In vivo effects of γ-irradiation on the functional architecture of the lampbrush chromosomes in Pleurodeles (Amphibia,Urodela)

In vivo irradiation of ovaries of Pleurodeles poireti by -rays leads to structural rearrangement of lampbrush chromosomes in late vitellogenic oocytes (stages V and VI). The loops collapse into the chromomeres and the axes condense. Doses between 200 and 2,000 rads have been tested. We observed that such changes were dependent on the irradiation dose though the chronological order of the events was irrespective of the dose. The maximum effect was attained about 10 h after irradiation. The alterations are totally reversible. Over a period of 3 days, chromosomes gradually relax, regenerate loops and recover their normal appearance. In mid vitellogenic oocytes (stages III and IV) lampbrush chromosomes do not undergo radiation induced alterations. It seems that only full-grown oocytes are competent to respond to the ionizing-flow.     

Mitotic and meiotic chromosomes of Mabuya (Scincidae: Reptilia)

A study was carried out on conventionally stained mitotic and meiotic chromosomes of two species of lizards of the Scincidae: Mabuya caissara and M. macrorhyncha.On the basis of morphological, numerical and metric data, the chromosomes were divided into three groups: two groups of macrochromosomes (A and B) and one of microchromosomes (C). The karyotypes of males and females of both species showed 2n=32 and FN=50 and no differences were detected between the species.     

The location of 5S RNA genes in lampbrush polytene chromosomes from Drosophila

Drosophila polytene chromosomes were transformed into lampbrush-like structures by exposure to solutions of alkali-urea. In this process, the chromosomes shorten and widen, and the bands (chromomeres) extend laterally into loops leaving a central core between the paired homologues. The expanded polytene chromosomes are very similar in appearance to the true lampbrush chromosomes of amphibian oocytes and to ordinary chromosomes in pachytene. The denaturing effects of alkali-urea were partially counteracted by return of the treated chromosomes to Ringer solution. These observations are interpreted in terms of recent findings on protein backbones in chromosomes, and indicate that chromosomes generally may have very similar basic organization, despite differences due to species, polyteny and degree of condensation. To gain more information on the specific location of a structural gene, ¹²⁵I-labelled low molecular weight (containing 5S RNA) was hybridized in situ to normal and lampbrush-like polytene chromosomes. Autoradiography showed silver grain distribution for 5S RNA consistent with hybridization primarily to the loop regions of the lampbrush chromosomes rather than the core. This provides further indirect evidence that structural genes like 5S RNA may be located on the bands (chromomeres) and not the interbands of normal polytene chromosomes.     

Tetraploid-octoploid relationships and karyological evolution in the order Acipenseriformes (Pisces) karyotypes,nucleoli, and nucleolus-organizer regions in four acipenserid species

The karyotypes of four Acipenseriformes species, Acipenser gueldenstaedti, 2n=250±8, A. ruthenus, A. stellatus and Huso huso, 2n=118±2, are described. In all four karyotypes the majority of chromosomes are meta- and submetacentric macrochromosomes, and microchromosomes of different morphology make up about one third of the set. In A. ruthenus the NORs are located in the telomeric region of a pair of microchromosomes and at least in one pair of middle-size acrocentrics, and in A. stellatus and Huso huso also in the telomeric regions of at least one pair of microchromosomes. The modal number of active nucleoli in A. gueldenstaedti nuclei amounts to 6–8 (range 2–12), in A. ruthenus, A. stellatus and H. huso nuclei to 2–3 (range 1–6). The data obtained point to the tetraploid origin of Acipenseriformes species with 120 chromosomes and to the octoploid origin of species with 240–260 chromosomes.     

Cytogenetic Maps of Lampbrush Chromosomes of Newts of the Genus Pleurodeles: An Algorithm of Lampbrush Chromosome Identification inPleurodeles waltl by Immunocytochemical Staining of Landmark Loops with Polyclonal Anti-Ro52 Antisera

Our work was aimed at developing a simple and effective method of identification of most or all chromosomes of Pleurodelesnewts. To this end, we used DAPI staining of the chromomeres of newt lampbrush chromosomes and immunochemical reactions between the ribonucleoproteins of landmark lateral loops and polyclonal antibodies against human zinc-finger protein Ro52 (52-kDa Ro/SS-A). A method has been developed to obtain lampbrush chromosome preparations in newts of the genes Pleurodeles. Cytological maps of P. waltl chromosomes (Spanish population/subspecies) showing distributions of chromomeres and marker landmark loops along the chromosome length were constructed.     

The somatic chromosome complements of 16 species of falconiformes (Aves) and the karyological relationships of the order

Using short term leucocyte culture techniques, the somatic chromosome complements of 16 species of diurnal birds of prey, belonging to four different families of the order Falconiformes were studied. The karyotypes are described and illustrated, and of some species idiograms are presented. In accordance with the family classification, four karyologically different groups can be distinguished in the Falconiformes: (1) Cathartidae, with karyotypes which show only 7 pairs of biarmed macrochromosomes and a considerable number of small acrocentrics and microchromosomes (the diploid numbers are approximately 80). This is the only group in which really large macrochromosomes are found (over 10% TCL); (2) Falconidae, the karyotypes of which include only a single pair of biarmed macrochromosomes, all other elements being acrocentrics of medium to small size or microchromosomes (diploid numbers of approximately 84 and 52); (3) the secretary bird (Sagittariidae), with 36 biarmed macrochromosomes and 44 small acrocentrics and microchromosomes (2n=80 approximately); (4) Accipitridae, the representatives of which never possess more than about 8 real microchromosomes, while their karyotypes show varying numbers of biarmed and acrocentric macrochromosomes of small to medium size (diploid numbers range from 78 to 60).The possible karyological relationships within each of these groups are briefly discussed, while a more extensive discussion is dedicated to the possible relationships between these groups, and those between them and other avian taxa.The variation in karyotypic structures found in the Falconiformes is much wider than that in other avian groups. However, it remains an unanswered question whether this karyological heterogenelty points to a polyphyletic origin of the diurnal birds of prey. Especially the chromosome complements of the Accipitridae are most uncommon among birds, because of their extremely low numbers of real microchromosomes. However, of all the Falconiformes only the karyotypes of the Cathartidae have clear counterparts outside the order, since nearly identical complements were found in representatives of the Phoenicopteriformes and Gruiformes.The present work was partially carried out at the Institute of Genetics and the Center for Clinical Cytogenetics (both in Utrecht).     

Karyotypic characterization of <Emphasis Type="Italic">Trachemys dorbigni</Emphasis> (Testudines: Emydidae) and <Emphasis Type="Italic">Chelonoidis (Geochelone) donosobarrosi</Emphasis> (Testudines: Testudinidae), two species of Cryptodiran turtles from Argentina

We describe for the first time the karyotypes of two species of Cryptodiran turtles from Argentina, namely, Trachemys dorbigni (Emydidae) and Chelonoidis (Geochelone) donosobarrosi (Testudinidae). The karyotype of T. dorbigni (2n = 50) consists of 13 pairs of macrochromosomes and 12 pairs of microchromosomes, whereas the karyotype of C. donosobarrosi (2n = 52) consists of 11 pairs of macrochromosomes and 15 pairs of microchromosomes. Fluorescence in situ hybridization (FISH) with a (TTAGGG)n telomeric probe showed that the chromosomes of these species have four telomeric signals, two at each end, indicating that none of the chromosomes of T. dorbigni and C. donosobarrosi are telocentric. The fact that no interstitial telomeric signals were observed after FISH, suggests that interstitial telomeric sequences did not have a major role in the chromosomal evolution of these species. Additional data will be needed to elucidate if interstitial telomeric sequences have a major role in the karyotypic evolution of Testudines.     

A novel approach to cytotaxonomic and cytogenetic studies in the genus Triturus using monoclonal antibodies to lampbrush chromosomes antigens

Monoclonal antibodies against germinal vesicle antigens from Pleurodeles oocytes crossreact with lampbrush chromosomes of various Triturus species: C36/6, A33/22 and B71/22 bind to most lateral loops, B24/3 labels the spheres, while A1/5 and B81 give a distribution of fluorescent loops which is highly reproducible and species specific. — The antigens involved were characterized by immunoblotting of electrophoretic gels of germinal vesicle proteins and the molecular weights of those that bound to monoclonal antibodies C36/6, A33/22, B24/3 and C3/1 were determined. — The possible relationship between sites immunostained by some monoclonal antibodies and given DNA sequences distributed along the chromosomes is discussed. A new approach to cytotaxonomic and cytogenetic studies through the use of monoclonal antibodies on lampbrush chromosomes is offered, which can give new insight into the molecular mechanisms of speciation and karyological evolution in European newt species.     

Multiplicity of B microchromosomes in a siberian population of mice <Emphasis Type="Italic">Apodemus peninsulae</Emphasis> (2<Emphasis Type="Italic">n</Emphasis> = 48 + 4–30 B chromosomes)

Differentiation of four Siberian populations of East-Asian (Korean) field mice (Apodemus peninsulae) inhabiting the basin of the mid-stream of the Yenisei River was carried out according to the variants of the B chromosome system. A multiplicity of B microchromosomes (from 4 to 30) was found for the first time in all 26 mice from the left shore of the Yenisei River in the mid-stream area. All of them probably belong to a population with B microchromosomes. It is likely that in this population further reorganization of B microchromosomes into B macrochromosomes typical of this species does not occur. Two mice from this population had a large number of B chromosomes (26) earlier not observed in this species. In one mouse, the modal number of B microchromosomes was 30. This is a new maximum number of B chromosomes in this mouse species.     

Chromosome 1 in crested and marbled newts (Triturus)

The heteromorphic chromosomes 1 of Triturus cristatus carnifex and T. marmoratus were studied in mitotic metaphase after staining with the Giemsa C-banding technique and with the fluorochromes, DAPI (AT-specific) and mithramycin (GC-specific). They were also examined in the lampbrush form under phase-contrast before fixation and after fixation and staining with Giemsa. Chromosomes 1 of T.c. carnifex are asynaptic and achiasmatic throughout most of their long arms. They are also heteromorphic in most of their long arms for the patterns of Giemsa and fluorochrome staining and the distribution of distinctive lampbrush loops. The heteromorphic regions correspond to the regions that are asynaptic and achiasmatic. They stain more strongly with mithramycin and more weakly with DAPI than the remainder of the chromosomes, signifying that their DNA is relatively rich in GC. The patterns of staining with Giemsa and fluorochromes and the distributions of distinctive lateral loops vary from one animal to another in the same species and even in the same population. The asynaptic and achiasmatic regions of chromosomes 1 in T. marmoratus extend throughout the whole of the long arms and well beyond the heterochromatic region. Chiasmata form only in the short arm and occasionally in the short euchromatic segment at the tip of the long arms. The staining patterns of chromosomes 1 in T. marmoratus differ from those in T.c. carnifex although, like carnifex, their DNA is relatively GC-rich. The chromosomes 1 of T. marmoratus are more submetacentric than those of T.c. carnifex. In T. marmoratus chromosome 1B is about 12% shorter than 1A. There is a short paracentric inversion heterozygosity in the long arm of chromosome 1B in T. marmoratus which probably accounts for the lack of chiasmata in the euchromatin that separates the centromere from the start of the heterochromatin. In both carnifex and marmoratus, embryos that are homomorphic for chromosome 1 arrest and die at the late tailbud stage of development. The same applies to F₁ hybrid embryos T.c. carnifex x T. marmoratus, and this has permitted identification of chromosomes 1A and 1B in both species. There is no correspondence between patterns of Giemsa or fluorochrome staining of the heteromorphic regions of chromosome 1 and any feature of the lampbrush chromosomes. However, the short euchromatic ends of the long arms of chromosomes 1 in both species are distinguished in the lampbrush form by a series of uniformly small loops of fine texture associated with very small chromomeres. The Giemsa C-staining patterns of both chromosomes 1A and 1B are different in each of the four subspecies of T. cristatus. T.c. karelinii stands out by having unusually large masses of Giemsa C-staining centromeric heterochromatin on all but 1 of its 12 chromosomes. A scheme is proposed for the evolution of chromosome 1 in T. cristatus and T. marmoratus, based on all available cytological and molecular data.     

Lampenbürstenchromosomen in den Oocytenkernen von Sepia officinalis

The nuclei of the growing oocytes of Sepia officinalis contain lamp-brush chromosomes with clearly demonstrable chromomeres bearing pairs of lateral loops (Fig. 4). Similar to the findings of Callan and Lloyd (1960) in amphibian oocytes the chromosomes of Sepia exhibit some specially organized loops which can be used as landmarkers for recognizing certain chromosomes (Fig. 5). Maximal loop despiralization occurs only in nuclei of follicles during their initial growth phase. The following developmental period is characterized by a successive contraction of loops and chromosome axes (Fig. 7), despite the fact that the diameter of the oocyte nucleus enlarges still three times. In the oldest nuclei hundreds of nucleolus-like granules arise near the chromosomes which later spread over the entire nucleus (Fig. 9).

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Herrn Professor Dr. K. Bier () in dankbarer Verehrung gewidmet.     

Identification of the lampbrush chromosome loops which transcribe 5S ribosomal RNA in Notophthalmus (Triturus) viridescens

The loops which transcribe 5S ribosomal RNA in lampbrush chromosomes of the newt, Notophthalmus (Triturus) viridescens, were identified by hybridizing purified 5S DNA to nascent 5S RNA in situ. The genes which code for 5S RNA were found near the centromeres of chromosomes 1, 2, 6, and 7 by hybridizing iodinated 5S RNA to denatured lampbrush and mitotic chromosomes in situ. These genes and their intervening spacer DNA were isolated from Xenopus laevis using sequential silver-cesium sulfate equilibrium centrifugations. This purified 5S DNA was iodinated and hybridized to non-denatured lampbrush chromosomes in situ, where it bound to nascent 5S RNA on loops at the base of the centromeres of chromosomes 1, 2, 6, and 7. The number of 5S genes present in the haploid chromosome complement of N. viridescens was determined. — The 5S loops were chosen for study, since (1) the synthesis of 5S RNA has been demonstrated during the lampbrush stage, (2) both 5S RNA and 5S DNA could be isolated in pure form, and (3) the localization of the repetitive 5S genes could be verified by conventional in situ hybridization procedures. These methods may be applicable to the identification of other loops, leading to a better understanding of lampbrush chromosome function.     

The W chromosome in the females of two Indian species of birds

The heterogametic females of the jungle babbler, Turdoides s. striatus and red-breasted parakeet, Psittacula alexandri fasciata belonging to the orders Passeriformes and Psittaciformes respectively in the subclass Carinatae have ZW sex chromosomes. The W chromosomes in both the species are of the size of smaller macrochromosomes or larger microchromosomes and they are easily identified in both species.State CSIR (U. P. Government) Research Assistant.