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 Ϸ33% of neuroblasts as aneuploid. Most cells lacked one chromosome, whereas others showed hyperploidy, monosomy, and͞or 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.

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.

Lysophosphatidic acid (LPA), a bioactive lipid produced by several cell types including postmitotic neurons and activated platelets, is thought to be involved in various biological processes, including brain development. Three cognate G protein-coupled receptors encoded by lpa 1 /lp A1 /Edg-2/Gpcr26, lpa 2 /lp A2 /Edg-4, and lpa 3 /lp A3 / Edg-7 mediate the cellular effects of LPA. We have previously shown that deletion of lpa 1 in mice results in craniofacial dysmorphism, semilethality due to defective suckling behavior, and generation of a small fraction of pups with frontal hematoma. To further investigate the role of these receptors and LPA signaling in the organism, we deleted lpa 2 in mice. Homozygous knockout (lpa 2 (؊/؊) ) mice were born at the expected frequency and displayed no obvious phenotypic abnormalities. fibroblasts. Thus, although LPA 2 is not essential for normal mouse development, it does act redundantly with LPA 1 to mediate most LPA responses in fibroblasts.

These results indicate a nonessential role for LP B3 in normal development of mouse but show nonredundant cellular signaling mediated by a single type of S1P receptor. Sphingosine 1-phosphate (S1P)1 is a potent lysophospholipid mediator that exerts diverse biological effects on many types of cells and tissues. S1P is produced from activated platelets and many other cell types and affects fundamental cellular processes including proliferation, differentiation, survival, adhesion, migration, morphogenesis, and cytoskeletal rearrangement (reviewed in Refs. 1-6). S1P has been proposed to act both as an extracellular mediator and an intracellular second messenger. Recent progress in the identification of specific G protein-coupled receptors that can account for the extracellular effects induced by S1P has improved our understanding of the mechanisms of action of this lipid (reviewed in Refs. 1-6).To date, five cognate G protein-coupled receptors have been identified as mammalian high affinity S1P receptors: LP B1 / EDG-1, LP B2 /H218/AGR16/EDG-5, LP B3 /EDG-3, LP B4 /NRG-1/ EDG-8, and LP C1 /EDG-6 (reviewed in Refs. 6 -8). All S1P receptors belong to a larger lysophospholipid (LP) receptor subfamily, which also includes receptors for lysophosphatidic acid (LPA), a bioactive lipid that is structurally and biologically related to S1P. Each of the LP receptors couples to multiple subsets of heterotrimeric G proteins (including G q , G i/o , and G 12/13 ) and thus drives different signal transduction pathways. Also, the receptor genes are expressed in spatially and temporally different patterns in mice (9, 10), 2 suggesting specific roles for each receptor in vivo. It was reported recently that LP B1 -null mice are embryonic lethal because of incomplete vascular maturation (11), showing the essential role of LP B1 in mouse development. In zebrafish, a single point mutation in an lp B ortholog, mil, led to abnormal heart development (12). To determine in vivo functions and roles of the LP B3 receptor in mammals, we have disrupted lp B3 in mice. Unexpectedly, LP B3 -null mice were viable and fertile and developed normally with no gross phenotypic abnormality, although selective loss of S1P signal transduction pathways was observed in mouse embryonic fibroblast (MEF) cells. These results continue to clarify physiological functions and roles of the LP B3 receptor in vivo. EXPERIMENTAL PROCEDURES Materials-[␣-32 P]Deoxy-CTP and myo-[2-3 H]inositol were purchased from PerkinElmer Life Sciences. S1P and LPA (1-oleoyl-2-hydroxy-sn-glycero-3-phosphate) were purchased from Avanti Polar Lipids (Alabaster, AL). GTP␥S, platelet-derived growth factor (BB homodimer), and pertussis toxin (PTX) were purchased from Calbiochem. Anti-EDG-3 (LP B3 ) carboxyl and amino terminus monoclonal antibodies were purchased from Exalpha Biological Inc. (Boston, MA). Rhotekin Rho binding domain agarose and PAK-1 p21-binding domain agarose were purchased from Upstate Biotechnology, Inc. (Lake Placid, NY). The pFlox targeting vector (13) and R1 embryonic ...

Lysophosphatidic acid (LPA) is a phospholipid that has extracellular signaling properties mediated by G protein-coupled receptors. Two LPA receptors, LPA(1) and LPA(2), 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 LPA(1) LPA(2) 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.