Marcy A. Kingsbury

Chromosomal variation in neurons of the developing and adult mammalian nervous system

A basic assumption about the normal nervous system is that its neurons possess identical genomes. Here we present direct evidence for genomic variability, manifested as chromosomal aneuploidy, among developing and mature neurons. Analysis of mouse embryonic cerebral cortical neuroblasts in situ detected lagging chromosomes during mitosis, suggesting the normal generation of aneuploidy in these somatic cells. Spectral karyotype analysis identified ≈33% of neuroblasts as aneuploid. Most cells lacked one chromosome, whereas others showed hyperploidy, monosomy, and/or trisomy. The prevalence of aneuploidy was reduced by culturing cortical explants in medium containing fibroblast growth factor 2. Interphase fluorescence in situ hybridization on embryonic cortical cells supported the rate of aneuploidy observed by spectral karyotyping and detected aneuploidy in adult neurons. Our results demonstrate that genomes of developing and adult neurons can be different at the level of whole chromosomes.

Constitutional Aneuploidy in the Normal Human Brain

The mouse brain contains genetically distinct cells that differ with respect to chromosome number manifested as aneuploidy (Rehen et al., 2001); however, the relevance to humans is not known. Here, using double-label fluorescence in situ hybridization for the autosome chromosome 21 (chromosome 21 point probes combined with chromosome 21 “paint” probes), along with immunocytochemistry and cell sorting, we present evidence for chromosome gain and loss in the human brain. Chromosome 21 aneuploid cells constitute ∼4% of the estimated one trillion cells in the human brain and include non-neuronal cells and postmitotic neurons identified by the neuronspecific nuclear protein marker. In comparison, human interphase lymphocytes present chromosome 21 aneuploidy rates of 0.6%. Together, these data demonstrate that human brain cells (both neurons and non-neuronal cells) can be aneuploid and that the resulting genetic mosaicism is a normal feature of the human CNS.

Non-proliferative effects of lysophosphatidic acid enhance cortical growth and folding

Lysophosphatidic acid (LPA) is a phospholipid that has extracellular signaling properties mediated by G protein–coupled receptors. Two LPA receptors, LPA1 and LPA2, are expressed in the embryonic cerebral cortex, suggesting roles for LPA signaling in cortical formation. Here we report that intact cerebral cortices exposed to extracellular LPA ex vivo rapidly increased in width and produced folds resembling gyri, which are not normally present in mouse brains and are absent in LPA1 LPA2 double-null mice. Mechanistically, growth was not due to increased proliferation but rather to receptor-dependent reduced cell death and increased terminal mitosis of neural progenitor cells (NPCs). Our results implicate extracellular lipid signals as new influences on brain formation during embryonic development.

Mesotocin and nonapeptide receptors promote estrildid flocking behavior.

Why Birds of a Feather Flock Together The biological determination of sociality, that is, why one might choose to associate with others and how many, has been unclear. Goodson et al. (p. 862) show that in gregarious finches, oxytocin-like receptors and their cognate ligand, mesotocin, are associated with group size choices. Receptor distributions clearly differentiate territorial species from flocking species. Furthermore, these compounds appear to play a role in affecting choice in affiliation in mammals, and thus may be conserved across evolutionary distant taxa. Oxytocin and oxytocin-like receptors control group size preference in a songbird, suggesting an evolutionarily conserved role in social affiliation. Proximate neural mechanisms that influence preferences for groups of a given size are almost wholly unknown. In the highly gregarious zebra finch (Estrildidae: Taeniopygia guttata), blockade of nonapeptide receptors by an oxytocin (OT) antagonist significantly reduced time spent with large groups and familiar social partners independent of time spent in social contact. Opposing effects were produced by central infusions of mesotocin (MT, avian homolog of OT). Most drug effects appeared to be female-specific. Across five estrildid finch species, species-typical group size correlates with nonapeptide receptor distributions in the lateral septum, and sociality in female zebra finches was reduced by OT antagonist infusions into the septum but not a control area. We propose that titration of sociality by MT represents a phylogenetically deep framework for the evolution of OT’s female-specific roles in pair bonding and maternal functions.

Aneuploid neurons are functionally active and integrated into brain circuitry

The existence of aneuploid cells within the mammalian brain has suggested the influence of genetic mosaicism on normal neural circuitry. However, aneuploid cells might instead be glia, nonneural, or dying cells, which are irrelevant to direct neuronal signaling. Combining retrograde labeling with FISH for chromosome-specific loci, distantly labeled aneuploid neurons were observed in expected anatomical projection areas. Coincident labeling for immediate early gene expression indicated that these aneuploid neurons were functionally active. These results demonstrate that functioning neurons with aneuploid genomes form genetically mosaic neural circuitries as part of the normal organization of the mammalian brain.

Lysophosphatidic acid as a novel cell survival/apoptotic factor

Lysophosphatidic acid (LPA) activates its cognate G protein-coupled receptors (GPCRs) LPA(1-3) to exert diverse cellular effects, including cell survival and apoptosis. The potent survival effect of LPA on Schwann cells (SCs) is mediated through the pertussis toxin (PTX)-sensitive G(i/o)/phosphoinositide 3-kinase (PI3K)/Akt signaling pathways and possibly enhanced by the activation of PTX-insensitive Rho-dependent pathways. LPA promotes survival of many other cell types mainly through PTX-sensitive G(i/o) proteins. Paradoxically, LPA also induces apoptosis in certain cells, such as myeloid progenitor cells, hippocampal neurons, and PC12 cells, in which the activation of the Rho-dependent pathways and caspase cascades has been implicated. The effects of LPA on both cell survival and apoptosis underscore important roles for this lipid in normal development and pathological processes.

Evolving nonapeptide mechanisms of gregariousness and social diversity in birds.

Of the major vertebrate taxa, Class Aves is the most extensively studied in relation to the evolution of social systems and behavior, largely because birds exhibit an incomparable balance of tractability, diversity, and cognitive complexity. In addition, like humans, most bird species are socially monogamous, exhibit biparental care, and conduct most of their social interactions through auditory and visual modalities. These qualities make birds attractive as research subjects, and also make them valuable for comparative studies of neuroendocrine mechanisms. This value has become increasingly apparent as more and more evidence shows that social behavior circuits of the basal forebrain and midbrain are deeply conserved (from an evolutionary perspective), and particularly similar in birds and mammals. Among the strongest similarities are the basic structures and functions of avian and mammalian nonapeptide systems, which include mesotocin (MT) and arginine vasotocin (VT) systems in birds, and the homologous oxytocin (OT) and vasopressin (VP) systems, respectively, in mammals. We here summarize these basic properties, and then describe a research program that has leveraged the social diversity of estrildid finches to gain insights into the nonapeptide mechanisms of grouping, a behavioral dimension that is not experimentally tractable in most other taxa. These studies have used five monogamous, biparental finch species that exhibit group sizes ranging from territorial male-female pairs to large flocks containing hundreds or thousands of birds. The results provide novel insights into the history of nonapeptide functions in amniote vertebrates, and yield remarkable clarity on the nonapeptide biology of dinosaurs and ancient mammals. This article is part of a Special Issue entitled Oxytocin, Vasopressin, and Social Behavior.

Aneuploidy in the normal and diseased brain

Abstract.The brain is remarkable for its complex organization and functions, which have been historically assumed to arise from cells with identical genomes. However, recent studies have shown that the brain is in fact a complex genetic mosaic of aneuploid and euploid cells. The precise function of neural aneuploidy and mosaicism are currently being examined on multiple fronts that include contributions to cellular diversity, cellular signaling and diseases of the central nervous system (CNS). Constitutive aneuploidy in genetic diseases has proven roles in brain dysfunction, as observed in Down syndrome (trisomy 21) and mosaic variegated aneuploidy. The existence of aneuploid cells within normal individuals raises the possibility that these cells might have distinct functions in the normal and diseased brain, the latter contributing to sporadic CNS disorders including cancer. Here we review what is known about neural aneuploidy, and offer speculations on its role in diseases of the brain.

Lysophosphatidic Acid Signaling May Initiate Fetal Hydrocephalus

Blockade of lysophosphatidic acid signaling provides a new strategy for treating fetal hydrocephalus. Is the Cause of Hydrocephalus Blood Simple? Hydrocephalus or “water on the brain” is caused by accumulation of cerebrospinal fluid (CSF) in the cerebral ventricles during fetal development and is one of the most common neurological disorders of newborns, occurring in 1 in 1500 live births. One apparent cause of hydrocephalus is bleeding into the cerebral ventricles or brain tissue of the fetus, suggesting that factors or components in blood may trigger development of this severe neurological disorder. The most common treatment is surgical insertion of an intraventricular shunt that drains excess CSF from the cerebral ventricles, but this approach only relieves intracranial pressure and does not solve the root cause of the disorder. Yung et al. set out to investigate which factors in blood trigger hydrocephalus using an in vivo fetal mouse model that they developed. They identify a blood-borne lipid called lysophosphatidic acid (LPA) as a potential cause of hydrocephalus and show that when LPA is prevented from binding to its receptor LPA1 by a receptor antagonist, that hydrocephalus does not develop in fetal mice. The authors injected serum, plasma, or red blood cells into the cerebral ventricles of the brains of fetal mice in utero at 13.5 days of gestation. The animals were then assessed prenatally 1 or 5 days later or postnatally at several different time points. Injection of serum or plasma but not red blood cells induced CSF accumulation and hydrocephalus, with animals displaying enlarged heads, dilated ventricles, and thinning of the cortex. The investigators reasoned that LPA, a blood-borne lipid that is known to be important for the developing cerebral cortex, might be involved in the development of hydrocephalus. When they injected a solution containing LPA into the cerebral ventricles of fetal mice in utero, the mice did indeed develop severe hydrocephalus. The authors wondered how an increase in LPA might affect cortical development and lead to hydrocephalus. They show that injection of LPA resulted in altered adhesion and mislocalization of neural progenitor cells along the surface of the ventricles and that this mislocalization depended on expression of the LPA1 receptor by these cells. When the researchers repeated their experiments with fetal mice lacking the LPA1 receptor, they were unable to induce hydrocephalus. The key finding came with their demonstration that an LPA1 receptor antagonist blocked the ability of LPA to induce hydrocephalus in the fetal mice. These results suggest that LPA and its LPA1 receptor may be new therapeutic targets for developing drugs that could be used in conjunction with surgery to treat this debilitating neurological disease. Fetal hydrocephalus (FH), characterized by the accumulation of cerebrospinal fluid, an enlarged head, and neurological dysfunction, is one of the most common neurological disorders of newborns. Although the etiology of FH remains unclear, it is associated with intracranial hemorrhage. Here, we report that lysophosphatidic acid (LPA), a blood-borne lipid that activates signaling through heterotrimeric guanosine 5′-triphosphate–binding protein (G protein)–coupled receptors, provides a molecular explanation for FH associated with hemorrhage. A mouse model of intracranial hemorrhage in which the brains of mouse embryos were exposed to blood or LPA resulted in development of FH. FH development was dependent on the expression of the LPA1 receptor by neural progenitor cells. Administration of an LPA1 receptor antagonist blocked development of FH. These findings implicate the LPA signaling pathway in the etiology of FH and suggest new potential targets for developing new treatments for FH.

Lysophosphatidic acid in neural signaling

The physiological and pathological importance of lysophosphatidic acid (LPA) in the nervous system is underscored by its presence, as well as the expression of its receptors in neural tissues. In fact, LPA produces responses in a broad range of cell types related to the function of the nervous system. These cell types include neural cell lines, neural progenitors, primary neurons, oligodendrocytes, Schwann cells, astrocytes, microglia, and brain endothelial cells. LPA-induced cell type-specific effects include changes in cell morphology, promotion of cell proliferation and cell survival, induction of cell death, changes in ion conductance and Ca2+ mobilization, induction of pain transmission, and stimulation of vasoconstriction. These effects are mediated through a number of G protein-coupled LPA receptors that activate various downstream signaling cascades. This review provides a current summary of LPA-induced effects in neural cells in vitro or in vivo in combination with our current understanding of the signaling pathways responsible for these effects.