Ellipsoid Body and Medulla Defects and Locomotion Disturbances in sbr (<Emphasis Type="Italic">small bristles</Emphasis>) Mutants of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

The sbr gene is an ortholog of evolutionarily conservative nxf1 (nuclear export factor) genes that control nuclear-cytoplasmic transport of mRNA in various eukaryotic organisms. Mutations of sbr exhibit a broad range of pleiotropic effects, which are characteristic of “housekeeping” genes. Certain allele-specific manifestations of the sbr gene in neurogenesis and behavior facilitate a deeper understanding of not only universal but also highly specialized functions of this gene. Among such characteristic features of adult males with an sbr¹² mutation are reduced locomotor activity as revealed in the negative geotaxis test and significant morphological disruptions of the ellipsoid body and the medulla, both of which are important for locomotion. The character of defects in the ellipsoid body and the medulla suggests that the SBR protein is essential for the normal formation and functioning of these nerve centers, and that the protein carries not only universal but also specialized functions.     

Chromosome nondisjunction in <Emphasis Type="Italic">Drosophila</Emphasis> strains mutant for tumor suppressor Merlin

The effect of mutation for gene Merlin on chromosome disjunction in Drosophila during meiosis was genetically studied. Chromosome nondisjunction was not registered in females heterozygous for this mutation and containing structurally normal X chromosomes. In cases when these females additionally contained inversion in one of chromosomes X, a tendency toward the appearance of nondisjunction events was observed in individuals containing mutation in the heterozygote. The genetic construct was obtained allowing the overexpression of protein corresponding to a sterile allele Mer ³ in the germ cell line. This construct relieves the lethal effect of Mer ⁴ mutation. The ectopic expression of this mutant protein leads to chromosome nondisjunction in male meiosis.     

Integrated gene mapping and synteny studies give insights into the evolution of a sex proto-chromosome in <Emphasis Type="Italic">Solea senegalensis</Emphasis>

The evolution of genes related to sex and reproduction in fish shows high plasticity and, to date, the sex determination system has only been identified in a few species. Solea senegalensis has 42 chromosomes and an XX/XY chromosome system for sex determination, while related species show the ZZ/ZW system. Next-generation sequencing (NGS), multi-color fluorescence in situ hybridization (mFISH) techniques, and bioinformatics analysis have been carried out, with the objective of revealing new information about sex determination and reproduction in S. senegalensis. To that end, several bacterial artificial chromosome (BAC) clones that contain candidate genes involved in such processes (dmrt1, dmrt2, dmrt3, dmrt4, sox3, sox6, sox8, sox9, lh, cyp19a1a, amh, vasa, aqp3, and nanos3) were analyzed and compared with the same region in other related species. Synteny studies showed that the co-localization of dmrt1-dmrt2-drmt3 in the largest metacentric chromosome of S. senegalensis is coincident with that found in the Z chromosome of Cynoglossus semilaevis, which would potentially make this a sex proto-chromosome. Phylogenetic studies show the close proximity of S. senegalensis to Oryzias latipes, a species with an XX/XY system and a sex master gene. Comparative mapping provides evidence of the preferential association of these candidate genes in particular chromosome pairs. By using the NGS and mFISH techniques, it has been possible to obtain an integrated genetic map, which shows that 15 out of 21 chromosome pairs of S. senegalensis have at least one BAC clone. This result is important for distinguishing those chromosome pairs of S. senegalensis that are similar in shape and size. The mFISH analysis shows the following co-localizations in the same chromosomes: dmrt1-dmrt2-dmrt3, dmrt4-sox9-thrb, aqp3-sox8, cyp19a1a-fshb, igsf9b-sox3, and lysg-sox6.     

Sex chromosomal dimorphisms narrated by X-chromosome translocation in a spiny frog (<Emphasis Type="Italic">Quasipaa boulengeri</Emphasis>)

Background

In the general model of sex chromosome evolution for diploid dioecious organisms, the Y (or W) chromosome is derived, while the homogametic sex presumably represents the ancestral condition. However, in the frog species Quasipaa boulengeri, heteromorphisms caused by a translocation between chromosomes 1 and 6 are not related to sex, because the same heteromorphic chromosomes are found both in males and females at the cytological level. To confirm whether those heteromorphisms are unrelated to sex, a sex-linked locus was mapped at the chromosomal level and sequenced to identify any haplotype difference between sexes.

Results

Chromosome 1 was assigned to the sex chromosome pair by mapping the sex-linked locus. X-chromosome translocation was demonstrated and confirmed by the karyotypes of the progeny. Translocation heteromorphisms were involved in normal and translocated X chromosomes in the rearranged populations. Based on phylogenetic inference using both male and female sex-linked haplotypes, recombination was suppressed not only between the Y and normal X chromosomes, respectively the Y and translocated X chromosomes, but also between the normal and translocated X chromosomes. Both males and females shared not only the same translocation heteromorphisms but also the X chromosomal dimorphisms in this frog.

Conclusions

The reverse of the typical situation, in which the X is derived and the Y has remained unchanged, is known to be very rare. In the present study, X-chromosome translocation has been known to cause sex chromosomal dimorphisms. The X chromosome has gone processes of genetic differentiation and/or structural changes by chance, which may facilitate sex chromosome differentiation. These sex chromosomal dimorphisms presenting in both sexes may represent the early stages of sex chromosome differentiation and aid in understanding sex chromosome evolution.

     

Chromosomal polymorphism in <Emphasis Type="Italic">Steindachneridion</Emphasis><Emphasis Type="Italic">melanodermatum</Emphasis> Garavello, 2005 (Siluriformes,Pimelodidae): a reappraisal the existence of sex chromosome system in the species

Fifty-five specimens of Steindachneridion melanodermatum were analyzed using molecular and conventional cytogenetic tools. Two polymorphisms were found: one involving the length of nucleolar organizer regions and another involving two submetacentric chromosomes previously identified as sex chromosomes. The polymorphism was confirmed by homogeneity between male and female karyotypes. Nucleotide sequencing and physical chromosome mapping were also used to identify and characterize one class of repetitive DNA, named SmAluI-Rex3. Based on the results and literature the present study offers an update of the occurrence of sex chromosome system in this species.     

Discovery of the youngest sex chromosomes reveals first case of convergent co-option of ancestral autosomes in turtles

Most turtle species possess temperature-dependent sex determination (TSD), but genotypic sex determination (GSD) has evolved multiple times independently from the TSD ancestral condition. GSD in animals typically involves sex chromosomes, yet the sex chromosome system of only 9 out of 18 known GSD turtles has been characterized. Here, we combine comparative genome hybridization (CGH) and BAC clone fluorescent in situ hybridization (BAC FISH) to identify a macro-chromosome XX/XY system in the GSD wood turtle Glyptemys insculpta (GIN), the youngest known sex chromosomes in chelonians (8–20 My old). Comparative analyses show that GIN-X/Y is homologous to chromosome 4 of Chrysemys picta (CPI) painted turtles, chromosome 5 of Gallus gallus chicken, and thus to the X/Y sex chromosomes of Siebenrockiella crassicollis black marsh turtles. We tentatively assign the gene content of the mapped BACs from CPI chromosome 4 (CPI-4) to GIN-X/Y. Chromosomal rearrangements were detected in G. insculpta sex chromosome pair that co-localize with the male-specific region of GIN-Y and encompass a gene involved in sexual development (Wt1—a putative master gene in TSD turtles). Such inversions may have mediated the divergence of G. insculpta sex chromosome pair and facilitated GSD evolution in this turtle. Our results illuminate the structure, origin, and evolution of sex chromosomes in G. insculpta and reveal the first case of convergent co-option of an autosomal pair as sex chromosomes within chelonians.     

Chromosome painting and comparative physical mapping of the sex chromosomes in <Emphasis Type="Italic">Populus tomentosa</Emphasis> and <Emphasis Type="Italic">Populus deltoides</Emphasis>

Dioecious species accounted for 6% of all plant species, including a number of crops and economically important species, such as poplar. However, sex determination and sex chromosome evolution have been studied only in few dioecious species. In poplar, the sex-determining locus was mapped to chromosome 19. Interestingly, this locus was mapped to either a peritelomeric or a centromeric region among different poplar species. We developed an oligonucleotide (oligo)-based chromosome painting probe based on the sequence of chromosome 19 from Populus trichocarpa. We performed chromosome painting in P. tomentosa and P. deltoides. Surprisingly, the distal end on the short arm of chromosome 19, which corresponds to the location of the sex-determining locus reported in several species, was not painted in both species. Thus, the DNA sequences associated with this region have not been anchored to the current chromosome 19 pseudomolecule, which was confirmed by painting of somatic metaphase chromosome 19 of P. trichocarpa. Interestingly, the unpainted distal ends of the two chromosome 19 did not pair at the pachytene stage in 22–24% of the meiotic cells in the two species, suggest that these regions from the sex chromosomes have structurally diverged from each other, resulting in the reduced pairing frequency. These results shed light on divergence of a pair of young sex chromosomes in poplar.     

Deleterious mutations in various <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> strains carrying meiotic mutation <Emphasis Type="Italic">c(3)G</Emphasis>

In the absence of meiotic recombination, deleterious mutations, decreasing the viability, are accumulated and fixed in small Drosophila populations. Study of the viability of hybrid progenies of three laboratory Drosophila melanogaster strains carrying meiotic mutation c(3)G ¹⁷ has suggested that the deleterious mutations are negatively synergistic in their interaction. The deleterious mutations localized to the pericentromeric region of chromosome 3 are threefold more efficient as compared with the mutations located in distal regions. Substitution of a new chromosome for the balancer chromosome in a strain with meiotic mutation c(3)G ¹⁷ partially restores (by ～20%) the viability of homozygotes c(3)G ¹⁷ /c(3)G ¹⁷ over the first 20–30 generations. Further cultivation for 30 generations with the same balancer again decreases the viability to the initial level. An epigenetic nature of deleterious mutations is discussed.     

Peculiarities of Mutation Process in X Chromosome of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> Z<Superscript>3314</Superscript> Line from Zvenigorodka (Ukraine) Natural Population

The Drosophila melanogaster Z³³¹⁴ line isolated from a Zvenigorodka (Ukraine) natural population is characterized by the manifestation and emergence of a wide spectrum of molecular aberrations. Among them, two types (the wing venation anomaly and violation of the leg segmentation) were the most represented. It was demonstrated that the frequency of manifestation (penetrance) and the expressiveness of these phenotypic aberrations increase with an increase in the temperature. When the Z³³¹⁴ line is bred in the laboratory, autosomal visible rase (ra: 3–97.3) mutation, which leads to reduction of a part of dorso-central and scutellaria macrochaetae, was detected (isolated and identified). A number of genetic peculiarities that determined the consistency and prospects of the study were found during the mutation process study in the Z³³¹⁴ line. The Z³³¹⁴ line is characterized by a high frequency of the emergence of visible mutations in the X-Z³³¹⁴ chromosome, which persisted for a long time of the breeding under laboratory conditions (from 2003 to 2011). Locus-specific high genetic instability in the singed locus in the X-Z³³¹⁴ chromosome persisted from the moment of emergence of the first mutant alleles in 2006 until the end of the study. The emergence of mutations was observed both during the line breeding “inside” (in the case of brother–sister crossings) and after the crossings of the X-Z³³¹⁴ chromosome carrier males with females of the С(1)DX,ywf/Y laboratory line with linked X chromosomes.     

Coinheritance of Chromosomes 3 and 11 in the Patients with Autosomal Recessive Polycythemia from Chuvachia

Inheritance of chromosomes 3 and 11 in the families with Chuvash autosomal recessive polycythemia and in control group with no disease symptoms was examined using polymorphic dinucleotide markers D3S1597 and D3S1263, mapped to region 3p25, and D11S4111, D11S4127, and D11S1356, mapped to region 11q23. All patients were homozygous for the C598T mutation in the VHL gene (3p25). The analysis showed that in 75% of the cases, chromosome 3 carrying C598T mutation was coinherited with certain chromosome 11, which differed from 50%, expected upon independent inheritance of each chromosome. In case of chromosome 3 without C598T mutation, this pattern was observed neither in healthy sibs form the families with autosomal recessive polycythemia (44%), nor in the control group (43%). These results suggest that in case of the C598T mutation in the VHL gene, chromosomal loci 3p25 and 11q23 are inherited not independently, compared to the inheritance of these loci in the absence of the mutation in healthy sibs from the affected families χ² = 16.14, p < 0.001), and also in the control family sample (χ² = 17.91, p < 0.001).     

Molecular cytogenetic characterization of <Emphasis Type="Italic">Triticum timopheevii</Emphasis> chromosomes provides new insight on genome evolution of <Emphasis Type="Italic">T. zhukovskyi</Emphasis>

Triticum timopheevii (2n = 4x = 28, GGA^tA^t) is a tetraploid wheat formerly cultivated in western Georgia. The natural allopolyploid Triticum zhukovskyi is a hexaploid taxon originated from hybridization of T. timopheevii with cultivated einkorn T. monococcum (2n = 2x = 14, A^mA^m). Karyotypically T. timopheevii and T. zhukovskyi differ from other tetraploid and hexaploid wheats and were assigned to the section Timopheevii of the genus Triticum L. Triticum timopheevii and T. zhukovskyi are resistant to many fungal diseases and therefore could potentially be utilized for wheat improvement. We were aiming to precisely identify all T. timopheevii chromosomes and to trace the evolution of T. zhukovskyi. For this, we developed a set of molecular cytogenetic landmarks based on eleven DNA probes. Each chromosome can now be characterized by two to eight probes. The pTa-535 sequence allows the identification of all A^t-genome chromosomes, whereas G-genome and some A^t-genome chromosomes can be identified using (GAA/CTT) _n and pSc119.2 probes. The probes pAesp_SAT86, pAs1, Spelt-1, Spelt-52 and 5S and 45S rDNA can be applied as additional markers to discriminate particular chromosomes or chromosomal regions. The distribution of (GAA/CTT) _n , pTa-535 and pSc119.2 DNA probes on T. timopheevii chromosomes is distinct from other tetraploid wheats and can therefore be used to track individual chromosomes in introgression programs. Our study confirms the origin of T. zhukovskyi from hybridization of T. timopheevii with T. monococcum; however, we show that the emergence was accompanied by changes involving mostly A^t-genome chromosomes. This may be due to the presence of two closely related A-genomes in the T. zhukovskyi karyotype.     

End-to-End Association of <Emphasis Type="Italic">X</Emphasis> and <Emphasis Type="Italic">Y</Emphasis> Chromosomes in Mouse Meiosis

ACCORDING to the hypothesis of Crew and Koller¹ and Koller and Darlington², there are homologous segments in the X and Y chromosomes of the mouse and other mammals. The homologous regions in the mouse were believed to be localized in the extremely short arms proximal to the kinetochores. The end-to-end association at meiosis was thought to be the result of the formation of a chiasma between these homologous regions³. Electron microscopy revealed a short synaptonemal complex in mouse meiotic cells⁴. However, partial sex linkage has never been demonstrated in the mouse⁵ and other authors^6–10 believe that the X and Y chromosomes associate only by connexion between the chromosome ends furthest from the centromeres.     

Quinacrine Fluorescence Patterns and Terminal DNA Labelling of Human <Emphasis Type="Italic">C</Emphasis> Group Chromosomes

THE human C group chromosomes have been difficult to study because they have rather similar morphology. Application of the quinacrine fluorescent staining technique developed by Caspersson et al.¹ now allows the identification of individual chromosomes and of the chromosome segments involved in translocations because the fluorescent patterns are not altered by the translocation^2–4. We have reported the value of this technique in analysing abnormalities of the D⁴ and G³ groups. We report here a variety of structural changes of C group chromosomes which have been characterized in this way, as well as the terminal DNA replication pattern of the C group chromosomes.     

Check of Gene Number during the Process of rDNA Magnification

THE multiple sequences of rDNA (DNA complementary to ribosomal RNA) of the Drosophila genome are localized at the bobbed locus, located in the X chromosome, position 66 and in the short arm of the Y chromosome^1,2. Wild bobbed (bb⁺) is that locus which, without a partner, gives rise to a normal phenotype. That locus which in similar conditions is incapable of giving rise to a normal phenotype is called a bobbed mutation (bb) and contains fewer genes for rRNA. The number of genes for rRNA in different individuals can vary considerably. One mechanism for rDNA variation is unequal crossing over³. Another mechanism, described by Tartof⁴, becomes apparent when individual flies, carrying only one bobbed locus, are constructed and only if such a locus is on the X chromosome; that is, if one constructs Xbb⁺/O males (and also Xbb/O males) or Xbb⁺/X_NO- females. Such individuals show a higher rDNA content than expected from the analysis of the same locus in Xbb⁺/Xbb⁺ females or in Xbb⁺/Ybb⁺ males. The increase of rDNA in this case is not inheritable⁴.     

The C-terminus of DSX<Superscript>F5</Superscript> protein acts as a novel regulatory domain in <Emphasis Type="Italic">Bombyx mori</Emphasis>

The doublesex gene regulates the somatic sexual development of Bombyx mori by alternatively splicing into sex-specific splice forms. In our previous study, the splice form Bmdsx ^F7 , which encodes the BmDSX^F5 protein, was found to be expressed in a female-specific manner and to contain a novel C-terminus. In this study, we aimed to investigate the role of this C-terminus. Two transgenic lines, L1 and L2, were constructed to ectopically express Bmdsx ^F7 in males. Phenotype and W chromosome-specific polymerase chain reaction (PCR) analysis showed that developmental abnormalities and sex reversal did not occur. Moreover, the sex ratio was also normal. Quantitative PCR revealed that the expression levels of SP1 and Vg were upregulated in the fat body of transgenic males. Additionally, the expression level of PBP was downregulated in the antenna of transgenic males. The results suggested that the C-terminus of BmDSX^F5 functioned as a regulatory domain during regulation of downstream target gene expression and that BmDSX^F5 participated in the sexual development of somatic cells together with other DSX proteins in B. mori.     

Genetic Collection of Meiotic Mutants of Rye <Emphasis Type="Italic">Secale cereale</Emphasis> L.

Genetic collection of meiotic mutants of winter rye Secale cereale L. (2n = 14) was created. Mutations were detected in inbred F₂ generations after self-fertilization of the F₁ hybrids, obtained by individual crossing of rye plants (cultivar Vyatka) or weedy rye with plants from autofertile lines. The mutations cause partial or complete plant sterility and are maintained in collection in a heterozygous state. Genetic analysis accompanied by cytogenetic study of meiosis has revealed six mutation types. (1) Nonallelic asynaptic mutations sy1 and sy9 caused the formation of only axial chromosome elements in prophase and anaphase. The synaptonemal complexes (SCs) were absent, the formation of the chromosome “bouquet” was impaired, and all chromosomes were univalent in meiotic metaphase I in 96.8% (sy1) and 67% (sy2) of cells. (2) Weak asynaptic mutation sy3, which hindered complete termination of synapsis in prophase I. Subterminal asynaptic segments were always observed in the SC, and at least one pair of univalents was present in metaphase I, but the number of cells with 14 univalents did not exceed 2%. (3) Mutations sy2, sy6, sy7, sy8, sy10, and sy19, which caused partially nonhomologous synapsis: change in pairing partners and fold-back chromosome synapsis in prophase I. In metaphase I, the number of univalents varied and multivalents were observed. (4) Mutation mei6, which causes the formation of ultrastructural protrusions on the lateral SC elements, gaps and branching of these elements. (5) Allelic mutations mei8 and mei8-10, which caused irregular chromatin condensation along chromosomes in prophase I, sticking and fragmentation of chromosomes in metaphase I. (6) Allelic mutations mei5 and mei10, which caused chromosome hypercondensation, defects of the division spindle formation, and random arrest of cells at different meiotic stages. However, these mutations did not affect the formation of microspore envelopes even around the cells, whose development was blocked at prophase I. Analysis of cytological pictures of meiosis in double rye mutants reveled epistatic interaction in the mutation series sy9 > sy1 > sy3 > sy19, which reflects the order of switching these genes in the course of meiosis. The expression of genes sy2 and sy19 was shown to be controlled by modifier genes. Most meiotic mutations found in rye have analogs in other plant species.     

New insights into sex chromosome evolution in anole lizards (Reptilia,Dactyloidae)

Anoles are a clade of iguanian lizards that underwent an extensive radiation between 125 and 65 million years ago. Their karyotypes show wide variation in diploid number spanning from 26 (Anolis evermanni) to 44 (A. insolitus). This chromosomal variation involves their sex chromosomes, ranging from simple systems (XX/XY), with heterochromosomes represented by either micro- or macrochromosomes, to multiple systems (X₁X₁X₂X₂/X₁X₂Y). Here, for the first time, the homology relationships of sex chromosomes have been investigated in nine anole lizards at the whole chromosome level. Cross-species chromosome painting using sex chromosome paints from A. carolinensis, Ctenonotus pogus and Norops sagrei and gene mapping of X-linked genes demonstrated that the anole ancestral sex chromosome system constituted by microchromosomes is retained in all the species with the ancestral karyotype (2n?=?36, 12 macro- and 24 microchromosomes). On the contrary, species with a derived karyotype, namely those belonging to genera Ctenonotus and Norops, show a series of rearrangements (fusions/fissions) involving autosomes/microchromosomes that led to the formation of their current sex chromosome systems. These results demonstrate that different autosomes were involved in translocations with sex chromosomes in closely related lineages of anole lizards and that several sequential microautosome/sex chromosome fusions lead to a remarkable increase in size of Norops sagrei sex chromosomes.