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J B Searle

Publications and source records attributed to J B Searle.

At least 37 records · Page 2Linked to original sources
PubMed1998

Chromosomal segregation and fertility in Robertsonian chromosomal heterozygotes of the house musk shrew (Suncus murinus, Insectivora, Soricidae).

Crucial to our understanding of chromosomal variation and evolution in mammals are detailed studies of chromosomal heterozygotes, with analyses of chromosomal segregation and chromosome-derived infertility. We studied segregation and fertility in hybrids between karyotypic races of the house musk shrew Suncus murinus. These individuals were heterozygous for up to five Robertsonian fusions (Rbs) and an insertion of heterochromatin in an autosome. All variant chromosomes showed Mendelian segregation and all Rbs segregated independently of each other in the progeny of double heterozygotes. Litter size in single and even multiple Rb heterozygotes was no smaller than that in the less fertile parental strain. The effects of genetic background were more important in determining litter size than Rb heterozygosity for the shrews that we examined.

Animals↗
PubMed1998

Chromosomal heterozygosity and fertility in house mice (Mus musculus domesticus) from Northern Italy.

Following the discovery of over 40 Robertsonian (Rb) races of Mus musculus domesticus in Europe and North Africa, the house mouse has been studied extensively as an ideal model to determine the chromosomal changes that may cause or accompany speciation. Current models of chromosomal speciation are based on the assumption that heterozygous individuals have a particularly low fertility, although recent studies indicate otherwise. Despite their importance, fertility estimates for the house mouse are incomplete because traditional measurements, such as anaphase I nondisjunction and germ cell death, are rarely estimated in conjunction with litter size. In an attempt to bridge this gap, we have taken advantage of the house mouse hybrid zone in Upper Valtellina (Lombardy, Italy) in which five Rb races interbreed. We present data on the fertility of naturally occurring ("wild-caught") hybrids and of offspring from laboratory crosses of wild-caught mice ("laboratory-reared"), using various measurements. Wild-caught mice heterozygous for one fusion were more infertile than predicted from past studies, possibly due to genic hybridity; laboratory-reared heterozygotes carrying seven or eight trivalents at meiosis I and heterozygotes carrying one pentavalent also had low fertilities. These low fertilities are especially significant given the probable occurrence of a reinforcement event in Upper Valtellina.

Animals↗
PubMed1997

Genetic distinctiveness of a village population of house mice: relevance to speciation and chromosomal evolution.

A population of house mice, Mus musculus domesticus, from the village of Migiondo was found to be genetically distinct from nearby populations in Upper Valtellina (Italian Alps). At the supernatant malic enzyme locus, Mod1, the only alleles found in Migiondo (c and n2) were virtually absent from the other populations in the valley, which were characterized by allele a. The extraordinary genetic distinctiveness of the Migiondo population is apparently the result of genetic drift, perhaps coupled with a founder event, and attests to the existence of nearly impenetrable geographic barriers around the village isolating it from other settlements only a few hundred metres away. The Mod1 features of the house mice in Migiondo are reminiscent of the characteristics of house mice on maritime islands. The genetic confirmation of the geographic isolation of Migiondo is of interest because there is evidence that this village may have been the site of recent speciation and extinction events. The data are also of significance given the phenomenal chromosomal variation in house mice from the vicinity of the Alps. It has frequently been proposed that genetic drift/founder events are of importance in the fixation of chromosomal rearrangements; this study provides the first direct evidence for their occurrence in alpine mouse populations.

Alleles↗
PubMed1997

Novosibirsk revisited 24 years on: chromosome polymorphism in the Novosibirsk population of the common shrew Sorex araneus L.

A Robertsonian fusion polymorphism in the common shrew (Sorex araneus L.), first described in Academgorodok near Novosibirsk (western Siberia) in 1970-72, was re-examined in 1994-95. The polymorphism in the 1970s involved chromosome arm combinations go, jl, mp and qr, i.e. each of these combinations was present in both a metacentric and a twin-acrocentric state in the population at that time. The twin-acrocentric morph for go occurred at low frequency in 1970-72 and was not observed in 1994-95. The polymorphism for arm combinations jl, mp and qr was still observed in 1994-95 and there was no significant difference in metacentric/twin-acrocentric frequencies compared with the previous sample. This is the third well-documented example in which the chromosome polymorphism in the common shrew has been found to be unchanged over a period of 20+ years. Although the polymorphism for qr may be associated with a chromosomal hybrid zone with a cline centre 200 km away, there is no definitive explanation for the other polymorphisms.

Animals↗
PubMed1997

Robertsonian chromosomal variation in the house musk shrew (Suncus murinus, Insectivora:Soricidae) and the colonization history of the species.

A high-resolution G-banding technique was used to identify five metacentrics that characterize Suncus murinus from Sri Lanka. These metacentrics were shown to be the product of Robertsonian fusion of acrocentric chromosomes identical to those in the standard karyotype defined by M.B. Rogatcheva et al. Two of the metacentrics in the Sri Lankan shrews (Rb(10.12) and Rb(14.15)) were the same as those reported by C.H. Sam et al. in Malayan populations of S. murinus. This finding provides strong support for the suggestion of T.H. Yosida that metacentric-carrying shrews colonized Malaya from Sri Lanka and hybridized with individuals of standard karyotype, generating the Robertsonian polymorphism now observed. In addition to the Robertsonian variation in S. murinus, we have used our high resolution technique (G- and C-banding) to characterize variants on chromosome 7, the X chromosome, and the Y chromosome.

Animals↗
PubMed1997

Chromosome location of sixteen genes in the common shrew, Sorex araneus L. (Mammalia, Insectivora).

This report extends the genetic map of the common shrew (Sorex araneus) by use of a clone panel of shrew-Chinese hamster and shrew-mouse hybrid cells (Pack et al., 1995; Matyakhina et al., 1996). This set of hybrid clones made it possible to assign the shrew genes for isocitrate dehydrogenase 2 (IDH2), inorganic pyrophosphatase (PP), glutamicpyruvate transaminase (GPT), adenosine kinase (ADK), glucuronidase 2 (GUSB) and acid phosphatase 2 (ACP2) to chromosome ik; the genes for adenylate kinases 1 and 3 (AK1 and AK3) to chromosome af; the genes for glutamate-oxaloacetate transaminase 2 (GOT2), peptidase D (PEPD) and growth hormone (GH) to chromosome hn; the gene for phosphoglucomutase 2 (PGM2) to chromosome go, the gene for enolase 1 (ENO1) to chromosome ji, the gene for ornithine carbamoyl-transferase (OTC) to chromosome de, the gene for aminoacylase 1 (ACY1) to arm m (chromosome mp), the gene for glutamate-oxaloacetate transaminase 1 (GOT1) to arm q (chromosome qr). Thus, the genetic map of the common shrew now contains 33 genes and it is possible to compare the syntenic associations with other species.

Animals↗
PubMed1996

Corticosterone and interchromosomal race discrimination in the house mouse.

We report results of a study on emotional arousal, as reflected by corticosterone variation, following dyadic encounters within and between chromosomal races of the house mouse (Mus musculus domesticus). Three contiguous chromosomal races from northeast Scotland were analyzed (2n = 32, 2n = 36, 2n = 40). Within-race encounters resulted in similar average corticosterone levels in mice from the three races. For all three races, certain of the between-race encounters resulted in a significant increase in corticosterone relative to those following within-race encounters. These results confirm our previous observations of a differential behavioral treatment of house mice from the same vs from a different chromosomal race, and support our proposition for behavioral discrimination between chromosomal races of this species in northeast Scotland.

Aggression↗
PubMed1996

Chromosome localization of the loci for PEPA, PEPB, PEPS, IDH1, GSR, MPI, PGM1, NP, SOD1, and ME1 in the common shrew (Sorex araneus).

This report extends the genetic map of the common shrew (Sorex araneus) by adding chromosome assignments for ten genes to the seven already mapped (Pack et al. 1995). A somatic cell hybrid panel was used for the mapping. The genes for peptidase A (PEPA) and isocitrate dehydrogenase-1 (IDH1) map to chromosome de; the genes for phosphoglucomutase-1 (PGM1), superoxide dismutase-1 (SOD1), and mannosephosphate isomerase (MPI) are located on chromosome af; the genes for nucleoside phosphorylase (NP) and glutathione reductase (GSR) are on chromosome ik; and the genes for peptidase S (PEPS), malic enzyme-1 (ME1), peptidase B (PEPB) are found on chromosomes jl, go, and mp respectively.

Aminopeptidases↗
PubMed1996

A study of meiotic pairing, nondisjunction and germ cell death in laboratory mice carrying Robertsonian translocations.

Frequencies of anaphase I nondisjunction, germ cell death and pairing abnormalities at pachytene were assessed in male mice singly heterozygous and homozygous for the Robertsonian (Rb) translocations: Rb (1.3)1Bnr, Rb(11.13)4Bnr and Rb(10.11)8Bnr. Rb homozygotes showed low frequencies of nondisjunction but substantial germ cell death. This germ cell death could not be attributed to problems at pachytene as Rb homozygotes showed no increase in pairing abnormalities over the (C3H/HeH x 101/H)F1 controls. Instead genic factors are involved. Rb heterozygotes showed substantial frequencies of nondisjunction and even greater germ cell death than found in the homozygotes. Pachytene pairing abnormalities were observed and it appears that these, together with genic factors, cause physiological perturbation of meiocytes, thereby promoting germ cell death, with nondisjunction of the trivalent as a sublethal response.

Anaphase↗
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

Gene mapping in the common shrew (Sorex araneus; Insectivora) by shrew-rodent cell hybrids: chromosome localization of the loci for HPRT, TK, LDHA, MDH1, G6PD, PGD, and ADA.

We selected the common shrew (Sorex araneus) to generate the first insectivore gene map. Shrew-Chinese hamster and shrew- mouse somatic cell hybrid cells were constructed. When the 119 shrew-rodent clones were characterized, only shrew chromosomes were found to have segregated. A panel of hybrid clones was selected for gene assignment. The genes for hypoxanthine phosphoribosyl transferase (HPRT), glucose-6- phosphate dehydrogenase (G6PD), and malate dehydrogenase 1 (MDH1) were assigned to shrew Chromosome (Chr) de [which is the product of a tandem fusion between the 'original' mammalian X Chromosome (Chr) and an autosome], the gene for adenosine deaminase (ADA) and 6-phosphogluconate dehydrogenase se (PGD) to Chromosome jl, the gene for thymidine kinase (TK) to Chromosome hn, and the gene for lactate dehydrogenase (LDHA) to chromosome ik. Further studies in progress.

Adenosine Deaminase↗
PubMed1995

Pattern and frequency of nocodazole induced meiotic nondisjunction in oocytes of mice carrying the 'tobacco mouse' metacentric Rb(16.17)7Bnr.

Oocytes from (C3H/HeH x 101/H)F1 and Rb(16.17)7Bnr homozygous females were exposed to a range of doses of nocodazole in vitro. The spindle poison caused a dose dependent increase in metaphase I (MI) arrest and hyperploidy. A concentration of 0.03 microgram/ml was found to induce a maximum hyperploid frequency of 3.1% and 11.6% respectively without a high level of MI arrest. Between 0.03 and 0.05 microgram/ml MI arrest increased substantially and reached a frequency of approximately 90%. In a further experiment oocytes from Rb7 homozygous, heterozygous and 3H1 females were exposed to 0.03 microgram/ml nocodazole 4, 6 or 8 h after the onset of maturation. The phase at which the spindle was inhibited resulted in a specific pattern of nondisjunction which in turn was dependent on whether the female carried an Rb metacentric. 3H1 oocytes gave a normally distributed pattern of increase in aneuploid frequency (over the spontaneous value) centering around a 6 h application. This was thought to be due to the interaction of chromosomes with the microtubules of the spindle during attachment and/or alignment. In contrast both Rb homozygotes and heterozygotes gave the same biphasic response, with a high frequency of aneuploidy in the oocytes when nocodazole was applied 4 and 8 h after the onset of maturation. In Rb homozygotes we demonstrated that the Rb bivalent underwent nondisjunction more frequently than the average acrocentric, when nocodazole was administered early.(ABSTRACT TRUNCATED AT 250 WORDS)

Anaphase↗
PubMed1994

The HSR on chromosome 1 of the house mouse, Mus domesticus: distribution and frequency in Switzerland.

A total of 357 house mice (Mus domesticus) from 83 localities uniformly distributed throughout Switzerland were screened for the presence of a homogenously staining region (HSR) on chromosome 1. Altogether 47 mice from 11 localities were HSR/+ or HSR/HSR. One sample of 11 individuals all had an HSR/HSR karyotype. Almost all mice with the variant were collected from the Rhone valley (HSR frequency: 61%) and Val Bregaglia (HSR frequency: 81%). For samples from most of the area of Switzerland, the HSR was absent. There was no strong association between the geographic distribution of the HSR and the areas of occurrence of metacentrics. However, at Chiggiogna the HSR was found on Rb (1.3). Possible explanations for the HSR polymorphism are discussed.

Animals↗
PubMed1994

Mitochondrial DNA variation and the evolution of Robertsonian chromosomal races of house mice, Mus domesticus.

The house mouse, Mus domesticus, includes many distinct Robertsonian (Rb) chromosomal races with diploid numbers from 2n = 22 to 2n = 38. Although these races are highly differentiated karyotypically, they are otherwise indistinguishable from standard karyotype (i.e., 2n = 40) mice, and consequently their evolutionary histories are not well understood. We have examined mitochondrial DNA (mtDNA) sequence variation from the control region and the ND3 gene region among 56 M. domesticus from Western Europe, including 15 Rb populations and 13 standard karyotype populations, and two individuals of the sister species, Mus musculus. mtDNA exhibited an average sequence divergence of 0.84% within M. domesticus and 3.4% between M. domesticus and M. musculus. The transition/transversion bias for the regions sequenced is 5.7:1, and the overall rate of sequence evolution is approximately 10% divergence per million years. The amount of mtDNA variation was as great among different Rb races as among different populations of standard karyotype mice, suggesting that different Rb races do not derive from a single recent maternal lineage. Phylogenetic analysis of the mtDNA sequences resulted in a parsimony tree which contained six major clades. Each of these clades contained both Rb and standard karyotype mice, consistent with the hypothesis that Rb races have arisen independently multiple times. Discordance between phylogeny and geography was attributable to ancestral polymorphism as a consequence of the recent colonization of Western Europe by mice. Two major mtDNA lineages were geographically localized and contained both Rb and standard karyotype mice. The age of these lineages suggests that mice have moved into Europe only within the last 10,000 years and that Rb populations in different geographic regions arose during this time.

Animals↗
PubMed1994

Oogenesis in homozygotes and heterozygotes for Robertsonian chromosomal rearrangements from natural populations of the common shrew, Sorex araneus.

Female common shrews in their first pregnancy were collected near Oxford (UK) from the hybrid zone between the Oxford and Hermitage races. These races differ by Robertsonian chromosomal rearrangements and both Robertsonian heterozygotes and homozygotes are found in the zone. The three homozygotes examined in this study had significantly more oocytes than the six heterozygotes. Among the heterozygotes, the number of oocytes tended to be lower in more severely heterozygous individuals; one double heterozygote was particularly depleted. Although there were, on average, 41% fewer primordial follicles in the ovaries of the heterozygotes than those of the homozygotes, there was no significant difference in the numbers of growing follicles between the karyotypic classes. These data suggest that Robertsonian heterozygotes may have a shorter reproductive lifespan than do homozygotes, but the numbers of follicles being recruited for ovulation at a particular instance during the fertile period does not appear to differ between homozygotes and heterozygotes. Morphological differences between the follicles of homozygotes and heterozygotes were not detected. Only 0.12% of healthy growing follicles were biovular.

Animals↗
PubMed1993

Female multiple mating behaviour in the common shrew as a strategy to reduce inbreeding.

Three hypotheses concerning potential genetic benefits of female multiple mating behaviour are evaluated for the common shrew. In a high-density population, many successful copulations took place between individuals estimated to be close relatives (e.g. full or half siblings). Juveniles resulting from such matings tended to be relatively small at weaning, and were generally less likely to survive to sexual maturity than more outbred individuals. Multiple paternity was discovered in eight of nine litters examined. The incidence of matings between close relatives, the cost of inbreeding, and the high incidence of multiple paternity presented are each consistent with the hypothesis that female multiple mating is a strategy to reduce inbreeding. That is, if females cannot always distinguish close kin, then they may copulate with several different males and so reduce the risk that all their offspring will be sired by a close relative.

Animals↗