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The human X chromosome has a unique biology that was shaped by its evolution as the sex chromosome shared by males and females. We have determined 99.3% of the euchromatic sequence of the X chromosome. Our analysis illustrates the autosomal origin of the mammalian sex chromosomes, the stepwise process that led to the progressive loss of recombination between X and Y, and the extent of subsequent degradation of the Y chromosome. LINE1 repeat elements cover one-third of the X chromosome, with a distribution that is consistent with their proposed role as way stations in the process of X-chromosome inactivation. We found 1,098 genes in the sequence, of which 99 encode proteins expressed in testis and in various tumour types. A disproportionately high number of mendelian diseases are documented for the X chromosome. Of this number, 168 have been explained by mutations in 113 X-linked genes, which in many cases were characterized with the aid of the DNA sequence.

Hereditary motor and sensory neuropathies, to which Charcot-Marie-Tooth (CMT) disease belongs, are a common cause of disability in adulthood. Growing awareness that axonal loss, rather than demyelination per se, is responsible for the neurological deficit in demyelinating CMT disease has focused research on the mechanisms of early development, cell differentiation, and cell-cell interactions in the peripheral nervous system. Autosomal recessive peripheral neuropathies are relatively rare but are clinically more severe than autosomal dominant forms of CMT, and understanding their molecular basis may provide a new perspective on these mechanisms. Here we report the identification of the gene responsible for hereditary motor and sensory neuropathy-Lom (HMSNL). HMSNL shows features of Schwann-cell dysfunction and a concomitant early axonal involvement, suggesting that impaired axon-glia interactions play a major role in its pathogenesis. The gene was previously mapped to 8q24.3, where conserved disease haplotypes suggested genetic homogeneity and a single founder mutation. We have reduced the HMSNL interval to 200 kb and have characterized it by means of large-scale genomic sequencing. Sequence analysis of two genes located in the critical region identified the founder HMSNL mutation: a premature-termination codon at position 148 of the N-myc downstream-regulated gene 1 (NDRG1). NDRG1 is ubiquitously expressed and has been proposed to play a role in growth arrest and cell differentiation, possibly as a signaling protein shuttling between the cytoplasm and the nucleus. We have studied expression in peripheral nerve and have detected particularly high levels in the Schwann cell. Taken together, these findings point to NDRG1 having a role in the peripheral nervous system, possibly in the Schwann-cell signaling necessary for axonal survival.

There is a wide range of human autoimmune diseases, but the molecular background of autoimmunity remains poorly understood (Ollier 1992). Despite the identification of a number of genetic susceptibility factors, the etiology of most autoimmune diseases remains elusive. In this context, the study of autoimmune conditions with Mendelian inheritance could provide a boost for unraveling pathogenic pathways involved in human autoimmunity. Autoimmune polyendocrinopathy candidiasis ectodermal dystrophy [APECED, Online Mendelian Inheritance in Man (OMIM) 240300] is an autosomal recessive disease resulting in a variable combination of failure of the parathyroid glands, adrenal cortex, gonads, and pancreatic β cells (Ahonen 1985). Ectodermal dystrophies, vitiligo, and chronic mucocutaneous candidiasis are also frequently observed among APECED patients (Ahonen et al. 1990; Perheentupa 1996). APECED is a rare disease particularly enriched in genetic isolates, such as the Finnish population, Iranian Jews, and Sardinians (Ahonen 1985; Zlotogora and Shapiro 1992; Clemente et al. 1997). After demonstration of genetic linkage and locus homogeneity on chromosome 21q22.3 (Aaltonen et al. 1994; Bjorses et al. 1996), the APECED gene was cloned and called AIRE for autoimmune regulator (The Finnish–German APECED Consortium 1997; Nagamine et al. 1997). The AIRE gene encodes a nuclear factor of unknown function that harbors two PHD zinc fingers—a modular domain found in many proteins involved in chromatin-mediated regulation of transcription (Schindler et al. 1993; Aasland et al. 1995). Moreover, striking structural similarities were observed between AIRE and human Sp100/Sp140 proteins, suggesting that they derive from a common ancestor. In addition to the zinc fingers, AIRE and Sp140 also share a putative DNA-binding domain called SAND domain and a stretch of 90 amino acids in their amino-terminal region (Gibson 1998). Sp100 proteins localize to specific nuclear structures called nuclear bodies and represent a target of autoantibodies in patients with primary biliary cirrhosis (Szostecki et al. 1990). As a first step toward investigating AIRE biochemical properties and for engineering a mouse model for APECED, we have cloned and characterized the murine AIRE homolog. Here we report comparative genomic sequence analysis of the AIRE loci and AIRE expression pattern on mouse and human histological sections.

Three skua specimens with a colouration pattern of the Chilean skua were observed at Potter Peninsula, King George Island, Antarctica. Two of these were breeding birds. However, they showed a pattern of mitochondrial DNA typical for South Polar skua. These birds thus represent hybrids originating from male Chilean skua. The third bird could not be caught. It appeared to be indistinguishable from Chilean skua.

Hydroxyapatite cement (BoneSource®) and brushite calcium phosphate cement (chronOS™ Inject) were tested for fixation of glass ceramic implants (Bioverit®) in experimentally created cranial defects in 24 adult New Zealand White rabbits. Aim of the in vivo study was to assess and compare the biocompatibility and osseointegration of the implanted materials. Macroscopic and histological evaluations were performed 1 month, 3 months, and 6 months postoperatively. All implanted materials were well tolerated by the surrounding tissue. Both bone cements exhibited osteoconductive properties. Differences could be detected regarding to the rates of cement resorption and new bone formation. The brushite cement was resorbed faster than the hydroxyapatite cement. The chronOS™ Inject samples exhibited a higher rate of connective tissue formation and an insufficient osseointegration. BoneSource® was replaced by bone with minimal invasion of connective tissue. New bone formation occurred faster compared to the chronOS™ Inject group. Bioverit® implants fixed with BoneSource® were successfully osseointegrated.

The International Human Genome Sequencing Consortium (IHGSC) recently completed a sequence of the human genome. As part of this project, we have focused on chromosome 8. Although some chromosomes exhibit extreme characteristics in terms of length, gene content, repeat content and fraction segmentally duplicated, chromosome 8 is distinctly typical in character, being very close to the genome median in each of these aspects. This work describes a finished sequence and gene catalogue for the chromosome, which represents just over 5% of the euchromatic human genome. A unique feature of the chromosome is a vast region of approximately 15 megabases on distal 8p that appears to have a strikingly high mutation rate, which has accelerated in the hominids relative to other sequenced mammals. This fast-evolving region contains a number of genes related to innate immunity and the nervous system, including loci that appear to be under positive selection--these include the major defensin (DEF) gene cluster and MCPH1, a gene that may have contributed to the evolution of expanded brain size in the great apes. The data from chromosome 8 should allow a better understanding of both normal and disease biology and genome evolution.

Careful manual annotation of the human reference sequence provides a solid basis for the identification of disease-associated genes. Toward this end, we focused on a medically relevant 2.6-Mb region of the human chromosome Xp11.4 between markers DXS9851 and DXS9751 and identified 16 transcription units according to the Vertebrate Genome Annotation (Vega) rules. In order to validate these annotations, we performed a comprehensive RT-PCR expression analysis and a human-mouse comparison. This revealed, despite the high overall genomic conservation of the region, remarkable differences of the gene content between human and mouse. Whereas 12 of 16 annotations were confirmed by RT-PCR in human tissues, for only seven genes mouse orthologs could be identified and found to be expressed. This indicates that a comprehensive and experimentally supported annotation effort of the human genome simultaneously highlights regions with striking differences in gene organization to other species and may indicate evolutionary events specific to the human lineage demanding further functional analyses.

Hereditary motor and sensory neuropathy type Lom, initially identified in Roma (Gypsy) families from Bulgaria, has been mapped to 8q24. Further refined mapping of the region has been undertaken on DNA from patients diagnosed across Europe. The refined map consists of 25 microsatellite markers over approximately 3 cM. In this collaborative study we have identified a number of historical recombinations resulting from the spread of the hereditary motor and sensory neuropathy type Lom gene through Europe with the migration and isolation of Gypsy groups. Recombination mapping and the minimal region of homozygosity reduced the original 3 cM hereditary motor and sensory neuropathy type Lom region to a critical interval of about 200 kb. (C) 2000 Elsevier Science B.V.

Specific antisera against protein-conjugated γ-aminobutyric acid (GABA) were used in immunocytochemical staining procedures to study the distribution of the putative GABA-like immunoreactive neurons in the optic lobes of Periplaneta. GABA-like immunoreactive structures are evident in all three optic neuropil regions. Six different populations of GABAergic neurons, whose perikarya are grouped around the medulla, are found within the optic lobe. The number of these immunoreactive cells varies greatly and corresponds to the number of ommatidia of the eye. In the proximal part of the lamina, a coarse network of GABA-positive fibres is recognizable. These are the processes of large field tangential cells whose fibres pass through the distal surface of the medulla. A second fibre population of the lamina is made up of the processes of the centrifugal columnar neurons whose perikarya lie proximally to the medulla. The medulla contains 9 layers with GABAergic elements of variable immunoreactivity. Layers 1, 3, 5, 7 and 9 exhibit strong labelling, as a result of partial overlapping of the processes of centrifugal and centripetal columnar neurons, tangential fibres and/or lateral processes of perpendicular fibres and (possibly) processes of amacrines. A strong immunoreactivity is found in the proximal and distal layers of the lobula.