Insect hygroreceptor responses to continuous changes in humidity and air pressure.

The most favored model of humidity transduction views the cuticular wall of insect hygroreceptive sensilla as a hygromechanical transducer. Hygroscopic swelling or shrinking alters the geometry of the wall, deforming the dendritic membranes of the moist and dry cells. The small size the sensilla and their position surrounded by elevated structures creates technical difficulties to mechanically stimulate them by direct contact. The present study investigated hygroreceptors on the antennae of the cockroach and the stick insect. Accurately controlled, homogeneous mechanical input was delivered by modulating air pressure. Both the moist and dry cells responded not only to changes in air pressure but also in the opposite direction, as observed during changes in air humidity. The moist cell's excitatory response to increasing humidity and increasing air pressure implies that swelling of the hygroscopic cuticle compresses the dendrites, and the dry cell's excitatory response to decreasing humidity and decreasing air pressure implies that shrinking of the hygroscopic cuticle expands the dendrites. The moist and dry cells of the stick insect are more sensitive to pressure changes than those of the cockroach, but the responses to air pressure are generally weaker than to humidity. Therefore the hygroreceptive sensilla differ in their physical properties and constitutions. Furthermore, the mechanical parameters associated with homogeneous changes in air pressure on the sensillum surface can only partially account for the responses of the moist and dry cells of both species to humidity stimulation.

Mitochondrial DNA sequence variation in the eastern house mouse, Mus musculus: comparison with other house mice and report of a 75-bp tandem repeat.

The control region and flanking tRNAs were sequenced from 139 Mus musculus mitochondrial DNAs (mtDNAs) from mice collected at 44 localities extending from Germany to Japan. Among the 36 types of M. musculus mtDNA resolved, five have an added 75-bp direct repeat; the two copies within an individual differ by two to four base substitutions. Among 90 M. domesticus mtDNAs sequenced, 12 new types were found; 96 M. domesticus types have now been identified by sequencing this segment. Representative mtDNAs from M. castaneus, M. macedonicus, M. spicilegus and M. spretus were also sequenced. A parsimony tree for the M. musculus mtDNAs is about half as deep as the tree for the M. domesticus mtDNAs, which is consistent with the idea that M. musculus is genetically less diverse and younger than M. domesticus. The patterns of variation as a function of position are similar but not identical in M. musculus and M. domesticus mtDNAs. M. castaneus and M. musculus mtDNAs are allied, at a tree depth about three times as great as the start of intra-M. musculus divergence. The coalescence of the M. musculus and M. castaneus mtDNAs is about half as deep as their coalescence with the M. domesticus mtDNA lineages. The mtDNAs of the aboriginal M. macedonicus and M. spicilegus are each other's closest relatives, at a tree depth greater than the deepest intracommensal node. The mtDNA results support the view that the aboriginal M. spretus is the sister group of the other five species.

Low diversity of t haplotypes in the eastern form of the house mouse, Mus musculus L.

In previous studies, 13 different recessive embryonic lethal genes have been associated with t haplotypes in the wild mice of the species Mus domesticus. In this communication we have analyzed five populations of Mus musculus for the presence and identity of t haplotypes. The populations occupy geographically distant regions in the Soviet Union: Altai Mountains, western and eastern Siberia, Azerbaijan and Turkmenistan. No t haplotypes were found in mice from eastern Siberia. In the remaining four populations, t haplotypes occurred with frequencies ranging from 0.07 to 0.21. All the t haplotypes extracted from these populations and analyzed by the genetic complementation test were shown to carry the same lethal gene tcl-w73. In one population (that of western Siberia), another lethal gene (tcl-w5) was found to be present on the same chromosome as tcl-w73. This situation is in striking contrast to that found in the populations of the western form of the house mouse, M. domesticus. In the latter species, tcl-w73 has not been found at all and the different populations are characterized by the presence of several different lethal genes. The low diversity of t haplotypes in M. musculus is consistent with lower genetic variability of other traits and indicates a different origin and speciation mode compared to M. domesticus. Serological typing for H-2 antigenic determinants suggests that most, if not all, of the newly described t haplotypes might have arisen by recombination of tw73 from M. musculus with t haplotypes from M. domesticus either in the hybrid zone between the two species or in regions where the two species mixed accidentally.

Polymorphism of unique noncoding DNA sequences in wild and laboratory mice.

Two DNA probes, D17Tu1 and D17Tu2, were isolated from a genomic DNA library containing only two mouse chromosomes, one of which is chromosome 17, carrying the major histocompatibility complex (H-2), as well as the t complex genes. The D17Tu1 probe was mapped to the centromeric region of chromosome 17 and the D17Tu2 probe to the S region of the H-2 complex. Neither of the two probes appeared to detect any genes, but both contained unique, nonrepetitive sequences. Typing of DNA obtained from a large panel of mice revealed the presence of four D17Tu1 patterns in inbred mouse strains, one very common, one less common, and two present in one strain each. The two common patterns could not be detected in appreciable frequencies in the European wild mice tested (one of the two patterns was, however, found in Australian wild mice). Conversely, the patterns found frequently in European wild mice are absent in the laboratory mice. We therefore conclude that wild mice from the sampled regions of Europe could not have provided the ancestral stocks from which inbred strains were derived. Only one D17Tu1 pattern was found in all the populations of Mus musculus tested, while eight patterns were found in Mus domesticus, with virtually all the populations being polymorphic. We suggest that this difference reflects different modes in which the two species colonized Europe. The distribution of the D17Tu2 patterns in inbred strains correlates with the distribution of H-2 haplotypes.

A cDNA clone from the sea lamprey Petromyzon marinus coding for a scavenger receptor Cys-rich (SRCR) domain protein.

Our knowledge of the immune system in the early vertebrates, the Agnatha, and the molecules involved in their immune reactions is fragmentary. By serendipity we discovered a cDNA clone in a library made from gut poly(A)+RNA of the sea lamprey, Petromyzon marinus (Pema), that translates into the SREG (SRCR-EGF, see below) protein which resembles cell-membrane proteins of mammalian immune cells. The putative translated product is a type-I integral membrane glycoprotein which contains two scavenger receptor Cys-rich (SRCR) domains flanking five epidermal growth factor (EGF)-like repeats. The two SRCR domains are closely related to CD6 (expressed on human lymphocytes), WC1 (expressed on mammalian CD4-CD8(-)-gamma delta T cells) and M130 (expressed on human macrophages). The Pema-SREG may therefore be involved in intercellular contacts and cell activation or differentiation in the immune system. It is thus a potential marker that can be used to investigate the lamprey immune system.

Characterization of dentin matrix protein 1 gene in crocodilia.

Several clones containing DMP1 cDNA were isolated from a caiman tooth library by screening with a platypus DMP1 probe. The caiman DMP1 shows little amino acid sequence similarity to mammalian DMP1s for much of its length. A few highly conserved regions can, however, be identified that correspond to the slowly evolving parts of the corresponding mammalian genes. Southern blot analysis using probes comprising either conserved regions or longer segments of the gene indicates that only a single DMP1 locus exists. In coding regions, exon-intron boundaries and reading frames are shared by caiman and mammalian genes with the exception of exons 1 and 5, which are longer in the caiman. The repetitive sequence of the last exon is shared by mammals and caiman as are the high Ser content and acidity due to a high proportion of Asp and Glu residues. The conserved mammalian cell-attachment signal Arg-Gly-Asp is absent in the caiman DMP1. In contrast to the amelogenin gene, the DMP1 gene appears to evolve rapidly in vertebrates.

Evidence for insertion of a new intron into an Mhc gene of perch-like fish.

The evolution of the major histocompatibility complex (Mhc) has been studied to understand the origin of the immune system, of which it constitutes an essential part. In the present study, the Mhc is used to shed light on questions regarding the origin of introns and the phylogeny of fishes. The organization of the coding (exon) and non-coding (intron) regions of both class I and class II major histocompatibility complex (Mhc) genes is highly conserved in all vertebrate classes; the only variation observed until now is in the number of exons encoding the membrane-anchoring part. Moreover, there is a good correspondence between the exon-intron organization at the DNA level and the division into structurally and functionally defined domains at the protein level. Here we describe the first major exception to this uniformity. The immunoglobulin-like domain of the class II beta-chains in perch-like fishes (Percomorpha) is not encoded in one exon, as it is in all other vertebrates studied thus far, but in two exons. The length of the extra intron varies from gene to gene and from species to species, but is generally less than 200 base pairs (b.p.). Only one of the sequenced introns is about 500 b.p. long. In some of the genes, the intron contains a hexamer repeat. The repeat is present in the transcript at the site at which the intron interrupts exon 3 in the genomic DNA. The intron may therefore have arisen by repeated tandem duplication of this sequence.(ABSTRACT TRUNCATED AT 250 WORDS)

The origin and age of haplochromine fishes in Lake Victoria, east Africa.

According to a widely held view, the more than 300 species of haplochromine cichlid fishes in Lake Victoria (LV), East Africa, originated from a single founder species in less than 12,000 years. This view, however, does not follow from the published geological and molecular evidence. The former does indeed suggest that the LV basin dried out less than 15,000 years ago, but it does not provide any information about the species that re-colonized the new lake or that remained in the rivers draining the area. The molecular evidence is inconclusive with respect to the origin of the LV haplochromines because cichlids from critical regions around LV were not adequately sampled; and as far as the age of the LV haplochromines is concerned, it in fact led to an estimate of 250,000-750,000 years old. In the present study, mitochondrial DNA (control region) variation was determined by heteroduplex and sequencing analyses of more than 670 specimens collected at widely distributed East African riverine and lacustrine localities. The analyses revealed the existence of seven haplogroups (I-VII) distinguishable by characteristic substitutions. All endemic LV samples tested fell into one of these haplogroups (V) which, however, was also found to be present at various other localities, both riverine and lacustrine, outside LV. Within this haplogroup, four subgroups (VA through VD) could be distinguished, two of which (VB and VC) were represented in LV and at other localities. The great majority of the LV haplochromine species could be classified as belonging to the VC subgroup, which was found only in LV and in the rivers draining into it. Hence, while the endemic haplochromine species of LV could not have originated from a single founding population, the lake does harbour a large species flock which probably arose in situ.

Fine structure of olfactory sensilla in myriapods and arachnids.

Structural features of various types of olfactory sensilla are reviewed. 1) Sensilla basiconica which differ in form and size are found on the antennae of centipedes and millipedes. Their walls show longitudinal slits or grooves that either open into the sensillum lumen or do not penetrate the cuticle. In other such sensilla the outer surface is pierced by pores and the inner surface grooved and pocketed. These sensilla are innervated by one to six sensory cells. Their unbranched outer dendritic segments extend to the tip of the sensillum. The sensory cells are surrounded by two or three sheath cells which terminate at the sensillum base or form a continuous tube around the entire length of the outer dendritic segments. 2) Temporal organs of centipedes are located between the insertion of the antenna and the ocelli. These sensilla consist of a shallow cuticular ring with a central sensory plate made up by a layer of unperforated cuticle or a capsule with a mushroom-shaped structure inside formed by fibrous-looking cuticle. A dozen sensory cells with unbranched outer dendritic segments innervate each sensillum. They extend toward the sensory cuticle and pass just below it. Numerous sheath cell processes run parallel to the outer dendritic segments up to the sensory cuticle. 3) Thread-like flagella of Pauropoda are found on the antennae. They possess a flexible unperforated cuticular wall. These sensilla contain nine sensory cells surrounded by several sheath cells which form a continuous cytoplasmic tube around the outer dendritic segments. 4) Single-walled sensilla with numerous plugged pores penetrating the cuticular wall occur on the tarsus of the first leg in ticks. Each sensillum is innervated by 4-15 sensory cells. Three sheath cells terminate in the base of the sensillum. 5) Double-walled sensilla with spoke canals are found on the first tarsus of ticks. Their shaft is longitudinally grooved. Pore canals lead inward from the bottom of the grooves and open into vase-shaped chambers. From its base these canals extend into the lumen of the sensillum which contains unbranched outer dendritic segments of 1-2 sensory cells. 6) Single-walled sensilla with pore openings occur on the distal tarsal segments of the first leg of whip spiders. These sensilla are innervated by 40-45 sensory cells. Their unbranched outer dendritic segments fill the shaft lumen and extend partly into the wall pores. Microvillus-shaped sheath cell processes line the inner surface of the cuticular wall.(ABSTRACT TRUNCATED AT 400 WORDS)

Automated laser fluorescence analysis of randomly amplified polymorphic DNA: a rapid method for investigating nosocomial transmission of Acinetobacter baumannii.

A rapid method for genotyping Acinetobacter baumannii based on PCR-fingerprinting with fluorescent primers was evaluated. Automated laser fluorescence analysis (ALFA) enabled on-line generation of high resolution DNA-fingerprints during polyacrylamide gel electrophoresis of randomly amplified polymorphic DNA (RAPD) products. The results were in concordance with macro-restriction fragment patterns produced by pulse-field gel electrophoresis (PFGE) of ApaI digests of chromosomal DNA. RAPD-ALFA was able to identify homologous strains suggestive of horizontal transmission in < 8 h after colonies were obtained on solid media, whereas PFGE analysis took c. 90 h. Speed and digitised data format renders RAPD-ALFA attractive for routine in-house epidemiological screening of isolates from intensive care and other hospital units.

Typing of methicillin-resistant Staphylococcus aureus isolates from Düsseldorf by six genotypic methods.

Nosocomial infections caused by methicillin-resistant Staphylococcus aureus (MRSA) represent an increasing problem in hospitals. Quick and reliable typing methods are required to obtain information about the relatedness of MRSA isolates and to allow faster implementation of appropriate infection control measures. This investigation describes the distribution of MRSA isolates from 11 hospitals in the Düsseldorf region of Germany, and the ability of six different genotypic typing techniques -- pulsed-field gel electrophoresis (PFGE), random amplification of polymorphic DNA (RAPD), 16S-23S rDNA spacer amplification, protein A-gene PCR, PCR characterisation of the hypervariable region (HVR) adjacent to mecA, and coagulase gene-PCR -- to detect different unrelated types. Of 7814 S. aureus isolates tested, 489 (6.3%) were MRSA, of which 183 were selected for subsequent molecular analyses on the basis of being the first MRSA isolated from colonised or infected patients. Larger hospitals had a higher incidence of MRSA and a greater variability in genotypes than smaller hospitals. All methods confirmed the presence of two main clonal types. The ability of techniques to detect different unrelated types was found to be as follows: PFGE, 28 types; 16S-23S rDNA spacer-amplification, 10 types; RAPD, nine types; protein A-gene PCR, five types; HVR-PCR, five types; and coa gene-PCR, two types. Combination of PFGE and one other PCR-based method (spacer-amplification, RAPD or protein-A gene PCR) provided the best resolution of types and allowed the identification of subtypes. Similar molecular types were identified with international MRSA isolates. Although PCR-based techniques have the advantage of rapid performance and easy handling, their discriminatory capacity is inferior compared to the more labour intensive PFGE.

Origin of the North American house mouse.

The house mouse, Mus domesticus, was introduced to the American continent in the post-Columbian era. We have used mouse chromosome 17 DNA probes to trace the origin of the wild house mice on the East Coast of the United States. Of the four probes used, one in particular proved to be informative in this regard. The D17Tu20 probe defines a polymorphism at a locus telomeric of the H-2 complex. TaqI restriction enzyme digests of genomic DNA blotted and hybridized with the D17Tu20 probe revealed the existence of restriction fragments shared by mice from the Atlantic coast of England, France, and the United States but absent in all other tested populations sampled from different parts of the world. This unique polymorphic pattern apparently arose by the loss of two restriction sites in the population on the coast of Brittany. The mutations then presumably spread to England, and from there to the United States. Since the mutations are also present in mice from Florida, English (rather than Spanish) mouse populations may have been either the sole or the main source of immigrants to the eastern United States. This conclusion is also supported by data obtained with the other probes. Presence of the D17Tu20 mutations in some of the laboratory strains indicates that American wild mice contributed to the gene pool of the inbred strains. We postulate that the colonization of North America by English wild mice began in the second half of the seventeenth century.

Continuous tonic spike activity in spider warm cells in the absence of sensory input.

The warm cells of the spider tarsal organ respond very sensitively to low-amplitude changes in temperature and discharge continuously as the rate of change in temperature reaches zero. To test whether the continuous tonic discharge remains without sensory input, we blocked the warm cell's receptive region by Epoxy glue. The activity continued in this situation, but its dependence on temperature changes was strongly reduced. We interpret this to mean that the warm cells exhibit specific intrinsic properties that underlie the generation of the tonic discharge. Experiments with electrical stimulation confirmed the observation that the warm cells persist in activity without an external drive. In warm cells with blocked receptive region, the response curves describing the relationship between the tonic discharge and the level of depolarization is the same for different temperatures. In warm cells with intact receptive region, the curves are shifted upward with rising temperature, as if the injected current is simply added to the receptor current. This indicates a modulating effect of the receptor current on the tonic discharge. Stimulation causes a change in the tonic discharge rate and thereby enables individual warm cells to signal the direction in addition to the magnitude of temperature changes.

Unusual fine structure of sensory hair triad of the millipede, Polyxenus.

Three sensory hairs are inserted at right angles to teach other at the temporal region of the head of Polyxenus. They display structural features characteristic of trichobothria and of scolopidia as well. They also manifest several unusual details: 1) The dendritic cilia are enclosed within a capsule formed by enveloping cells. 2) The dendritic cilia are interconnected by desmosome-like junctions. 3) The 9 X 2+0 organization of the dendritic ciliary microtubules is maintained over the entire length of the cilia. 4) Neither a tubular body nor even so much as an inflation of the dendritic cilia develop. 5) Pores and pore tubules occur in the lower halves of the hairs. This uncommon combination of structural details renders the modality of the adequate stimulus uncertain. Though most features suggest a mechanoreceptor, the hairs could function as chemo-, hygro- and/or thermoreceptors as well.

Low rates of change enhance effect of humidity on the activity of insect hygroreceptors.

The inability to measure humidity during stimulation has so far prevented us from understanding the contribution of moist cells and dry cells to orientation in a gradient of humidity. The problem was solved in the present study by means of a UV-absorption hygrometer that made it possible to monitor humidity at a rate of 100 Hz. The antennal moist and dry cells of the cockroach were exposed to humidities alternatively falling or rising at low rates between -1% RH s(-1) and +1% RH s(-1) (relative humidity). Impulse frequency of both types of cells depended simultaneously on instantaneous humidity and its rate of change. High frequencies of the moist cells signal high humidity. But at a given humidity, the response frequency is higher still when humidity is also rising. Conversely, high frequencies of the dry cell signal low humidity, and frequency is higher still at a given humidity when humidity is also falling. These responses ensure that the cockroach spent a minimum time in environments where desiccation or hydration occur and may thus protect the animal from emerging accidentally from under cover into moving air. In the constant-humidity retreat of the cockroach, fluctuating or even drifting discharge frequencies could serve as an early warning: return!

Nature genetic basis and evolution of the haemoblobin polymorphism in Chironomus.

Chironomus larvae exhibit considerable haemoblobin polymorphism. Chironomus tnetans has 10 and C. pallidivittatus has 8 electrophoretically different Hb-chains. With the exception of one Hb-chain, all are species-specific. The hybrid which is fertile, shows the Hb-pattern of both parents. In the F2 and subsequent generations, considerable chromosome rearrangements occurs. Since the chromosomes of the parent species can be distinguished in the polytene state, Hb-patterns can be correlated with specific chromosomal constitutions. All the species-specific Hb-genes are located on one chromosome. This finding suggests that the Hb-genes have evolved through multiple gene duplications. Different mechanisms for gene duplication are discussed.

Major histocompatibility complex (MHC) class II polymorphism and paternity in the monogamous Hypogeomys antimena, the endangered, largest endemic Malagasy rodent.

Sequence variation at a major histocompatibility complex (MHC) class II gene was examined in Hypogeomys antimena, a monogamous endemic rodent of Madagascar. The study was conducted throughout its remaining geographical range (20 x 40 km) by direct sequencing and single-strand conformation polymorphism (SSCP). The objectives of the study were: (i) to investigate levels of polymorphism in the MHC complex of a highly endangered species that experienced a severe reduction in population size; and (ii) to investigate the genetic mating system by assessing the frequency of extra-pair paternity (EPP) as EPP might have important consequences to increase gene flow and, therefore, genetic variability within a population. The amplified gene segment had a very low variability (only two alleles) in H. antimena compared with other mammalian species. The alleles segregated consistently with Mendelian expectations in families. No case of EPP was found. The present data suggest no difference between the social and the genetic mating system.

Threshold for detecting temperature changes in a spider thermoreceptor.

1. The threshold for detecting a change in temperature of a warm receptor in the wandering spider Cupiennius salei was determined by means of its frequency-dependent noise. To accomplish this, the warm receptor was regarded as a linear system consisting of two components, an amplifier (gain of the frequency response) and noise at its input added to the temperature stimulus (input noise density). 2. The frequency response was investigated with sinusoidal temperature modulations at frequencies between 0.05 and 12.8 Hz. The gain increased by 3.5 dB/octave in the frequency range between 0.05 and 6.4 Hz, from 0.19 to 3.1 degrees C-1. However, at the highest frequency, 12.8 Hz, the gain was reduced. 3. The noise density of the warm receptor was measured by the root-mean-square noise amplitude of the gain. The output noise density of the warm receptor, which describes the noise density of the gain, was constant at approximately 0.2 Hz-0.5 in the 0.05 to 6.4 Hz range, and increased at higher frequencies. The input noise density, given by the ratio of output noise density to gain, decreased by -2.7 dB/octave between 0.05 and 6.4 Hz, from 1.1 to 0.12 degrees C*Hz-0.5. 4. To define the threshold for detection of temperature changes from the input noise density, the energy of the threshold was equated to the energy of the noise. Assuming a signal-to-noise ratio of 1 and an upper limiting frequency of 10 Hz, the threshold estimated for the wandering spider Cupiennius ranges from 0.6 to 0.08 degrees C, depending on whether the inputs from only 1 or all 70 warm receptors of the 10 tarsal organs are combined.