Heterosis of adult mouse (Mus musculus) ultrasonic vocalizing

Four sets of adult mice (Mus musculus), each comprised of individuals from two inbred strains and both reciprocal F₁ crosses, were tested during male-female and female-female dyadic encounters for their emission of 70-kHz ultrasonic vocalizations. For each sex-dyad type of each set, a single progeny mean representing both reciprocal F₁ groups was calculated and compared to (1) the average value from the inbred parents and (2) the higher mean of the within-set progenitor inbred strains. In addition to demonstrating strain-and sex-influenced ultrasonic vocalizing levels, the results indicated that for each set examined, the F₁-progeny mean amount of ultrasonic vocalizing significantly exceeded the average inbred parent value. This was true for both dyad types, providing strong evidence that ultrasonic vocalizing displlays a directional dominance mode of inheritance in both female and male mice. Moreover, for female-female dyads of all four sets and for male-female dyads of three of four sets, the F₁-progeny mean amount of ultrasonic vocalizing significantly exceeded that of the highest progenitor inbred strain. Analyses of ultrasonic vocalizing latencies yielded similar hybrid-inbred differences. Collectively, these findings are interpreted as being consistent with the notion that, for both sexes of mice, ultrasonic vocalizing is a phenotypically heterotic behavioral trait.This research was supported, in part, by a Florida State University Psychobiology Fellowship awarded to J.C.M. and by NINCDS Grant NS 15560.     

Meiotic synapsis of homogeneously staining regions (HSRs) in chromosome 1 ofMus musculus

About 50 copies of a long-range repeat DNA family with a repeat size of roughly 100 kb and with sequence homology to mRNAs are clustered in the G-light band D of chromosome 1 of the house mouse,Mus musculus. We studied amplified versions of the cluster which are found in many wild populations ofM. musculus. They are cytogenetically conspicuous as one or two C-band positive homogeneously staining regions (single- and double band HSRs) which increase the mitotic length of chromosome 1. The double band HSR was phylogenetically derived from a single band HSR by a paracentric inversion. In homozygous condition, such HSRs contribute, albeit not as much as expected from their mitotic length, to the synaptonemal complex (SC) length of chromosome 1. In HSR heterozygous animals an elongation of the SCs was not noticeable. In single band HSR heterozygous males, synapsis proceeds regularly and continuously from the distal telomere towards the centromeric end without forming buckles. Thus, the single band HSR has no adverse effect on pairing. The same straight pairing behaviour was found in the majority of double band HSR heterozygous spermatocytes. This shows that extensive nonhomologous pairing can take place in the earliest phase of synapsis. Synapsis was discontinuous, leaving the central part of the bivalent 1 asynapsed, in only 14.3% of double band HSR heterozygous cells. In such cells the chromosome 1 SC is completed at a later stage of meiosis. The delay is presumably an effect of the inversion that includes one HSR band and the segment between the two HSR bands.     

Lung deformation and macrophage displacement in smoke-exposed and normal mice (Mus musculus) following different fixation procedures

Summary Lung deformation (shrinkage or inflation) and displacement of pulmonary parenchymal macrophages were evaluated after immersion fixation, intratracheal instillation of fixative and lung lavage followed by intratracheal fixative instillation in cigarette smoke-exposed, sham-treated and control pallid male mice. Lung volume displacement and lung section and alveolar area analysis revealed that degree of deformation was uniform in lungs from all treatment groups fixed by immersion but not by instillation of fixative and fixative instillation following lavage. In situ pulmonary parenchymal macrophage number per lung section area of fixative-instilled lungs and lavaged lungs followed by fixative instillation was significantly greater than in those following immersion fixation in all corresponding treatment groups. A paucity of macrophages was noted in airways of fixative-instilled and lavaged followed by instillation of fixative lungs. Pulmonary macrophages were uniformly distributed throughout lung parenchyma following immersion fixation, while in fixative-instilled and lavaged prior to instillation of fixative lungs these cells tended to be concentrated in alveoli near terminal bronchioles. Lavage procedures removed an unknown portion of lung macrophages and appeared to ineffectively sample the pulmonary parenchymal macrophage population. Intratracheal instillation of fixative with or without prior lavage apparently alters the distribution of pulmonary macrophages by displacing airway phagocytes into the alveoli. Data reported suggest that fractional estimates of in situ lung parenchymal macrophage population can be obtained by counting the number of these cells per area of tissue from lungs fixed by immersion.     

Chromosomal rearrangements underlying karyotype differences between Chinese pangolin (Manis pentadactyla) and Malayan pangolin (Manis javanica) revealed by chromosome painting

The Chinese pangolin (Manis pentadactyla), a representative species of the order Pholidota, has been enlisted in the mammalian whole-genome sequencing project mainly because of its phylogenetic importance. Previous studies showed that the diploid number of M. pentadactyla could vary from 2n = 36 to 42. To further characterize the genome organization of M. pentadactyla and to elucidate chromosomal mechanism underlying the karyotype diversity of Pholidota, we flow-sorted the chromosomes of 2n = 40 M. pentadactyla, and generated a set of chromosome-specific probes by DOP-PCR amplification of flow-sorted chromosomes. A comparative chromosome map between M. pentadactyla and the Malayan pangolin (Manis javanica, 2n = 38), as well as between human and M. pentadactyla, was established by chromosome painting for the first time. Our results demonstrate that seven Robertsonian rearrangements, together with considerable variations in the quantity of heterochromatin and in the number of nucleolar organizer regions (NORs) differentiate the karyotypes of 2n = 38 M. javanica and 2n = 40 M. pentadactyla. Moreover, we confirm that the M. javanica Y chromosome bears one NOR. Comparison of human homologous segment associations found in the genomes of M. javanica and M. pentadactyla revealed seven shared associations (HSA 1q/11, 2p/5, 2q/10q, 4p+q/20, 5/13, 6/19p and 8q/10p) that could constitute the potential Pholidota-specific signature rearrangements.     

Chromosomal evolution of Arvicolinae (Cricetidae, Rodentia). I. The genome homology of tundra vole, field vole, mouse and golden hamster revealed by comparative chromosome painting

Cross-species chromosome painting has become the mainstay of comparative cytogenetic and chromosome evolution studies. Here we have made a set of chromosomal painting probes for the field vole (Microtus agrestis) by DOP-PCR amplification of flow-sorted chromosomes. Together with painting probes of golden hamster (Mesocricetus auratus) and mouse (Mus musculus), the field vole probes have been hybridized onto the metaphases of the tundra vole (Microtus oeconomus). A comparative chromosome map between these two voles, golden hamster and mouse has been established based on the results of cross-species chromosome painting and G-banding comparisons. The sets of paints from the field vole, golden hamster and mouse identified a total of 27, 40 and 47 homologous autosomal regions, respectively, in the genome of tundra vole; 16, 41 and 51 fusion/fission rearrangements differentiate the karyotype of the tundra vole from the karyotypes of the field vole, golden hamster and mouse, respectively.     

Chromosomal evolution of Arvicolinae (Cricetidae, Rodentia). II. The genome homology of two mole voles (genus Ellobius), the field vole and golden hamster revealed by comparative chromosome painting

Using cross-species chromosome painting, we have carried out a comprehensive comparison of the karyotypes of two Ellobius species with unusual sex determination systems: the Transcaucasian mole vole, Ellobius lutescens (2n = 17, X in both sexes), and the northern mole vole, Ellobius talpinus (2n = 54, XX in both sexes). Both Ellobius species have highly rearranged karyotypes. The chromosomal paints from the field vole (Microtus agrestis) detected, in total, 34 and 32 homologous autosomal regions in E. lutescens and E. talpinus karyotypes, respectively. No difference in hybridization pattern of the X paint (as well as Y paint) probes on male and female chromosomes was discovered. The set of golden hamster (Mesocricetus auratus) chromosomal painting probes revealed 44 and 43 homologous autosomal regions in E. lutescens and E. talpinus karyotypes, respectively. A comparative chromosome map was established based on the results of cross-species chromosome painting and a hypothetical ancestral Ellobius karyotype was reconstructed. A considerable number of rearrangements were detected; 31 and 7 fusion/fission rearrangements differentiated the karyotypes of E. lutescens and E. talpinus from the ancestral Ellobius karyotype. It seems that inversions have played a minor role in the genome evolution of these Ellobius species.     

Cloning and chromosomal localization of MYO15A to chromosome 5 of the dog (Canis familiaris)

Mutations in the myosin XVA gene (MYO15A) cause congenital non-syndromic deafness in humans and mice. Therefore, the MYO15A gene represents a candidate gene for hereditary hearing loss in dogs. Using a human cDNA to screen a dog BAC library, we isolated a canine BAC clone. Sequencing of the BAC ends confirmed homology to the human gene. To facilitate future linkage studies, we report the physical mapping of the canine MYO15A gene to CFA5q23-q24 by FISH and RH mapping. This revised version was published online in July 2006 with corrections to the Cover Date.     

Behavioral Characterization of Wild Derived Male Mice (<Emphasis Type="Italic">Mus musculus musculus</Emphasis>) of the PWD/Ph Inbred Strain: High Exploration Compared to C57BL/6J

PWD/Ph is an inbred mouse strain derived from wild mice trapped in central Czech Republic. These mice are of the Mus musculus musculus subspecies, whose ancestors separated from those of Mus musculus domesticus about one million years ago. There is a high degree of variation in the genomic sequence and a wide range of phenotypes between PWD/Ph and standard laboratory inbred mouse strains, the genomes of which are principally Mus musculus domesticus in origin, making PWD/Ph mice an useful resource for complex trait research. As a first step in taking advantage of this resource, a preliminary characterization of the behavior of PWD/Ph mice was performed. Groups of 10 PWD/Ph and C57BL/6J male mice were tested in the open field, novel object exploration task and Morris water maze. PWD/Ph were marginally more anxious than C57BL/6J mice in the open field but subsequently displayed much higher levels of exploration and lower anxiety than C57BL/6J mice following introduction of a novel object. As C57BL/6J itself is rated as highly explorative among classical inbred strains, PWD/Ph probably represents an extreme among mouse strains for this specific behavior. PWD/Ph and C57BL/6J mice differed in their water escape training profiles in the Morris water maze, perhaps reflecting different motivational factors. However, there were no differences in overall cognitive ability (spatial learning) as both groups learned to find the hidden platform and performed equally well when the location of the platform was changed. This is the first quantification of the behavior of PWD/Ph mice and the results are promising for the potential of the consomic panel currently being generated with PWD/Ph and C57BL/6J as a tool for the molecular dissection of behavior.     

Genetic correlation between two types of nesting inMus musculus: Direct and indirect selection

The genetic correlation between maternal nesting (weight of cotton used in the nest built on the day of parturition) and thermoregulatory nesting (total weight of individual nests built on four consecutive days) was estimated from the correlated response of the former to selection for the latter. The best estimate was r_A=0.58±0.32, indicating a substantial amount of common genetic influence. Indirect selection seems to have produced a greater response in maternal nesting than could have been achieved by direct selection.This research was supported by Grants HD11293 and GM21993 from the National Institutes of Health. The author is the recipient of NIH Research Career Development Award ES00042.     

High chromosome conservation detected by comparative chromosome painting in chicken, pigeon and passerine birds

Chicken chromosome paints for macrochromosomes 1-10, Z, and the nine largest microchromosomes (Griffin et al. 1999) were used to analyze chromosome homologies between chicken (Gallus gallus domesticus: Galliformes), domestic pigeon (Columba livia: Columbiformes), chaffinch (Fringilla coelebs Passeriformes), and redwing (Turdus iliacus: Passeriformes). High conservation of syntenies was revealed. In general, both macro- and microchromosomes in these birds showed very low levels of interchromosomal rearrangements. Only two cases of rearrangements were found. Chicken chromosome 1 corresponds to chromosome 1 in pigeon, but to chromosomes 3 and 4 in chaffinch and chromosomes 2 and 5 in redwing. Chicken chromosome 4 was shown to be homologous to two pairs of chromosomes in the karyotypes of pigeon and both passerine species. Comparative analysis of chromosome painting data and the results of FISH with (TTAGGG)n probe did not reveal any correlation between the distribution of interstitial telomere sites (ITSs) and chromosome rearrangements in pigeon, chaffinch and redwing. In chaffinch, ITSs were found to co-localize with a tandem repeat GS (Liangouzov et al. 2002), monomers of which contain an internal TTAGGG motif.     

Identification by R-banding and FISH of chromosome arms involved in Robertsonian translocations in several deer species

We constructed and analyzed the RBG-banded karyotype of five deer species: Chital (Axis axis), White-lipped deer (Cervus albirostris), Rusa deer (Cervus timorensis russa), Sambar deer (Cervus unicolor) and Eld's deer (Cervus eldi siamensis). Among these five species, only Eld's deer had been previously karyotyped using R-banding. In order to identify all the chromosome correspondences with cattle and precisely which chromosome arms are involved in Robertsonian translocations, we compared the karyotypes of these five species with those of the closely related and well-characterized species, cattle (Bos taurus) and Vietnamese Sika deer (Cervus nippon pseudaxis). Among these six deer species (the five above plus the Vietnamese Sika deer), we found thirteen different Robertsonian translocations involving nineteen different chromosome arms. Thirteen chromosome arms were identified by comparison of R-banding patterns only and the remaining six were either confirmed or identified by FISH-mapping of bovine or caprine probes previously localized in cattle. Finally, we observed that five of the thirteen Robertsonian translocations are shared by at least two species and that some chromosome arms are more frequently involved in Robertsonian translocations than others. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparative chromosome painting map between two Ryukyu spiny rat species, <Emphasis Type="Italic">Tokudaia osimensis</Emphasis> and <Emphasis Type="Italic">Tokudaia tokunoshimensis</Emphasis> (Muridae,Rodentia)

Ryukyu spiny rats (genus Tokudaia) are indigenous species that are confined to three islands of the Nansei Shoto archipelago, Amami-Oshima, Tokunoshima and Okinawa-jima, Japan. Tokudaia tokunoshimensis from Tokunoshima Island and Tokudaia osimensis from Amami-Oshima Island are closely related taxonomically, although their karyotypes are quite different: the diploid chromosome numbers and sex chromosome constitution are 2n = 45, X0/X0 for T. tokunoshimensis and 2n = 25, X0/X0 for T. osimensis. We conducted comparative chromosome painting with chromosome-specific DNA probes of the laboratory mouse (Mus musculus) to molecularly examine the chromosome homology between T. tokunoshimensis and T. osimensis, and deduced a possible ancestral karyotype of Tokudaia species and the process of evolutionary chromosome rearrangements. The proposed ancestral karyotype with the diploid number of 2n = 48, XX/XY was similar to the karyotype of T. tokunoshimensis, and the karyotype of T. osimensis would then have been established through at least 14 chromosomal changes, mainly centric fusion and tandem fusion, from the ancestral karyotype. The close karyological relationship between the ancestral karyotypes of Tokudaia and Apodemus also suggests that the chromosomal evolution in the Tokudaia-Apodemus lineage has been very slow and has accelerated only recently in the branch leading to T. osimensis.     

Sheep/human comparative map in a chromosome region involved in scrapie incubation time shows multiple breakpoints between human chromosomes 14 and 15 and sheep chromosomes 7 and 18

A chromosome region involved in scrapie incubation time was identified on sheep chromosome 18 (OAR18). Since OAR18 (and OAR7) share conserved chromosome segments with human chromosomes HSA14 and HSA15, a dense map of type I markers was constructed by FISH mapping of bacterial artificial chromosomes containing genes located on these human chromosomes. In this study, we used the complete human sequence information (gene positions in megabases, Mb) to locate approximately one gene every 2 Mb on HSA15 (19 genes mapped between 19.51 and 66.02 Mb) and on HSA14 (11 genes between 73.24 and 102.62 Mb). Combined with previous work carried out in cattle and goats, our results made it possible to refine the comparative map between ruminants and humans for these two highly rearranged chromosomes (10 segments on HSA15 and 7 on HSA14). Furthermore, we identified relatively short intervals containing evolutionary breakpoints, which is a prerequisite to position them precisely. This work is also the first step in the cloning of the region involved in scrapie incubation period in sheep. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reconstruction of the ancestral ferungulate karyotype by electronic chromosome painting (E-painting)

By comparing high-coverage and high-quality whole genome sequence assemblies it is now possible to reconstruct putative ancestral progenitor karyotypes, here called protokaryotypes. For this study we used the recently described electronic chromosome painting technique (E-painting) to reconstruct the karyotype of the 85 million-year-old (MYA) ferungulate ancestor. This model is primarily based on dog (Canis familiaris) and cattle (Bos taurus) genome data and is highly consistent with comparative gene mapping and chromosome painting data. The protokaryotype bears 23 autosomal chromosome pairs and the sex chromosomes and preserves most of the chromosomal associations described previously for the boreo-eutherian protokaryotype. The model indicates that five interchromosomal rearrangements occurred during the transition from the boreo-eutherian to the ferungulate ancestor. From there on 66 further interchromosomal rearrangements took place in the lineage leading to cattle and 61 further interchromosomal rearrangements in the lineage to dog. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Centromere repositioning in the X chromosome of XO/XO mammals,Ryukyu spiny rat

Two species of Ryukyu spiny rat, Tokudaia osimensis and Tokudaia tokunoshimensis, have an XO/XO sex chromosome constitution with no cytogenetically visible Y chromosome in both sexes. The single X chromosomes of T. osimensis and T. tokunoshimensis are submetacentric and subtelocentric, respectively. It was therefore suggested that a pericentric inversion event occurred in the X chromosome of either species. To identify X chromosome rearrangements that have occurred between the two species, we mapped 22 mouse cDNA clones of the X-linked genes on the chromosomes of the two species by direct R-banding FISH. The gene orders of the X chromosomes were conserved in the two species, whereas the position of the centromere on the X chromosome was different. This result indicates that the rearrangement which occurred in either of the X chromosomes after the two species diverged from a common ancestor involved not pericentric inversion but centromere repositioning.     

Assignment of chromosome rearrangements between X chromosomes of human and cattle by laser microdissection and Zoo-FISH

Cross-species fluorescence in-situ hybridization (Zoo-FISH) was performed on cattle metaphase spreads using Homo sapiens X chromosome (HSAX) painting probes specific for the p- and q-arms to identify the cytogenetic location of a chromosome breakpoint between HSAX and the Bos taurus X chromosome (BTAX). The existence of a breakpoint is strongly suggested by recent radiation hybrid and FISH mapping results. Hybridization probes were generated by microdissection of HSAX p- and q-arms using the contact-free technology of Laser Microdissection and Pressure Catapulting (LMPC), amplification of the isolated chromosome material by DOP-PCR, and labelling of the PCR products with digoxigenin in a secondary PCR. Independent Zoo-FISH of the two painting probes on bovine metaphase chromosomes (detected by antidigoxigenin-fluorescein) resulted in clear hybridization signals on BTAX. A breakpoint was identified between HSAXp and HSAXq on BTAX, and narrowed down between the G-bands BTAXq25 and BTAXq26. The assumed centromere transposition between HSAX and BTAX associated with the rearranged chromosome segments is supported by cytogenetic assignments of the genes BGN and G6PD to BTAX.^†Authors contributed equally to this work.     

Comparative chromosome banding analysis of three South American species of rice rats of the genus Oryzomys (Rodentia, Sigmodontinae)

Comparative G- and C-banding analysis in three species of rice rats, namely Oryzomys megacephalus from Peru and French Guiana, O. yunganus (Peru) and O. nitidus (Bolivia) was carried out. It revealed that Peruvian O. megacephalus (2N=52, NFa=62) and that from French Guiana (2N=54, NFa=64) differ from each other by one Rb translocation and one heterochromatic arm addition/deletion. Three further Rb translocations separate them from O. yunganus (2N=58, NFa=62). Only 16 out of 39 autosomal pairs of O. nitidus (2N=80, NFa=86) shared homologous banding patterns with O. yunganus, 4 of which were involved in tandem translocations to form the larger chromosomes in two other taxa. The study suggests that O. megacephalus, O. yunganus and O. laticeps studied previously form a monophyletic group in good agreement with earlier molecular and morphological data. By contrast, the limited homologous banding patterns found between them and O. nitidus cast doubt on its belonging to the same phylogenetic lineage. In the light of available chromosomal and molecular data, the significance of intra- and interspecies karyotypic variability within Oryzomys and its relevance to systematics and phylogeny of the genus are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Loss of telomeric sites in the chromosomes ofMus musculus domesticus (Rodentia: Muridae) during Robertsonian rearrangements

Mouse chromosomes possessing multiple Robertsonian rearrangements (Rb chromosomes) have been examined using fluorescencein situ hybridization with the telomeric consensus sequence (TTAGGG)_n. No hybridization signals were detected at the primary constriction of Rb chromosomes. This observation leads us to conclude that the formation of Rb chromosomes in the mouse is invariably associated with the loss of telomeric regions. More significantly, a further alteration in regions flanking the primary constrictions was observed after hybridizing with a minor satellite DNA probe to Rb chromosomes. It seems likely that the breakpoints required for a Robertsonian process do not include telomeric sites exclusively but extend to the adjacent pericentromeric regions of the original acrocentric chromosomes. In contrast to previous reports, these observations demonstrate the elimination of substantial amounts of chromosomal DNA during the formation of mouse Rb chromosomes.     

Comparative chromosome mapping of sex-linked genes and identification of sex chromosomal rearrangements in the Japanese wrinkled frog (Rana rugosa, Ranidae) with ZW and XY sex chromosome systems

There are regional variations of sex chromosome morphologies in the Japanese wrinkled frog, Rana rugosa (2n = 26): heterogametic ZZ/ZW-type and XX/XY-type sex chromosomes, and two different types of homomorphic sex chromosomes. To search for homology between the ZW and XY sex chromosomes and the chromosome rearrangements that have occurred during sex chromosomal differentiation in R. rugosa, we performed chromosome mapping of sexual differentiation genes for R. rugosa by FISH. Three genes, AR, SF-1/Ad4BP and Sox3, were localized to both the ZW and XY chromosomes, and their locations were all different between the Z and W and between the X and Y. AR and SF-1/Ad4BP were located on the short arms of the W and X and the long arms of Z and Y, and Sox3 was mapped to the different locations on the long arms between the Z and W and between the X and Y, probably as a result of multiple rearrangements that occurred during the process of sex chromosome differentiation. However, the chromosomal locations of three genes were almost consistent between the Z and Y and between the W and X, indicating that the Z and Y chromosomes and the W and X chromosomes were respectively derived from the same origins. Dmrt1, which is located on avian sex chromosomes, was localized to autosomes in R. rugosa with both the ZW and XY sex chromosomes, suggesting that Dmrt1 might not be related to sex determination in this species.