Polytene chromosome sof monogenic and amphogenic Chrysomya species (Calliphoridae,diptera): analysis of banding patterns and in situ hybridization with Drosophila sex determining gene sequences

Standard maps for the five banded polytene chromosomes found in trichogen cell nuclei of the monogenic blowfly Chrysomya rufifacies and the amphogenic Chrysomya pinguis are presented. The chromosomes are highly homologous in the two species; differences in banding patterns are predominantly caused by one pericentric and ten paracentric inversions. In chromosome 5 of the amphogenic Chrysomya phaonis, also analysed in this paper, an additional paracentric inversion was observed. The distribution of species specific inversions indicates that the monogenic C. rufifacies is phylogenetically older than the amphogenic species. The maternal sex realizer locus F'/f on polytene chromosome 5 of C. rufifacies is not associated with a structural heterozygosity. Chromosome pair 6 of C. rufifacies and the sex chromosome pair of C. pinguis are under-replicated in polytene nuclei; they consist of irregular chromatin granules, frequently associated with nucleolus material. Evolution of heteromorphic sex chromosomes in Chrysomya is probably correlated with heterochromatin accumulation. A search for sex determining genes in Chrysomya was initiated using sex determining sequences from Drosophila melanogaster for in situ hybridization. The polytene band 41A1 on chromosome 5 of monogenic and amphogenic Chrysomya species contains sequences homologous to the maternal sex determining gene daughterless (da). Homology to the zygotic gene Sex-lethal (Sxl) of Drosophila is detected in band 39A1 on chromosome 5 of C. rufifacies. The findings reported here are the first evidence for a possible homology between the da gene of Drosophila and the maternal sex realizer F of C. rufifacies. An hypothesis for the evolution of the maternal effect sex determination of C. rufifacies is proposed.Dedicated to Professor Dr. Fritz-Helmut Ullerich on the occasion of his 60th birthday     

The Nucleolar Chromosome in Hepatics.: II. A Phylogenetic Speculation

Abstract

1. The gametophytic chromosome set of Riccardia pinguis (L.) Gray shows signs of diploid origin.

2. The basic chromosome number of the Anthocerotae makes it possible that the ancestor of the Hepaticae belonged broadly, to this class.

3. The simplest way in which the chromosome complement of the Anthocerotae may be related to that of the Hepaticae is by diploidy; a complement produced in this way would have the same features as that of R. pinguis.

4. On the basis of morphological evidence it has previously been suggested that the Anthocerotae may be ancestral to the Hepaticae, and that the connexion may be through a plant resembling Riccardia (Campbell, 1940).     

The karyotype of Lacerta horváthi (Reptilia,Sauria, Lacertidae)

The chromosomes of Lacerta horváthi have been studied by means of conventional, C-banding, and silver-NOR techniques. The karyotype of this species, characterized by 36 acrocentric macrochromosomes, lacks the typical pair of microchromosomes shared by all other lacertid lizards. It is hypothesized that the microchromosomes could have been translocated to the large elements of the karyotype. The occurrence of such a rearrangement in the chromosome complement of L. horváthi underlines its isolation from the other species of the subgenus Archaeolacerta. The C-banding analysis evidences the existence of a female sex heteromorphism in which the W-chromosome has the same shape and size of the Z, but differs from it in being completely heterochromatic. The nucleolar organizer regions (NORs) are located on a pair of medium size chromosomes in subtelomeric position, where the standard Giemsa-staining reveals secondary constrictions.     

Disposition of ribosomal DNAs in the chromosomes of perennial oats (Poaceae: Aveneae)

The chromosomal loci of 5S and 45S ribosomal DNAs (rDNAs) and the activity of nucleolar‐organizing regions (NORs) were analysed in perennial oats of the genera Ammophila, Amphibromus, Arrhenatherum, Avena, Deschampsia, and Helictotrichon s.l. (Poaceae: Aveneae) using fluorescence in situ hybridization, staining with chromomycin/4′,6‐diamidino‐2‐phenylindole (DAPI), and silver impregnation. All chromosomes with a secondary constriction were nucleolar active. In chromosomes without a secondary constriction, NORs corresponded exclusively to broad bands of 45S rDNA with chromomycin‐positive, DAPI‐negative, and silver‐positive stainability. Additional minor bands of 45S rDNA showed no nucleolar activity. 5S rDNA was localized mostly in loci different from the nucleolar‐active 45S rDNA. If both rDNAs occurred within the same chromosome, they were at largely corresponding distances from the centromere, irrespective of their particular localization in either the same chromosome arm or in opposite arms. In the latter case, 5S rDNA was never more distal to the centromere than 45S rDNA. A new model was devised to explain this non‐random distribution of both rDNAs in nucleolar‐organizing chromosomes, which identified the Rabl orientation of chromosomes as ensuring a spatial proximity of 5S to 45S rDNA in interphase nuclei, even if they were localized in opposite arms. The possible role of the Rabl orientation in determining the spread and accumulation of 5S rDNA sequences in further chromosomes of the genome was discussed. B chromosomes were devoid of 5S rDNA, but most contained 45S rDNA and were nucleolar active. In some large groups of species, the number and arrangement of 5S and 45S rDNA sites in the chromosomes were remarkably uniform, especially in Helictotrichon subgenus Helictotrichon and Helictotrichon subgenus Pratavenastrum. Such distribution patterns have survived many speciation processes and have also remained widely unchanged in polyploids. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 193–210.     

Chromosomes of African Hepatics—Jubulae

Abstract

The chromosome numbers of five species belonging to the Jubulae have been described, and are as follows:

Lejeuneaceae

Cololejeunea cf. dissita, n = 9.

Arehilejeunea autoiea Vanden Berghen, n=9.

Caudalejeunea hanningtonii (Mitt.) Schiffn., n =9.

Mastigolejeunea florea (Mitt.) Steph., n=9.

Frullaniaceae

Frullania spongiosa Steph., female, n = 9.

F. spongiosa Steph., male, n=8.

The author wishes to thank Dr E. W. Jones for assistance in identifications, especially with Cololejeunea cf. dissita.     

The fine structure of nuclei as revealed by electron microscopy

Summary The process of nucleolus formation has been studied by electron microscopy in spermatogonia of new-born, 15-day-old mice. One of two heteropycnotic sex chromosomes is concerned with nucleolus formation in the type A spermatogonia. The evidence for such formation has been presented with regard to behaviour and fine structure of both sex chromosome and nucleolus, Nucleolar material appears at one of two heteropycnotic sex chromosomes which are closely attached to the nuclear envelope. The two sex chromosomes approach each other, and subsequently one of them migrates into the central part of the nucleoplasm, being related to the nucleolar material which develops to show a nucleolar configuration. The sex chromosomes are homogeneously electron dense during the nucleolus formation, but assume a vesicular form at the middle stage of its development. The nucleolus is mostly of fibrillar and amorphous components at early stages of its development, but the granular components increases in amount as development proceeds. The final, mature nucleolus is composed of irregularly twisted nucleolonemata consisting of granular components, separated from fibrillar and amorphous areas. The compactly dense sex chromosome remains closely connected with the mature nucleolus.     

Evolution of ZZ/ZW and XX/XY sex-determination systems in the closely related medaka species, <Emphasis Type="Italic">Oryzias hubbsi</Emphasis> and <Emphasis Type="Italic">O. dancena</Emphasis>

A DM-domain gene on the Y chromosome was identified as the sex-determining gene in the medaka, Oryzias latipes, and named DMY (also known as dmrt1bY). However, this gene is absent in most Oryzias fishes, suggesting that closely related species have another sex-determining gene. In fact, it has been demonstrated that the Y chromosome in O. dancena is not homologous to that in O. latipes, whereas both species have an XX/XY sex-determination system. Through a progeny test of sex-reversed fish and a linkage analysis of isolated sex-linked DNA markers, we show that O. hubbsi, which is one of the most closely related species to O. dancena, has a ZZ/ZW system. In addition, genetic and fluorescence in situ hybridization mapping of the sex-linked markers revealed that sex chromosomes in O. hubbsi and O. dancena are not homologous, indicating different origins of these ZW and XY sex chromosomes. Furthermore, we found that O. hubbsi has morphologically heteromorphic sex chromosomes, in which the W chromosome has 4,6-diamidino-2-phenylindole (DAPI)-positive heterochromatin blocks and is larger than the Z chromosome, although such differentiated sex chromosomes have not been observed in other Oryzias species. These findings suggest that a variety of sex-determining mechanisms and sex chromosomes have evolved in Oryzias.     

Meiosis and pollen mitosis in diploid and triploid Colocasia antiquorum Schott.

The relationship between diploid and triploid forms of Colocasia antiquorum Schott. was assessed through comparative meiotic and pollen mitotic studies. Owing to poor spreading of the chromosomes of both materials, karyological observations on pachytene nuclei were limited to a few chromosomes. Among the two nucleolar chromosomes and a metacentric, telochromomere-bearing chromosome of the diploid, the latter and one of the nucleolar chromosomes characterized by a heteropycnotic short arm were identified in both bivalent and trivalent associations in the triploid. The homologues in these cases were homomorphic and intimately paired. Two types of heteromorphic bivalents exhibiting partial pairing of homomorphic segments were also recorded in the triploid. Among the 14 bivalents of the diploid at diakinesis, two were nucleolus-associated. In the triploid, chromosomal associations at diakinesis included trivalents (2 to 9), bivalents and univalents, and the chiasma frequency per paired chromosome was lower than in the diploids. In 21.6 percent of the PMCs at this stage intragenomic pairing of one or two chromosomes was observed. Post-diakinesis stages in the diploid were regular while in the triploid they were marked by various irregularities in a majority of the cells. However, fertility (stainability), size and divisional frequency of pollen in both materials were remarkably similar. Chromosome numbers in pollen nuclei in the triploid ranged from 8 to 25. Based on these data an autopolyploid origin for the triploid Colocasia and a lower base number than the gametic chromosome number for this genus are advanced.     

A contribution to the knowledge of epiphyllous bryophytes of Bioko Island (Equatorial Guinea), including additional remarks on non-epiphyllous species

Abstract

A collection of epiphyllous bryophytes from Bioko Island was investigated. It contained 57 epiphyllous bryophytes, comprising 55 hepatics and two mosses. Three taxa, Cololejeunea eustacei Pócs, Colura calderae Pócs and Lejeunea halei Robinson subsp. africana Pócs, are new to science. Cololejeunea papilliloba Steph. is new to Africa, five species of hepatics are new to West Africa, and an additional 31 species of hepatics are newly reported from Bioko Island. The second part of the paper deals with records of non-epiphyllous collections. Fourteen species are reported for the first time for Bioko Island. Actinodontium dusenii Broth. is made a synonym of Actinodontium streptopogoneum Broth. The following new combination is proposed: Wijkia rigidicaule (Müll.Hal. ex Broth.) Frank Müll., comb. nov. (Basionym: Acanthocladium rigidicaule Müll.Hal. ex Broth.).     

Selective staining of X chromosome segments in Schistocerca gregaria after denaturation and reassociation procedures

The DNA of fixed mitotic and meiotic chromosomes and of spermatides of Schistocerca gregaria males was heat denaturated and then differentially reassociated in a Giemsa buffer or in acridine orange buffer solution. After this procedure, two to three large, selectively stained regions are seen in the X chromosome of spermatocytes and spermatides. Denaturation and reassociation experiments have shown that after differential reassociation such a selective stainability of chromosome regions is characteristic for the presence of fast-reassociating, i.e., repetitive DNA (Stockert and Lisanti, 1972). The possible presence of repetitive DNA in the X chromosome regions concerned can not be the only reason for the occurrence of the heavily stained segments after reassociation because (1) these segments are obtained in positively heteropycnotic X chromosomes, but not in negatively heteropycnotic Xs and (2) they do not occur in positively heteropycnotic X chromosomes when the histones have been extracted before the denaturation and reassociation processes. Contrary to the latter statement, the heavily stained X chromosomal regions are preserved when the histones are removed after the denaturation and reassociation steps. — It is assumed that the heavily stained X chromosome segments represent DNA reassociation complexes which are only formed if histones are present. It is discussed whether the formation of the X chromosome complexes depends on a specific chromatin configuration within positively heteropycnotic X chromosomes.     

Larval polytene chromosomes of black flies (Simulium) from Thailand. I. Comparison among five species in the subgenus Gomphostilbia enderlein

Larval polytene chromosome maps of Simulium (G.) asakoae and S. (G.) sp. g in the ceylonicum-group and S. (G.) angulistylum, S. (G.) decuplum and S. (G.) siamense in the batoense-group of the subgenus Gomphostilbia from Thailand are presented. These species have three pairs of chromosomes (2n = 6). Light stained centromeric bands were observed in the chromosomes of S. (G.) asakoae, S. (G.) sp. g, S. (G.) decuplum and S. (G.) siamense, whereas heavy dark centromeric bands were present in S. (G.) angulistylum. The best distinguishing character of Simulium species in the subgenus Gomphostilbia is the position of the nucleolar organizer in the short arm of chromosome I. The Ring of Balbiani and the double bubble are located in chromosome arm IIS in all species except for S. (G.) angulistylum, which showed these cytological markers in chromosome arm IIIS. A low chromosomal polymorphism was recorded in all species except for S. (G.) sp. g, which exhibited a standard polytene chromosome. Inversion polymorphisms found in this study conformed to Hardy–Weinberg equilibrium and were not associated with sex. These species have different specific markers and banding patterns although homologous banding sequences were found in chromosome arm IIS in S. (G.) asakoae, S. (G.) sp. g, S. (G.) decuplum and S. (G.) siamense and chromosome arm IIIS in S. (G.) angulistylum. Our results showed no evidence of a sibling species complex within any taxon.     

End-to-end chromosome attachments in mitotic interphase and their possible significance to meiotic chromosome pairing

Cytological studies on telophase and early prophase in roottip cells of several plant species (Allium cepa, 2n=16; four Crepis species, including Crepis capillaris, 2n=6; Callitriche hermaphroditica, 2n=6; Nigella arvensis, 2n=12; Secale cereale, 2n=14) revealed that chromosome ends are attached two by two forming chains of chromosomes (interphase associations). In these chains homologous chromosomes are presumably located adjacent to each other. In Crepis capillaris it was observed that the two nucleolar chromosomes form a separate ring one end attached to the ring of the four remaining chromosomes and the other end attached to the nucleolus. It is proposed that these end-to-end attachments have significance for chromosome pairing in meiosis. The adjacent location of homologous chromosomes in the interphase associations would facilitate rapid and regular synapsis.     

Karyotype variation in Drosophila birchii

Drosophila birchii, a member of the melanogaster species group of the subgenus Sophophora, is common in the tropical rain forests of the Australia-New Guinea areas. Chromosome squashes are easily prepared from the larval ganglion cells and the sex chromosomes are readily recognizable. The species exhibits a remarkable karyotype variation. The metaphase plate figures, in general, show two pairs of V's, one pair of dots and one pair of sex chromosomes. Variations in metaphase chromosome morphology are found in the X (with four types), the Y (with three types) and chromosome IV (with two types). Chromosomal interchanges between X- and Y-chromosomes Type I are postulated to be involved in the differentiation of sex chromosome morphology while the modification of chromosome IV seems likely to be a result of the acquisition of extra heterochromatin. These chromosome types form seven distinct metaphase plate figures, all encountered in wild populations, thus giving D. birchii the most variable karyotype in the genus Drosophila.     

X-Y chromosome synapsis and recombination in 3 vole species of Asian lineage of the genus Microtus (Rodentia: Arvicolinae)

The pattern of X-Y chromosome pairing in male meiosis is an important taxonomic feature of grey voles of the genus Microtus. Asynaptic sex chromosomes have been found in the majority of species of the Palearctic phylogenetic lineage of this genus, while normal X-Y synapsis has been observed in the species of subgenus Pallasiinus belonging to the Asian phylogenetic lineage. We analyzed sex chromosome pairing and recombination in M. maximowiczii, M. mujanensis and M. fortis which also belong to the Asian phylogenetic lineage (subgenus Alexandromys). Using immunostaining for the proteins of the synaptonemal complex (SCP3) and recombination nodules (MLH1) we demonstrated that X and Y chromosomes of these species paired and recombined in a short subtelomeric region. This indicates that the sex chromosomes of these species retain an ancestral fully functional pseudoautosomal region, which has been lost or rearranged in the asynaptic species of the genus Microtus.     

Minute Y chromosomes and karyotype evolution in Madagascan iguanas (Squamata: Iguania: Opluridae)

Iguanas (Pleurodonta) are predominantly distributed in the New World, but one previously cytogenetically understudied family, Opluridae, is endemic to Madagascar and the adjacent Grand Comoro archipelago. The aim of our contribution is to fill a gap in the cytogenetic understanding of this biogeographically puzzling lineage. Based on examination of six species, we found that oplurids are rather conservative in karyotype, which is composed of 36 chromosomes as in most iguanas. However, the species differ in the position of the nucleolar organizer region and heterochromatic blocks and in the accumulation and distribution of interstitial telomeric sequences (ITSs), which suggests cryptic intra‐ and interchromosomal rearrangements. All tested species share the XY sex‐determining system homologous to most other iguana families. The oplurid Y chromosome is degenerated, very small in size but mostly euchromatic. Fluorescence in situ hybridization with probes composed of microsatellite motifs revealed variability among species in the accumulation of particular repeats on the Y chromosome. This variability accounts for the differences in the detection of sex chromosomes across the species of the family using comparative genome hybridization (CGH) technique. Our study demonstrates the limits of the commonly used CGH technique to uncover sex chromosomes even in organisms with heteromorphic and sequentially largely differentiated sex chromosomes.     

African Hepatics. XXX: The genus Radula Dumortier

Abstract

Fifteen species of Radula from Africa and the Mascarenes are described, of which R. pseudoflaccida is new. The following species are newly reduced to synonyms: R. angustata Steph., R. capensis Steph., R. guineensis Steph., R. macroloba Steph., R. molleri Steph., R. pirottae Gola and R. spongiosa Steph. R. caespitosa Steph. is transferred from R. tabularis Steph. to R. madagascariensis Gottsche.

Habit, stem-structure, leaf-cuticle, perianth and spores provide valuable taxonomic characters which have received little or no attention and which show some degree of correlation. The range of forms shown by the lobule in a single species represent stages in its development.     

The absence of the somatic association of centromeres of homologous chromosomes in grass mitotic metaphases

Root-tip metaphases from Hordeum vulgare (19 cells), H. marinum (11 cells), Aegilops umbellulata (10 cells) and Zea mays (10 cells) were completely reconstructed from electron micrographs of serially sectioned nuclei. The identity of each chromosome was found by measuring the volumes of its two arms and the presence or absence of a secondary constriction at the nucleolar organising region. With the position of the centromere in three dimensions, these data were used to analyse the relative positions of homologous and heterologous centromeres. In 31 out of the 50 cells analysed, homologues were on average further apart than heterologues. Except for two nucleolar organising chromosomes, there was no evidence of any tendency for the distances between different homologue types to be differently distributed from distances between heterologues. Average distances between homologues of the single nucleolar organising chromosome (linkage group 6) of Zea (2n = 20) were lower than the average for heterologues and the interhomologue distances were distributed significantly differently from the separation distances of chromosome 6 to other chromosomes. Presumably this association occurred because of nucleolar fusion in the previous interphase. Homologues of one of the two nucleolar organising chromosomes of A. umbellulata were also distributed significantly differently from heterologues, with a tendency for homologues to lie farther apart than the average heterologous pair. These results do not support previous work using squashed and spread metaphase preparations (some including abnormal, marked chromosomes) for these species.     

The behavior and morphology of the X and Y chromosomes during prophase I in the Sitka deer mouse (Peromyscus sitkensis)

Surface-spread, silver-stained primary spermatocytes from individuals of the Sitka deer mouse (Peromyscus sitkensis) were analyzed by electron microscopy. Pairing of the X and Y chromosomes is initiated at early pachynema and is complete by mid pachynema. The pattern of sex chromosome pairing is unique in that it is initiated at an interstitial position, with subsequent synapsis proceeding in a unidirectional fashion towards the telomeres of the homologous segments. One-third the length of the X and two-thirds the length of the Y are involved in the synaptonemal complex of the sex bivalent. Various morphological complexities develop in the heteropycnotic (unpaired) segments as pachynema progresses, but desynapsis is not initiated until diplonema. Analysis of C-banded diakinetic nuclei indicated that sex chromosome pairing involves the heterochromatic short arm of the X and the long arm of the heterochromatic Y. An interstitial chiasma between the X and Y was observed in the majority of the diakinetic nuclei. The observation of a substantial pairing region and chiasma formation between the sex chromosomes of these deer mice is interpreted as indicating homology between the short arm of the X and the long arm of the Y.