Heteromorphism for chromosome 1, a requirement for normal development in crested newts

In all adult males and females of T. cristatus most of the long arm of chromosome 1 is achiasmate and heteromorphic with respect to Giemsa C-staining pattern. This heteromorphism correlates well with the heteromorphism seen by previous investigators on the lampbrush chromosomes of adult females. The heteromorphism has nothing to do with sex determination. All those fertile eggs of T. cristatus that develop normally beyond blastula are capable of development through to late tail-bud stage, but 50% of them arrest at late tail-bud and ultimately die. Homomorphism for the long arm of chromosome 1 can only be found in those embryos that arrest at late tailbud. The same findings apply to T. marmoratus, which also shows heteromorphism for chromosome 1, but not to T. alpestris, which has homomorphic chromosomes 1 and a potential 100% developmental success rate.     

Evidence for two successive pericentric inversions in sex lampbrush chromosomes of Rana rugosa (Anura: Ranidae)

The objective of this study was to clarify the course of inversions by which a ZW sex chromosome dimorphism has become established in Rana rugosa. Fortunately, R. rugosa preserves three different forms of sex chromosomes in the several isolated populations. In both males and females, the homomorphic sex chromosomes from Hiroshima were closely similar to Z, while those from Isehara were slightly different from the Z. Females from Hirosaki demonstrated heteromorphic sex chromosomes. In this study, the configuration and pairing behavior of sex lampbrush chromosomes were examined in the female offspring produced from a cross between a female from Hiroshima and a male from Isehara, as well as the female offspring of a female from Hirosaki and the male from Isehara. For the sex lampbrush chromosomes from Hiroshima and Isehara, chiasmata were exclusively formed between the distal regions of the long arms of one sex chromosome and the terminal regions of the short arms of the other. As a result, landmarks arranged in reverse order were observed in the achiasmatic regions of these chromosomes. For the sex lampbrush chromosomes from Isehara and Hirosaki, on the other hand, chiasma formation was mainly confined to the lower half of the chromosomes corresponding to the long arms, and the landmarks in the achiasmatic regions of these chromosomes were disposed in the opposite direction to each other. These results seem to indicate that in the primitive sex chromosomes of the Hiroshima type two pericentric inversions occurred, leading to the differentiation of the W chromosomes. This is the first report to substantiate the process of sex chromosome differentiation experimentally. Received: 10 November 1996; in revised form: 22 April 1997 / Accepted: 24 April 1997     

Chromosome banding in amphibia

The distribution of constitutive heterochromatin on the chromosomes of Triturus a. alpestris, T. v. vulgaris and T. h. helveticus (Amphibia, Urodela) was investigated. Sex-specific chromosomes were determined in the karyotypes of T. a. alpestris (chromosomes 4) and T. v. vulgaris (chromosomes 5). The male animals have one heteromorphic chromosome pair, of which only one homologue displays heterochromatic telomeres in the long arms; the telomeres of the other homologue are euchromatic. This chromosome pair is always homomorphic and without telomeric heterochromatin in the female animals. There is a highly reduced crossing-over frequency between the heteromorphic chromosome arms in the male meiosis of T. a. alpestris; in T. v. vulgaris no crossing-over at all occurs between the heteromorphic chromosome arms. No heteromorphisms between the homologues exist on the corresponding lampbrush chromosomes of the female meiosis. In T. h. helveticus no sex-specific heteromorphism of the constitutive heterochromatin could be determined. The male animals of this species, however, already possess a chromosome pair with a greatly reduced frequency of chiasma-formation in the long arms. The C-band patterns and the pairing configurations of the sex-specific chromosomes in the male meiosis indicate an XX/XY-type of sex-determination for the three species. A revision of the literature about experimental interspecies hybridizations, gonadic structure of haploid and polyploid animals, and sex-linked genes yielded further evidence in favor of male heterogamety. The results moreover suggest that the heterochromatinization of the Y-chromosome was the primary step in the evolution of the sex chromosomes.     

Lampbrush chromosomes and chiasmata of sex-reversed crested newts

Triturus cristatus carnifex provides a particularly clear example of sexual dimorphism for chiasma frequency and localisation. Oocytes from normal XX females routinely carry one proximal chiasma on each arm of their lampbrush bivalents. Spermatocytes from normal XY males have more numerous and relatively distal chiasmata. Lampbrush chromosomes from the oocytes of sex-reversed XY neofemales are found to resemble those from normal oocytes in having one proximal chiasma on each bivalent arm. A comparison of particular markers on the heteromorphic long arm of chromosome 1 provides evidence to equate the lampbrush 1A to somatic 1A, and confirms previous reports that lampbrush chromosome 1A is slightly longer than 1B. The XY sex bivalent of neofemales does not show any obvious heteromorphy of recognised marker loops. Received: 9 September 1997 / Accepted: 16 October 1997     

Banding patterns in newt chromosomes by the giemsa stain

Specific banding patterns can be produced on the mitotic chromosomes of the newt species Triturus vulgaris meridionalis and T. italicus by using the Giemsa stain technique. These bands are most useful cytogenetic markers in karyotyping, since they facilitate identification of the individual elements of the complements. Evaluation of the shape of chromosomes as well as of the banding patterns produced by the Giemsa stain indicates that the karyotypes of T. vulgaris meridionalis and T. italicus are differentiated: hence the specific distinction of the two Salamandrids, still debated by taxonomists, appears supported by chromosome evidence. — Most of the bands seem to correspond to the heterochromatic tracts observable on mitotic chromosomes from embryos and larvae either untreated or submitted to cold treatment. Besides, the comparison of mitotic karyotypes and lampbrush maps shows that the bands located near the centromeric regions of mitotic chromosomes probably correspond to the so-called bars visible on either side of centromeres of lampbrush chromosomes, while some of the subterminal bands may correspond to the sphere.This work was financially supported by C. N. R., Roma.     

Complete meiotic pairing of crested newt chromosomes.

The longest chromosome (number 1) of Trituturus cristatus carries a heteromorphic segment, a heterozygosity perpetuated by a balanced lethal system. The heteromorphic segment is regarded as achiasmate and has been claimed to be asynaptic. Direct observations of chromosome pairing in spermatocytes and oocytes yield some cases where all homologous chromosomes appear to be completely paired, but the individual bivalents could not be identified as pachytene is not particularly clear in this species. The long arms of bivalent 1 usually remain attached by a terminal chiasma in spermatocytes of T. c. cristatus but the corresponding chiasma is only rarely present in T. c. carnifex spermatocytes. Synaptonemal complexes have been measured in both spermatocytes and oocytes of T. c. cristatus. A karyotype constructed from these measurements matches the main features of somatic and lampbrush chromosome karyotypes, indicating that all chromosomes must be completely paired and proportionately represented as synaptonemal complex. The total length of synaptonemal complex is much the same in spermatocytes and oocytes and is similar to the length in spermatocytes of Xenopus laevis. These two amphibian examples supplement a recent survey of other vertebrate classes to reinforce its conclusion that synaptonemal complex length is not related to genome size in vertebrates.     

Banding patterns on lampbrush chromosomes of Triturus marmoratus (Amphibia Urodela) by the Giemsa stain

Lampbrush chromosome preparations from the newt species Triturus marmoratus have been submitted to a banding procedure by using a Giemsa stain technique (C-banding) as well as variants of the method. Centromeres, most of telomeres, the nucleolus organizing region and some segments along the chromosome axes appear to be differently stained. The centromere positions have been indicated on the maps of the lampbrush complement of the species. The possible relationships between banding and chromosome structure and organization are briefly discussed.     

Characterization of the lampbrush chromosomes of the marbled newt Triturus marmoratus (Latreille, 1800)

The maps of the lampbrush chromosomes of Triturus marmoratus oocytes were constructed on the basis of their lengths and major morphological characters such as giant fusing loops, dense matrix loops, lumpy objects, axial granules, lateral globules and reflected fusions; a nucleolus organizing region occurs subterminally on the right side of chromosome X. — Bivalent I appears morphologically asymmetrical, its two partners being of different lengths and bearing heteromorphic loops and other heterozygous structures: this heteromorphism may indicate that the two partners of bivalent I represent the ZW heterochromosomes of the species. Finally, an autoradiographic study has been performed in order to ascertain the pattern of ³H-uridine incorporation shown by the most typical landmarks and nucleoli.This work was financially supported by C.N.R., Roma.     

Absence of chiasmata from the heteromorphic region of chromosome I during spermatogenesis in Triturus cristatus carnifex

Analysis of squash preparations of spermatocytes from crested newts, Triturus cristatus carnifex, has shown that in most cells at least one large bivalent regularly fails to form chiasmata in one arm-pair. Feulgen microphotometry of diplotene and metaphase bivalents has shown that it is the largest bivalent in each cell which shows chiasma failure in one arm-pair. A C-banding technique which identifies chromosome I by virtue of a long, darkly stained region in its long arm, was used to confirm the absence of chiasmata from one arm-pair of the longest bivalent, and specifically from the darkly stained region. The achiasmate region which chromosome I exhibits during spermatogenesis, corresponds to the heteromorphic region of oocyte lampbrush bivalent I in which chiasmata never form. A possible correlation between the complete absence of crossing-over from the heteromorphic region and unusual cytological and molecular features which it exhibits, are discussed.     

Differential staining of plant chromosomes with Giemsa

Simple Giemsa staining techniques for revealing banding patterns in somatic chromosomes of plants are described. The value of the methods in the recognition of heterochromatin was demonstrated using five monocotyledonous and two dicotyledonous species. In Trillium grandiflorum the stronger Giemsa stained chromosome segments were shown to be identical with the heterochromatic regions (H-segments) revealed by cold treatment. Preferential staining of H-segments was also observed in chromosomes from three species of Fritillaria and in Scilla sibirica. Under suitable conditions the chromosomes of Vicia faba displayed a characteristic banding pattern and the bands were identified as heterochromatin. The Giemsa techniques proved to be more sensitive than Quinacrine fluorescence in revealing a longitudinal differentiation of the chromosomes of Crepis capillaris, where plants with and without B-chromosomes were examined. Again all chromosome types had their characteristic bands but there was no difference in Giemsa staining properties between the B-chromosomes and those of the standard complement.     

In situ hybridization of ribosomal DNA labelled with 125iodine to metaphase and lampbrush chromosomes from newts

Methods are described for in situ hybridization of ribosomal DNA from Xenopus laevis, labelled in vitro with ¹²⁵iodine, to mitotic and lampbrush chromosomes from Triturus cristatus carnifex. The hybridization reaction was carried out in a mixture containing 50% formamide, 4 x SSC, 0.1 M KI, at 37° C, or in 2 x SSC, 0.1 M KI at 65° C. Autoradiographs of mitotic metaphases from 2 males showed labelling over the middle of the short arm of one chromosome IX in each metaphase. In some cases, a region near the end of a longer chromosome was also labelled. In lampbrush preparations, labelling was confined to a region identified as about 53 units, near the middle of the short arm of both halves of bivalent IX. The usefulness of the technique and the significance of the labelling of only 1 of the 2 chromosomes IX in mitotic preparations are discussed.     

The Giemsa banding patterns of the standard and four reconstructed karyotypes of Vicia faba

The Giemsa banding patterns of the standard karyotype of Vicia faba and of four new karyotypes with easily interdistinguishable chromosomes due to interchanges and inversions are described and compared with the data of other authors on preferential Giemsa staining in Vicia faba. All karyotypes contain 14 easily reproducible marker bands which characterize chromosome segments known to be heterochromatic. It is shown that the preferential Giemsa staining of chromosome regions is a valuable tool for the localization of translocation and inversion points in the chromosomes of the reconstructed Vicia karyotypes. A close correlation exists between banding patterns, segment extension by incorporation into chromosomal DNA of azacytidine and mutagen-specific clustering of induced chromatid aberrations in the new karyotypes.     

Satellite DNA III and alkaline Geimsa staining.

Satellite DNA III visualized by staining chromosomes with Giemsa at pH 10-12. Evidence is presented that besides the secondary constriction of chromosome 9, satellite III contained in considerable amount in the long arms of chromosome 20, giving rise to a clearly visible secondary constriction just below the centromere. The latter finding confirms that reported by Bobrow et al. (1972). The long arms of the Y chromosome also show strong staining with alkaline Giemsa, the region of staining corresponding exactly with the intensely flourescing area. This is interpreted as possible evidence for the presence of satellite DNA III in the distal long arms of the human Y chromosome.     

Localization of translocation breakpoints in somatic metaphase chromosomes of barley

Karyotype analyses based on staining by acetocarmine followed by Giemsa N-banding of somatic metaphase chromosomes of Hordeum vulgare L. were carried out on 61 reciprocal translocations induced by X-irradiation. By means of computer-based karyotype analyses all of the 122 breakpoints could be localized to defined sites or segments distributed over the seven barley chromosomes. The pre-definition of translocations with respect to their rearranged chromosome arms from other studies rendered it possible to define the break positions even in translocations having exchanged segments equal in size and the breakpoints located distally to any Giemsa band or other cytological marker. The breakpoints were found to be non-randomly spaced along the chromosomes and their arms. All breaks but one occurred in interband regions of the chromosomes, and none of the breaks was located directly within a centromere. However, short and long chromosome arms recombined at random. An improved tester set of translocations depicting the known break positions of most distal location is presented.     

尾斑瘰螈的核型和C带研究

用常规Giemsa染色和BSG技术研究了尾斑瘰螈的核型和C带。该螈的染色体数 为2n=24,包括9对中部着丝粒染色体和3对亚中部着丝粒染色体(Nos. 7、10、11);BSG显带处理后全部染色体都显示了弱的着丝粒带,同时还显示了46条近着丝粒区插入带; 其核型和C带均不同于已研究过的国内蝾螈科动物,未发现与性别有关的异形色体。