The X-chromosome in the larval salivary glands of hybrids Drosophila insularis × Drosophila tropicalis

Summary The crossDrosophila insularis ×Drosophila tropicalis produces viable but completely sterile hybrids. Chromosomes have been studied in the cells of the salivary glands in hybrid larvae. The euchromatic sections of the chromosomes of the two species remain completely unpaired in the hybrid, despite the obvious similarities of the disc patterns in many portions of these chromosomes. A common chromocenter is nevertheless formed, owing to a mutual attraction of the heterochromatic sections adjacent to the centromeres in all the chromosomes. The condition of the chromosomes in the female and male cells is represented schematically in Fig. 1. The X-chromosomes show a remarkable difference in behavior in the cells of the two sexes. The euchromatic strands representing the X-chromosome are appreciably greater in width but somewhat paler in staining in male than in female larvae. This is a visible counterpart of the genetic phenomenon of dosage compensation.The work reported in this article has been supported in part under Contract No. AT-(30-1)-1151, U. S. Atomic Energy Commission     

CHROMOSOMAL BASIS OF DOSAGE COMPENSATION IN DROSOPHILA : III. Early Completion of Replication by the Polytene X-Chromosome in Male: Further Evidence and Its Implications

Thymidine-³H labeling patterns on the X (section 1 A to 12 E of Bridges' map) and 2 R (section 56 F to 60 F of Bridges' map) segments in the salivary gland chromosomes of Drosophila melanogaster have been analyzed in male and female separately. The observed patterns fit, with a few exceptions, in a continuous to discontinuous labeling sequence. In nuclei with similar labeling patterns on the 2R segment in both sexes, the number of labeled sites on the X in male is always less than in female X's. The labeling frequency of the different sites on the male X is considerably lower than those on the female X's, while the sites on the 2R segment have very similar frequency in the two sexes. The rate of thymidine-³H incorporation (as judged by visual grain counting) is relatively higher in male X than in female X's. It is concluded that the model sequence of replication in polytene chromosomes follows a continuous to discontinuous labeling sequence, and that the single X in male completes its replication earlier than either the autosomes in male or the X's in female. This asynchronous and faster rate of replication by the polytene X-chromosome in male substantiates the hypothesis of hyperactivity of the single X in male as the chromosomal basis of dosage compensation in Drosophila.     

Mechanisms of sex determination and X-chromosome dosage compensation

Abnormalities in chromosome number have the potential to disrupt the balance of gene expression and thereby decrease organismal fitness and viability. Such abnormalities occur in most solid tumors and also cause severe developmental defects and spontaneous abortions. In contrast to the imbalances in chromosome dose that cause pathologies, the difference in X-chromosome dose used to determine sexual fate across diverse species is well tolerated. Dosage compensation mechanisms have evolved in such species to balance X-chromosome gene expression between the sexes, allowing them to tolerate the difference in X-chromosome dose. This review analyzes the chromosome counting mechanism that tallies X-chromosome number to determine sex (XO male and XX hermaphrodite) in the nematode Caenorhabditis elegans and the associated dosage compensation mechanism that balances X-chromosome gene expression between the sexes. Dissecting the molecular mechanisms underlying X-chromosome counting has revealed how small quantitative differences in intracellular signals can be translated into dramatically different fates. Dissecting the process of X-chromosome dosage compensation has revealed the interplay between chromatin modification and chromosome structure in regulating gene expression over vast chromosomal territories.     

The dose effect ofma-l+ andry+ on xanthine dehydrogenase activity inDrosophila melanogaster

Summary Two loci,ma-l ⁺ andry ⁺, necessary for xanthine dehydrogenase activity inDrosophila melanogaster have been studied for dosage effects utilizing deficiencies and duplications induced for this purpose. Comparisons of one, two and three doses ofma-l ⁺ in the female or one and two doses in the male indicate that there is no increase in specific enzyme activity with dose. On the other hand, comparisons of one, two and three doses ofry ⁺ in the male and female reveal an increase in enzyme activity that is roughly proportional to dose. Since dosage ofry ⁺ is limiting, whereas that ofma-l ⁺ is not, the final concentration of xanthine dehydrogenase is shown to depend on the number of doses ofry ⁺.The implications of these findings with respect to the hypothesis of dosage compensation and to the mechanism of control of enzyme and protein concentration are discussed.Operated by Union Carbide Corporation for the U.S. Atomic Energy Commission.     

Patterns of puffing activity in the salivary gland chromosomes of Drosophila

Salivary gland X chromosome puffing patterns are described for the Oregon stock of Drosophila melanogaster and for the Berkeley stock of D. simulans. In D. melanogaster regular phase specific puffing was recorded at 21 loci in the third larval instar and subsequent prepupal stage. A comparison of the X chromosome puffing patterns of male and female larvae failed to show any qualitative differences although in the males a group of puffs were active for a longer time during development than in females. The X chromosome puffing patterns of D. simulans are similar to those described for D. melanogaster although two puffs (4F 1–4 and 7B 1–3) were active in D. simulans but not in D. melanogaster. The sex differences in puffing observed in D. melanogaster were also observed in D. simulans.     

Pollinators entering female dioecious figs: why commit suicide?

In the dioecious fig/pollinator mutualism, the female wasps that pollinate figs on female trees die without reproducing, whereas wasps that pollinate figs on male trees produce offspring. Selection should strongly favour wasps that avoid female figs and enter only male figs. Consequently, fig trees would not be pollinated and fig seed production would ultimately cease, leading to extinction of both wasp and fig. We experimentally presented pollinators in the wild (southern India) with a choice between male and female figs of a dioecious fig species, Ficus hispida L. Our results show that wasps do not systematically discriminate between sexes of F. hispida. We propose four hypotheses to explain why wasp choice has not evolved, and how a mutualism is thus maintained in which all wasps that pollinate female figs have zero fitness.     

The mode of genetic transmission of a gouty family with increased phosphoribosylpyrophosphate synthetase activity

Summary The mode of genetic transmission of gout and increased activity of phosphoribosylpyrophosphate synthetase (PRPPS) was studied in one family. Among 15 members of Family F, two male members had gout and had PRPPS activity of erythrocyte lysates three times higher than normal subjects. Five female members had activity 2.5 times higher than normal. The difference between the activities of male and female affected members was statistically significant (P<0.05). To examine the genetic trait of this abnormal PRPPS, the incorporation of ³H-adenine into erythrocytes or lymphocytes was studied using autoradiography. The number of grains which show the uptake of labeled adenine into cells revealed a normal distribution pattern in two normal persons and in two male patients, and a mixed pattern of the two cell populations in two female affected members. These results suggested mosaicism in female members and X-linked dominant transmission of this trait. Thermal inactivation of PRPPS of an affected female was intermediate between that from a normal subject and that from the affected males. This result showed the heterogeneity of the PRPPS from the hemolysate of an affected famale. The genotype of PRPPS on the X-chromosome was assumed and the lod score between PRPPS and Xg was also estimated. From these findings and electrophoretical study, it was suggested that the abnormal enzyme was a mutant enzyme transmitted in an X-linked dominant trait, and that the mutation occurred on the structural gene of the PRPPS.     

On the karyotype of the tahr Hemitragus jemlahicus and the Y-chromosome of goats and sheep

Somatic chromosomes of a female and male Himalayan thar, Hemitragus jemlahicus (H. Smith) are described. The diploid number is 48, there are 12 atelocentric and 34 telocentric autosomes in both sexes, the X-chromosome is meta- or submetacentric. The morphological appearance of the Y-chromosome is compared with that of other bovid species including recent observations on the goat Capra hircus.Supported by Contract No. PH 43-63-13 between the National Cancer Institute of the National Institutes of Health and the University of California.     

Territorial behavior of both sexes in the water striderMetrocoris histrio (Hemiptera: Gerridae) during the mating season

Territorial behavior of overwintered individuals of Metrocoris histriowas observed in an upstream area. Adults of both sexes held territories, but male territories were larger than those of females. Severe competition occurred among males for territories which give them access to receptive females. The effects of male body length and midleg length on establishment of territories were not significant. The effect of female midleg length on activity of females entering preferred foraging sites was equally not significant. Instead, territorial behavior increased with male age and males stayed longer at prime sites. Females of intermediate age were likely to occupy prime sites. Females had longer territory residence time than males. The sexes were dimorphic with respect to midleg length, and dimorphism in M. histriomay be related to a difference in life history, in that sexual selection may be relaxed due to asynchronous adult emergence patterns.     

A new mutation in exon 7 of NEMO gene: late skewed X-chromosome inactivation in an incontinentia pigmenti female patient with immunodeficiency

Incontinentia pigmenti is an X-linked genodermatosis, lethal in males. Affected females survive because of X-chromosome dizygosity and negative selection of cells carrying the mutant X-chromosome, and for this reason the skewed X inactivation pattern is often used to confirm the diagnosis. The most frequent mutation is a deletion of part of the NEMO gene (NEMOΔ4–10), although other mutations have been reported. Mutations of NEMO which do not abolish NF-κB activity totally permit male survival, causing an allelic variant of IP called hypohidrotic ectodermal dysplasia and immunodeficiency (HED-ID). We present a non-classical IP female patient who also suffered transient immunodeficiency because of a late and progressive selection against peripheral blood cells carrying an active mutated X-chromosome. This finding suggests that in the absence of known mutation the X-inactivation studies used in genetic counselling can induce mistakes with some female patients. At the age of 3 years and 6 months, all immunodeficiency signs disappeared, and the X-chromosome inactivation pattern was completely skewed. The low T cell proliferation and CD40L expression corroborate the important role of NEMO/ NF-κB pathway in T cell homeostasis. The decreased NEMO protein amount and the impaired IkBα degradation suggest that this new mutation, NM_003639: c.1049dupA, causes RNA or protein instability. To our knowledge, this is the first time that selection against the mutated X-chromosome in X-linked disease has been documented in vivo.     

Males vs. female meiotic prophase in a grasshopper,Arcyptera microptera (Orthoptera: Acridiae)

Female and male first meiotic prophase are analyzed in the grasshopper Arcyptera microptera with special reference to the heteropycnotic chromatin. Differences in the behaviour of the megameric and X-chromosomes, in nuclear size and in the response to C-banding treatment are described. The evidence for a distinctive meiotic prophase in both sexes is compared with results obtained in other species of grasshoppers by other authors using more advanced stages. The discussion centers around the role of the diffuse stage and the differential behaviour of the X-chromosome in the two sexes.     

Sex‐related spatial patterns of Poa ligularis in relation to shrub patch occurrence in northern Patagonia

Abstract. Poa ligularis is a dioecious species and a valuable forage plant which is widespread in the arid steppe of northern Patagonia (Argentina). The vegetation in these areas consists of a system of perennial plant patches alternating with bare soil areas defining contrasting micro‐environments. We hypothesized that (1) male and female individuals of P. ligularis are spatially segregated in different micro‐environments, (2) the intensity of spatial segregation of sexes depends on plant structure and (3) spatial segregation of sexes is enhanced by competitive interactions between the sexes within the vegetation patches. We analysed the spatial distribution of female and male individuals in relation to the spatial pattern of vegetation in two areas differing in their vegetation structure. The location of P. ligularis within patches where either male, female or both sexes occurred was also analysed. The results indicate that different patterns of spatial distribution of sexes of P. ligularis may be found at the community level depending on the dominant life forms and geometric structure of plant patches. Where patches are of a lower height, with a high internal patch cover, individuals of both sexes are concentrated within patch canopies. In sites characterized by large, tall patches and less internal patch cover suitable microsites for female and male P. ligularis occur both within and outside the patch with males located at further distances from the patch edge. Where the patch is large and tall enough to allow the establishment of males and females at relatively high numbers, males occupy the patch periphery or even colonize the interpatch bare soil. These spatial patterns are consistent with selective traits in which females better tolerate intraspecific competition than males, while males tolerate wider fluctuations in the physical environment (soil moisture, nitrogen availability, wind intensity, etc.).     

Patterns of puffing activity in the salivary gland chromosomes of Drosophila

Patterns of puffing activity during the third larval instar and the prepupal period of two different strains of D. melanogaster (Oregon and vg6) are compared. The variation in puffing activity observed is both quantitative (involving the mean size or timing of activity of individual puffs) and qualitative. The pattern of activity of 64% of the puffs is the same in the two strains, 12% show strain differences in puff size and 19% in the time of their activity. One puff (64C) is active only in one of the strains (vg6). In genetic experiments this puff segregates normally and the puff locus has been mapped genetically to a site coincident with, or at least very close to, the cytogenetic position of the puff. In heterozygotes the puff is homozygous only when the maternal and paternal homologues are synapsed. When the homologues are asynapsed only the homologue from the vg6 parent is puffed at 64C. With the exeption of some strains closely related to vg6 no other strain of D. melanogaster has been found to possess puffing activity at 64C. In vg6/In(3LR)C165 heterozygotes 64C forms a heterozygous puff even when the homologues are synapsed. In the discussion consideration is given to the various factors that control puff size.     

DNS-Reduplikationsmuster bei den Riesen-Geschlechtschromosomen von Microtus agrestis

Summary The X-chromosome of Microtus agrestis (2 n=50), comprising about 20 per cent of the homogametic haploid (AX) set, is the largest X-chromosome reported so far in placental mammals. It is four times the size of the X possessed by a great majority of mammals, including the human and the mouse. The Y-chromosome is also enormous, almost three-fifths the size of the X.The present cytological study concerned somatic interphase and prophase nuclei as well as the DNA replication pattern revealed by labeling cultured bone marrow cells with tritiated thymidine.In the male nuclus, the entire Y as well as the long arm and proximal part of the short arm of the X are late labeling and positively heteropycnotic. In the female, one entire X is late labeling and condensed, while the other X shows the same labeling pattern as the male X. Thus the pattern of inactivation of this huge X is such that in each diploid nucleus of both sexes, the amount of euchromatic X-chromosome material is the same as it is in the majority of placental mammals in which the X comprises about five per cent of the haploid set.

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Wesentliche Teile der vorliegenden Arbeit werden von Gertraud Flinspach als Dissertation der Medizinischen Fakultät der Universität Freiburg i.Br. vorgelegt.