D. Formenti

Non-telomeric chromosome localization of (TTAGGG) n repeats in the genus Eulemur

The chromosomal distribution of the (TTAGGG)n telomeric repetitive sequences was studied in the Malagasy species Eulemur fulvus fulvus (2n = 60), Eulemur rubriventer (2n = 50), Eulemur coronatus (2n = 46) and Eulemur macaco (2n = 44). These sequences hybridize to the telomeres of all chromosomes of the four species and also to the pericentromeres of all chromosomes of E. fulvus, E. coronatus and E. macaco, with the exception of the pericentromeres of E. coronatus and E. macaco chromosomes 9, the homeologous E. fulvus chromosomes 2 and E. macaco chromosomes 1. In E. rubriventer only a very weak signal was detected at the pericentromeres of a few chromosomes. In E. fulvus, E. coronatus and E. macaco, non-telomeric (TTAGGG)n sequences collocalize with constitutive heterochromatin. The interspecific differences of the hybridization pattern of (TTAGGG)n sequences at the pericentromeres suggest that E. rubriventer branched off the common trunk before amplification of endogenous (TTAGGG)n sequences occurred in pericentromeric regions.

DNA content variability in primates

The DNA content of 58 species of primates out of the approximately 180 described (Chiarelli, 1972) , belonging to 29 out of the 54 existing genera is reported. The amount of nuclear DNA was measured microdensitometrically on lymphocytes of peripheral blood submitted to the Feulgen reaction. Genome size was found to range from 4.7 to 10.9 pg (respectively 65% and 150% the value observed in man, considered to be 7.3 pg). Generally speaking, in the group of species studied, no correlation was found between Feulgen-DNA content and chromosome number. At any rate, three different situations were revealed: (1) the lemurs of Madagascar, with a fairly low and constant DNA content and a highly variable chromosome number; (2) the genus Cercopithecus, showing a quite variable DNA content, occasionally related to the chromosome number; (3) the subfamily Papiinae, in which both the chromosome number and the DNA content appear exceptionally constant. The hypothesis of a different influence of selective pressure on the two parameters, in relation to different environments, is also discussed. According to this hypothesis, these differences would have led to the development of cytologic conditions which are the reflection of different evolutionary pathways.

Sperm-chromatin maturation in the mouse

SummaryCytochemical techniques were used to study chromatin during spermiogenesis and sperm maturation in the mouse, starting from the stages at which the substitution of somatic histones by testis-specific proteins occurs. It was possible to distinguish and analyze the different temporal incidence of two processes involved in sperm maturation, i.e. chromatin condensation (a tridimensional highly compacted arrangement) and chromatin stabilization (a tough structure, which protects the genome DNA). The first process, involving a reduction in the nuclear size and a decrease in the amount of sperm DNA accessible to specific cytochemical reactions and stainings, was found to reach its maximum in caput-epididymidis spermatozoa, in which electron microscopy revealed that the sheared chromatin was mainly organized into 120-Å-thick knobby fibers. No further changes were found in sperm up to their appearance in the fallopian tubes. On the contrary, chromatin stabilization, the onset of which occurs in the testis (at the late spermatid stage) via the formation of -S−S- cross-links, is completed in the vas deferens, where chromatin has a superstructure consisting of thicker fibers, with diameters of 210 and 350 Å. The reductive cleavage of disulfides in vas-deferens spermatozoa does not completely destroy the superstructure of sperm chromatin, which could indicate ‘coiling’ of the basic knobby fiber. In fact, when the ion concentration was increased, the chromatin of vas-deferens spermatozoa appeared to be organized into fibers with diameters similar to those of the caput epididymidis. This unique organization of mature sperm chromatin should have an essential role in the fast swelling of spermatozoa during fertilization.

Feulgen-DNA Content and C-Banding of Robertsonian Transformed Karyotypes in Dugesia Lugubris

SUMMARYIn the planarian species, Dugesia lugubris, two biotypes are found: E (2n = 8, n = 4) and F (2n = 6, n = 3); on the basis of karyometric studies it has been hypothesized that the second was derived from the first through a Robert-sonian mechanism of centric fusion. The quantitative cytochemical data reported here confirm the hypothesis of karyotype evolution, since there are no significant differences between the DNA content of the nucleus in the two biotypes. The regenerative blastemas of both biotypes contain a number of cellular populations with a variable Feulgen-DNA content; these correspond to successive doublings of the 2C diploid content. In addition, metaphase plates with multistranded chromosomes have been found. A difference between the chromosome C-banding in the two biotypes has also been observed.

Feulgen-DNA amounts and karyotype lengths of three planarian species of the genusDugesia

Genome sizes of the planariansD. lugubris (2n=8),D. polychroa (2n=8) andD. benazzii (2n=16) were evaluated on metaphase plates by measuring both the Feulgen-DNA contents and the karyotype lengths. In the three species, genome sizes are significantly different; this finding rules out the possibility of a karyotype evolution through simple chromosome rearrangements betweenD. lugubris andD. polychroa. A different Feulgen-DNA content per unit length of karyotype in the three species studied was also found, which suggests that DNA could be differently packed along metaphase chromosomes.

DNA content variability in several species of Australian and South American marsupials

Abstract The evaluation of DNA content in Australian marsupials (Martin & Hayman, 1967; Bick & Jackson, 1967) together with the morphological analysis of the karyotype (which shows a strong variability: 2n between 10 and 32 with modes at 14 and 22) has yielded useful information for the phylogenetic analysis of this order. In this paper the DNA content, evaluated microdensitometrically as Feulgen-DNA, is compared in 6 species of South American marsupials (Lutreolina crassicaudata Desmarest, Marmosa pusilla Desmarest, Marmosa agilis Burmeister, Didelphis marsupialis Linneus, Didelphis azarae. Temminck, Monodelphis dimidiata Wagner) and 5 species of Australian marsupials (Perameles gunnii Gray, Perameles nasuta Geoffroy, Macropus giganteus Zimmermann, Macropus robustus Gould and Potorous tridactylus Kerr). No data had so far been reported on the nuclear DNA content of the South American species. The mean values in the Australian and South American marsupials, are 124% and 120% respectively of those observed...

First data on the nuclear DNA content (Feulgen-positive material) of Perodicticus potto

Abstract The nuclear DNA content (Feulgen-positive material) of Perodicticus potto , measured on lymphocytes from six animals of the subspecies edwarsi (Gabon) and potto (Dahomey and Liberia) is quite homogeneous around a mean value of 6·87 ± 0·15 pg. A difference of 1·5% has been found between sexes in each subspecies; the possible relation of this fact to the characteristics of the karyotype is discussed.

Genome size and «C-heterochromatic-DNA» in man and the african apes

The genome sizes and the amounts of DNA after C-banding pretreatments (C-heterochromatic DNA) were measured by quantitative cytochemical methods in man and the African apes,Gorilla gorilla andPan troglodytes. As evaluated by flow cytometry on propidium-iodide-stained lymphocytes, gorilla and chimpanzee have genome sizes larger than man. On the basis of the different resistance of metaphase chromosome DNA to the C-banding procedure, two genome compartments were defined, i.e.,C-heterochromatic-DNA andeuchromatic-DNA. The latter proved to be fairly constant in man and the African apes (as well as in two hylobatid species), whereas the variable amounts ofC-heterochromatic-DNA account well for the interspecific differences of genome size among the hominoid species studied so far. During karyotype diversification, quantitative changes (with either gains or losses) ofC-heterochromatic-DNA seem to have taken place independently in the hylobatid and the man/African ape lineages.

Image analysis as a simple and useful tool for evaluating the constitutive heterochromatin (C-banding) in human chromosomes

Image analysis can contribute to those fields of cytogenetics that are influenced most by subjectivity, especially evaluation of chromosome regions that are histochemically polymorphic. C-banding of human or primate chromosomes may be used as a typical example of this concept. In addition, using it quantitatively it is useful in studies of population cytogenetics of man and Primates.Therefore, the aim of this study was to determine the best conditions for measurement by image analysis of C-positive regions in a sample of 29 normal subjects.We looked for relationships of chromosomal C-positive areas with the dimensions of the corresponding metaphases. Finally, we suggest some criteria for potential use of C-banding in population and comparative studies.