Recent Hybridization Research Articles

Genetic Identification of Centropomine Fishes

The purposes of this study were to evaluate the present species classification, to develop genetic methods for diagnosing morphologically indistinguishable juveniles, and to investigate the potential for introgressive hybridization for species of the percoid fish genus Centropomus (Pisces: Centropomidae). We analyzed specimens representing all nominal species using allozyme electrophoretic data and sequence data from a 618-base-pair portion of the mitochondrial DNA (mtDNA) 16S ribosomal RNA (rRNA) gene. Outgroup taxa from the confamilial genus Lates were also included. Results of the allozyme analysis, based on 27 presumed protein-coding gene loci, were in good agreement with the most recent taxonomic revision of the genus. All morphological species were identifiable by diagnostic allozyme loci except the largescale fat snook C. mexicanus (also known as the constantino snook), which was distinguishable from its sympatric sibling species, the fat snook C. parallelus by a significant allele frequency difference at G3PDH* and Mexican snook C. poeyi which was distinguishable from its transisthmian sister species, white snook C. viridis by a significant allele frequency difference at GPI-1*. Results of the 16S rRNA analysis were also highly congruent with the morphologically based taxonomic revision. All morphological species were unambiguously characterized using 16S rRNA sequence, including those species not identifiable by allozymes. The number of autapomorphic base substitutions for each species ranged from 2 to 12. The minimum number of base substitutions that separated any pair of taxa was 11; no substitutions were observed within taxa. Composite restriction patterns generated by five restriction endonucleases distinguish the 12 nominal species. For species identification, keys based on allozymes and on restriction enzyme analysis of the 16S rRNA gene were formulated for the genus. No conclusive evidence for recent or ongoing hybridization between species was observed.

Pressure effects on the superconductivity and magnetic order ofY1−xPrxBa2Cu4O8

Pressure effects on the superconductivity and magnetic order of polycrystalline ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ $(0<~x<~1)$ were investigated. It was found that ${T}_{c}$ decreases monotonically with Pr concentration x from ${T}_{c}\ensuremath{\sim}80\mathrm{K}$ for $x=0$ to ${T}_{c}\ensuremath{\sim}6\mathrm{K}$ for $x=0.7.$ The critical Pr concentration ${x}_{\mathrm{cr}}$ required to suppress the ${T}_{c}$ to zero is estimated to be around 0.72, which is larger than that (\ensuremath{\sim}0.55) in ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}.$ The normal-state resistivity remains in the same order of magnitude through whole series in contrast to a metal-insulator transition observed in ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}.$ A change of sign in the value of ${(dT}_{c}{/dP)}_{P=0}$ in ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ with Pr doping is observed which is similar to that of ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}.$ The ${T}_{N}$ in ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ decreases with increasing external pressure as in ${\mathrm{PrBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7}.$ The results for ${T}_{c}$ and ${T}_{N}$ variations with Pr doping and pressure effect in ${\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{4}{\mathrm{O}}_{8}$ cannot be fully explained by the recent hybridization theory.

Molecular characterization of a novel amplicon at 1q21-q22 frequently observed in human sarcomas.

In a recent comparative genomic hybridization (CGH) study of a panel of sarcomas, we detected recurrent amplification of 1q21-q22 in soft tissue and bone tumours. Amplification of this region had not previously been associated with sarcoma development, but occasional amplification of CACY/S100A6 and MUC1 in 1q21 had been reported for melanoma and breast carcinoma respectively. Initial screening by Southern blot analysis showed amplification of S100A6, FLG and SPRR3 in several sarcomas and, in a first attempt to characterize the 1q21-q22 amplicon in more detail, we have now investigated the amplification status of these and 11 other markers in the region in 35 sarcoma samples. FLG was the most frequently amplified gene, and the markers located in the same 4.5-Mb region as FLG showed a higher incidence of amplification than the more distal ones. However, for most of the 14 markers, amplification levels were low, and only APOA2 and the anonymous marker D1S3620 showed high-level amplifications (> tenfold increases) in one sample each. We used fluorescence in situ hybridization (FISH) to determine the amplification patterns of two overlapping yeast artificial chromosomes (YACs) covering the region between D1S3620 and FLG (789f2 and 764a1), as well as two more distally located YACs in nine selected samples. Six samples had amplification of the YAC containing D1S3620 and, in three, 764a1 was also included. Five of these tumours showed normal copies of the more distal YACs; thus, it seems likely that an important gene may be located within 789f2, or very close. Two samples had high copy numbers of the most distal YACs. Taken together, FISH and molecular analyses indicate complex amplification patterns in 1q21-q22 with at least two amplicons: one located near D1S3620/789f2 and one more distal.

Molecular and Osteological Heron Phylogenies: Sources of Incongruence

Payne and Risley's (1976) comparison of 33 osteological characters of herons was the first cladistic estimate of heron phylogeny. Among their findings were two major clades: (1) Boat-billed Heron (Cochlearius cochlearius), night-herons, and bitterns; and (2) ti- ger-herons and day-herons. In contrast, more recent DNA-DNA hybridization comparisons, cladistic analyses of vocalizations, and mtDNA sequence data portray a more asymmetric phylogeny, with day-herons and night-herons forming a clade with bitterns as their sister group, and tiger-herons and the Boat-billed Heron branching basally. To explore the source of the disagreement between these phylogenetic estimates, we reanalyzed the osteological data using modern cladistic methods and compared the results with the DNA-DNA hybrid- ization tree using taxonomic congruence analysis. Character-by-character comparisons be- tween trees and among lineages within trees suggest that similar cranial morphology in the relatively unrelated tiger-herons and day-herons has resulted in the misleading attraction of these two lineages in osteological estimates of phylogeny. Apparent convergence in bill mor- phology and modifications of orbital structures for nocturnal feeding in night-herons and Boat-billed herons have led to further disagreement between data sets. In part, problems in the osteological data stem from the relatively small character matrix of Payne and Risley (1976), but ultimately they may derive from using highly adaptive characters to reconstruct phylogeny. In this case, the cranial characters are functionally correlated as part of the pi- scivorous heron Bauplan. As such, they relate to the forces responsible for speciation and divergence in the early history of the group but may not be useful for phylogenetic inference. The discovery of bias in cranial characters underscores the value of taxonomic congruence analysis and the need to explore cases of phylogenetic incongruence. Received 19 June 1996, accepted 24 June 1997. CONGRUENCE ANALYSIS of independent esti- mates of phylogeny is a useful method for judging phylogenetic accuracy (Mickevich and Johnson 1976). Agreement in branching pat- terns in trees from different data sets provides strong evidence of phylogeny (Bledsoe and Raikow 1990, Swofford 1991, Miyamoto and Fitch 1995). When phylogenies disagree, how- ever, interesting lessons about evolution and the mechanics of phylogenetic estimation also may be learned. Incongruence can result from biased data derived from poor sampling strat- egies (e.g. using correlated characters) or idio- syncrasies of evolution (e.g. differences in rates of character change or character convergence) in one or both data sets (Wiley 1981, Patterson et al. 1993). Because the discovery and expli- cation of characters that have evolved in unusu- al ways are main goals of evolutionary biology, the analysis of incongruence is an interesting

The hypothesis of hybrid origin of Poa jemtlandica supported by morphometric and isoenzyme data

Morphometric and isozyme data were used to test the hypothesis that the pseudoviviparous Poa jemtlandica has originated as a hybrid between the sexual P flexuosa and the facultative apomict P alpina. Plants were sampled from three localities in southern Norway. In addition, some Icelandic plants were included. Both morphometric and isozyme data clearly support the hybrid hypothesis. Poa jemtlandica was morphologically intermediate between its supposed parents in several individual characters as well as in a discriminant analysis. Seven enzyme systems were analysed. Eight areas of activity were interpreted as “loci”, each of which certainly represented several duplicated genes in these plants which all are polyploid. A total of 27 different multilocus phenotypes was observed: ten phenotypes in P alpina var. vivipara, eight phenotypes in I. alpina var. alpina, seven phenotypes in P jemtlandica, and three phenotypes in P flexuosa. The phenotype of Icelandic P jemtlandica was identical to that of P. jemtlandica from one of the Norwegian localities. Additive electrophoretic patterns were observed for P jemtlandica at four individual “loci”. At the remaining “loci” some phenotypes of P. jemtlandica were most similar to P. flexuosa, others to P alpina. The data also suggest that P jemtlandica has originated several times, but there is no indication of frequent or recent hybridization where the species coccur today.

Medical Innovations: Historiography, Heterogeneity and `The Mangle of Practice'

A notable feature of much recent historiography of medicine has been the extent to which it has embraced the agendas of other fields of enquiry. Medical Innovations in Historical Perspective is a good example of this process.' The volume is presented to us by John Pickstone (both editor and series editor) as medical history which has been enlightened by input from the sociology of technology, the sociology of scientific knowledge and the theory of economic history, to mention only three. The explicit intention is 'to present ... medicine as [an] aspect of modem culture, analysing [its] economic, social and political aspects' (ix) and 'to investigate the uses and consequences of technical knowledge, and how it was shaped within particular economic, social and political structures' (ix). There can be no doubt that the quality and sophistication of the debate in medical history has been raised by such encompassing agendas. But, one might still ask, has the incorporation of sociological emphases been done in such a manner as brings optimum benefit to the historiography? Despite much recent cross-fertilization and professional hybridization, sociology of science and the history of science (and medicine) retain distinctive professional characteristics. This was demonstrated, not so long ago, by the differing responses of the two camps to John Law's essay on Portuguese Imperial expansion.2 Arguing that due weight had not been previously given to interaction with the physical environment in accounts of social change, Law emphasized the importance of agencies such as wind, tide and current, and the partial control painfully and gradually achieved

Phylogenetic relationships and introgression patterns between incipient parapatric species of Italian brown trout (Salmo trutta L. complex)

AbstractGenetic variation at 47 protein loci was investigated in 16 wild brown trout populations from the Po basin and three major domesticated stocks used for stocking this area. Twenty‐four loci were polymorphic and large frequency differences were found at 15 of them. The most significant allozyme variations were congruent with the mtDNA sequence polymorphism previously observed in the same samples. We confirmed the occurrence of two parapatric incipient species, Salmo marmoratus and S. trutta fario, previously identified by morphological traits. These two species were fixed or nearly fixed for alternate alleles at eight loci (Nei's standard genetic distance = 0.16–0.18), but introgression was detected between adjacent samples of the two forms. Divergence levels at both mtDNA and nuclear loci suggested that the differentiation between S. marmoratus and S. trutta fario started between 3 and 1 million years before present. Variation at protein loci and mtDNA supported the hypothesis that the third species found in this area, S. carpio (an endemic population of the lake Garda) was issued from a recent hybridization of the two first species. Finally, we showed that three of the major Italian fish‐farm strains originated from the Atlantic side and displayed substantial genetic differences with the natural populations of the Po basin. Most of these populations were contaminated by stocking with introgression rate ranging from 0 to 70% and measures of protection and restoration of the rich genetic diversity present in this area should be urgently applied.

Excited states of the C 60 dimer

Recent investigations are reported on two different sorts of fullerene dimer. The first type is a simple cluster of two C 60 molecules, i.e., a van der Waals complex. The second one is a covalently bound system. The nature of the electronic excitations has been studied for these model systems. It is found that for the van der Waals complex the low-lying excitations remain localized on one monomer and, thus, they are precursors of the Frenkel-type excitons in the crystal. At significantly higher energies, one obtains so-called charge transfer type excitations, which are precursors of the Wannier excitons. The picture of different excitations resembles that of a very weakly bound system, e.g., two benzene molecules at 5 Å from each other. For the covalent dimer, we considered the binding situation where there are two single bonds between the monomers. The extent of the conjugation between the two C 60 molecules is monitored by the change in the excitation energies. The lowest-lying transitions were observed at higher energies than those in the monomer. This feature is quite unusual for a system exhibiting at least partial conjugation, and it is in agreement with recent band structure calculations and hybridization studies in the fullerene polymer.

Melanin-concentration hormone updated functional considerations

The melanin-concentrating hormone (MCH) is a vertebrate neuropeptide produced in hypothalamic perikarya whose fibers project to most regions of the brain and into the spinal cord. Its role as a neurohypophyseal color-change hormone is peculiar to teleost fish, but recent studies in mammals suggests that MCH itself, and other peptides derived from the same precursor, may participate in multiple functions in the central nervous system, modulating behavior and the perception of sensory information. Recent hybridization studies in mammals have greatly increased our understanding of the response of the MCH system to environmental factors, such as osomotic challenge, lactation, stress, and changes in corticosteroid levels. Further studies in lower vertebrates are needed to highlight the physiologically important functions that have led to the structural conservation of the MCH peptide during vertebrate evolution

DNA Markers Reveal Hybrids Between Two Diverse Background Genotypes in Australian Collections of the Bean Rust Fungus Uromyces appendiculatus

Two classes of molecular markers, RFLPs (restriction fragment length polymorphisms) and RAPDs (random amplified polymorphic DNA) were used to assess genetic diversity among Australian bean rust isolates (Uromyces appendiculatus (Pers.) Unger var. appendiculatus) collected from diverse geographic locations spanning the period 1973-1990. Initially we screened 22 isolates using WLPs from five DNA probes. This was followed by analysis of a subset of 12 of these isolates using RFLPs from 10 cDNA probes and RAPDs from 10 arbitrary primers for a comprehensive evaluation of background genotype. Polymorphic bands revealed the existence of two divergent clusters of isolates, representing genotypes designated A and B. The RFLP markers showed 30% band dissimilarity between A and B, and RAPDs 16% dissimilarity. Isolates in a third cluster (genotype AB) exhibited most of the polymorphic bands present in A and B, but no unique polymorphic bands of their own, indicating that they had most probably arisen from recent hybridisation between isolates of genotype A and B. The subset of 12 isolates included 10 race phenotypes, but no clear correlation between background genotype (as assessed by RFLP and RAPD markers) and race phenotype was evident. We suggest that Australian races of bean rust have most probably evolved by a combination of mutation to virulence from common A and B background genotypes, and genetic recombination.

Advances in the theory and practice of DNA-hybridization as a systematic method.

DNA hybridization continues in the 1990s to provide insight into phylogeny and evolution. The resilience of this 30-year-old distance technique may be attributed to its fundamental power as a comparative method, as well as to advances in our understanding of its operation and improvements in experimental design and data analysis. These attributes and advances, along with the assumptions and limitations of DNA hybridization, are discussed in this paper. Examples are provided of recent DNA hybridization studies of molecular, morphological, and behavioral systematics and evolution.

The evolutionary ecology of Daphnia.

In order to generate genetic markers from both nuclear and mitochondrial DNA, we used three PCR-based techniques (RAPD, mtDNA-RFLPs, and sequencing of an amplified mtDNA fragment) to illuminate various aspects of the population genetics of large-lake Daphnia species. Estimations of genetic diversity at different taxonomic levels integrated with ecological data revealed insights into the genetic components of the evolutionary process of interspecific hybridization in these Daphnia species, which had previously been documented with allozyme markers. Our new molecular data suggest the occurrence of recent hybridization and backcrossing events, and allow the identification of the maternal species of hybrid clones.

Crustal modification during subduction-zone magmatism: Evidence from the southern Salar de Uyuni region (20°-22°S), central Andes

Late Cenozoic volcanic rocks erupted in the southern Salar de Uyuni region of the central Andes provide evidence for recent modification of both the lower and upper continental crust during subduction-zone magmatism. At a given SiO 2 content, K 2 O and related incompatible trace element concentrations increase eastward in basaltic andesite samples and are associated with increasing Sr isotopic ratios and decreasing Sr concentrations. These data favor a model in which basaltic andesite magmas are contaminated by lower continental crust that becomes increasingly more mafic toward the active volcanic front because of relatively recent intrusion and hybridization by primary basaltic magmas. Compositions of andesitic lavas continue the geochemical trends established by the basaltic andesite samples except that Sr isotopic ratios of lavas erupted at the arc front are constant to slightly decreasing with increasing SiO 2 contents. Assimilation of upper-crustal rocks that also vary in composition across the strike of the arc is the most plausible mechanism to produce the distinct Sr isotopic trends of the andesitic lavas. At the volcanic front, the magmas producing the andesitic lavas assimilated rocks within the Quaternary volcanic and plutonic complex of the Andean arc itself. Toward the east, the magmas assimilated basement rocks that become progressively older with distance from the volcanic front because of diminishing modification by late Cenozoic arc magmatism. Thus, the across-arc geochemical trends in the southern Salar de Uyuni region are consequences of spatial variations in the composition of the lower and upper continental crust, and these variations appear to be linked to the subduction process itself.

Response to Wayne, Nowak, and Phillips and Henry: Use of Molecular Characters in Conservation Biology

In our recent letter (Dowling et al. 1992), we stated our concerns over two interrelated issues: (1) the use of genetic (i.e., molecular) characters in identifying species and their hybrids, and (2) the role of hybridization in evolution. The letter was stimulated by Wayne and Jenks' (1991) analysis of mitochondrial DNA (mtDNA) variation in the red wolf, Canis rufus, and subsequent interpretations presented in both the professional (e.g., Gittleman & Pimm 1991) and popular literature (e.g., Rennie 1991). Although consequences for conservation of the red wolf were addressed in those papers, our letter was focused more on the broader implications for conservation of endangered taxa. In this issue, Nowak (1992) and Phillips and Henry (1992) have presented views generally in accord with ours, providing additional behavioral, ecological, morphological, and paleontological evidence supporting distinctiveness of the red wolf and its continued protection under the United States' Endangered Species Act. Nowak concludes that the red wolf is (1) neither the product of ongoing or recent hybridization between coyote (C latrans) and gray wolf (C lupus) nor, (2) a taxon of hybrid origin, but (3) represents a descendant from an intermediate stage in wolf evolution. We concur with his first conclusion but await further data to evaluate the second and third. The only current evidence inconsistent with the last alternative is the lack of distinctiveness among mtDNA sequences from red and gray wolves. Wayne and Jenks (1991) presumably expected differences as predicted from the standard rate of mtDNA evolution based on the calibration from primates (Hillis & Moritz 1990). Explanation of such a discordance requires only a reduction in rate of mtDNA evolution in wolves relative to primates, and such rate variation has been documented for a variety of organisms (e.g., Avise et al. 1992; Martin et al. 1992). The most appropriate test of an hybrid origin will be provided by analysis of codominant, single locus, nuclear gene markers alluded to by Phillips and Henry (1992). Also in this issue, Wayne (1992) takes exception to

Systematics and Phylogeny of the Ipomopsis aggregata Group (Polemoniaceae): Traditional and Molecular Approaches

A system of classification of the Ipomopsis aggregata group based on traditional field and herbarium methods has been restudied recently by another group of workers using molecular systematic methods (allozymes and cpDNA). The molecular systematists have claimed that there is not a good correspondence in general between the taxonomic relationships based on allozymes and those based on morphology. In fact, the patterns of relationship indicated by morphological and by molecular methods are reasonably congruent, with one or two exceptions. Molecular evidence revealed that the taxon I. tenuituba subsp. macrosiphon was misclassified in the original system; and on the basis of this molecular and other supplementary evidence it is segregated here as a distinct species, Ipomopsis macrosiphon, comb. nov. The molecular systematists concluded from the high genetic similarities (I) between taxa that speciation is relatively recent in the I. aggregata group, but this conclusion conflicts with the phylogenetic sequence inferred from traditional lines of evidence. Reanalysis of one test case involving a pair of taxa with a high genetic similarity in allozymes indicates that the high I value is a result of recent hybridization, and is not a valid indicator of time of divergence. High I values for some other pairs of taxa may well have the same explanation. The problem of reconciling and integrating traditional and molecular systematic evidence arises frequently in other plant groups; this general problem is discussed.

Tumor necrosis factor-α gene expression in the tissues of normal mice

Although TNF-α is traditionally associated with macrophage activation during neoplasia and acute inflammation, recent Northern blot hybridization studies indicate that gene expression occurs in the absence of pathology. In order to identify the cellular sources of endogenous message and protein, normal mouse tissues were tested for TNF-α mRNA using in situ hybridization and for the corresponding protein by immunocytochemistry. Unexpectedly, specific TNF-α message was readily detected in hepatocytes, kidney tubule epithelial cells, various populations of spleen cells and neurons. TNF-α protein was present in the same liver and kidney cells as those that contained TNF-α mRNA, was low in spleen cells, and was absent in neurons. These results suggest that cells other than macrophages are the major sources of TNF-α gene products in normal tissues, indicate that regulation is accomplished by more than one mechanism, and are consistent with the postulate that products of this gene contribute to normal physiological processes.

Patterns of variation and relationships in the Eucalyptus Alpina–E. baxteri complex (Myrtaceae) based on leaf volatile oils

In the stringybark eucalypts, the baxteri clade consists of E. arenacea, from South Australia and northwestern Victoria, E. baxteri, mainly from the Great Dividing Range of Victoria, and E. alpina, an endemic taxon from the Grampian Ranges of Victoria. Populations of these taxa were sampled from across their geographic and morphological ranges. Phenetic and phylogenetic analyses were undertaken of the leaf volatile oil composition of the sampled plants. On the basis of these analyses, E. arenacea emerges as a cohesive, monophyletic species, while E. baxteri is a variable and probably paraphyletic species. Populations on Kangaroo Island, South Australia, are variable and intermediate, and may represent recent intergradation between the two species. Populations of E. baxteri from the Grampians are distinctive chemically, but not morphologically, within the species. Recent hybridisation between this form of E. baxteri and E. alpina was shown to be occuning within the Grampians. E. alpina is a highly variable taxon, and probably polyphyletic as currently recognised. Three distinct forms were recognised within E. alpina. The first, and most distinctive, is from the southern Serra Range; the second is from the northern Serra Range and Wonderland Range; the third, and most similar to E. baxteri, is from the Victoria Range.

Origin and early evolution of Aves: dinosaurs, ancient birds, and mtDNA sequences

Recently a general cladistic framework for early avian evolution has emerged. Postcranial modifications in the wrist joint and elsewhere firmly establish birds as a diversified subgroup of maniraptoran theropods. And the best known Mesozoic avians–Archaeopteryx and Late Cretaceous Hesperornis and Ichthyornis –have been positioned as successive sister taxa to living birds. Within this framework, however, several basic phylogenetic questions need to be addressed: (1) Which maniraptorans are most closely related to birds? (2) How was the modern avian skeleton built during the first third of avian history, between Archaeopteryx and Late Cretaceous Hesperornis and Ichthyornis? (3) And what are the relationships between the major groups of living birds?Avian origins. Synapomorphies listed by Ostrom and others to unite birds and other theropods typically apply to all maniraptorans or higher-level theropod clades, leaving unsettled the question of which maniraptorans constitute the immediate outgroups to birds. Deinonychosauria is confirmed as the sister-group to Aves, based principally on synapomorphies of the pectoral and pelvic girdles. In contrast to some previous suggestions, this study supports monophyly of Deinonychosauria (uniting dromaeosaurids and troodontids), with a single origin of the hyper-extendable, raptorial digit II of the pes.Sinornis and the evolution of powered flight and perching. Archaeopteryx lacks the profound modifications of the avian skeleton that characterize Ichthyornis and modern birds. Recent discovery of Lower Cretaceous birds has brought to light important intermediate stages in the transformation of the avian skeleton. Sparrow-sized Sinornis, discovered in Lower Cretaceous lake deposits in China, exhibits features that are associated with sustained powered flight; the laterally directed glenoid and V-shaped ulnare suggest that the wing was capable of tight flexion during flight. Features unrelated to the flight apparatus, in contrast, have not been altered; the skull is toothed, the manal digits are flexible and clawed, and gastralia are present beneath the rib cage.Higher-level relationships among living birds. The deep branching history of living birds occurred before the end of the Cretaceous and can be reconstructed from anatomical and genetic evidence in living birds. DNA sequences have been obtained from the mitochondrial cytochrome b gene in a variety of living birds. These data are consistent with a basal split between palaeognaths and neognaths and support the basal position of galliforms and anseriforms among neognaths. Piciforms appear to be closely related to passeriforms, and Corvida does not appear to be monophyletic, in contrast to recent DNA-DNA hybridization results.

In situ hybridization demonstrates vasopressin gene transcription in hypothalamic neurons of crossbred hypertensive × diabetes insipidus rats

In situ hybridization, Northern blotting, and solution hybridization assay were used to examine vasopressin-gene messenger ribonucleic acid (mRNA) transcripts in hypothalamic tissue from live strains of rats: Long Evans, Wistar Kyoto, and diabetes insipidus (Brattleboro) rats, spontaneously hypertensive stroke-prone rats, and cross-bred diabetes insipidus × spontaneously hypertensive strokeprone rats. A 290 base-pair, single-stranded RNA probe, with 221 bases complementary to exon (of the vasopressin gene was synthesized by the SP6 transcription vector system. This probe labeled appropriate neurohypophysial hypothalamic neurons, as well as suprachiasmatic nucleus cells, in tissue samples from all five strains of rats. Confirming other recent hybridization results with diabetes insipidus rat brain tissue, diabetic animals were found to transcribe their mutated vasopressin gene. In addition, this investigation found that the cross-bred diabetic hypertensive rat also synthesizes a vasopressin-gene messenger ribonucleic acid transcript. Quantitative analyses of solution and in situ hybridization results suggested the cross-bred diabetic hypertensive rat exhibits a level of vasopressin-gene messenger ribonucleic acid similar to diabetes insipidus rats. This observation is consistent with previous data on the cross-bred diabetic hypertensive rat which suggests they inherit the mutant vasopressin gene from Brattleboro rats.

Ultrastructural localization of factor VIII procoagulant antigen in human liver hepatocytes.

Factor VIII is generally believed to circulate in blood as a multimeric complex of two glycoproteins which are physiologically and immunologically distinct. One component of the factor VIII complex is factor VIII procoagulant activity (FVIII:C) which is associated with factor VIII/procoagulant antigen (FVIII:Ag, formerly FVIII/CAg). The second, larger unit of the complex is factor VIII/von Willebrand factor (vWF:Ag, formerly factor VIII-related antigen or FVIIIRAg). FVIII:C has anti-haemophilic activity and is defective or deficient in patients with classical haemophilia, and vWF:Ag is absent in patients with von Willebrand disease. FVIII:Ag was demonstrated recently in endothelial cells lining hepatic sinusoids, by using immunoperoxidase staining and light microscopy, whereas biochemical data had indicated its presence predominantly in the hepatocyte fractions and in lesser amounts in endothelial cells. Moreover, recent hybridization experiments detected FVIII:C messenger RNA in liver and kidney tissues. Despite several efforts, the cells responsible for FVIII:C synthesis have not been unequivocally identified. Here we use protein A-gold complex labelling to demonstrate the ultrastructural localization of FVIII:C in human liver cells; the results indicate that hepatocytes may synthesize FVIII:Ag.