Segregation Of Sex Chromosomes Research Articles

P-198. Segregation of sex chromosomes in spermatozoa of 46,XY/47,XXY men by multicolour fluorescence in-situ hybridization

P-198. Segregation of sex chromosomes in spermatozoa of 46,XY/47,XXY men by multicolour fluorescence in-situ hybridization

O-121. Segregation of sex chromosomes in a Klinefelter patient (47,XXY)

With the recent advance in the techniques of assisted reproduction, it is now possible to overcome male infertility associated with severe oligospermia or azoospermia with alternatives other than sperm donation. This is the case for some patients carrying the Klinefelter syndrome with a somatic karyotype 46,XY/47,XXY or 47,XXY. Despite a deeply defective spermatogenesis in 47,XXY patients, intracouple fertilization can be achieved with the use of intracytoplasmic sperm injection (ICSI) (1). Therefore, one should consider the risk of transmitting an aneuploidy, which would be likely to involve the sex chromosomes but could also involve the autosomes. In patients carrying a mosaic Klinefelter syndrome (46,XY/ 47,XXY), previous studies of sex chromosome segregation by sperm karyotyping (2) or fluorescent in situ hybridization (FISH) (3) or HIS (4) have shown that the percentage of hyperhaploid spermatozoa (24,XY) ranged from 0.9% to 2.1%. In subjects carrying a homogeneous somatic karyotype 47,XXY, previous data have shown variable hyperhaploidies rates, ranging from 1.36% to 25%, as well as variable sex ratios (5–7). The aim of the present work was to collect more data in order to better evaluate the risk of sex chromosome aneuploidies in the spermatozoa (and in the potential offspring) of these patients. Using multicolor FISH, the segregation of the chromosomes X, Y, and 1 was analyzed in 502 spermatozoa from a sperm sample of a first 47,XXY patient, who was a candidate for ICSI. The percentage of hyperhaploid spermatozoa 24,XY was 3.6%, which represents more than 10 times this abnormality in control donors. The sex ratio (23X/23Y) was 1.12. This work confirms that a few germinal cells with a 47,XXY chromosomal constitution are able to achieve meiosis and spermiogenesis and produce mature spermatozoa. However, a high interindividual variability seems to appear when the data from the few published studies are compared. Indeed, the presence of a remaining spermatogenesis, the sex ratio and the percentage of spermatozoa carrying a sex chromosomes hyperhaploidy are different from one 47,XXY patient to another. Therefore, a study of the sex chromosome segregation in these patients seems to be appropriate when they are candidates for ICSI. Moreover, the segregation of the autosomes might also be disturbed, but this remains to be studied. It is under current investigation in the present case.

Genetic interactions between mei-S332 and ord in the control of sister-chromatid cohesion.

The Drosophila mei-S332 and ord gene products are essential for proper sister-chromatid cohesion during meiosis in both males and females. We have constructed flies that contain null mutations for both genes. Double-mutant flies are viable and fertile. Therefore, the lack of an essential role for either gene in mitotic cohesion cannot be explained by compensatory activity of the two proteins during mitotic divisions. Analysis of sex chromosome segregation in the double mutant indicates that ord is epistatic to mei-S332. We demonstrate that ord is not required for MEI-S332 protein to localize to meiotic centromeres. Although overexpression of either protein in a wild-type background does not interfere with normal meiotic chromosome segregation, extra ORD+ protein in mei-S332 mutant males enhances nondisjunction at meiosis II. Our results suggest that a balance between the activity of mei-S332 and ord is required for proper regulation of meiotic cohesion and demonstrate that additional proteins must be functioning to ensure mitotic sister-chromatid cohesion.

Checkpoint control in crane-fly spermatocytes: unattached chromosomes induced by cytochalasin D or latrunculin treatment do not prevent or delay the start of anaphase

Variable numbers of bivalents and sex chromosomes do not attach to the spindle when prophase or early prometaphase cranefly spermatocytes (2n=8) are treated with cytochalasin D or latrunculin. The unattached bivalents lie in the cytoplasm or at the spindle pole, and they do not delay onset of autosomal anaphase; sometimes they disjoin at the same time as the attached bivalents, so they respond to the global signals that initiate anaphase. Unattached sex chromosomes do not delay autosomal anaphase, either. Of various interpretations of these data, we think the best explanation is that the checkpoint system responds to physical rather than chemical cues; we think that the spindle is a “tensegral” structure, that chromosomes need to interact with the spindle in order to be recognised by the anaphase-onset “checkpoint control”, and that the physical interaction of chromosomes with spindle acts as a signalling network. Cytochalasin D and latrunculin treatments delay onset of sex chromosome anaphase (which normally occurs about 15 min after autosomal anaphase) and cause altered patterns of sex-chromosome segregation.

Cytogenetics of collared lemmings (Dicrostonyx groenlandicus). I. Meiotic behavior and evolution of the neo-XY sex-chromosome system.

Electron-microscopic analysis of surface-spread synaptonemal complexes at pachynema and light-microscopic analysis of chromosomal configurations at diakinesis/metaphase I corroborate the hypothesized neo-XY derivation of the sex chromosomes of Dicrostonyx groenlandicus. Although an intact neo-XY pairing configuration was observed in a relatively small percentage of the pachytene cells in each individual, the high incidence of neo-XY bivalents at diakinesis/metaphase I suggests that the other observed pachytene configurations were artifacts of the physical stresses of the surface-spreading procedure. The very low frequency (0.6%) of univalent neo-X and neo-Y chromosomes at diakinesis and metaphase I is attributable to consistent synapsis and recombination between their homologous autosomally derived segments. The resultant stability of the sex bivalent through metaphase I may have increased the efficacy of sex-chromosome segregation, and thereby played a mechanistic role in the evolutionary incorporation of the neo-XY sex-chromosome constitution in D. groenlandicus.

The heredity of sex determination in tilapias

Evidence for the genetic mechanism of sex determination in tilapias has been generated from interspecific hybridization, chromosome manipulations, sex inversion and intraspecific investigations. In some interspecific hybrids and hybrid derivatives, Mendelian segregations are found in sex ratio, i.e., 0 : 1, 1 : 1 and 1 : 3 segregations. Attempts were made to explain these ratios by a dual system of sex chromosomes whereby, in some species, the female is homogametic and the male heterogametic, while in another group of species the opposite is the case. This model, alone, is not capable of explaining further sets of empirical data, since in other crosses and gynogenetic broods sex ratios are variable and non-Mendelian. Series of single-pair, intraspecific spawns showed that sex ratio is a continuously variable trait, with a mean of about 50% and, in at least one species, a range of 0–100%. Sex ratio was also shown to be a stable trait and to respond to selection, behaving like a quantitative trait. Based on these facts, we hypothesize that some sex-determining factors are concentrated on one pair of chromosomes which thereby become the sex chromosomes. Presumably crossing-over takes place between these sex chromosomes, as demonstrated in other fish species. Further genetic determinants of sex are situated on other chromosomes, the autosomes. Segregation of sex chromosomes brings about Mendelian sex segretions in the absence of variation in autosomally carried sex determinants. Non-Mendelian sex segregations, continuous variation in sex ratios and response to selection could result from variation in autosomal sex determinants and crossing-over between sex chromosomes. We suggest that the genetic mechanism of sex determination in tilapias is analogous to that in platyfish, depending on variation in both sex chromosome and autosomally carried factors. Empirical evidence for this is not available for tilapias, due to the absence of sex-linked markers. In such a complex system, the chances of producing “super males”, which generate all-male broods with any female, in either interor intraspecific combination, appear small. We suggest that intraspecific investigations have a better chance than interspecific ones of advancing our knowledge of sex determination in tilapias, as well as producing stable broodstocks generating sex ratios tending to all-male progenies.

Female-Biased Sex Ratio at Hatching in the Green Woodhoopoe

Female-Biased Sex Ratio at Hatching in the Green Woodhoopoe

Structure, function, and evolutionary significance of the reproductive system in males of Hebrus ruficeps and H. pusillus (heteroptera, gerromorpha, hebridae).

In Holland, bugs of the species Hebrus pusillus and H. ruficeps have one generation per year and overwinter as unmated adults. Males have two testes with two follicles + vasa efferentia each, paired vasa deferentia and seminal vesicles, an ejaculatory duct, and a protrusible phallus comprising an articulatory apparatus, phallotheca, endosoma, and paired claspers. The skeletomusculature of this system is described (it has 12 paired and four unpaired muscles) and its functions in generating and transferring sperm (summarized in Figs. 70-75) are reconstructed from study of living bugs, dissections, whole mounts, and serial sections. Males of both species produce sperm >2 mm long from stem spermatogonia in the germarium of each follicle. Initial definitive spermatogonia divide synchronously three times to form clones of eight, interconnected, primary spermatocytes. These enlarge up to 43-fold in males of H. pusillus and 78-fold in those of H. ruficeps, undergo meiosis, and, after adult emergence, complete their differentiation into bundles of 32 sperm which coil transversely about the periphery of each follicle at its base. These begin to enter the vasa efferentia in mid August, rupture, and release their sperm into the seminal vesicles where they are stored overwinter. Most spermatocyte and spermatid cysts remaining in the testes degenerate in fall, leaving only stem spermatogonia and a few early spermatocysts in the germaria. Males of H. pusillus begin to mate the first warm days of spring but only the most persistent succeed. A male jumps on the back of a female, induces her to lower her ovipositor, and, within 12 min (@ 18-24°C), introduces the endosoma of his phallus up its shaft and fills his seminal duct with sperm. The female draws this into her gynatrial sac at the end of copulation and transfers it into her spermatheca in about 30 min, the sperm reversing themselves within it so that their heads face towards its mouth. The male may stay on her back for up to 2 hours and may copulate again up to three times before leaving to mate with other females. Males of H. pusillus may be sexually active for months after overwintering, because spermatogonia in their germaria reactivate in spring to produce additional sperm. Those of H. ruficeps do not and males mate successfully only until their supply of overwintered sperm is exhausted. The chromosome complement of H. pusillus males is 2N = 22 + XY. The X and Y chromosomes are of unequal length, form a pseudo pair at metaphase I, and segregate to opposite poles at anaphase I-the first instance of pre-reductional segregation of sex chromosomes to be recorded in the Gerromorpha. The chromosome complement of H. ruficeps may be 2N = 24 + XO but the nature of two chromosomes was not resolved. The single X segregates to half the spermatids at anaphase II.

Meiotic association and segregation of the achiasmatic giant sex chromosomes in the male field vole (Microtus agrestis)

Controversy exists regarding the meiotic behaviour of the giant sex chromosomes during spermatogenesis in the field vole, Microtus agrestis. Both univalents and bivalents have been observed between diakinesis and metaphase I. These differences seem to be dependent on the technique used. The present study employs electron microscopy of serially sectioned testes tubules and light microscopy of microspread preparations to re-examine the behaviour of sex chromosomes during meiosis. In microspreads, about one-third of the early pachytene nuclei examined showed end joining of the X and Y axes. The longitudinal heterogeneity of the chromosomes in the form of axial thickenings allowed the detection of two different end-joining patterns. In the remaining early pachytene cells as well as in all mid to late pachytene cells seen, the X and Y axes had, though near to each other, no contact in the form of a synaptonemal complex. If a synaptonemal complex is a prerequisite for genetic exchange, the sex chromosomes in M. agrestis males must be achiasmatic. The analysis of serial sections through an early pachytene and a late prophase I nucleus with the electron microscope revealed that the sex chromosomes occupied a common area. By metaphase I, the centromeres of the X and Y were oriented towards opposite spindle poles while the chromosomes remained attached to one another by their distal segments at the level of the metaphase I plate. As a consequence of the large size of the sex chromosomes their centromeres lay close to the spindle poles. In anaphase I the sex chromosomes maintained their metaphase position until the autosomes approached the spindle poles. During autosomal migration a medial constriction developed where the sex chromosomes were mutually associated, the X and Y became separated, and joined the autosomes. In metaphase II the chromatids of the sex chromosomes lay side by side and exhibited a delayed separation in the subsequent anaphase. It is suggested that heterochromatin, which represents a major part of both sex chromosomes, plays a role in the association of the two achiasmatic sex chromosomes in metaphase I and in the delayed separation of the chromatids of the sex chromosomes in anaphase II.

Sex determination and sex differentiation in coccidia: gametogony and oocyst production after monoclonal infection of cats with free-living and intermediate host stages of Isospora (Toxoplasma) gondii.

Clones of single oocysts, single sporocysts, single sporozoites, single proliferative parasites, single cysts and single cystozoites of Isospora (Toxoplasma) gondii (KB-strain) were made under visual control using a de Fonbrune micromanipulator. Cloning was successful in 28, 32, 21, 8, 54 and 7% of the trials, respectively. All clones were used for monoclonal infection in non-immune conventionally reared (CV) or specified pathogen-free (SPF) cats. Pre-patent and patent periods, sporulation percentages of excreted oocysts, mouse infectivity of sporulated oocysts, antibody response and immunity to reinfection of CV cats were determined. For these parameters almost no differences were observed between monoclonal infections and infections described with the non-cloned KB-strain. In all cats autopsied during the patent period, 5-8 days post-infection, macrogametes, microgametes and oocysts were found. Since meiosis occurs during sporulation and since all free-living and intermediate host stages proved to be bisexual, it is concluded that sex differentiation in I. (T) gondii is not determined by segregation of sex chromosomes or sex genes but is caused by some final host factor(s) that induce(s) differential gene expression in genetically identical cells.

SEX CHROMOSOME MEIOTIC DRIVE IN DROSOPHILA MELANOGASTER MALES

In Drosophila melanogaster males, deficiency for X heterochromatin causes high X-Y nondisjunction and skewed sex chromosome segregation ratios (meiotic drive). Y and XY classes are recovered poorly because of sperm dysfunction. In this study it was found that X heterochromatic deficiencies disrupt recovery not only of the Y chromosome but also of the X and autosomes, that both heterochromatic and euchromatic regions of chromosomes are affected and that the "sensitivity" of a chromosome to meiotic drive is a function of its length. Two models to explain these results are considered. One is a competitive model that proposes that all chromosomes must compete for a scarce chromosome-binding material in Xh(-) males. The failure to observe competitive interactions among chromosome recovery probabilities rules out this model. The second is a pairing model which holds that normal spermiogenesis requires X-Y pairing at special heterochromatic pairing sites. Unsaturated pairing sites become gametic lethals. This model fails to account for autosomal sensitivity to meiotic drive. It is also contradicted by evidence that saturation of Y-pairing sites fails to suppress meiotic drive in Xh(- ) males and that extra X-pairing sites in an otherwise normal male do not induce drive. It is argued that meiotic drive results from separation of X euchromatin from X heterochromatin.

Chromosomal segregational mechanisms in ant-lions (Myrmeleontidae, Neuroptera)

In a single male specimen of Myrmeleon mexicanum Banks the sex chromosomes, normally X and Y, were replaced by what appeared to be X1X2 and Y. These segregated as expected on that interpretation in only half of the spermatocytes — in the other half, one X and the Y segregated from the other X. This atypical segregation is explicable on the assumption that one of the supposed Xs is a supernumerary, not a sex chromosome, and the diploid complement of the male comprises six pairs of autosomes plus a supernumerary and the X and Y sex chromosomes. The orientation of the X chromosomes at first metaphase was variable: kinetochoric activity may be localized midway the length of the chromosome, as in gonial mitosis, or terminally. Comparative study of three congeneric species, seven of Brachynemurus, one of Psammoleon, and one of Vella showed normal segregation in all, and no evidence for secondary kinetochoric activity. In nine of the species studied one pair of autosomes was unconjoined at first metaphase in 0.3%–1.2% of primary spermatocytes. These autosomes segregated precociously with the sex chromosomes in the central unit of the spindle. In one exceptional male of Brachynemurus hubbardi Currie all first meiotic metaphases showed this behavior, and a compound X1X2/Y1Y2 system was thus simulated. Bivalent formation replaced distance segregation of sex chromosomes in 0.4%–3.2% of the spermatocytes in seven of the thirteen species studied. These sex-bivalents frequently displayed partial or complete failure in congression.

Digynic triploidy in rabbit blastocysts after delayed insemination.

SUMMARYThe origin of triploid (3N) 5½-day blastocysts in rabbits is inferred from the segregation of sex chromosomes and of an autosomal M-marker whose properties are described. 39 triploids and no tetraploids were scored among 1454 chromosomally scored blastocysts. A delay of 8 h between an ovulatory injection and subsequent insemination raised the estimated normal incidence of 0·59% triploid blastocysts to 3·13%. The increase is ascribed primarily to digyny (17 blastocysts), and to diandry probably mediated by dispermy (1 blastocyst). The triploid components of the two 2N/3N mosaics and the one 3N/6N were digynic. Neither superovulation nor insemination of excessive numbers of spermatozoa could be shown to give rise to triploid embryos. The diandric triploid was X Y Y, the first of this constitution apparently reported in the rabbit. There was some evidence that X X Y triploid blastocysts up to 5½-day gestation are more viable than X X X. In the 2N/3N mosaics each component had been entered by one spermatozoon, and the dliploid component could not have been merely a contamination by dliploid maternal somatic cells. In 2N/4N, 2N/4N/8N and 3N/6N mosaics, each polyploid component showed an exact doubling of the marker chromosome constitution of a component of lower ploidy; their origin is ascribed to doubling or redoubling of chromosome number in isolated embryonic cells. With earlier data included, 49·08 (± s.e. 1·96)% of 652 diploid blastocysts were X Y. 460 non-experimental weaned rabbits were all cliploid.

Genetic studies on heterochromatin in Drosophila melanogaster and their implications for the functions of satellite DNA

In Drosophila melanogaster the centromeric heterochromatin of all chromosomes consists almost entirely of several different satellite DNA sequences. In view of this we have examined by genetic means the meiotic consequences of X chromosomes with partial deletions of their heterochromatin, and have found that the amount and position of recombination on each heterochromatically deleted X is substantially different from that of a normal X. It appears that the amount of heterochromatin is important in modifying the "centromere effect" on recombination.--In all the deleted Xs tested, chromosome segregation is not appreciably altered from that of a nondeleted control chromosome. Thus satellite DNA does not appear to be an important factor in determining the regular segregation of sex chromosomes in Drosophila. Additionally, since X chromosomes with massive satellite DNA deficiencies are able to participate in a chromocenter within salivary gland nuclei, a major role of satellite DNA in chromocenter formation in this tissue is also quite unlikely.--In order to examine the mechanisms by which the amount of satellite DNA is increased or decreased in vivo, we have measured cytologically the frequency of spontaneous sister chromatid exchanges in a ring Y chromosome which is entirely heterochromatic and consists almost exclusively of satellite DNA. In larval neuroblast cells the frequency of spontaneous SCE in this Y is approximately 0.3% per cell division. Since there is no meiotic recombination in D. melanogaster males and since meiotic recombination in the female does not occur in heterochromatin, our results provide a minimum estimate of the in vivo frequency of SCE in C-banded heterochromatin (which is predominantly simple sequence DNA), without the usual complications of substituted base analogs, incorporated radioactive label or substantial genetic content.--We emphasise that: (a) satellite DNA is not implicated in any major way in recognition processes such as meiotic homologue recognition or chromocenter formation in salivaries, (b) there is likely to be continuous variation in the amount of satellite DNA between individuals of a species; and (c) the amount of satellite DNA can have a crucial functional role in the meiotic recombination system.

Influence of autosome movements and of sex-chromosome movements on sex-chromosome segregation in crane fly spermatocytes.

In crane fly spermatocyte meiosis 3 autosome half-bivalents normally move to each spindle pole in anaphase while the 2 amphitelic sex-chromosome univalents remain at the equator. The sex-chromosome univalents move to opposite poles after the autosomes reach the poles. — We used micromanipulation to detach half-bivalents in anaphase. When re-attached half-bivalents were syntelically oriented to the original pole, sex-chromosome segregation was usually not altered. When re-attached half-bivalents were amphitelically oriented, sex-chromosome segregation was usually altered: usually the amphitelic autosome segregated against one sex-chromosome while the other sex-chromosome remained at the equator. When re-attached half-bivalents were syntelically oriented to the opposite pole, sex-chromosome segregation was often altered: often one sex-chromosome moved normally to the spindle pole with 2 autosomal half-bivalents, while the other sex-chromosome did not move to the spindle pole with 4 autosomal half-bivalents, but remained at the equator. — The direction of motion of a sex-chromosome could be altered even after sex-chromosome segregation had begun, by suitable micromanipulation of the other sex-chromosome. — Amphitelic chromosomes that were not on the equator at the start of anaphase segregated predominantly to the closer spindle pole. Detached half-bivalents showed no preference for the closer pole when they re-attached with syntelic orientation. — We discuss some possible hypotheses for non-independent movements, and some implications of the results.

Karyotype variation in dermestid beetles.

The system of nucleolar controlled sex-chromosome segregation which characterises Xyp species of hide beetles is also present in the one species (haemorrhoidalis) with an XY system. This, coupled with the fact that the karyotype in the XY species is asymmetrical, whereas species with smaller y-chromosomes show greater symmetry, suggests that “erosion” of the y may have involved translocation of the material of the y onto the autosomes rather than simple loss. Finally, supernumerary y chromosomes present in laboratory cultures of two species (maculatus and frischii) demonstrate the efficiency of the sex nucleolus as a mechanism for securing segregation.

THE MECHANISM OF NON-RANDOM SEGREGATION OF SEX CHROMOSOMES IN MALE DROSOPHILA MIRANDA

THE MECHANISM OF NON-RANDOM SEGREGATION OF SEX CHROMOSOMES IN MALE DROSOPHILA MIRANDA

Uma nova modalidade de sexo-determinação no grilo sul-americano eneoptera surinamensis

Uma nova modalidade de sexo-determinação no grilo sul-americano eneoptera surinamensis

A case of the mosaicism in the silkworm egg, probably due to a recessive mutation

By application of high temperature shock many mosaics have been obtained in the silkworm egg. As a possible explanation, it was assumed that they are due to binucleated eggs, one of nuclei being a normaly fertilized egg-nucleus and the other being formed by fusion of two spermatozoan-nuclei. There are, however, some cases where this explanation does not apply. One of them, which I am dealing with, is presumably due to a recessive mutation.This type of mosaic was obtained in a heat-treated egg from a crossing of (PSY/PSY, Re Pe/Re Pe) _??_×(P y/P y, re pe/re pe) _??_. Of 4330 treated eggs, 74 were mosaics and of these only four caterpillars hatched out next spring, the rest all died during hybernation. One of the caterpillars (mp. 43) was heterozygous striped, which is usually expected from F1 offspring. The egg from which this caterpillar hatched out was an intermingled mosaic of black and pink serosa cells, as is shown in Fig. 1. The moth resulted from this caterpillar was female and had a mosaic eye on the left consisting of black and pink facets (Fig. 2). This heterozygous mosaic female was mated to p y/p y, pe/pe male. The segregation between PSY and Py was almost normal as is usually expected for FR1, while Pe-pe ratio was quite abnormal. The segregation of sex chromosomes was also normal in this female and gave normal sex ratio in her offspring. Thus abnormality is evidently limited to the Pe gene. As a possible explanation of this fact several assumptions may be done, but the recessive mutation of Pe to pe in the two cell stage seems to be most probable.From this mosaic, and others obtained in another way, we learn some important facts as follows;1. Pe gene does not secrete pe+ substance in the moth of this insect as well as in the egg, as was previously reported by the author. The same conclusion was also confirmed to be applicable to Re gene from another experiment.2. Mosaic pattern of the compound eye of this insect is very peculiar concerning to the distribution of mosaic tissues, i.e. the striated or band-like arrangement of facets of different colours (Fig. 3). Mosaic tissues do never arrange in a direction parallel to the plane of symmetry in the moth. This fact suggests the direction of development of the compound eyes.