A Contribution to the Taxonomy of the Genus Xiphinema Cobb, 1913

In a comparative study of different populations of Xiphinema, the significance of the female gonad structure in species determination is stressed, and monodelphic, pseudomonodelphic, and didelphic forms in the genus are defined. X. chambersi is redescribed and illustrated, X. ensiculiferum and X. krugi are redefined, and X. ensiculiferoides n.sp. and X. orthotenum n.sp. are described. Proposed new synonymies are: X. itanhaense = X. brasiliense; X. bulgariensis and X. conurum = X. italiae; X. ifacolum = X. basiri; X. macrostylum = X. ensiculiferum; X. truncatum = X. elongatum; and X. vulgare = X. setariae. X. yapoense is considered species inquirenda and X. obtusum a nomen dubium. The following eight subgenera of the genus Xiphinema are proposed: Radiphinema n. subg., Krugiphinema n. subg., Xiphinema n. subg., Elongiphinema n. subg., Halliphinema n. subg., Basiphinema n. subg., Rotundiphinema n. subg., and Diversiphinema n. subg. A key to the subgenera of Xiphinema is presented, plus a list of 50 species in the genus, their synonyms, and 10 species inquirendae.     

The origin of the genetical diversity of Microtus mandarinus chromosomes

Here we describe our comparative studies on two types of X chromosomes, namely X(M) and X(SM,) of the mandarin vole (Microtus mandarinus). By chromosome G- and C-banding analysis, we have found that two different types of X chromosomes exist in mandarin voles. The two types of X chromosomes present two different G- and C-banding patterns: the X(M) chromosome is a longer metacentric X chromosome which is C-band negative; and the X(SM) is a shorter submetacentric X chromosome which has one C-band at the centromere and another one at the middle part of the short arm. The X(SM) has 6 G-bands including one on the kinetochore, one in the middle of the short arm, and four on the long arm. The X(M) has 7 G-bands including one on the kinetochore, two on the short arm, and four on the long arm. We have further found that female voles can be grouped into three types based on the composition of the X chromosome but the male voles have only one type. The three female groups are: (1) female voles (X(M)X(SM)), in which the two X chromosomes are different, the longer one is metacentric and the shorter is submetacentric; (2) female vole (X(SM)X(SM)), in which the two X chromosomes are both submetacentric; (3) female vole (X(M)O), in which there is only one X chromosome that is metacentric. Surprisingly, we have never found female voles with X(M)X(M), females with X(SM)O or males with X(M)Y. We hypothesize that the X(SM) chromosome is derived from the X(M) through its breakage and re-joining. The paper also discusses the formation of X(M)O females.     

DNA methylation of the X chromosomes of the human female: an in situ semi-quantitative analysis

We present an in situ semi-quantitative analysis of the global DNA methylation of the X chromosomes of the human female using antibodies raised against 5-methylcytosine. The antibodies were revealed by immunofluorescence. Images were recorded by a CCD camera and the difference in intensity of fluorescence between active (early replicating) and inactive (late-replicating) X chromosomes was measured. Global hypomethylation of the late-replicating X chromosomal DNA was observed in three cases of fibroblast primary cultures that were characterized by numerical and structural aberrations of the X chromosomes [46,X,ter rea(X;X), 48,XXXX and 46,X,t(X;15)]. In these cases, the difference between early and late-replicating X chromosomes was significantly greater than the intrametaphasic variations, measured for a pair of autosomes, that result from experimental procedures. In cells with normal karyotypes, the differneces between the two X chromosomes were in the range of experimental variation. These results demonstrated that late replication and facultative heterochromatinization of the inactive X are two processes that are not related to global hypermethylation of the DNA     

The first transmembrane domain of the P2X receptor subunit participates in the agonist-induced gating of the channel.

Based on pharmacological properties, the P2X receptor family can be subdivided into those homo-oligomers that are sensitive to the ATP analog alphabeta-methylene ATP(alphabetameATP) (P2X(1) and P2X(3)) and those that are not (P2X(2), P2X(4), P2X(5), P2X(6), and P2X(7)). We exploited this dichotomy through the construction of chimeric receptors and site-directed mutagenesis in order to identify domains responsible for these differences in the abilities of extracellular agonists to gate P2X receptors. Replacement of the extracellular domain of the alphabetameATP-sensitive rat P2X(1) subunit with that of the alphabetameATP-insensitive rat P2X(2) subunit resulted in a receptor that was still alphabetameATP-sensitive, suggesting a non-extracellular domain was responsible for the differential gating of P2X receptors by various agonists. Replacement of the first transmembrane domain of the rat P2X(2) subunit with one from an alphabetameATP-sensitive subunit (either rat P2X(1) or P2X(3) subunit) converted the resulting chimera to alphabetameATP sensitivity. This conversion did not occur when the first transmembrane domain came from a non-alphabetameATP-sensitive subunit. Site-directed mutagenesis indicated that the C-terminal portion of the first transmembrane domain was important in determining the agonist selectivity of channel gating for these chimeras. These results suggest that the first transmembrane domain plays an important role in the agonist operation of the P2X receptor.     

Pericentric inversions of the X chromosome. A new observation and review of the published cases

A pericentric inversion of the X chromosome-inv(X) (p11.3q22) is transmitted in 3 generations. Male and female carriers are normal. The proposita is tetraplegic, severely retarded and suffers from general seizures. Grand mal seizures are known in the mother and grandmother. Different proportions of inactive X chromosomes in the proposita and the normal sister are discussed. The published cases of inv(X) are reviewed.     

The mating calls of 12 species and sub-species of the genus Xenopus (Amphibia : Anura)

The principal acoustic characteristics of the mating calls of 12 species and sub-species of the genus Xenopus were determined: X. laevis laevis, X. laevis petersi, X. laevis victorianus, X. gilli, X. muelleri, X. borealis, X. clivii, X. fraseri, X. ruwenzoriensis, X. wittei, X. vestitus and X. tropicalis . These calls are very specific, especially among species whose hybrids are particularly viable in the laboratory. Twin species have not been discovered. Most of the species emit calls with high harmonic frequencies of 16 kHz; these frequencies reach 80 and 150 kHz in X. I. laevis and X. ruwenzoriensis , the ultra-sound level. This was a previously unknown phenomenon in the Batrachians.     

Cytogenetics of fleas (Siphonaptera: Pulicidae). 1. Rat fleas of the genus Xenopsylla

Five populations of Xenopsylla cheopis exhibit a chromosome complement of 2n = 17, X1X2Y (male), and 2n = 18, X1X1X2X2 (female). A detailed analysis of populations of X. astia from Bombay and Trivandrum led to the identification of two distinct cytotypes which hybridisation studies indicated were sibling species. These are referred to as X. astia with a diploid chromosome number of 2n = 18, X1X2X3Y (male), and 2n = 20, X1X1X2X2X3X3 (female) and X. prasadii with 2n = 10, X1X2Y1Y2 (male), and 2n = 10 X1X1X2X2 (female). It is proposed that X. prasadii is derived from X. astia through translocation/fusion events since the average total chromosome lengths are remarkably similar in all three species.     

Pericentric inversion of the X chromosome: presentation of a case and review of the literature.

A large pericentric inversion of the X chromosome [inv(X)(p22.31q26.3)] was found to be transmitted in four generations through phenotypically normal males and females. In one female carrier, the inv(X) was late replicating in 70% of lymphocytes and 46% of skin fibroblasts. Steroid sulfatase (STS), an enzyme which normally escapes inactivation has been located to Xp22.32 and, in our case, has been moved to an aberrant position. We have assayed its activity in clones with the inv(X) inactive or the normal X inactive and found no significant differences. Thus, the STS locus escaped X inactivation in both the normal and the inverted X chromosomes. A review of the literature shows that almost half of the breakpoints on the short arm are found at region p22 and we propose that low-copy repetitive DNA segments along the X chromosome are responsible for non-homologous pairing and production of inversions.     

海南山蛭种群数量动态与气象因素关系研究

在海南岛橡胶林内,每月观测海南山蛭Ｈａｅｍａｄｉｐｓａ ｈａｉｎａｎａ种群数量Ｂａ,用逐步回归分析方法研究了１０个气象因子对海南山６种数量的影响,结果表明,１）每年海南山蛭种群数量不同,６ａ间影响海南山蛭种群数量的主要气候因素是Ｘ１（月雨量）、Ｘ３（月雨日）和Ｘ５（月有露日数）;２）海南岛５～１０月份为雨季,海南山蛭这种群数量明显增大,影响山蛭种群数量的主要气候因素是Ｘ５和Ｘ１６（月最大风速和）和     

A revised polytomous key for the identification of species of the genusXiphinema Cobb, 1913 (Nematoda: Longidoridae) with exclusion of theX. americanum-group: Supplement 2

Thirty-one species and one subspecies have been described since publication of the first supplement to the polytomous key toXiphinema spp. (see Loof & Luc, 1993). Of these, 11 species belonging to the X. americanum-group are not considered here. Of the 20 remaining species, 13 are considered valid, for which identification codes are given. Three species were described earlier, but had not come to authors' notice; two of them,X. chothecolla andX. clavatus (sic) have already been synonymised withX. radicicola (see Luc & Loof, 1993); codes are given for the third species,X. codiaei. Xiphinema adenohystherum, X. cohni, X. macrogastrum, X. nuragicum andX. sphaerocephalum were considered junior synonyms ofX. pyrenaicum by Baujardet al. (1996);X. hunaniense is considered a junior synonym ofX. radicicola andX. hispanum ofX. aceri. Changes in the group and/or identification codes are made forX. aceri, X. barense, X. dentatum, X. diversicaudatum, X. filicaudatum filicaudatum, X. globosum, X. hardingi, X. paritaliae (= X. dolosum), X. paulistanum, X. pyrenaicum andX. transkeiense. The specific nameX. swarti is emended toX. swartae. Information is given for computerisation of the key.     

Studies of the temporal relationship between the cytogenetic and biochemical manifestations of X-chromosome inactivation during the differentiation of LT-1 teratocarcinoma stem cells

Previous biochemical studies have suggested that both X chromosomes produce gene products when cells of the LT-1 teratocarcinoma stem cell line are maintained in the undifferentiated state, and that dosage compensation, the biochemical manifestation of X inactivation, occurs when the cells are induced to differentiate in vitro (Martin et al., 1978). In this study the differentiation of LT-1 cells in vitro is described in detail, and data from cytogenetic studies of the time of X-chromosome replication in LT-1 cells are presented. They show that as long as the cells are maintained in the undifferentiated state both X chromosomes in each cell show the isocyclic replication pattern typical of a genetically active chromosome. However, when the LT-1 cells are induced to differentiate under appropriate conditions, one of the two X chromosomes in each cell of a large proportion of the population displays the allocyclic (either early or late) replication pattern typical of an inactive X chromosome. These data thus confirm that undifferentiated LT-1 cells contain two active X chromosomes and that X inactivation occurs in differentiating cultures of LT-1 cells. It is further demonstrated that there is a close temporal correlation between the biochemical and cytogenetic manifestations of the X-inactivation process. In addition, we observed that although X inactivation does not occur in the absence of morphological differentiation, it does not always occur when the cells differentiate in vitro.     

Influence of the nature of the aromatic side-chain on the conductance of the channel of linear gramicidin: study of a series of 9,11,13,15-Tyr(O-protected) derivatives

This paper describes the single channel properties of a series of synthetic analogues of gramicidin A, where all four tryptophans are replaced either by tyrosine or by several O-protected (benzyl, methyl, ethyl or t-butyl) derivatives. It is shown that, although all analogues bear similar dipole moment on their side-chains, the conductance depends on the hydrophobicity of these protecting groups. An analysis of the conductance data suggests that the conductance is governed by the binding process and a possible explanation, based on conformational considerations, is proposed.Abbreviations GA X=tryptophane - GM X=phenylalanine - GN X=naphthylalanine - GQ8 X=8-quinolylalanine - GQ4 X=4-quinolylalanine - GT X=tyrosine - GTBzl X=O-benzyltyrosine - GTMe X=O-methyltyrosine - GTEt X=O-ethyltyrosine - GTBu X=O-t-butyltyrosine     

Fine mapping of the distal short arm of the human X chromosome using X/Y translocations.

The loci for steroid sulfatase (STS), the deficiency of which causes X-linked ichthyosis, the cell surface antigen 12E7 (MIC2X), and the blood group antigen Xg (Xg) have been mapped to Xp22.3. These loci are of particular interest since they do not appear to undergo X-chromosome inactivation. In an attempt to establish the relative order of STS and MIC2X, fibroblasts from carriers of four different X/Y translocations and an X/10 translocation were obtained and fused with mouse cell lines deficient in hypoxanthine phosphoribosyltransferase. The breakpoints on the X chromosome in these five translocations are in Xp22. Several independent clones from each fusion were isolated in HAT medium. The clones were examined cytogenetically, and in each case at least two independent clones were identified that have an active X/Y or X/10 translocation chromosome in the absence of other X or Y material. These clones were then tested for STS and 12E7 expression. In two of the X/Y translocations, the markers, STS and 12E7, were both absent. In the X/10 and a third X/Y translocation, both markers were retained. In each of three clones containing the fourth X/Y translocation, STS activity was retained but 12E7 antigenicity was lost. Assuming that this is a simple translocation and does not represent a more complex rearrangement, these results suggest that MIC2X is distal to STS.     

Studies on the activity of the X chromosomes in female teratocarcinoma cells in culture

Embryonal carcinoma cells derived from murine teratocarcinomas are able to differentiate into the same variety of tissue types as early embryonic cells. Because embryonal carcinoma cells resemble those of the embryo at a stage before X chromosome inactivation has occurred in females embyronal carcinoma cells containing two X chromosomes were examined to determine whether both are genetically active. The specific activities of X-linked enzymes were measured in embryonal carcinoma cells containing either one or two X chromosomes. The activities in both cell types were similar, suggesting that only one X chromosome was active in the female cells. Further support for this conclusion came from experiments in which azaguanine-resistant mutants were recovered with similar frequencies from embryonal carcinoma cell lines containing one and two X chromosomes. Late replication of an X chromosome DNA was detected in one embryonal carcinoma cell line with two X chromosomes but not in another. This suggests that cells of these two lines were arrested at different developmental stages, and that late DNA replication may not be a necessary adjunct of X inactivation. Evidence is presented which suggests that X chromosome reactivation does not occur during differentiation of the cells in vitro.     

Isolation and characterization of two repetitive DNA fragments located near the centromere of the mouse X chromosome

Two repetitive DNA fragments located on the mouse X chromosome are described. The fragments were isolated from a lambda phage library enriched in X-chromosomal sequences by flow sorting. Both fragments, which are repeated 20 to 50 times in the genome, were mapped to the mouse X chromosome by Southern blot hybridization to DNA from hybrid cells retaining the mouse X chromosome, by dosage analysis, and by in situ hybridization to mouse chromosomes. In mouse strain C57BL/10BK, one fragment appeared to be located only on the X chromosome, while the other fragment had homologous sequences on chromosome 11 in addition to the X chromosome. The latter fragment showed DNA variants between mouse strains, which are potentially useful for mapping. Both fragments cross-hybridized to another mouse species: Mus caroli. In this species, each fragment appeared to be located on the X chromosome, indicating that some X-chromosome repetitive sequences are partially conserved. In addition, one fragment cross-hybridized to human DNA.     

The chromosomal distribution of microsatellite repeats in the genome of the wolf fish Hoplias malabaricus, focusing on the sex chromosomes

Distribution of 12 mono-, di- and tri-nucleotide microsatellites on the chromosomes of 2 karyomorphs with 2 distinct sex chromosome systems (a simple XX/XY - karyomorph B and a multiple X(1)X(1)X(2)X(2)/X(1)X(2)Y - karyomorph D) in Hoplias malabaricus, commonly referred to as wolf fish, was studied using their physical mapping with fluorescence in situ hybridization (FISH). The distribution patterns of different microsatellites along the chromosomes varied considerably. Strong hybridization signals were observed at subtelomeric and heterochromatic regions of several autosomes, with a different accumulation on the sex chromosomes. A massive accumulation was found in the heterochromatic region of the X chromosome of karyomorph B, whereas microsatellites were gathered at centromeres of both X chromosomes as well as in corresponding regions of the neo-Y chromosome in karyomorph D. Our findings are likely in agreement with models that predict the accumulation of repetitive DNA sequences in regions with very low recombination. This process is however in contrast with what was observed in multiple systems, where such a reduction might be facilitated by the chromosomal rearrangements that are directly associated with the origin of these systems.