PubMed Health⌕ Search

Biomedical subjects

E Capanna

Publications and source records attributed to E Capanna.

At least 19 recordsLinked to original sources
PubMed2003

Cytogenetics of the genus Arvicanthis (Rodentia, Muridae). 3. Comparative cytogenetics of A. neumanni and A. nairobae from Tanzania.

The African rats of the genus Arvicanthis have been widely studied during recent years to clarify species boundaries and phylogenetic relationships. The wide chromosomal variability of the genus has been highlighted in several studies, with each accepted species characterised by its individual karyotypes and others being revealed as cryptic species. In the present paper we report the karyotype and the C- and G-banding patterns of the two species A. nairobae and A. neumanni from seven localities of Tanzania, an area of the range poorly studied. The two karyotypes were compared to that of A. niloticus, which is considered to be primitive. The karyotype of A. neumanni is characterised by 2n = 53-54 and NFa = 62. This karyotypic variability depends on a widespread Robertsonian polymorphism. The karyotype of A. nairobae shows 2n = 62 and NFa = 78; it diverges from that of A. niloticus through one reciprocal translocation, five inversions and three heterochromatic additions. The comparison with the karyotypes of other species of the genus showed that A. neumanni belongs to the east African lineage (with A. abyssinicus, A. blicki, A. niloticus), while A. nairobae is closer to the central and the west African representatives which were all previously under the name of A. niloticus (ANI-2, ANI-3, ANI-4). The distribution of A. nairobae in east Africa opens new scenarios in the biogeographical pattern of evolution of the genus.

Animals↗
PubMed2002

Contact zones between chromosomal races of Mus musculus domesticus. 3. Molecular and chromosomal evidence of restricted gene flow between the CD race (2n = 22) and the ACR race (2n = 24).

The contact zone between the Ancarano (ACR; 2n = 24) and Cittaducale (CD; 2n = 22) races of Mus musculus domesticus was studied. We used chromosomes and mitochondrial DNA (mtDNA) sequences of the control region as genetic markers to detect introgression between races. In total, 76 mice were trapped at 17 localities. Cytogenetic analysis was performed on 73 mice. A segment of the control region (468 bp) was sequenced in 41 specimens. The two races are distributed parapatrically and the contact zone was identified inside a village (Pizzoli). No mixed population was found in the study area. The contact zone does not correspond to any geographical or ecological barrier but is located in a zone of potentially high density of mice. The sequence analysis clearly demonstrates genetic differentiation between races (1.4% of sequence divergence). Hybridization is rare. Evidence of introgression was found in two individuals in the contact zone: one individual of the ACR race carries a metacentric belonging to the CD race, while another ACR individual carries a CD-like haplotype. In these ecological conditions, the observed distribution pattern and the very low level of hybridization suggest the presence of a premating mechanism of reproductive isolation.

Animals↗
PubMed2002

High-resolution organization of mouse telomeric and pericentromeric DNA.

We studied the organization of telomeric, major and minor satellite DNA sequences located in the pericentromeric regions of mouse telocentric and Robertsonian metacentric chromosomes by high-resolution fluorescence in situ hybridization. Molecular data have already proved that in telocentrics, from the physical chromosome end, telomeric sequences are followed by minor and then by major satellite DNA. We showed that the three families of repetitive DNA are organized as uninterrupted long-range cluster repeats and that there is no intermingling between telomeric and minor satellite DNA or between the major and the minor tandem repeats or with non-satellite DNA. The pericentromeric region of metacentric chromosomes consists of a small block of minor satellite DNA sandwiched between two blocks of major satellite DNA.

Animals↗
PubMed2002

Chromosomal characterization of Arvicanthis species (Rodentia, Murinae) from western and central Africa: implications for taxonomy.

A chromosome study of unstriped grass rats of the genus Arvicanthis (Rodentia, Murinae) in western and central Africa is presented. The observations extend the data available to 242 specimens from 59 localities. All individuals karyotyped belong to four karyotypic forms, or cytotypes, earlier described as ANI-1, ANI-2, ANI-3, and ANI-4 and are presumed to correspond to four distinct species. In order to provide diagnostic characters for these western and one central African Arvicanthis species, we standardized the chromosomal data available and developed a G- and C-banded chromosome nomenclature that allows easy species identification. Each form is characterized by a distinct geographical distribution, roughly following the biogeographical domains of western Africa, although their precise limits remain to be assessed. The sole area of sympatry detected is the region of the inner delta of the Niger River, where both ANI-1 and ANI-3 can be found. It is proposed that the three western African species ANI-1, ANI-3, and ANI-4 be renamed as A. niloticus, A. ansorgei, and A. rufinus, respectively.

Animals↗
PubMed2001

Pericentromeric organization at the fusion point of mouse Robertsonian translocation chromosomes.

In mammals, Robertsonian (Rb) translocation (the joining of two telo/acrocentric chromosomes at their centromere to form a metacentric) is the most effective process in chromosomal evolution leading to speciation; its occurrence also affects human health (through the induction of trisomies) and the fertility of farm animals. To understand the mechanism of Rb translocation, we used the house mouse as a model system and studied the organization of pericentromeric satellite DNAs (satDNA) of telocentrics and Rb chromosomes, both minor and major satDNA. The chromosome-orientation fluorescence in situ hybridization (CO-FISH) technique was used to analyze the major satDNA. To detect the very small amount of minor satDNA, a procedure was developed that combines CO-FISH with primed in situ labeling and conventional FISH and is five times more sensitive than the CO-FISH procedure alone. It was found that both the major and the minor satDNA tandem repeats are oriented head-to-tail in telocentric and Rb chromosomes, and their polarity is always the same relative to the centromere. We suggest that all tandemly repetitive satDNAs in a species probably are locked into such a symmetry constraint as a universal consequence of chromosomal evolution. Rb translocation breakpoints were found localized within the minor satDNA of telocentrics, and these sequences contributed symmetrically to the formation of the centromeric region of the Rb chromosomes. These results are important for an understanding of the geometry of Rb translocations and suggest the study of DNA orientation as a new tool for investigating these rearrangements.

Animals↗
PubMed2001

The other chromatin.

Current understanding of heterochromatin, thanks to molecular data, focuses on its performing several functions in evolution and development. Heterochromatin shows characteristic distribution patterns in karyotypes and contributes to the broad scattering of genome sizes through biological taxa. Heterochromatin remains compacted and thus different from properly stained euchromatin during somatic interphase. A minimum amount of heterochromatin, however, is required for it to be visible in light microscopy. It may further escape notice during the dynamic processes of embryogenesis and gametogenesis. Present-day biology is in search of specific proteins and DNA sequences that comprise heterochromatin. The data that result from overcoming the threshold of visibility will support understanding of interference by heterochromatin in ontogeny and evolution. The contributions of Sigrid and Wolfgang Beermann to the study of heterochromation diminution (DNA elimination) are recalled, and we also discuss the functions and effects of heterochromatin on differential DNA endoreplication and in speciation.

Animals↗
PubMed2001

Alteration of nuclear architecture in male germ cells of chromosomally derived subfertile mice.

The mammalian cell nucleus consists of numerous compartments involved in the regular unfolding of processes such as DNA replication and transcription, RNA maturation, protein synthesis and cell division. Knowledge is increasing of the relationships between high-order levels of chromatin organization and its spatial organization, and of how these relationships contribute to the various functions carried out in the nucleus. We have studied the spatial arrangement of mouse telocentric chromosomes 5, 11, 13, 15, 16 and 17, some of their metacentric Robertsonian derivatives, and X and Y chromosomes by whole chromosome painting in male germ (spermatogonia, pachytene spermatocytes and spermatids) and Sertoli cells of homozygous and heterozygous individuals. Using dual-colour fluorescence in situ hybridization we found that these chromosomes occupy specific nuclear territories in each cell type analysed. When chromosomes are present as Robertsonian metacentrics in the heterozygous state, that is, as Robertsonian metacentrics and their homologous telocentrics, differences in their nuclear positions are detectable: heterozygosity regularly produces a change in the nuclear position of one of the two homologous telocentrics in all the cell types studied. In the Robertsonian heterozygotes, the vast majority of the Sertoli cells show the sex chromosomes in a condensed state, whereas they appear decondensed in the Robertsonian homozygotes. As the Robertsonian heterozygosities we studied produce a chromosomally derived impairment of male germ-cell differentiation, we discuss the possibility that changes in chromosome spatial territories may alter some nuclear machinery (e.g., synapsis, differential gene expression) important for the correct unfolding of the meiotic process and for the proper functioning of Sertoli cells.

Animals↗
PubMed2000

Female gonad of moles, genus Talpa (Insectivora, mammalia): ovary or ovotestis?

The female gonads of moles (genus Talpa) are composed of a cortex, functioning as an ovary, and a medulla, which is structurally similar to that of the testis. In the female reproductive apparatus there are masculine glandular annexes, such as a bilobate prostate, two Cowper glands, and a penis-like clitoris. All these features have recently led to the hypothesis of the presence of hermaphroditism due to sex-reversal in Talpa. The purpose of this study is to understand the functional significance of the structural organization of the female gonads in order to verify this hypothesis. Histological, histochemical and ultrastructural analyses have been carried out on several gonads of both sexes of two species: T. europaea and T. romana, including three fetuses. In both species, the cortical region of the female gonad shows a regular oogenetic activity. While the medulla is composed of interstitial cells that are partly organized in cord-like structures, no spermatogenetic activity has been ever observed inside of them. A histochemical analysis shows that in both sexes the interstitial cells secrete steroids, presumably estrogens as well as androgens. The presence of androgens in the female gonads would therefore explain the persistence of male glandular annexes in the female reproductive apparatus and both the sexual and behavioral monomorphism typical of the genus Talpa. Nonetheless, the female gonad of moles is a real ovary and a well-defined gonochorism exists. Therefore, there is no reason to assert the presence of hermaphroditism due to sex reversal.

Androgens↗
PubMed2000

Allozyme variation and divergence in the phyllotine rodent Calomys hummelincki (Husson, 1960).

The aim of the present study was to assess the degree of genetic variation and divergence among six populations of Calomys hummelincki, a phyllotine rodent distributed in northern South America. With this information we will try to evaluate the two hypotheses of possible colonization and differentiation of this group of rodents postulated by Baskin and Reig. We studied 34 loci by electrophoretic analysis: 21 were monomorphic for all populations and 13 were polymorphic in at least one population, being P1% = 21.6% the mean value for all populations. The mean value of heterozygosity per locus was H = 0.075. Low values of genetic distance were observed among populations of the Llanos region (0.001 < D < 0.006). There was a larger genetic distance (D = 0.024) between the population from Isiro, in the northwestern semiarid region, and those from the Llanos region. The insular population of Aruba displayed the lowest value of genetic distance with the population from Isiro (D=0.014). The specimens from Sipao, on the right side of the Orinoco river, displayed the highest values of genetic distances in comparison with other populations of C. hummelincki (0.070 < D < 0.095). The relatively high differentiation was due to the fixation of new alleles, not found in other populations of C. hummelincki, at loci Idh-1 and Est-2. F-statistics and Nm values indicated reduced gene flow among the populations sampled. Despite the limited data, the results seem to support Reig's hypothesis about south to north colonization of genus Calomys in South America.

Alleles↗
PubMed2000

Contact zone between chromosomal races of Mus musculus domesticus. 2. Fertility and segregation in laboratory-reared and wild mice heterozygous for multiple robertsonian rearrangements.

Litter size, anaphase I nondisjunction and X-Y dissociation at metaphase I were studied in homozygous and heterozygous house mice from a central Italian chromosomal hybrid zone between the CD (2n=22) race and the standard race (2n=40). We also observed the segregation of the two chromosomal forms (Robertsonian and non-Robertsonian) in male and female multiple heterozygotes from the karyotype of their offspring and chromosomal arm counts of metaphase II. Litter size was significantly reduced in the F1 hybrids, but there was no difference in litter size between male and female F1s. Fertility in wild mice decreased with increasing numbers of structural heterozygosities (0-5). Some metacentrics appear to be under meiotic drive but there was no rule as to which of the two forms was favoured in backcrosses. An original observation of a negative correlation between the length of metacentrics and transmission rate was described in hybrids. Slight cosegregation of chromosomes with a similar morphology was present in the progeny of males and females. These observations are discussed in relation to the stability of this hybrid zone through time.

Anaphase↗
PubMed1999

Lazzaro Spallanzani: At the roots of modern biology.

The scientific work of Lazzaro Spallanzani is outlined, with emphasis on the elements of originality in his introduction of the experimental method in biology. Particular stress is placed on Spallanzani's contribution to solving the Theoria Generationis, from the problems connected with the spontaneous generation of living creatures to those of natural fertilization and artificial insemination and, finally, those of regeneration. J. Exp. Zool. (Mol. Dev. Evol.) 285:178-196, 1999.

Biology↗
PubMed1999

Contact zones between chromosomal races of Mus musculus domesticus. 1. Temporal analysis of a hybrid zone between the CD chromosomal race (2n=22) and populations with the standard karyotype.

A temporal analysis of a hybrid zone between chromosomal races of Mus musculus domesticus was performed to evaluate its dynamics over a 20-year period. The transect chosen was one previously analysed by Spirito et al. (1980) across the hycbrid zone between the chromosomal race CD 2n=22 (central Italy) and the surrounding populations with standard karyotype (2n=40). The results show that 20 years of hybridization have not had any significant effect on the position of this hybrid zone, nor on the location of its extreme margin, except for one site for which passive transport of mice may have been important. The absence of a significant shift of the tension zone excludes a possible imbalance between the two cytotypes; a fitness superiority of one homozygote greater than 0.01 would have produced an appreciable shift of the zone. The internal chromosomal structure of the zone shows a constant gradual increase in metacentric chromosome frequency towards the localities nearest the area inhabited by the 22-CD homozygote population. This contrasts with the previously reported data which indicated an irregular trend, particularly evident for the Rb(3.8), Rb(5.17) and Rb(6.13) chromosomes. For each Rb metacentric, we observed greater values of FST in the past sample than in the present one. These differences reveal a tendency towards the homogenization of adjacent populations, perhaps because of greater migration between adjacent demes resulting from increased commercial traffic. The Mantel test was performed for both temporal samples. A positive correlation between the geographical and chromosomal differentiation was demonstrated.

Animals↗
PubMed1998

[Grassi's archives of the museum of comparative anatomy of Rome University "La Sapienza"].

The documents, reprints, books, correspondence of Grassi, found in his room at the University of Rome when he died, have been kept in the Institute of Comparative Anatomy, directed by Grassi himself from 1896 until 1925. This fund keeps documents concerning the whole life of the scientist, with a special reference to the Roman period. Numerous are the documents concerning his malariological studies between 1898 and 1910. A first reconaissance has been made in 1980 and then, twice in 1994 and 1998, the fund has been reorganized and an inventory of it has been made. It is collected in 48 boxes containing archivistic documents, 11 boxes of reprints and other publications. The inventory of archival documents has been computerized.

Academies and Institutes↗
PubMed1997

Genome composition in Venezuelan spiny-rats of the genus Proechimys(Rodentia, Echimyidae). I. Genome size, C-heterochromatin and repetitive DNAs in situ hybridization patterns.

The genome sizes of the Venezuelan spiny-rats Proechimys guairae guairae (2n = 48) and P. trinitatis (2n = 62) were evaluated and proved to be 12.5 +/- 0.5 pg and 12.6 +/- 0.3 pg respectively, the highest so far recorded among mammals; also the C-heterochromatin (32.7%, Coefficient of Variation [CV] 3.8 and 35.8%, CV 4.4) and GC (44.2%, CV 2.7 and 43.6%, CV 2.9) contents are very high. Highly repetitive (rep) DNAs were isolated from restriction enzyme digested genomic DNAs of both species. The intra- and inter-specific chromosomal allocations of these rep DNAs were analyzed by direct and cross-hybridizations. Results show that the two genomes harbour several rep DNA families which show both species-specificity and interspecific relatedness in their in situ hybridization patterns. The rep DNA families show an equilocal distribution at both the pericentromeric areas of all chromosomes and in the whole arms of two pairs of the uniarmed group, suggesting co-evolution of the rep DNAs. P. g. guairae BamHI digested DNA, when cloned and sequenced, proved to consist of a long "composite" unit (1,239 bp) containing two copies of each of 75-bp and 110-bp internal subrepeats. Karyotype restructuring between P. g. guairae and P. trinitatis, mainly due to Robertsonian changes, was accompanied by slight intra- and intergenomic movements of the putative satellite DNA families within stable genome sizes and C-heterochromatin contents. We discuss the findings obtained in Proechimys in the light of those regarding the kangaroo rat, the pocket gopher and the house mouse; they support the idea that karyotype restructuring could be the expression of molecular driven events of rep DNA amplification and homogenisation through non-homologous chromosomes.

Animals↗
PubMed1995

Robertsonian metacentrics of the house mouse lose telomeric sequences but retain some minor satellite DNA in the pericentromeric area.

A combination of cytogenetic and molecular biology techniques were used to study the molecular composition and organisation of the pericentromeric regions of house mouse metacentric chromosomes, the products of Robertsonian (Rb) translocations between telocentrics. Regardless of whether mitotic or meiotic preparations were used, in situ hybridisation failed to reveal pericentromeric telomeric sequences on any of the Rb chromosomes, while all metacentrics retained detectable, although reduced (average 50 kb), amounts of minor satellite DNA in the vicinity of their centromeres. These results were supported by slot blot hybridisation which indicated that mice with 2n=22 Rb chromosomes have 65% of telomeric sequences (which are allocated to the distal telomeres of both Rb and telocentric chromosomes and to the proximal telomeres of telocentrics) and 15% the amount of minor satellite, compared with mice with 2n=40 all-telocentric chromosomes. Pulsed field gel electrophoresis and Southern analysis of DNA from Rb mice showed that the size of the telomeric arrays is similar to that of mice with all-telocentric chromosomes and that the minor satellite sequences were hybridising to larger fragments incorporating major satellite DNA. Since the telomeric sequences are closer to the physical end of the chromosome than the minor satellite sequences, the absence of telomeric sequences and the reduced amount of minor satellite sequences at the pericentromeric region of the Rb metacentrics suggest that the breakpoints for the Rb translocation occur very close to the minor satellite-major satellite border. Moreover, it is likely that the minor satellite is required for centromeric function, 50-67 kb being enough DNA to organise one centromere with a functionally active kinetochore.

Animals↗
PubMed1995

Whole-arm reciprocal translocation (WART) between Robertsonian chromosomes: finding of a Robertsonian heterozygous mouse with karyotype derived through WARTs.

The karyotype of a mouse trapped in a hybrid zone between a Robertsonian (Rb) population (2n = 22) and a population with the standard karyotype (2n = 40-alltelocentrics) shows two Rb chromosomes with new arm compositions. We suggest that whole-arm reciprocal translocations between Rb chromosomes gave rise to the new chromosome constitution and that such events can greatly help in understanding house mouse karyotype diversification and chromosomal speciation.

Animals↗