P. Arana

The chromosomal distribution of phosphorylated histone H3 differs between plants and animals at meiosis

Abstract Plant (Secale cereale, Triticum aestivum) and animal (Eyprepocnemis plorans) meiocytes were analyzed by indirect immunostaining with an antibody recognizing histone H3 phosphorylated at serine 10, to study the relationship between H3 phosphorylation and chromosome condensation at meiosis. To investigate whether the dynamics of histone H3 phosphorylation differs between chromosomes with a different mode of segregation, we included in this study mitotic cells and also meiotic cells of individuals forming bivalents plus three different types of univalents (A chromosomes, B chromosomes and X chromosome). During the first meiotic division, the H3 phosphorylation of the entire chromosomes initiates at the transition from leptotene to zygotene in rye and wheat, whereas in E. plorans it does so at diplotene. In all species analyzed H3 phosphorylation terminates toward interkinesis. The immunosignals at first meiotic division are identical in bivalents and univalents of A and B chromosomes, irrespective of their equational or reductional segregation at anaphase I. The grasshopper X chromosome, which always segregates reductionally, also shows the same pattern. Remarkable differences were found at second meiotic division between plant and animal material. In E. plorans H3 phosphorylation occurred all along the chromosomes, whereas in plants only the pericentromeric regions showed strong immunosignals from prophase II until telophase II. In addition, no immunolabeling was detectable on single chromatids resulting from equational segregation of plant A or B chromosome univalents during the preceding anaphase I. Simultaneous immunostaining with anti-tubulin and anti-phosphorylated H3 antibodies demonstrated that the kinetochores of all chromosomes interact with microtubules, even in the absence of detectable phosphorylated H3 immunosignals. The different pattern of H3 phosphorylation in plant and animal meiocytes suggests that this evolutionarily conserved post-translational chromatin modification might be involved in different roles in both types of organisms. The possibility that in plants H3 phosphorylation is related to sister chromatid cohesion is discussed.

Evolution of a complex B-chromosome polymorphism in the grasshopper Eyprepocnemis plorans

B-chromosome systems in several Spanish natural populations of Eyprepocnemis plorans are reported. The geographical distributions of the fourteen types of B chromosomes, which were classified according to size, C-banding pattern, and meiotic behaviour, are described. The results indicate a common origin for most types and a possible independent origin for a few secondary B variants. The origin and mechanisms of evolution of this B chromosome polymorphism are discussed.

Chromosome C-banding patterns in Spanish Acridoidea

The karyotypes of 47 Spanish acridold grasshoppers have been analyzed by means of C-banding in both mitotic and meiotic cells. The most frequent location of C-heterochromatin occurs in centromeric and telomeric regions whereas interstitial C-bands are very scarce. No clear relationship between similarities in C-banding patterns and taxonomic proximity has been found. Negatively heteropycnotic regions are described; their uniform location and distribution suggest that they could represent a functional chromosome structure as nucleolar organizers.

Mitotic microtubule development and histone H3 phosphorylation in the holocentric chromosomes of Rhynchospora tenuis (Cyperaceae).

In the present work we report the phosphorylation pattern of histone H3 and the development of microtubular structures using immunostaining techniques, in mitosis of Rhynchospora tenuis (2n = 4), a Cyperaceae with holocentric chromosomes. The main features of the holocentric chromosomes of R. tenuis coincide with those of other species namely: the absence of primary constriction in prometaphase and metaphase, and the parallel separation of sister chromatids at anaphase. Additionaly, we observed a highly conserved chromosome positioning at anaphase and early telophase sister nuclei. Four microtubule arrangements were distinguished during the root tip cell cycle. Interphase cells showed a cortical microtubule arrangement that progressively forms the characteristic pre-prophase band. At prometaphase the microtubules were homogeneously distributed around the nuclear envelope. Metaphase cells displayed the spindle arrangement with kinetochore microtubules attached throughout the entire chromosome extension. At anaphase kinetochoric microtubules become progressively shorter, whereas bundles of interzonal microtubules became increasingly broader and denser. At late telophase the microtubules were observed equatorially extended beyond the sister nuclei and reaching the cell wall. Immunolabelling with an antibody against phosphorylated histone H3 revealed the four chromosomes labelled throughout their entire extension at metaphase and anaphase. Apparently, the holocentric chromosomes of R. tenuis function as an extended centromeric region both in terms of cohesion and H3 phosphorylation.

Chiasma interference and centromere co-orientation in a spontaneous translocation heterozygote of Euchorthippus pulvinatus gallicus (Acrididae; Orthoptera)

The meiosis of an individual of the species Euchorthippus pulvinatus gallicus heterozygous for a reciprocal translocation involving chromosomes 3 and 6 has been analysed using the Giemsa C-banding technique. It is concluded that: (i) Chiasma interference in the quadrivalent seems to act only at the arm level. There is no interference across the translocation break point. No interchromosomal chiasma interference could be demonstrated, (ii) The results concerning the co-orientation of the quadrivalent suggest that the length of the chromosomal segments between two adjacent centromeres at metaphase I is related with their orientation behaviour.

Spontaneous translocations between B chromosomes and the normal complement in the grasshopper Eyprepocnemis plorans

A translocation between a B chromosome and a medium-size autosome and a centric fusion between the B and the X chromosome were found in two different natural populations of Eyprepocnemis plorans. The cytological behaviour of both interchanges is described and discussed. These interchanges are highly asymmetrical and may be the beginning of an integration of B chromosomes into the genome of this species.

Chromosomal Strategies for Adaptation to Univalency

The orientation and segregation behaviour of different types of univalents, namely sex chromosomes, B chromosomes and autosomal univalents, were analysed in living spermatocytes of eight evolutionarily distant grasshopper species. The meiotic behaviour of each univalent was characterized in terms of velocity of prometaphase movements, frequency of reorientations, types of final orientation at metaphase I and modes of segregation at anaphase I. All these features were found to vary between different univalents. Certain combinations of these traits, defining a ‘chromosomal strategy’, appear commonly together in certain chromosome types, indicating that they are the result of selection acting on the chromosomes to increase transmission effectiveness. The sex univalents show in general a strategy in which all the features favouring an eventual equational segregation at anaphase I tend to be minimized. There is much more variation in behaviour among B chromosomes than among X chromosomes, which is a reflection of their heterogeneous nature. Induced autosomal univalents are studied in Locusta migratoria. They show a very irregular behaviour, indicating their lack of adaptation to univalency.

Mitochondrial DNA sequence variability in red-legged partridge, Alectoris rufa, Spanish populations and the origins of genetic contamination from A. chukar

The analysis of 135 mitochondrial D-loop sequences of the Iberian autochthonous red-legged partridge (Alectoris rufa) from wild population hunting bags from various locations and fowl runs in Spain yielded 37 different haplotypes. Among these, three haplotypes correspond to chukar partridges (Alectoris chukar), indicating genetic introgression from birds illegally introduced for restocking: three individuals carrying such haplotypes where found in natural populations, one appeared among those sampled on a mass reproduction farm and the remaining 10 in another fowl-run. The geographical origin of the contaminating chukar haplotypes could be assigned to the most easterly area of the chukar partridge geographical distribution in China. Molecular diversity parameters in the A. rufa samples indicate a considerable amount of genetic variation. ΦST showed significant differences among populations that are not explained by geographical distance alone. Particularly, one northern population (Palencia) shows a certain degree of genetic differentiation that could reflect a previously suggested subspecies division.

A comparative study of orientation at behavior of univalent in living grasshopper spermatocytes

Orientational movements and modes of segregation at anaphase I were analyzed in three different types of univalents in living spermatocytes of the grasshopper species Eyprepocnemis plorans, namely the sex univalent, three types of accessory chromosomes and spontaneous and induced autosomal univalents. When two or more univalents were present in the same spindle, their dynamics were directly compared. Chromosomes may show variable velocity and number of reorientations: the X and the most common B types (B1 and B2) are slow and rarely reorient, a more geographically restricted B (B5) is faster and reorients more often, and autosomal univalents are the fastest and show the highest frequency of reorientations. Nonetheless, the X and the accessories are rigorously reductional at anaphase I whereas autosomal univalents often fail to migrate or divide equationally. This indicates that orientational and segregational behavior are controlled mainly by chromosomal rather than cellular characteristics and that chromosomes may display a great variety of strategies to achieve regular segregation.

The effect of B chromosomes on mating success of the grasshopper Eyprepocnemis plorans

The mating ability of E. plorans was tested in laboratory conditions in six experimental units composed of ten males and fifteen females during 31 days. When significant differences were found (three from the six cages, and in totals) they involved a decrease of matings involving males with B chromosomes. The same tendency seems to exist in females, but to a lesser extent, so that a significant effect is only detected when the totals are considered. Accessory chromosomes also delay, in both sexes, the occurrence of the first mating. No mating preferences depending on the number of Bs were detected.