Heterosis without selectional coadaptation inDrosophila ananassae

Summary The relative viabilities of homozygous and heterozygous karyotypes were measured by making crosses between strains ofD. ananassae homozygous for ST or inverted gene orders in the second and third chromosomes. The strains utilized during the present study originated from widely separated localities in India, Kuala Lumpur and Kota Kinabaru, Malaysia and Chian Mai, Thailand. The presence of heterosis in many interpopulation crosses is evident from the results which show that the inversion heterozygotes formed by chromosomes coming from distant populations exhibit heterosis. On the other hand, heterosis is absent in two intrapopulation crosses. Thus the present results provide evidence that heterozygosis for many genes and gene complexes does produce high fitness without previous selectional coadaptation.     

In situ inversion of the conjugative transposon Tn916 in Enterococcus faecium DPC3675

Enterococcus faecium DPC3675 is a derivative of E. faecium DPC1146 which contains a single copy of the conjugative transposon Tn916. Although the transposon is observed to be oriented in one direction in individual colonies, DNA extracted from cultures grown from these colonies contains the transposon in both orientations, as determined by PCR analysis and sequencing of the transposon/chromosome junctions. Therefore, Tn916 possesses a hitherto unreported ability to invert within a particular insertion site during growth in broth.     

Infrared thermal imaging based study of localized cold stress induced thermoregulation in lower limbs: The role of age on the inversion time

Thermoregulatory control of human body temperature is of paramount importance for normal bodily functions. Exposure of the upper and lower limbs to localized cold stress can cause cold-induced injuries and often lower limbs are more susceptible to damages from cold-induced injuries. In this study, we use infrared thermal imaging to probe localized cold stress induced cutaneous vasoconstriction of lower limbs in 33 healthy subjects. The cold stress is actuated by applying ice to the plantar surfaces of the lower limbs for 180 s and after removal of the cold stress, infrared thermography is utilized to non-invasively monitor the time-dependent variations in vein pixel temperatures on the dorsal surfaces of the stimulated and non-stimulated feet. It is observed that the vein pixel temperature of the stimulated foot showed a non-monotonic variation with time, consisting of an initial decrease and the presence of an inversion time, beyond which temperature is regained. The initial decrease in vein pixel temperature of the stimulated foot is attributed to the reduced blood flow caused by the cold stress induced severe vasoconstriction. Beyond the inversion time, the vein pixel temperature is found to increase due to rewarming of the surrounding skin. Experimental findings indicate that the inversion time linearly increased with the age of the subject, indicating a reduced thermoregulatory efficiency for the aged subjects. This study provides a thermal imaging-based insight into the skin temperature re-distribution during the early stages of blood perfusion in lower limbs, after an exposure to a localized acute cold stress. Statistical analyses reveal that subject height, weight, body-mass index and gender do not influence the inversion time significantly. The experimental findings are important towards rapid evaluation of personnel fitness for deployment in extreme cold environment, treatment of cold-induced injuries and probing of thermoregulatory impairments.     

Simulation of genetic control. Homozygous-viable pericentric inversions in field-female killing systems

Summary The GENCON simulation program GC5 is designed to simulate genetic population control using field-female killing (FK) systems carying pericentric inversions in addition to Y-linked translocations and deleterious mutations. Homozygous-viable pericentric inversions are included on the same chromosomes as the deleterious mutations, in repulsion to the Y-linked translocation. Released males transmit the inversions and mutations to their daughters and the translocation to their sons. Daughters are semisterile regardless of the type of male they mate with, because products of crossing-over within the inversions carry inviable duplications and deficiencies. Compared to present FK systems, inversion-containing strains give higher levels of genetic death, with both faster initial suppression and greater persistence of genetic death from field-reared descendants if releases are interrupted. At low release rates, both types of FK system are more effective than sterile males.     

Neisseria gonorrhoeae contains multiple copies of a gene that may encode a site-specific recombinase and is associated with DNA rearrangements

A 960-bp ORF potentially encoding a site-specific recombinase has been cloned from Neisseria gonorrhoeae MS11-A. This ORF was designated piv_Ng on the basis of similarity of the deduced amino acid sequence to the Piv proteins of Moraxella spp. that are site-specific invertases. Southern hybridization and sequence analysis revealed that there were multiple copies of piv_Ng sequence within the genomes of N. gonorrhoeae strains tested, but not in several other neisserial species. Southern hybridization and sequence analysis further suggested that piv_Ng sequences may be associated with genomic rearrangements.     

Patterning of the heart field in the chick

In human development, it is postulated based on histological sections, that the cardiogenic mesoderm rotates 180° with the pericardial cavity. This is also thought to be the case in mouse development where gene expression data suggests that the progenitors of the right ventricle and outflow tract invert their position with respect to the progenitors of the atria and left ventricle. However, the inversion in both cases is inferred and has never been shown directly. We have used 3D reconstructions and cell tracing in chick embryos to show that the cardiogenic mesoderm is organized such that the lateralmost cells are incorporated into the cardiac inflow (atria and left ventricle) while medially placed cells are incorporated into the cardiac outflow (right ventricle and outflow tract). This happens because the cardiogenic mesoderm is inverted. The inversion is concomitant with movement of the anterior intestinal portal which rolls caudally to form the foregut pocket. The bilateral cranial cardiogenic fields fold medially and ventrally and fuse. After heart looping the seam made by ventral fusion will become the greater curvature of the heart loop. The caudal border of the cardiogenic mesoderm which ends up dorsally coincides with the inner curvature. Physical ablation of selected areas of the cardiogenic mesoderm based on this new fate map confirmed these results and, in addition, showed that the right and left atria arise from the right and left heart fields. The inversion and the new fate map account for several unexplained observations and provide a unified concept of heart fields and heart tube formation for avians and mammals.     

Monitoring of the genetic structure of natural populations: change of the effective population size and inversion polymorphism in <Emphasis Type="Italic">Drosophila subobscura</Emphasis>

We analyzed changes in the genetic structure and effective population size of two ecologically distinct populations of Drosophila subobscura over several years. Population sizes of D. subobscura in beech and oak wood habitats for a period of 6 years were estimated by the capture-mark-release-recapture method. Inversion polymorphism parameters were also assessed in the same populations for a period of 3 years. Significant differences in the numbers of individuals were observed between sexes. This affected the effective population sizes between particular years. The ratio of the effective size over the cenzus dropped significantly in beech wood in 2 years. Although overall heterozygosity remained unchanged during the years in both habitats, frequencies of gene arrangements on five chromosomes show variability. After the bottleneck, some complex chromosomal arrangements appeared for the first time in both populations. Standard gene arrangements of chromosome A increased in frequency over the years in each habitat, while the complex arrangements remain rather stable and specific for each population. The results obtained indicate that the population structure may significantly change if the effective size of D. subobscura population is reduced, which is mostly related to microclimatic changes in habitats. Based on the results to date, monitoring of microevolutionary changes by using D. subobscura and its relatives seems a promising way to study the effects of global climate changes.     

Interaction of metal ions with D-glucobenzothiazoline: isolation and characterization of the resultant products

Six different metal-ion complexes of D-glucobenzothiazoline were synthesized and characterized by analytical and spectral techniques. Formation of different types of species (ML and ML(2)) were observed with Cu(2+), Ag(+), Cd(2+), Hg(2+), and Zn(2+) ions. Existence of an anomeric mixture in the case of the Cu(2+) complex is identified from the EPR spectra, and the results were further supported by the simulated spectra. The structures were proposed based on different studies.     

A family of human Y chromosomes has dispersed throughout northern Eurasia despite a 1.8-Mb deletion in the azoospermia factor c region

The human Y chromosome is replete with amplicons-very large, nearly identical repeats-which render it susceptible to interstitial deletions that often cause spermatogenic failure. Here we describe a recurrent, 1.8-Mb deletion that removes half of the azoospermia factor c (AZFc) region, including 12 members of eight testis-specific gene families. We show that this "b2/b3" deletion arose at least four times in human history-likely on inverted variants of the AZFc region that we find exist as common polymorphisms. We observed the b2/b3 deletion primarily in one family of closely related Y chromosomes-branch N in the Y-chromosome genealogy-in which all chromosomes carried the deletion. This branch is known to be widely distributed in northern Eurasia, accounts for the majority of Y chromosomes in some populations, and appears to be several thousand years old. The population-genetic success of the b2/b3 deletion is surprising, (i) because it removes half of AZFc and (ii) because the gr/gr deletion, which removes a similar set of testis-specific genes, predisposes to spermatogenic failure. Our present findings suggest either that the b2/b3 deletion has at most a modest effect on fitness or that, within branch N, its effect has been counterbalanced by another genetic, possibly Y-linked, factor.