Colcemid sensitivity of fission yeast and the isolation of colcemid-resistant mutants.

Cell division of the fission yeast, Schizosaccharomyces pombe, is reversibly inhibited by the antimitotic agent Colcemid (N-deacetyl-N-methylcolchicine) in nutrient medium. Cell growth continiues until all cells become nonseparating cell doublets in a V configuration. Mutants have been isolated capable of uninhibited growth in the presence of concentrations of Colcemid mycostatic for the parent strain.

Immunolocalization of CENP-A suggests a distinct nucleosome structure at the inner kinetochore plate of active centromeres.

The trilaminar kinetochore directs the segregation of chromosomes in mitosis and meiosis. Despite its importance, the molecular architecture of this structure remains poorly understood [1]. The best known component of the kinetochore plates is CENP-C, a protein that is required for kinetochore assembly [2], but whose molecular role in kinetochore structure and function is unknown. Here we have raised for the first time monospecific antisera to CENP-A [3], a 17 kD centromere-specific histone variant that is 62% identical to the carboxy-terminal domain of histone H3 [4,5] and that resembles the yeast centromeric component CSE4 [6]. We have found by simultaneous immunofluorescence with centromere antigens of known ultrastructural location that CENP-A is concentrated in the region of the inner kinetochore plate at active centromeres. Because CENP-A was previously shown to co-purify with nucleosomes [7], our data suggest a specific nucleosomal substructure for the kinetochore. In human cells, these kinetochore-specific nucleosomes are enriched in alpha-satellite DNA [8]. However, the association of CENP-A with neocentromeres lacking detectable alpha-satellite DNA, and the lack of CENP-A association with alpha-satellite-rich inactive centromeres of dicentric chromosomes together suggest that CENP-A association with kinetochores is unlikely to be determined solely by DNA sequence recognition. We speculate that CENP-A binding could be a consequence of epigenetic tagging of mammalian centromeres.

Redefining the risks of prenatally ascertained supernumerary marker chromosomes: a collaborative study.

BACKGROUND: A marker chromosome is defined as a structurally abnormal chromosome that cannot be identified by routine cytogenetics. The risk for phenotypic abnormalities associated with a marker chromosome depends on several factors, including inheritance, mode of ascertainment, chromosomal origin, and the morphology, content, and structure of the marker. METHODS: to understand the karyotype-phenotype relationship of prenatally ascertained supernumerary de novo marker chromosomes, we combined data from prenatal cases obtained from 12 laboratories with those from studies in the literature. We were able to obtain cytogenetic and phenotypic data from 108 prenatally ascertained supernumerary de novo marker chromosomes to refine the phenotypic risk associated with these markers. Because of the growing number of cases and because more techniques are available to delineate marker morphology, we have been able to group risk estimates into subcategories, such as by marker type and whether there are ultrasound abnormalities. RESULTS: If a de novo supernumerary marker chromosome is found prenatally, our data suggest there is a 26% risk for phenotypic abnormality when there is no other information defining the marker (such as chromosomal origin or information about the existing phenotype). However, if high resolution ultrasound studies are normal, this risk reduces to 18%. CONCLUSIONS: Our findings strongly support the value of additional genetic studies for more precisely defining the risk in individual cases involving marker chromosomes.

The human Jurkat (FHCRC-11) cell line is heterogeneous in ploidy and cell size and releases detergent-soluble DNA.

Jurkat (FHCRC-11) cells, a human lymphoblastic leukemic line, were characterized as being hypotetraploid with a characteristic deletion in the short arm of chromosome 2 from the terminus to band 24. Although Jurkat cells were size heterogeneous, variability in ploidy was not correlated with density and size differences observed when cells were fractionated by means of gradient centrifugation using Nycodenz as the supporting medium. Also no difference was seen in the chromosome distribution of cells cultured from different portions of the gradient. During cell division Jurkat cells incorporated [3H]thymidine ([3H]TdR) into newly made DNA, including a small percentage that was released into the soluble fraction upon detergent lysis. Small light cells from the top portion of the gradient were more efficient on a per cell basis in incorporating [3H]TdR into DNA from both the detergent-soluble and detergent-insoluble fractions. However, due to the hypotetraploid nature of these cells a definitive assignment to a specific stage in the cell cycle was not possible.

The role of the sex-determining region Y gene in the etiology of 46,XX maleness.

The condition of 46,XX maleness is characterized by testicular development in subjects who have two X chromosomes but who lack a normal Y chromosome. Several etiologies have been proposed to explain 46,XX maleness: 1) translocation of the testis-determining factor from the Y to the X chromosome, 2) mutation in an autosomal or X chromosome gene which permits testicular determination in the absence of TDF, and 3) undetected mosaicism with a Y-bearing cell line. We evaluated 10 affected subjects who were ascertained for different reasons and who had several distinct phenotypes. Six subjects had inherited sequences from the short arm of the Y chromosome including the sex-determining region Y gene (SRY). Five of the subjects were pubertal at the time of evaluation and had a phenotype similar to that of Klinefelter syndrome with evidence of Sertoli cell and Leydig cell dysfunction. One subject had evidence from Southern blot analysis and in situ hybridization for the presence of an intact Y chromosome in approximately 1% of cells. Three subjects lacked Y sequences by Southern blot analysis and by polymerase chain reaction amplification of SRY. These subjects were ascertained in the newborn period because of congenital anomalies. One had multiple anomalies including cardiac abnormalities; one had cardiac anomalies alone; and one had ambiguous genitalia. Our data confirm the genetic heterogeneity of 46,XX maleness, in which some subjects have SRY while other subjects lack it. In addition, there is phenotypic heterogeneity among subjects who lack SRY suggesting that there is also genetic heterogeneity within this subgroup.

Spectral studies on 33258 Hoechst and related bisbenzimidazole dyes useful for fluorescent detection of deoxyribonucleic acid synthesis.

Absorption, fluroescence and circular dichroism measrements on 33258 Hoechst-deoxyribonucleic acid (DNA) complexes are consistent with the existence of two types of dye-binding interactions. One type, which persists at elevated solution ionic strength, is highly specific for adenine-thymine-rich DNA. Dye bound under this condition exhibits efficient fluorescence and strong optical activity. A less specific, largely electrostatic interaction is associated with less intense fluorescence and weaker optical activity. The fluorescence of 33258 Hoechst and several other bisbenzimidazole dyes is less when bound to poly(deoxyadenylate-5-bromodeoxyuridylate) than when bound to poly(deoxyadenlyate-deoxythymidylate). Quenching of 33258 Hoechst fluorescence can also be used to detect biosynthetic incorporation of 5-bromodeoxyuridine into the DNA of living cells. This property of 33258 Hoechst should allow fluorescence-activated cell and chromosome sorting according to the extent of DNA synthesis, providing a bridge between biochemical and cytologic analyses of processes related to DNA replication.

Recent developments in the detection of deoxyribonucleic acid synthesis by 33258 Hoechst fluorescence.

A number of applications of the detection of deoxyribonucleic acid synthesis by fluorescence microscopy are illustrated. These include (a) the analysis of sister chromatid exchanges and sister chromatid segregation at mitosis, (b) the location of chromosome regions containing deoxyribonucleic acid with an asymmetric distribution of thymine residues between polynucleotide chains and (c) the detection of late replicating regions in metaphase chromosomes. The suppression of 33258 Hoechst fluorescence by 5-bromodeoxyuridine incorporated biosynthetically into interphase nuclei is demonstrated both in fixed cytologic preparations and in unfixed cultured cells. Many of the cytologic observations described might form a basis for future biochemical studies.

Molecular analysis of a complex chromosomal rearrangement and a review of familial cases.

A complex chromosome rearrangement (CCR) involving chromosomes 7, 8, and 13 was detected in a phenotypically normal woman ascertained through her mentally retarded son with abnormal phenotype. He had a karyotype with 47 chromosomes including an extra der(13). In initial banding studies the CCR in the mother was interpreted as a three-way translocation. Fluorescence in situ hybridization with whole chromosome libraries and a telomere-specific probe was used to better characterize the rearrangement. Combined data allowed us to reinterpret the CCR as a translocation and an insertion. A review of 35 familial CCRs involving at least three chromosomes led to the following observations: 1) familial CCRs tend to have fewer chromosomes involved and fewer break-points than do de novo CCRs; 2) familial transmission is mainly observed through female carriers although the origin of de novo cases is paternal; 3) an apparent excess of balanced female carriers among the offspring of index carriers was noted; and 4) meiotic segregation resulting in malformed liveborn infants is most frequently due to adjacent-1 segregation, followed by 4:2 segregation; no adjacent-2 segregation was observed.

Fragile site in chromosome 12 in a patient with two miscarriages.

A heritable fragile site at 12q13 is described in lymphocytes from a woman with a history of multiple miscarriage. The fragile site was not typically folate-sensitive, being expressed in standard medium. The presence of this fragile site may have led to meiotic chromosome breakage and consequent infertility.

A paternally derived inverted duplication of 7q with evidence of a telomeric deletion.

We report on a de novo constitutional rearrangement involving the long arm of chromosome 7 in a second trimester fetus with the karyotype of 46,XX, inv dup del (7)(pter-q36::q36-q21.2:) pat. Both a large duplication (q21.2-q36) and a small deletion (within q36) were confirmed by FISH studies. DNA analysis on the family showed that the abnormal chromosome was derived from a single paternal homolog. A mechanism is proposed in light of this finding. The phenotype at autopsy was consistent with reported cases of similar duplications in chromosome 7 in that hydrocephalus, a depressed nasal bridge, low set ears, microretrognathia and a short neck were present.

Sexual discordance in monozygotic twins.

We report on monozygotic (MZ) twins who were discordant for phenotypic sex and Ullrich-Turner syndrome (UTS). The nonviable female was hydropic with cystic hygromas, ventricular septal defect, bicuspid aortic valve, polysplenia, intestinal malrotation, and small ovaries. The male was phenotypically normal. The monochorionic, diamniotic placenta had hydropic changes limited to the UTS infant's side. Skin samples from the infants and blood from their parents were obtained for cytogenetic and molecular analysis. Karyotypes of the twins were 45,X and 46,XY. Quinacrine polymorphisms on 7 chromosomes and RFLP analysis at 8 loci showed complete identity. MZ twins discordant for phenotypic sex have been described previously. Most of these show evidence of mosaicism in a 45,X patient with a normal 46,XY cell line, and a normal 46,XY male. While the issue of mosaicism in our case cannot be fully resolved, no mosaicism was found in 50 cells analyzed cytogenetically from each culture or by PCR analysis of a Y-specific sequence. The twins probably originated from either postzygotic nondisjunction or anaphase lag, followed or accompanied by twinning. The discordant placental morphology suggests an embryonic origin of at least part of the placental mesenchymal core.

Segregation of a familial balanced (12;10) insertion resulting in Dup(10)(q21.2q22.1) and Del(10)(q21.2q22.1) in first cousins.

An interchromosomal insertion in 3 generations of a family was ascertained through two developmentally delayed first cousins. Cytogenetic analysis using G-banding and chromosome painting showed an apparently balanced direct insertion of chromosome 10 material into chromosome 12, ins(12;10)(q15;q21.2q22.1), in the mothers and grandfather of these children. The proposita inherited only the derivative 10 chromosome, resulting in deletion of 10q21.2 --> 22.1 while her cousin inherited only the derivative 12, resulting in duplication of 10q21.2 --> 22.1. A comparison of the proposita with published deletion cases suggests a pattern of anomalies attributable to deletion of the 10q21 --> q22 region: developmental delay, hypotonia, a heart murmur, telecanthus, broad nasal root and ear abnormalities. This is the first report of a nontandem duplication of the 10q21 --> q22 region. The phenotype of the cousin with the duplication does not overlap greatly with published tandem 10q duplications. Finally, this report reaffirms the importance of obtaining family studies of patients with interstitial chromosomal abnormalities.

Unbalanced translocation, t(18;21), detected by fluorescence in situ hybridization (FISH) in a child with 18q- syndrome and a ring chromosome 21.

We report on an 8-year-old girl with minor anomalies consistent with 18q- syndrome and mild developmental delay. Initially cytogenetics showed a terminal deletion of chromosome 21 with mosaicism for a small ring chromosome 21 as the only apparent karyotypic abnormality: mos 45,XX,-21/46,XX,+r(21) (48%/52%). Further studies including FISH and DNA analysis demonstrated a de novo unbalanced translocation of chromosomes 18 and 21 with the likely breakpoints in 18q23 and 21q21.1. Most of 21q was translocated to the distal long arm of one chromosome 18, and this derivative 18 appeared to lack 18q23-qter. The small ring chromosome 21 [r(21)], present in only 52% of the patient's blood lymphocytes, did not appear to be associated with the abnormal phenotype since all 13 chromosome 21 markers that were examined in genomic DNA were present in 2 copies, and the phenotype of the patient was consistent with the 18q- syndrome. The karyotype was reinterpreted as mos 45,XX,-18,-21,+der(18) t(18;21) (q23;q21.1)/46,XX,-18,-21,+der(18) t(18;21) (q23;q21.1), +r(21) (p13q21.1) (48%/52%). These results demonstrate the power of FISH in conjunction with DNA analysis for examination of chromosome rearrangements that may be misclassified by traditional cytogenetic studies alone.

Ring chromosome 21: characterization of DNA sequences at sites of breakage and reunion.

We have presented studies of an unusual child with an r21 chromosome who lacks the phenotype of Down syndrome. We have sequenced the region of the breakpoint in the normal DNA fragment and have isolated the abnormal breakpoint fragment as a 7.5-kb EcoRI fragment. We have preliminary evidence localizing the breakpoint to a few hundred base pairs of 21q DNA. Since the child lacks the classical phenotype of Down syndrome, further studies of the DNA distal to the breakpoint on the long arm of chromosome 21 may help us to elucidate "genes" important to the phenotype of Down syndrome.

Fetal anomalies associated with an inversion duplication 13 chromosome.

We report the cytogenetics and pathology of a fetus with holoprosencephaly associated with an inversion duplication 13 chromosome. The pathology is compared with that found in cases of partial duplication (trisomy) and deficiency (monosomy) of chromosome 13 described in the literature. To our knowledge, this is the first time holoprosencephaly has been associated with this particular inversion duplication 13 chromosome. Careful pathology and complete chromosomal studies proved useful in counseling this couple.

Isolated fetal ascites detected by sonography: an unusual presentation of Turner syndrome.

The prenatal sonographic diagnosis of Turner syndrome usually depends upon the discovery of a cystic hygroma or nonimmune hydrops fetalis. This report describes isolated fetal ascites as a newly recognized presentation of the disorder. Intrapartum fetal paracentesis permitted atraumatic vaginal birth. The etiology of the ascites in this case was congenital intestinal lymphangiectasia, consistent with the generalized lymphatic hypoplasia previously described in Turner syndrome.

Fetal ascitic fluid: a new source of lymphocytes for rapid chromosomal analysis.

BACKGROUND: The cells found in ascites can be processed like amniotic fluid for fetal karyotyping. We have characterized these cells and used them for a rapid cytogenetic result. CASES: Three patients presented with massive fetal ascites detected by sonography. Samples of ascitic fluid were obtained at fetal paracentesis. Cells from the fluid were cultured using standard methods for fetal blood, and were compared with fetal blood lymphocytes and amniocytes. The length of time in culture, chromosome morphology, and mitotic index of ascitic fluid cells were equivalent to those of fetal blood. In the third case, we performed immunophenotyping on the ascitic fluid cells. CONCLUSION: Ascitic fluid contains lymphocytes that permit rapid chromosomal analysis within 96 hours.

Ambiguous genitalia in an elderly woman with a mosaic 45,X/46,X,dic(Y)(Q11.2) karyotype.

A 66-year-old woman presented with clitoromegaly since childhood, primary amenorrhea, no breast development, and a large right inguinal hernia. A mosaic karyotype was identified containing a predominant 45,X cell line and a cell line with 46 chromosomes, one X chromosome, and a small dicentric Y chromosome with a breakpoint in band qII.2. The patient underwent hysterectomy, bilateral gonadectomy, inguinal hernia repair, clitoral recession, and formation of a neointroitus. A dysgerminoma was identified in the right dysgenetic gonad. This report demonstrates the natural history of untreated mixed gonadal dysgenesis and the importance of early evaluation and treatment, as well as the molecular characterization of a dicentric Y chromosome.

Magnetic orientation of spiny lobsters in the ocean: experiments with undersea coil systems

The western Atlantic spiny lobster Panulirus argus undergoes an annual migration and is also capable of homing to specific dens in its coral reef environment. Relatively little is known, however, about the orientation cues that lobsters use to guide their movements. To determine whether lobsters can orient to the earth's magnetic field, divers monitored the orientation of lobsters tethered inside magnetic coil systems submerged offshore in the Florida Keys, USA. Each coil could be used to reverse either the horizontal or vertical component of the earth's field. Tethered lobsters walking inside the coils often established and maintained consistent courses towards specific directions. After a lobster had established a course, it was exposed to one of three conditions: (1) a reversal of the horizontal component of the earth's field; (2) a reversal of the vertical component of the earth's field; or (3) no change in the ambient field (controls). Lobsters subjected to the horizontal field reversal deviated significantly from their initial courses. In contrast, control lobsters and those subjected to the reversed vertical field did not. These results demonstrate that spiny lobsters possess a magnetic compass sense. Because inverting the vertical component of the earth's field had no effect on orientation, the results suggest that the lobster compass is based on field polarity and thus differs from the inclination compasses of birds and sea turtles. The magnetic compass of lobsters may function in homing behavior, in guiding the autumn migration or in both.