Search PubMed⌕ Search

Biomedical subjects

C Tyler-Smith

Publications and source records attributed to C Tyler-Smith.

At least 37 records · Page 2Linked to original sources
PubMed2000

A neocentromere in the DAZ region of the human Y chromosome.

We describe a novel rearranged human Y chromosome consisting of an inverted duplication of the long arm heterochromatin and a small amount of euchromatin: rea(Y)(qter-q11.2::q11.2-qter). The normal centromere has been deleted and a neocentromere containing CENP-A, -C, -E and Mad2 but not CENP-B has formed close to the breakpoint. A 2.7 Mb yeast artificial chromosome contig spanning the breakpoint was constructed and the breakpoint was localised to a region of <120 kb close to the DAZ gene cluster. Combined immunofluorescence and fluorescence in situ hybridisation showed that the centromeric protein-binding domain of the neocentromere was located near the breakpoint and within the DAZ cluster.

Adult↗
PubMed2000

New uses for new haplotypes the human Y chromosome, disease and selection.

Recent discoveries of many new genes have made it clear that there is more to the human Y chromosome than a heap of evolutionary debris, hooked up to a sequence that happens to endow its bearer with testes. Coupled with the recent development of new polymorphic markers on the Y, making it the best-characterized haplotypic system in the genome, this gives us new opportunities to assess its role in disease and selection, through association studies with phenotypes such as infertility and cancers. However, the peculiar genetics of this bizarre chromosome means that we should interpret such studies particularly cautiously.

Biological Evolution↗
PubMed2000

Mapping of a human centromere onto the DNA by topoisomerase II cleavage.

We have mapped the positions of topoisomerase II binding sites at the centromere of the human Y chromosome using etoposide-mediated DNA cleavage. A single region of cleavage is seen at normal centromeres, spanning approximately 50 kb within the centromeric alphoid array, but this pattern is abolished at two inactive centromeres. It therefore provides a marker for the position of the active centromere. Although the underlying centromeric DNA structure is variable, the position of the centromere measured in this way is fixed relative to the Yp edge of the array, and has retained the same position for >100,000 years.

Cell Line↗
PubMed2000

TSPY variants in six loci on the human Y chromosome.

We have studied the structure, organization, and evolution of the human TSPY gene family by mapping three sequence variants identified through RT-PCR analysis onto genomic clones derived from two different YAC contigs. TSPY gene family members occur in at least six locations on the human Y chromosome, and each cluster contains a unique combination of variants. Our data further suggest that an 18-bp tandem duplication found in TSPY exon 1 originated from an unequal sister chromatid exchange between two tandemly arranged TSPY clusters.

Cell Cycle Proteins↗
PubMed1999

Relationship between amount of esterase and gene copy number in insecticide-resistant Myzus persicae (Sulzer).

Overproduction of the insecticide-degrading esterases, E4 and FE4, in peach-potato aphids, Myzus persicae (Sulzer), depends on both gene amplification and transcriptional control, the latter being associated with changes in DNA methylation. The structure and function of the aphid esterase genes have been studied but the determination of their copy number has proved difficult, a common problem with gene amplification. We have now used a combination of pulsed-field gel electrophoresis and quantitative competitive PCR to determine relative esterase gene copy numbers in aphid clones with different levels of insecticide resistance (R1, R2 and R3). There are approx. 4-fold increases between susceptible, R1, R2 and R3 aphids, reaching a maximum of approx. 80 times more genes in R3; this gives proportionate increases in esterase protein relative to susceptible aphids. Thus there is no overexpression of the amplified genes, in contrast with what was thought previously. For E4 genes, the loss of 5-methylcytosine is correlated with a loss of expression, greatly decreasing the amount of enzyme relative to the copy number.

5-Methylcytosine↗
PubMed1999

Y-chromosomal DNA haplotype differences in control and infertile Italian subpopulations.

Y-chromosomal DNA haplotypes were determined in 74 infertile and 216 control Italian males using eight biallelic markers. A significant difference in haplotype frequency was found, but could be explained by the geographical origins of the samples. The Y chromosome is thus a sensitive marker for population substructuring and may be useful for determining whether two population samples come from a single population, for example in association studies.

Case-Control Studies↗
PubMed1999

The central Siberian origin for native American Y chromosomes.

Y chromosomal DNA polymorphisms were used to investigate Pleistocene male migrations to the American continent. In a worldwide sample of 306 men, we obtained 32 haplotypes constructed with the variation found in 30 distinct polymorphic sites. The major Y haplotype present in most Native Americans was traced back to recent ancestors common with Siberians, namely, the Kets and Altaians from the Yenissey River Basin and Altai Mountains, respectively. Going further back, the next common ancestor gave rise also to Caucasoid Y chromosomes, probably from the central Eurasian region. This study, therefore, suggests a predominantly central Siberian origin for Native American paternal lineages for those who could have migrated to the Americas during the Upper Pleistocene.

Genetic Variation↗
PubMed1999

Transmission of a fully functional human neocentromere through three generations.

An unusual Y chromosome with a primary constriction inside the long-arm heterochromatin was found in the amniocytes of a 38-year-old woman. The same Y chromosome was found in her husband and brother-in-law, thus proving that it was already present in the father. FISH with alphoid DNA showed hybridization signals at the usual position of the Y centromere but not at the primary constriction. Centromere proteins (CENP)-A, CENP-C, and CENP-E could not be detected at the site of the canonic centromere but were present at the new constriction, whereas CENP-B was not detected on this Y chromosome. Experiments with 82 Y-specific loci distributed throughout the chromosome confirmed that no gross deletion or rearrangement had taken place, and that the Y chromosome belonged to a haplogroup whose members have a mean alphoid array of 770 kb (range 430-1,600 kb), whereas that of this case was approximately 250 kb. Thus, this Y chromosome appeared to be deleted for part of the alphoid DNA. It seems likely that this deletion was responsible for the silencing of the normal centromere and that the activation of the neocentromere prevented the loss of this chromosome. Alternatively, neocentromere activation could have occurred first and stimulated inactivation of the normal centromere by partial deletion. Whatever the mechanism, the presence of this chromosome in three generations demonstrates that it functions sufficiently well in mitosis for male sex determination and fertility and that neocentromeres can be transmitted normally at meiosis.

Adult↗
PubMed1999

Recent male-mediated gene flow over a linguistic barrier in Iberia, suggested by analysis of a Y-chromosomal DNA polymorphism.

We have examined the worldwide distribution of a Y-chromosomal base-substitution polymorphism, the T/C transition at SRY-2627, where the T allele defines haplogroup 22; sequencing of primate homologues shows that the ancestral state cannot be determined unambiguously but is probably the C allele. Of 1,191 human Y chromosomes analyzed, 33 belong to haplogroup 22. Twenty-nine come from Iberia, and the highest frequencies are in Basques (11%; n=117) and Catalans (22%; n=32). Microsatellite and minisatellite (MSY1) diversity analysis shows that non-Iberian haplogroup-22 chromosomes are not significantly different from Iberian ones. The simplest interpretation of these data is that haplogroup 22 arose in Iberia and that non-Iberian cases reflect Iberian emigrants. Several different methods were used to date the origin of the polymorphism: microsatellite data gave ages of 1,650, 2,700, 3,100, or 3,450 years, and MSY1 gave ages of 1,000, 2,300, or 2,650 years, although 95% confidence intervals on all of these figures are wide. The age of the split between Basque and Catalan haplogroup-22 chromosomes was calculated as only 20% of the age of the lineage as a whole. This study thus provides evidence for direct or indirect gene flow over the substantial linguistic barrier between the Indo-European and non-Indo-European-speaking populations of the Catalans and the Basques, during the past few thousand years.

Base Sequence↗
PubMed1999

Variation in short tandem repeats is deeply structured by genetic background on the human Y chromosome.

Eleven biallelic polymorphisms and seven short-tandem-repeat (STR) loci mapping on the nonrecombining portion of the human Y chromosome have been typed in men from northwestern Africa. Analysis of the biallelic markers, which represent probable unique events in human evolution, allowed us to characterize the stable backgrounds or haplogroups of Y chromosomes that prevail in this geographic region. Variation in the more rapidly mutating genetic markers (STRs) has been used both to estimate the time to the most recent common ancestor for STR variability within these stable backgrounds and to explore whether STR differentiation among haplogroups still retains information about their phylogeny. When analysis of molecular variance was used to study the apportionment of STR variation among both genetic backgrounds (i.e., those defined by haplogroups) and population backgrounds, we found STR variability to be clearly structured by haplogroups. More than 80% of the genetic variance was found among haplogroups, whereas only 3.72% of the genetic variation could be attributed to differences among populations-that is, genetic variability appears to be much more structured by lineage than by population. This was confirmed when two population samples from the Iberian Peninsula were added to the analysis. The deep structure of the genetic variation in old genealogical units (haplogroups) challenges a population-based perspective in the comprehension of human genome diversity. A population may be better understood as an association of lineages from a deep and population-independent gene genealogy, rather than as a complete evolutionary unit.

Africa, Northern↗
PubMed1999

Attenuation of green fluorescent protein half-life in mammalian cells.

The half-life of the green fluorescent protein (GFP) was determined biochemically in cultured mouse LA-9 cells. The wild-type protein was found to be stable with a half-life of approximately 26 h, but could be destabilized by the addition of putative proteolytic signal sequences derived from proteins with shorter half-lives. A C-terminal fusion of a PEST sequence from the mouse ornithine decarboxylase gene reduced the half-life to 9.8 h, resulting in a GFP variant suitable for the study of dynamic cellular processes. In an N-terminal fusion containing the mouse cyclin B1 destruction box, it was reduced to 5.8 h, with most degradation taking place at metaphase. The combination of both sequences produced a similar GFP half-life of 5.5 h. Thus, the stability of this marker protein can be controlled in predetermined ways by addition of the appropriate proteolytic signals.

Animals↗
PubMed1999

Quantitative measurement of mammalian chromosome mitotic loss rates using the green fluorescent protein.

We have measured the mitotic loss rates of mammalian chromosomes in cultured cells. The green fluorescent protein (GFP) gene was incorporated into a non-essential chromosome so that cells containing the chromosome fluoresced green, while those lacking it did not. The proportions of fluorescent and non-fluorescent cells were measured by fluorescence activated cell sorter (FACS) analysis. Loss rates ranged from 0.005% to 0.20% per cell division in mouse LA-9 cells, and from 0.02% to 0.40% in human HeLa cells. The rate of loss was elevated by treatment with aneugens, demonstrating that the system rapidly identifies agents which induce chromosome loss in mammalian cells.

Aneuploidy↗
PubMed1999

Two male patients with ring Y: definition of an interval in Yq contributing to Turner syndrome.

Turner syndrome is thought to result from the haploinsufficiency of genes on the sex chromosomes, but these genes have not been identified yet. We describe two males with deleted ring Y chromosomes, one (TS) with full Turner syndrome and one (DM) without. TS has short stature, skeletal anomalies, lymphogenic obstruction, cardiovascular abnormalities, and miscellaneous features including pigmented naevi, antimongoloid slanting of the palpebral fissures, and widely spaced nipples. In contrast, DM has short stature but no other specific Turner stigmata except high arched palate and a few pigmented naevi. Since little chromosomal mosaicism was detected, the different segments of the Y chromosome retained by these two males identify the location of one or more "anti-Turner" genes. Most of the Yp pseudoautosomal region and Yq were deleted from both patients during the formation of the ring chromosome, while the Y specific portion of Yp and the centromere were retained. The major difference detected was an interval of proximal Yq present in DM and deleted in TS. None of the previously identified genes, DFFRY, DBY, UTY, or TB4Y, lies entirely within this interval, although DFFRY was truncated by DM's breakpoint. These data suggest that one or more additional "anti-Turner" gene(s) remains to be identified in the region of Yq proximal to DFFRY.

Adolescent↗
PubMed1999

Deletion polymorphism in the human COL1A2 gene: genetic evidence of a non-African population whose descendants spread to all continents.

We report the frequencies of a deletion polymorphism at the alpha 2 (1) collagen gene (COL1A2) and argue that this distribution has major implications for understanding the evolution of modern humans immediately after their exodus from sub-Saharan Africa as well as their subsequent spread to all continents. The high frequency of the deletion in non-African populations and its complete absence in sub-Saharan African groups suggest that the deletion event occurred just before or shortly after modern humans left Africa. The deletion probably arose shortly after the African exodus in a group whose descendants were among the ancestors of all contemporary populations, except for sub-Saharan Africans. This, of course, does not imply that there was a single migration out of Africa. The GM immunoglobulin haplotype GM*A,X G displays a similar distribution to that for the COL1A2 deletion, and these 2 polymorphisms suggest that the exodus from Africa may not have been a rapid dispersion to all other regions of the world. Instead, it may have involved a period of time for the savanna-derived gene pool to adapt to novel selective agents, such as bacteria, viruses, and/or environmental xenobiotics found in both animal and plant foods in their new environment. In this context these polymorphisms are indicators of the evolution that occurred before the diaspora of these populations to the current distribution of modern peoples.

Africa South of the Sahara↗
PubMed1999

Y-chromosome-specific microsatellite variation in Australian aboriginals.

The frequency distributions of 4 highly polymorphic Y-chromosome-specific microsatellites (DYS19, DYS390, DYS391, and DYS392) were determined in 79 unrelated Australian Aboriginal males from the Northern Territory. These results are compared with those observed in worldwide populations at both the locus and the haplotype level. Common alleles in Aboriginals are DYS19*15 (49%), DYS19*14 (28%), DYS390*19 (39%), DYS390*24 (20%), DYS391*10 (72%), DYS392*11 (63%), and DYS392*13 (28%). No evidence of reduced gene diversity was observed for these Y-chromosome alleles. DYS390 exhibits the most complex arrangement, displaying a bimodal distribution composed of common alleles (*22-*26), and rare short alleles (*18-*20), with an intermediate allele (*21) being absent. DYS390*20, previously reported only in Papuans and Samoans, is observed for the first time in Aboriginals. Compared with a recent study of Aboriginals, our sample exhibits considerable diversity in the haplotypes associated with the rare DYS390*19 allele, indicating that this allele is of considerable antiquity, if it arose as a single deletion event. Combining all 4 Y-chromosome-linked microsatellites produced 41 unique haplotypes, which were linked using a median-joining network. This network shows that most (78%) of our Aboriginal haplotypes fall into 2 distinct clusters, which likely represent 2 separate lineages. Seven haplotypes are shared with haplotypes found in a recent study of Aboriginals, and 7 are shared with a Spanish population. The cluster of Aboriginal haplotypes associated with the short DYS390 alleles does not share any haplotypes with the Spanish, indicating that this cluster of haplotypes is unique to Australian Aboriginals. Limited data from 4 worldwide populations used to construct haplotypes based on 3 loci (DYS19, DYS390, DYS392) show that only 4 of these haplotypes are seen in Australian Aboriginals. Shared haplotypes may be the result of admixture and/or recurrent mutation at these loci. Expanding the haplotype analysis to include biallelic markers on the Y chromosome will resolve this issue.

Alleles↗