens are valuable approaches to probe synaptic mechanisms in living animals. The nematode Caenorhabditis elegans is a prime system to apply these methods to discover genes and dissect the cellular pathways underlying neurotransmission. Here, we review key approaches to understand neurotransmission and the action of psychiatric drugs in C. elegans. We start with early studies on cholinergic excitatory signaling at the neuromuscular junction, and move into mechanisms mediated by biogenic amines. Finally, we discuss emerging work toward understanding the mechanisms driving synaptic plasticity with a focus on regulation of protein translation.

Magnesium in schizophrenia

Many psychopathological symptoms, including schizophrenia, can be associated with magnesium metabolism disturbances. In the literature, contradictory data exist regarding magnesium levels in patients with this disorder. However, this situation might be caused by determination of extracellular concentration of magnesium; although, this is mainly an intracellular ion. There are no data concerning determination of the ionized fraction of magnesium in patients with schizophrenia, while the ionized fraction represents 67% of the total pool of magnesium in healthy people. Also, the mechanism of magnesium action-the effect of magnesium ions on NMDA and GABA receptors-has not yet been fully investigated. There are preliminary studies aimed at increasing the effectiveness of schizophrenia pharmacotherapy via magnesium supplementation. Multidirectional activity of magnesium can significantly increase its therapeutic effect in psychiatry. This observation is confirmed by recent studies conducted by various research teams. However, further studies on the role of magnesium supplementation in patients with schizophrenia are needed.

Clozapine Modulates Glucosylceramide, Clears Aggregated Proteins, and Enhances ATG8/LC3 in Caenorhabditis elegans

Defining the mechanisms of action of the antipsychotic drug (APD), clozapine, is of great importance, as clozapine is more effective and has therapeutic benefits in a broader range of psychiatric disorders compared with other APDs. Its range of actions have not been fully characterized. Exposure to APDs early in development causes dose-dependent developmental delay and lethality in Caenorhabditis elegans. A previous genome-wide RNAi screen for suppressors of clozapine-induced developmental delay and lethality revealed 40 candidate genes, including sms-1, which encodes a sphingomyelin synthase. One sms-1 isoform is expressed in the C. elegans pharynx, and its transgene rescues the sms-1 mutant phenotype. We examined pharyngeal pumping and observed that clozapine-induced inhibition of pharyngeal pumping requires sms-1, a finding that may explain the role of the gene in mediating clozapine-induced developmental delay/lethality. By analyzing multiple enzymes involved in sphingolipid metabolism, and by observing the effect of addition of various lipids directly to the worms, we suggest that glucosylceramide may be a key mediator of the effects of clozapine. We further observed that clozapine clears protein aggregates, such as α-synuclein, PolyQ protein, and α-1-antitrypsin mutant protein. In addition, it enhances ATG8/LC3. We conclude that clozapine appears to affect the development and induce lethality of worms, in part, through modulating glucosylceramide. We discuss the possible connections among glucosylceramide, protein aggregate clearance, and autophagy. Interactions, including mechanistic pathways involving these elements, may underlie some of the clinical effects of clozapine.

The Caenorhabditis elegans Excretory System: A Model for Tubulogenesis, Cell Fate Specification, and Plasticity

The excretory system of the nematode Caenorhabditis elegans is a superb model of tubular organogenesis involving a minimum of cells. The system consists of just three unicellular tubes (canal, duct, and pore), a secretory gland, and two associated neurons. Just as in more complex organs, cells of the excretory system must first adopt specific identities and then coordinate diverse processes to form tubes of appropriate topology, shape, connectivity, and physiological function. The unicellular topology of excretory tubes, their varied and sometimes complex shapes, and the dynamic reprogramming of cell identity and remodeling of tube connectivity that occur during larval development are particularly fascinating features of this organ. The physiological roles of the excretory system in osmoregulation and other aspects of the animal's life cycle are only beginning to be explored. The cellular mechanisms and molecular pathways used to build and shape excretory tubes appear similar to those used in both unicellular and multicellular tubes in more complex organs, such as the vertebrate vascular system and kidney, making this simple organ system a useful model for understanding disease processes.