Combined DNA-RNA Fluorescent In situ Hybridization (FISH) to Study X Chromosome Inactivation in Differentiated Female Mouse Embryonic Stem Cells

Fluorescent in situ hybridization (FISH) is a molecular technique which enables the detection of nucleic acids in cells. DNA FISH is often used in cytogenetics and cancer diagnostics, and can detect aberrations of the genome, which often has important clinical implications. RNA FISH can be used to detect RNA molecules in cells and has provided important insights in regulation of gene expression. Combining DNA and RNA FISH within the same cell is technically challenging, as conditions suitable for DNA FISH might be too harsh for fragile, single stranded RNA molecules. We here present an easily applicable protocol which enables the combined, simultaneous detection of Xist RNA and DNA encoded by the X chromosomes. This combined DNA-RNA FISH protocol can likely be applied to other systems where both RNA and DNA need to be detected.     

Chromosomal rearrangements associated with pelagic larval duration in Labridae (Perciformes)

The family Labridae is one of the largest and most important groups of reef fishes in the Southern Atlantic. There is a remarkable ecologic interest in this family because of their complex interactions in the reef environment. Predictions of genetic variability in fish based on biological patterns have often been contradictory. The present work aimed to increase the cytogenetic data about the family and verify the possible correlation between larval pelagic phase and chromosomal rearrangements based on the putative basal Perciformes karyotype (2n = 48a). Therefore, cytogenetic analyses were performed in the species Halichoeres brasiliensis (2n = 48, 48a, FN = 48); Halichoeres radiatus (2n = 48, 48a, FN = 48) and in three populations of Halichoeres poeyi (2n = 48, 4m + 44st-a, FN = 52) from Brazilian coastline. A conserved diploid number was observed in all species and populations. Single NORs were identified in H. brasiliensis and in two populations of H. poeyi (BA and RJ), while multiple NORs were observed in H. radiatus and in H. poeyi from Rio Grande do Norte. The constitutive heterochromatin is reduced and distributed over centromeric and pericentromeric regions. The ribosomal sites allowed differentiating two groups of H. poeyi along the Brazilian coast; one of them comprising the population from RN, bearing multiple NORs, and another representing the populations from BA and RJ, bearing single NORs. The recently separated species, H. brasiliensis and H. radiatus, although presenting similar diploid numbers and chromosomal formulae, could be distinguished by the number of NOR-bearing chromosomes. The results revealed an evolutionary pattern chiefly derived from pericentric inversions. The correlation between larval pelagic phase and cytogenetic data on Labridae indicates that the degree of karyotypic diversification reported within this family, ranging from a highly conserved to a derived pattern, is probably influenced by the species-specific duration of larval pelagic phase.     

Morphological Differences Between Radopholus citrophilus and R. similis

SEM observations of the external morphology of populations of Radopholus citrophilus and R. similis revealed several diagnostic differences. The cloaco-spicular orifice on males of R. citrophilus had three to seven genital papillae (anterior hypoptygmata), whereas males of R. similis were either smooth or had one or two shorter genital papillae (anterior hypoptygmata). Females of R. citrophilus had four annules in the region of the vulval opening, but R. similis had five annules in the same region. The labial disc and lateral lips appeared to be of diagnostic significance, but these areas were more susceptible to artifacts due to fixation. An unknown population of Radopholus from Puerto Rico with a chromosome number of n = 4 was morphologically similar to R. similis. These morphological differences provide additional support that R. citrophilus and R. similis are distinct species.     

Seeing Patterns: Models, Visual Evidence and Pictorial Communication in the Work of Barbara McClintock

Barbara McClintock won the Nobel Prize in 1983 for her discovery of mobile genetic elements. Her Nobel work began in 1944, and by 1950 McClintock began presenting her work on “controlling elements.” McClintock performed her studies through the use of controlled breeding experiments with known mutant stocks, and read the action of controlling elements (transposons) in visible patterns of pigment and starch distribution. She taught close colleagues to “read” the patterns in her maize kernels, “seeing” pigment and starch genes turning on and off. McClintock illustrated her talks and papers on controlling elements or transposons with photographs of the spotted and streaked maize kernels which were both her evidence and the key to her explanations. Transposon action could be read in the patterns by the initiated, but those without step by step instruction by McClintock or experience in maize often found her presentations confusing. The photographs she displayed became both McClintock's means of communication, and a barrier to successful presentation of her results. The photographs also had a second and more subtle effect. As images of patterns arrived at through growth and development of the kernel, they highlight what McClintock believed to be the developmental consequences of transposition, which in McClintock's view was her central contribution, over the mechanism of transposition, for which she was eventually recognized by others. Scientific activities are extremely visual, both at the sites of investigation and in communication through drawings, photographs, and movies. Those visual messages deserve greater scrutiny by historians of science. This revised version was published online in July 2006 with corrections to the Cover Date.     

Cytogenetic comparison and phylogeny of three species of Hylobatidae

Representatives of three subgenera of Hylobatidae, Hylobates (Symphalangus) syndactylus, H. (Nomascus) concolor and H. (Hylobates) agilis were compared karyotypically by G-banding, and silver staining. A greater degree of similarity (30-55%) was found among these groups than previous reports suggest; however, these figures are still considerably lower than chromosome similarities characteristic of all other catarrhine groups. Inversion, translocation, fission, and fusion have all played a role in restructuring hylobatid chromosomes since a common hominoid ancestor. H. syndactylus and H. concolor show the greatest G-band correspondence, and in addition share an unusual C-band distribution and an extremely rare nucleolar organizing region placement (on the Y chromosome). The latter two are probably shared derived traits, suggesting that these two species shared a common ancestor not shared by other hylobatids. These data suggest a branching order for these three hylobatid groups different from those derived by other morphological and biochemical methods.     

Unstable B-chromosomes in a European population of Allium schoenoprasutn L. (Liliaceae)

In Allium schoenoprasum , small, dichromatic B-chromosomes occur in 74% of plants at Lac de Tracens, Pare National des Pyrénées. B-chromosomes from Lac de Tracens were compared with the previously well characterized Bs from British populations of A. schoenoprasum at the River Wye, Powys, and were found to differ in terms of both their morphology and the level of mitotic instability. At Lac de Tracens, two morphological types of B-chromosome were observed: a telocentric of about 1.15 μm in length and a metacentric of about 1.35 μm in length; the most frequent B-type in the River Wye populations (B^-1) was not found. B-chromosomes from the River Wye are essentially stable at root tip mitosis, whereas 25 out of 29 plants from Lac de Tracens (86%) showed between-cell variation in B-number, with non-modal numbers in 330 out of 794 cells (41.6%). Most of the variability occurred within individual roots, rather than between roots of single bulbs or of sister bulbs. No meiotic pairing was observed between the different Bs in hybrids from the geographically isolated populations, suggesting a lack of homology. An independent origin of B-chromosomes in the British and French populations is suggested.     

Chromosome numbers in Compositae. XVIII.

Chromosome numbers and other cytogenetic data were determined from microsporocytes in 316 collections including 13 tribes of Compositae, mostly from Africa, Australia, Mexico, Central America, and South America. First reports are provided for 66 species and the genera Cassinia (2n ≈ 14_II), Feldstonia (2n = 11_II), Gochnatia (2n ≈ 23_II), and Pseudoconyza (n = 10). In addition, new chromosome numbers are established at the generic level in Acourtia, Calea, Craspedia, Gnaphalium, Helipterum, Liabum, Leucheria, Smallanthus, Trixis, and Viguiera and at the specific level in 13 additional species.     

Taxonomy of squirrel monkeys genus Saimiri (Cebidae,platyrrhini): A preliminary report with description of a hitherto unnamed form

Two groups of squirrel monkeys, genus Saimiri, are distinguished by external characters. The first, or Roman type, contains Saimiri boliviensis of upper Amazonia south of the Rio Marañón-Amazonas, with two subspecies of which S. boliviensis peruviensis is described as new. The second group, or Gothic type, contains three species: Saimiri sciureus with four subspecies distributed over much of tropical South America, Saimiri ustus of Brazil between the south bank Amazonian Rios Purús and Xingu, and S. oerstedi isolated on a Pacific coastal area straddling Costa Rica and Panamá. The geographic range of S. sciureus overlaps parts of those of S. ustus and S. boliviensis. Incomplete karyotypic data indicate that the diploid number of chromosomes for the genus is 44. Geographic variation is characterized by reduction from seven to six or five paired acrocentric autosomes through pericentric inversion with reciprocal increase in number of paired submetacentric or subtelocentric autosomes. Geographic distribution, behavior, sexual dimorphism including dichromatism, and hybridization are discussed. Ventral guide hairs for orientation of subprecocial newborn toward the maternal mammae are described. Distinguishing characters of species and subspecies are provided in a key. The taxons are listed with the taxonomy of each discussed, their geographic distribution plotted and mapped.     

Spermatogenesis in Triatoma williami Galvão,Souza and Lima (1965) (Hemiptera,Triatominae)

Cytogenetics has proven to be an important tool in the study of triatomine taxonomy. Triatoma williami is a triatomine that has been classified within the Matogrossensis subcomplex. In this study, the cytogenetic technique of lacto-aceto-orcein was used to confirm the karyotype of this species, which was found to be 2n = 22 (20A + XY). In this study, metaphases I and II were analyzed and the heteropyknotic pattern during the spermatogenesis and spermiogenesis was described, with results that corroborated the classification of T. williami in the Matogrossensis subcomplex.