Polyalanine expansion and frameshift mutations of the paired-like homeobox gene PHOX2B in congenital central hypoventilation syndrome

Congenital central hypoventilation syndrome (CCHS or Ondine's curse; OMIM 209880) is a life-threatening disorder involving an impaired ventilatory response to hypercarbia and hypoxemia. This core phenotype is associated with lower-penetrance anomalies of the autonomic nervous system (ANS) including Hirschsprung disease and tumors of neural-crest derivatives such as ganglioneuromas and neuroblastomas. In mice, the development of ANS reflex circuits is dependent on the paired-like homeobox gene Phox2b. Thus, we regarded its human ortholog, PHOX2B, as a candidate gene in CCHS. We found heterozygous de novo mutations in PHOX2B in 18 of 29 individuals with CCHS. Most mutations consisted of 5-9 alanine expansions within a 20-residue polyalanine tract probably resulting from non-homologous recombination. We show that PHOX2B is expressed in both the central and the peripheral ANS during human embryonic development. Our data support an essential role of PHOX2B in the normal patterning of the autonomous ventilation system and, more generally, of the ANS in humans.     

Mutations in CLCN2 encoding a voltage-gated chloride channel are associated with idiopathic generalized epilepsies

Idiopathic generalized epilepsy (IGE) is an inherited neurological disorder affecting about 0.4% of the world's population. Mutations in ten genes causing distinct forms of idiopathic epilepsy have been identified so far, but the genetic basis of many IGE subtypes is still unknown. Here we report a gene associated with the four most common IGE subtypes: childhood and juvenile absence epilepsy (CAE and JAE), juvenile myoclonic epilepsy (JME), and epilepsy with grand mal seizures on awakening (EGMA; ref. 8). We identified three different heterozygous mutations in the chloride-channel gene CLCN2 in three unrelated families with IGE. These mutations result in (i) a premature stop codon (M200fsX231), (ii) an atypical splicing (del74-117) and (iii) a single amino-acid substitution (G715E). All mutations produce functional alterations that provide distinct explanations for their pathogenic phenotypes. M200fsX231 and del74-117 cause a loss of function of ClC-2 channels and are expected to lower the transmembrane chloride gradient essential for GABAergic inhibition. G715E alters voltage-dependent gating, which may cause membrane depolarization and hyperexcitability.     

Cyclin-dependent kinase 2 is essential for meiosis but not for mitotic cell division in mice

We targeted the locus encoding the cyclin-dependent kinase 2 (CDK2) by homologous recombination in mouse embryonic stem (ES) cells. Embryonic fibroblasts lacking CDK2 proliferate normally and become immortal after continuous passage in culture. Elimination of a conditional Cdk2 allele in immortal cells does not have a significant effect on proliferation. Cdk2-/- mice are viable and survive for up to two years, indicating that CDK2 is also dispensable for proliferation and survival of most cell types. But CDK2 is essential for completion of prophase I during meiotic cell division in male and female germ cells, an unforeseen role for this cell cycle kinase.     

A very energetic supernova associated with the gamma-ray burst of 29 March 2003

Over the past five years evidence has mounted that long-duration (>2 s) gamma-ray bursts (GRBs)-the most luminous of all astronomical explosions-signal the collapse of massive stars in our Universe. This evidence was originally based on the probable association of one unusual GRB with a supernova, but now includes the association of GRBs with regions of massive star formation in distant galaxies, the appearance of supernova-like 'bumps' in the optical afterglow light curves of several bursts and lines of freshly synthesized elements in the spectra of a few X-ray afterglows. These observations support, but do not yet conclusively demonstrate, the idea that long-duration GRBs are associated with the deaths of massive stars, presumably arising from core collapse. Here we report evidence that a very energetic supernova (a hypernova) was temporally and spatially coincident with a GRB at redshift z = 0.1685. The timing of the supernova indicates that it exploded within a few days of the GRB, strongly suggesting that core-collapse events can give rise to GRBs, thereby favouring the 'collapsar' model.     

Craniometric evidence for Palaeoamerican survival in Baja California

A current issue on the settlement of the Americas refers to the lack of morphological affinities between early Holocene human remains (Palaeoamericans) and modern Amerindian groups, as well as the degree of contribution of the former to the gene pool of the latter. A different origin for Palaeoamericans and Amerindians is invoked to explain such a phenomenon. Under this hypothesis, the origin of Palaeoamericans must be traced back to a common ancestor for Palaeoamericans and Australians, which departed from somewhere in southern Asia and arrived in the Australian continent and the Americas around 40,000 and 12,000 years before present, respectively. Most modern Amerindians are believed to be part of a second, morphologically differentiated migration. Here we present evidence of a modern Amerindian group from the Baja California Peninsula in Mexico, showing clearer affinities with Palaeoamerican remains than with modern Amerindians. Climatic changes during the Middle Holocene probably generated the conditions for isolation from the continent, restricting the gene flow of the original group with northern populations, which resulted in the temporal continuity of the Palaeoamerican morphological pattern to the present.     

Trans-synaptic shift in anion gradient in spinal lamina I neurons as a mechanism of neuropathic pain

Modern pain-control theory predicts that a loss of inhibition (disinhibition) in the dorsal horn of the spinal cord is a crucial substrate for chronic pain syndromes. However, the nature of the mechanisms that underlie such disinhibition has remained controversial. Here we present evidence for a novel mechanism of disinhibition following peripheral nerve injury. It involves a trans-synaptic reduction in the expression of the potassium-chloride exporter KCC2, and the consequent disruption of anion homeostasis in neurons of lamina I of the superficial dorsal horn, one of the main spinal nociceptive output pathways. In our experiments, the resulting shift in the transmembrane anion gradient caused normally inhibitory anionic synaptic currents to be excitatory, substantially driving up the net excitability of lamina I neurons. Local blockade or knock-down of the spinal KCC2 exporter in intact rats markedly reduced the nociceptive threshold, confirming that the reported disruption of anion homeostasis in lamina I neurons was sufficient to cause neuropathic pain.     

Volume-regulated chloride channels associated with the human multidrug-resistance P-glycoprotein.

Expression of P-glycoprotein, the product of the MDR1 gene, confers multidrug resistance on cell lines and human tumours (reviewed in refs 1,2). P-glycoprotein (relative molecular mass 170,000) is an ATP-dependent, active transporter which pumps hydrophobic drugs out of cells, but its normal physiological role is unknown. It is a member of the ABC (ATP-binding cassette) superfamily of transporters, which includes many bacterial transport systems, the putative peptide transporter from the major histocompatibility locus, and the product of the cystic fibrosis gene (the cystic fibrosis transmembrane regulator, CFTR). CFTR is located in the apical membranes of many secretory epithelia and is associated with a cyclic AMP-regulated chloride channel. At least two other chloride channels are present in epithelial cells, regulated by cell volume and by intracellular Ca2+, respectively. Because of the structural and sequence similarities between P-glycoprotein and CFTR, and because P-glycoprotein is abundant in many secretory epithelia, we examined whether P-glycoprotein might be associated with one or other of these channels. We report here that expression of P-glycoprotein generates volume-regulated, ATP-dependent, chloride-selective channels, with properties similar to channels characterized previously in epithelial cells.     

Ein Beitrag zur Kenntnis von Lanatosid D

Summary A preparative method for the isolation of lanatoside D has been developed, and fundamental pharmacological characteristics of the pure compound have been established.The genuine glycoside has been converted to desacetyllanatoside D.