Differential fluorescent staining of porcine heterochromatin by chromomycin A3/distamycin A/DAPI and D 287/170

C-band fusion and behaviour of the involved chromosomes during meiotic prophase I of the male domestic pig

Behaviour of acrocentric chromosome synaptonemal complexes (SCs) and constitutive heterochromatin (C-band) during meiotic prophase I of the male domestic pig was studied using surface spreading and silver staining techniques. At late zygotene C-band regions of complete or incomplete SCs of the acrocentric chromosomes are represented by enlarged structures. At the same time these structures commenced fusion, which is accomplished at pachytene. Using kinetochores and NORs as markers, the pachytene metacentric, acrocentric, and nucleolar SCs can be distinguished. In 96.7% of the pachytene nuclei, either all or some of the acrocentric SCs are associated at their centromeric regions, forming one or two large globular or shapeless masses that represent chromocenters. The SCs are assorted at random in all types of association except in single association of all the SCs. Order of associated SCs varies from one association to another. The C-band region of SC, the portion inside the chromocenter core, is differentiated as thicker and darker structures from the chromocenter mass. A silver-positive core-like structure in meiotic chromosome C-bands, probably a vector for meiotic C-band ectopic pairing, provides faithful representations of C-band behaviour during meiosis.

Alkali-labile sites in sperm cells from Sus and Ovis species

Constitutive alkali-labile sites (ALSs) have been investigated using a protocol of DNA breakage detection-fluorescence in situ hybridization (DBD-FISH) in sperm cells from Sus domesticus (pig), Ovis gmelini musimon (mouflon) and Ovis aries (sheep). The results were compared with those obtained using leucocytes from the same species. Whole comparative genomic hybridization (W-CGH) showed that most of the constitutive ALSs in somatic and germ line cells in all species examined were constrained to particular repetitive satellite DNA sequences located in the pericentromeric constitutive heterochromatin of each chromosome. However, their relative abundance was different among cells of the same organism (leucocytes/sperm cells), and this trend was not maintained when the different species were compared. Thus, in mouflon, the density of ALSs in leucocytes when compared with that observed in sperm cells indicated abundance of the order of eight times less. In sheep, both leucocytes and sperm cells exhibited a large quantity of ALSs, being of the order of four times more abundant in sperm cells. In the pig genome, leucocytes showed a high abundance of ALSs (of the order of 12 times more that in sperm cells) but only involved the metacentric chromosomes of the karyotype. ALSs were not present in the acrocentric chromosomes. Contrary to mouflon and sheep, ALSs were relatively scarce in sperm cells from pig. These results suggest that ALSs are a transient structural feature in the cells of any organisms and point to a non-universal model of chromatin organization in sperm cells among mammals.

Effect of salinity on osmoregulatory patch epithelia in gills of the blue crab Callinectes sapidus

In euryhaline crabs, ion-transporting cells are clustered into osmoregulatory patches on the lamellae of the posterior gills. To examine changes in the branchial osmoregulatory patch in the blue crab Callinectes sapidus in response to change in salinity and to correlate these changes with other osmoregulatory responses, crabs were acclimated to a range of salinities between 10 and 35 ppt. When crabs that had been acclimated to 35 ppt were subsequently transferred to 10 ppt, both the size of the osmoregulatory patch on individual gill lamellae and the specific activity of Na+, K+-ATPase in whole-gill homogenates increased only after the first 24 h of exposure to dilute seawater. Enzyme activity and size of patch area increased gradually and reached their maxima (increasing by 200% and 60%, respectively) 6 days following transfer to 10 ppt seawater and then remained at these levels. Patch size at acclimation varied inversely with the salinity for seawater dilutions below 26 ppt (the isosmotic point of the crab), although it did not vary in salinities at or above 26 ppt. Thus, the size of the patch clearly is modulated with acclimation salinity, but it increases only in those salinities in which the crab hyperosmoregulates. An increase in the total RNA/DNA ratio in gill homogenates, the lack of mitotic figures in the lamellae, and the lack of incorporation of bromodeoxyuridine into nuclei of lamellar epithelial cells during acclimation to dilute seawater were interpreted as evidence that no cell proliferation had occurred and that increases in the size of the osmoregulatory patch occurred through differentiation of existing gas exchange cells or of undifferentiated epithelial cells into ion-transporting cells.

Chromosome restriction enzyme digestion in domestic pig (Sus scrofa) constitutive heterochromatin arrangement

The bimodal karyotype of pig appears to contain two types of constitutive heterochromatin, reflecting different satellite DNA families: GC-rich heterochromatin located mainly in the centromeric regions of the biarmed chromosomes, and less-GC-rich heterochromatin in the centromeric regions of the one-armed chromosomes. In order to better discriminate this constitutive heterochromatin, we treated pig chromosome preparations with eight different restriction endonucleases, followed by C-banding. This technique allowed an expedited characterization of the constitutive heterochromatin and demonstrated its great heterogeneity in pig chromosomes. Our work allowed the detection and identification of twenty-two heterochromatin subclasses (twelve centromeric, four interstitial, five telomeric, and the Yq band). Moreover, several cryptic interstitial and telomeric bands were revealed. The work presented here is useful not only for fundamental studies of chromosome banding and constitutive heterochromatin, but also offers a new approach for pig clinical cytogenetics.

FISH mapping and sequence analysis of 87 porcine BAC clones

Ninety-one bacterial artificial chromosomes (BAC) clones, selected effectively at random from our library, were used as probes for fluorescence in situ hybridization. Of these, 87 clones gave a specific signal in one, two or three different pair(s) of swine metaphase chromosomes. The ends of 35 BAC clones were sequenced in order to obtain information for comparative mapping. Fifteen of them gave useful comparative mapping information.

Microdissection of pig chromosomes: dissection of whole chromosomes, arms and bands for construction of paints and libraries

Chromosome microdissection is an important means to efficiently generate a large number of markers from a desired region of a genome. The present study was designed to initiate microdissection and amplification of DNA from whole chromosomes, arms, or bands of porcine chromosomes. The following pig (SSC) chromosomes/segments were scraped: SSC1p, SSC1q26-q2.13, SSC2q11-q14, SSC4q12-q25, SSC13, SSC13q12-q31, SSC13q32-q43, SSC13q32-q43, SSC15, and SSC16q21-q23. After amplification and PCR-labelling, the DNA from the dissected segments were painted back to normal metaphase chromosomes to test their identity. Microdissection of some of the segments (on SSC4, 13 and 15) coincides with the mapping of economically important traits. As a first step towards generation of markers, microcloning of amplified product from SSC1p and SSC15 was carried out. The libraries were screened with a (GT)15 oligonucleotide probe. Future prospects of such a work in farm animals are discussed.

Chromosomal variation in pocket gophers (Geomys) detected by sequential G-, R-, and C-band analyses

The chromosomes of six taxa, representing five species of Geomys (G. attwateri, G. breviceps, G. personatus, G. texensis, G. bursarius) were analysed for variation in G-band, R-band, sequential R-/DAPI-AMD, and sequential R-/C-band patterns. Eleven chromosomes had structural rearrangements resulting from deletion/addition events. Fission/fusion rearrangements occurred in two chromosomes, and a pericentric inversion was confirmed in only one chromosome. Eighteen of 34 autosomes had constitutive heterochromatin, with variation in its presence or absence, position, and quantity. The heterochromatic differences were seen both among species and between two subspecies of G. personatus. Chromomycin A3 fluorescent staining identified G-C rich regions in 31 of the autosomes with 29 showing variation in their presence or absence, position, and quantity, and identified a high degree of cryptic variation. The X chromosome was highly variable, with differences attributable to structural rearrangements and variation in chromomycin bright-staining regions.

C-banding with specific fluorescent DNA-ligands: a new approach to constitutive heterochromatin heterogeneity

The employment of certain DNA-specific fluorescent stains on unbanded and C-banded chromosomes of two species of grasshoppers shows remarkable differences among C-heterochromatic regions supposed to be similar in their base pair composition, according to their response to the standard fluorescence techniques. The possible interspersion of the opposite DNA base pairs in these regions as well as the role played by proteins in chromosome banding are discussed.

Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin

Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540-546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.

Evolutionary diversity of reverse (R) fluorescent chromosome bands in vertebrates

Mitotic chromosomes, interphase cell nuclei, and male meiosis of 41 species representing all vertebrate classes were analyzed with distamycin A/mithramycin counterstaining. The purpose of the study was to recognize differences and common characteristics in the reverse (R) fluorescent banding patterns in the chromosomes of vertebrate species at various stages of evolution. In contrast to the warm-blooded mammals and birds, the euchromatic segments in the chromosomes of most reptiles, amphibians, and fishes contain no multiple fluorescent R-bands. This is thought to be due to the absence of the long homogeneous regions (isochores) in the DNA of the cold-blooded vertebrates. Distamycin A/mithramycin banding specifically reveals the GC-rich constitutive heterochromatin in all vertebrates. In most of the vertebrate chromosomes examined, the heterochromatic regions have opposite staining properties with mithramycin and quinacrine. Mithramycin labels the nucleolus organizer regions very brightly in the karyotypes of fishes, amphibians, reptiles and birds, but not of mammals. The lack of mithramycin fluorescence at the nucleolus organizer regions of mammals is attributed to the relatively low level of redundancy of the GC-rich ribosomal DNA in their genomes. Studies on the various meiotic stages of the cold-blooded vertebrates show that the mithramycin labeling of the nucleolus organizers is independent of their state of activity. This can be confirmed by mithramycin fluorescence at the nucleoli of actinomycin-treated cells.

Fluorescent chromosome banding in inbred chicken: quinacrine bands, sequential chromomycin and Dapi bands

Highly inbred White Leghorn chickens were used for an investigation of the banding pattern of the macrochromosomes. A standard was set for the Q-bands. GC-specific fluorochrome chromomycin and the AT-specific Dapi were used in a sequential stain. The comparison of these two stains disclosed quantitative differences in the base distribution of the DNA. Factors responsibe for the binding mechanism and the appearance of the bands are discussed.

Genome evolution in pocket gophers (genus Thomomys). III. Fluorochrome-revealed heterochromatin heterogeneity

Heterochromatin is a dominant component of the genome in the bottae group of the pocket gopher genus Thomomys, having had a major role in the karyotypic evolution of member species. Heterochromatin characteristics of two subspecies of T. bottae and one of T. umbrinus were examined with fluorochrome dyes identifying presumptive GC- and AT-rich regions. In two karyotype forms of T. b. fulvus and in T. umbrinus, chromatin that fluoresces brightly with chromomycin A3 is also C-band positive, although not all heterochromatin fluoresces. However, in T. b. bottae, only euchromatic regions fluoresce brightly with chromomycin. Fluorescence patterns produced with DAPI are the reverse of the chromomycin banding in all karyotypic forms. Heterochromatin in these taxa is thus highly differentiated, exhibiting heterogeneity in staining characteristics, and presumably in underlying DNA sequences, both across the genome within a given chromosomal complement as well as among the different karyotypic races and species of the bottae group of pocket gophers.

Heterochromatin and nucleolus-organizer-region behaviour at male pachytene of Sus scrofa domestica

In the domestic pig (2n = 38) two types of constitutive heterochromatin can be differentiated by fluorescence counterstaining techniques. All 24 biarmed autosomes and the X chromosome have chromomycin A3-positive centromeric C-bands, whereas all 12 acrocentric chromosomes exhibit DA-DAPI-positive centromeric heterochromatin. Fluorescence analysis of male pachytene nuclei revealed that the DA-DAPI-positive C-bands form one or two large chromocentres per cell, while the chromomycin A3-bright C-material is well scattered. Hence, the bivalents formed by the acrocentric chromosome pairs are centromerically associated, whilst the submetacentric bivalents are not. Counce-Meyer spreading techniques were used to study the structure of synaptonemal complexes (SCs) both by light and electron microscopy. In general, the SCs of the domestic pig resemble those described for other mammals. The SC formed by the X and the Y may include up to 94.5% of the Y chromosome. In silver-stained microspreads each of the bivalents (nos. 8 and 10) bearing the nucleolus-organizer-regions (NORs) is connected to a pair of nucleoli, indicating that all four NORs are active during early meiotic stages. By contrast, in the majority of mitotic metaphases of phytohaemagglutinin-stimulated lymphocytes only one pair (no. 10) exhibited Ag-NOR staining. The significance of the chromosome disposition in the pachytene nucleus is discussed with regard to heterochromatin composition and karyotype evolution.