The influence of gene flow on population viability in an isolated urban caracal population

Wildlife populations are becoming increasingly fragmented by anthropogenic development. Small and isolated populations often face an elevated risk of extinction, in part due to inbreeding depression. Here, we examine the genomic consequences of urbanization in a caracal (Caracal caracal) population that has become isolated in the Cape Peninsula region of the City of Cape Town, South Africa, and is thought to number ~50 individuals. We document low levels of migration into the population over the past ~75 years, with an estimated rate of 1.3 effective migrants per generation. As a consequence of this isolation and small population size, levels of inbreeding are elevated in the contemporary Cape Peninsula population (mean FROH = 0.20). Inbreeding primarily manifests as long runs of homozygosity >10 Mb, consistent with the effects of isolation due to the rapid recent growth of Cape Town. To explore how reduced migration and elevated inbreeding may impact future population dynamics, we parameterized an eco-evolutionary simulation model. We find that if migration rates do not change in the future, the population is expected to decline, though with a low projected risk of extinction. However, if migration rates decline or anthropogenic mortality rates increase, the potential risk of extinction is greatly elevated. To avert a population decline, we suggest that translocating migrants into the Cape Peninsula to initiate a genetic rescue may be warranted in the near future. Our analysis highlights the utility of genomic datasets coupled with computational simulation models for investigating the influence of gene flow on population viability.

Antibiotics for Patients With a Planned Re-Laparotomy for Intra-Abdominal Infection

Background: Appropriate antimicrobial therapy for the management of intra-abdominal infection (IAI) continues to evolve based on available literature. The Study to Optimize Peritoneal Infection Therapy (STOP-IT) trial provided evidence to support four days of antibiotic agents in IAI post-source control but excluded patients with a planned re-laparotomy. This study aimed to determine the short- and long-term recurrent infection risk in this population. Patients and Methods: This is a single-center, retrospective, observational study of adult patients admitted to a quaternary medical center between January 1, 2016, and August 1, 2022, with IAI requiring planned laparotomy. Patients were designated as receiving five or less days of antibiotic agents (short course) or more than five days (long course) after source control. The primary outcome was IAI recurrence within 30 days. Results: Of the 104 patients who met inclusion criteria, 78 were included in analysis. Average age was 57 ± 13.3 years, 56% were male, 94% Caucasian, with a mean Acute Physiology and Chronic Health Evaluation (APACHE) II score of 17 ± 7.09. All other baseline characteristics and clinical severity markers were similar between the two groups. Regarding the primary outcome of IAI recurrence, there was no difference when comparing those who received short course versus those who received long course therapy (41.2% vs. 44.4%; p = 0.781). No differences were found between groups with respect to secondary outcomes. Conclusions: In patients admitted with IAI managed with planned re-laparotomy those who received short course antimicrobial therapy were not found to have an increase in IAI recurrence compared to those with longer courses of therapy.

Sustained use of marine subsidies promotes niche expansion in a wild felid

The use of marine subsidies by terrestrial predators can facilitate substantial transfer of nutrients between marine and terrestrial ecosystems. Marine resource subsidies may have profound effects on predator ecology, influencing population and niche dynamics. Expanding niches of top consumers can impact ecosystem resilience and interspecific interactions, affecting predator-prey dynamics and competition. We investigate the occurrence, importance, and impact of marine resources on trophic ecology and niche dynamics in a highly generalist predator, the caracal (Caracal caracal), on the Cape Peninsula, South Africa. Caracals have flexible diets, feeding across a wide range of terrestrial and aquatic prey. We use carbon and nitrogen stable isotope analysis of fur samples (n = 75) to understand trophic position and niche shifts in coastal and inland foragers, as well as the implications of a diet rich in marine resources. We found significant differences in isotope signatures between these groups, with higher δ13C (P < 0.05) and δ15N values (P < 0.01) in coastal foragers. Isotope mixing models reveal that these elevated signatures were due to non-terrestrial food subsidies, where approximately a third of coastal foraging caracal diet comprised marine prey. The addition of marine prey species to diet increased both the trophic level and isotope niche size of coastal foraging caracals, with potential impacts on prey populations and competition. Our results suggest that marine prey are an important dietary resource for coastal foraging caracals, where seabirds, including two endangered species, are a major component of their diet. However, there are likely risks associated with these resource benefits, as routine consumption of seabirds is linked with higher pollutant burdens, particularly metals. Increased encounters between this terrestrial predator and seabirds may be a result of increased mainland colonies due to changes in habitat availability and the highly opportunistic and generalist foraging behaviour of a native predator.

Trophic downgrading of an adaptable carnivore in an urbanising landscape

Urbanisation critically alters wildlife habitat and resource distribution, leading to shifts in trophic dynamics. The loss of apex predators in human-transformed landscapes can result in changes in the ecological roles of the remaining mesocarnivores. Decreased top-down control together with increased bottom-up forcing through greater availability of anthropogenic foods can result in a predation paradox. Understanding these changes is important for conserving ecological function and biodiversity in rapidly urbanising systems. Here, we use stable isotope analysis to provide insight into longer term changes in trophic position, niche width and overlap of an elusive, medium-sized urban adapter, the caracal (Caracal caracal) in and around the city of Cape Town, South Africa. Using fur samples (n = 168) from individuals along a gradient of urbanisation we find that overall caracals have a broad isotopic dietary niche that reflects their large variation in resource use. When accounting for underlying environmental differences, the intensity of anthropogenic pressure, measured using the Human Footprint Index (HFI), explained variation in both food subsidy use (δ13C values) and trophic status (δ15N values). The significantly higher δ13C values (P < 0.01) and lower δ15N values (P < 0.001) of caracals in more urbanised areas suggest that predator subsidy consumption occurs via predictable, anthropogenic resource subsidies to synanthropic prey. These prey species are predominantly primary consumers, resulting in shifts in diet composition towards lower trophic levels. Further, caracals using areas with higher HFI had narrower isotope niches than those in less impacted areas, likely due to their hyperfocus on a few lower trophic level prey species. This pattern of niche contraction in urban areas is retained when accounting for caracal demographics, including sex and age. The removal of apex predators in human-transformed landscapes together with reliable resource availability, including abundant prey, may paradoxically limit the ecological influence of the remaining predators, and bring about a degree of predator trophic downgrading. The dampening of top-down control, and thus ecosystem regulation, likely points to widespread disruption of trophic dynamics in rapidly developing areas globally.

Anthropogenic activities and age class mediate carnivore habitat selection in a human-dominated landscape

Human activities increasingly challenge wild animal populations by disrupting ecological connectivity and population persistence. Yet, human-modified habitats can provide resources, resulting in selection of disturbed areas by generalist species. To investigate spatial and temporal responses of a generalist carnivore to human disturbance, we investigated habitat selection and diel activity patterns in caracals (Caracal caracal). We GPS-collared 25 adults and subadults in urban and wildland-dominated subregions in Cape Town, South Africa. Selection responses for landscape variables were dependent on subregion, animal age class, and diel period. Contrary to expectations, caracals did not become more nocturnal in urban areas. Caracals increased their selection for proximity to urban areas as the proportion of urban area increased. Differences in habitat selection between urban and wildland caracals suggest that individuals of this generalist species exhibit high behavioral flexibility in response to anthropogenic disturbances that emerge as a function of habitat context.

A heavy burden: Metal exposure across the land-ocean continuum in an adaptable carnivore

Urbanisation and associated anthropogenic activities release large quantities of toxic metals and metalloids into the environment, where they may bioaccumulate and threaten both wildlife and human health. In highly transformed landscapes, terrestrial carnivores may be at increased risk of exposure through biomagnification. We quantified metallic element and metalloid exposure in blood of caracals (Caracal caracal), an adaptable felid inhabiting the rapidly urbanising, coastal metropole of Cape Town, South Africa. Using redundancy analysis and mixed-effect models, we explored the influence of demography, landscape use, and diet on the concentration of 11 metals and metalloids. Although species-specific toxic thresholds are lacking, arsenic (As) and chromium (Cr) were present at potentially sublethal levels in several individuals. Increased use of human-transformed landscapes, particularly urban areas, roads, and vineyards, was significantly associated with increased exposure to aluminium (Al), cobalt (Co) and lead (Pb). Foraging closer to the coast and within aquatic food webs was associated with increased levels of mercury (Hg), selenium (Se) and arsenic, where regular predation on seabirds and waterbirds likely facilitates transfer of metals from aquatic to terrestrial food webs. Further, several elements were linked to lower haemoglobin levels (chromium, mercury, manganese, and zinc) and elevated levels of infection-fighting cells (mercury and selenium). Our results highlight the importance of anthropogenic activities as major environmental sources of metal contamination in terrestrial wildlife, including exposure across the land-ocean continuum. These findings contribute towards the growing evidence suggesting cities are particularly toxic areas for wildlife. Co-exposure to a suite of metal pollutants may threaten the long-term health and persistence of Cape Town's caracal population in unexpected ways, particularly when interacting with additional known pollutant and pathogen exposure. The caracal is a valuable sentinel for assessing metal exposure and can be used in pollution monitoring programmes to mitigate exposure and promote biodiversity conservation in human-dominated landscapes.

A pachyderm perfume: odour encodes identity and group membership in African elephants

Group-living animals that live in complex social systems require effective modes of communication to maintain social cohesion, and several acoustic, olfactory and visual signaling systems have been described. Individuals need to discriminate between in- and out-group odour to both avoid inbreeding and to identify recipients for reciprocal behaviour. The presence of a unique group odour, identified in several social mammals, is a proposed mechanism whereby conspecifics can distinguish group from non-group members. African elephants (Loxodonta africana) live in stable, socially complex, multi-female, fission-fusion groups, characterized by female philopatry, male dispersal and linear dominance hierarchies. Elephant social behaviour suggests that individuals use odour to monitor the sex, reproductive status, location, health, identity and social status of conspecifics. To date, it is not clear what fixed or variable information is contained in African elephant secretions, and whether odour encodes kinship or group membership information. Here we use SPME GC-MS generated semiochemical profiles for temporal, buccal and genital secretions for 113 wild African elephants and test their relationship with measures of genetic relatedness. Our results reveal the existence of individual identity odour profiles in African elephants as well as a signature for age encoded in temporal gland and buccal secretions. Olfactory signatures for genetic relatedness were found in labial secretions of adult sisters. While group odour was not correlated with group genetic relatedness, our analysis identified "group membership" as a significant factor explaining chemical differences between social groups. Saturated and short-chain fatty acids (SCFAs), derived from key volatile compounds from bacterial fermentation, were identified in temporal, buccal and genital secretions suggesting that group odour in African elephants may be the result of bacterial elements of the gut microbiome. The frequent affiliative behavior of African elephants is posited as a likely mechanism for bacterial transmission. Our findings favour flexible group-specific bacterial odours, which have already been proposed for other social mammals and present a useful form of olfactory communication that promotes bond group cohesion among non-relatives in fission-fusion mammals.

Poisoned chalice: Use of transformed landscapes associated with increased persistent organic pollutant concentrations and potential immune effects for an adaptable carnivore

Wildlife around cities bioaccumulate multiple harmful environmental pollutants associated with human activities. Exposure severity can vary based on foraging behaviour and habitat use, which can be examined to elucidate exposure pathways. Carnivores can play vital roles in ecosystem stability but are particularly vulnerable to bioaccumulation of pollutants. Understanding the spatial and dietary predictors of these contaminants can inform pollutant control, and carnivores, at the top of food webs, can act as useful indicator species. We test for exposure to toxic organochlorines (OCs), including dichloro-diphenyl-trichloroethane (DDT) and polychlorinated biphenyls (PCBs), in a medium-sized felid, the caracal (Caracal caracal), across the peri-urban and agricultural landscapes of the city of Cape Town, South Africa. Concentrations in both blood (n = 69) and adipose tissue (n = 25) were analysed along with detailed spatial, dietary, demographic, and physiological data to assess OC sources and exposure risk. The analysis revealed widespread exposure of Cape Town's caracals to organochlorines: detection rate was 100% for PCBs and 83% for DDTs in blood, and 100% for both compounds in adipose. Caracals using human-transformed areas, such as vineyards and areas with higher human population and electrical transformer density, as well as wetland areas, had higher organochlorine burdens. These landscapes were also highly selected foraging areas, suggesting caracals are drawn into areas that co-incidentally increase their risk of exposure to these pollutants. Further, biomagnification potential was higher in individuals feeding on higher trophic level prey and on exotic prey. These findings point to bioaccumulation of OC toxicants and widespread exposure across local food webs. Additionally, we report possible physiological effects of exposure, including elevated white blood cell and platelet count, suggesting a degree of immunological response that may increase disease susceptibility. Cape Town's urban fringes likely represent a source of toxic chemicals for wildlife and require focused attention and action to ensure persistence of this adaptable mesocarnivore.

Broadening Predictive Understanding of Species’ Range Responses to Climate Change: The Case of Aloidendron dichotomum

Concerns have been raised about attribution of species range shifts to anthropogenic climate change. Species paleo-range projections are emerging as a means to broaden understanding of range shifts and could be applied to assist in attribution. Apparent recent range contraction in the Quiver Tree (Aloidendron dichotomum (Masson) Klopper and Gideon F.Sm) has been attributed to anthropogenic climate change, but this has been challenged. We simulated the paleo- and future geographic range of A. dichotomum under changing climate using species distribution models (SDMs) to provide a broader perspective on its range dynamics. Ensemble modelling of the Last Glacial Maximum (LGM), mid-Holocene, current, and projected 2070 time periods simulates a paleo-historical poleward expansion of suitable bioclimatic space for this species under natural climate change post-LGM, and projects an eastward shift towards 2070. During the LGM, suitable bioclimatic space for A. dichotomum was simulated to be restricted to the equatorward part of its current range. During the Pleistocene/mid-Holocene climate transition period, the species’ range is predicted to have expanded significantly polewards at an average rate of 0.4 km per decade, assuming constant tracking of its optimal climatic niche. By 2070, suitable bioclimatic space is projected to expand further eastward into the summer rainfall region of South Africa, and contract in its equatorward reaches. Simulated post-LGM shifts roughly match expectations based on preliminary phylogenetic information, further supporting the attribution of current population declines to anthropogenic climate change drivers. Equatorward populations are required to migrate south-eastwards at a rate roughly 15 times faster than that calculated for the LGM/mid-Holocene climate transition period to avoid local extirpation. A preliminary analysis of range-wide genetic variation reveals a cline of variation, with generally higher levels in the central and more northerly part of the species distribution, as expected from the proposed paleo-range of the species. A more detailed analysis of the species’ phylogeographic history could be used to test the proposed paleo-range dynamics presented here, and if confirmed, would provide strong support for the use of this species as an indicator of anthropogenic climate change and a powerful case study for testing the implementation of conservation actions.

Complex evolutionary history of felid anelloviruses

Anellovirus infections are highly prevalent in mammals, however, prior to this study only a handful of anellovirus genomes had been identified in members of the Felidae family. Here we characterise anelloviruses in pumas (Puma concolor), bobcats (Lynx rufus), Canada lynx (Lynx canadensis), caracals (Caracal caracal) and domestic cats (Felis catus). The complete anellovirus genomes (n = 220) recovered from 149 individuals were diverse. ORF1 protein sequence similarity network analysis coupled with phylogenetic analysis, revealed two distinct clusters that are populated by felid-derived anellovirus sequences, a pattern mirroring that observed for the porcine anelloviruses. Of the two-felid dominant anellovirus groups, one includes sequences from bobcats, pumas, domestic cats and an ocelot, and the other includes sequences from caracals, Canada lynx, domestic cats and pumas. Coinfections of diverse anelloviruses appear to be common among the felids. Evidence of recombination, both within and between felid-specific anellovirus groups, supports a long coevolution history between host and virus.

Female Southern White Rhinoceros Can Select Mates to Avoid Inbreeding

Current management models for many endangered species focus primarily on demographic recovery, often ignoring their intrinsic ecological requirements. Across the protected area network of southern Africa, most southern white rhinoceros are managed in populations of less than 50 individuals, experiencing restricted dispersal opportunities, and limited breeding male numbers due to their exclusive home range requirements. In the absence of information on the breeding structure of these populations, poor management decisions may require females to either forego a breeding opportunity or select to inbreed with close relatives. Here, we use a combination of social pedigree data together with genetic analyses to reconstruct the parentage of all 28 offspring produced in a 5-year period in a managed free-ranging southern white rhinoceros population. During this period, all breeding females (founders and first-generation daughters) had access to both a founder male (father to most of the daughters) and two recently introduced inexperienced males. We report that while founder females were more likely to breed with the founder male, their daughters, in contrast, were more likely to breed with the introduced males, thus avoiding inbreeding. However, we also found evidence of father-daughter inbreeding in this population, and contend that in the absence of choice, rather than forego a breeding opportunity, female white rhinoceros will inbreed with their fathers. We argue that to effectively conserve the southern white rhinoceros, managers need to understand the breeding structure of these small populations, particularly in terms of parentage and kinship.

Black-backed jackals (Canis mesomelas) from semi-arid rangelands in South Africa harbour Hepatozoon canis and a Theileria species but apparently not Babesia rossi

Despite the importance of disease as a wildlife management challenge in South Africa, baseline data on the epidemiology of pathogens occurring in free-ranging species has received little attention to date. Black-backed jackals (Canis mesomelas) are a wide-ranging, abundant carnivore with substantial economic importance due to their role in livestock depredation. They are known reservoirs hosts of Babesia rossi, a virulent pathogen in domestic dogs in sub-Saharan Africa. We investigated the prevalence and diversity of tick-borne pathogens (TPBs) including Babesia, Theileria, Hepatozoon, Ehrlichia and Anaplasma species, together with host-attached tick diversity, in a black-backed jackal population from the semi-arid Central Karoo, a small-livestock farming region in South Africa. Using reverse line blot hybridisation, we screened 43 blood samples and sequenced the 18S rRNA gene from positive samples to confirm and characterise pathogen identity using a phylogenetic framework. Hepatozoon canis, a ubiquitous pathogen of domestic and wild canids globally, was observed in 47% of jackals, while a Theileria sp. most similar to T. ovis, a piroplasm found in small livestock, was observed in 5% of jackals. No Babesia, Ehrlichia or Anaplasma species were identified, although a Sarcocystis sp. sequence was isolated from one jackal. Host-attached ticks (n = 20) comprised three species, Amblyomma marmoreum, Haemaphysalis elliptica/zumpti and Ixodes rubicundus, commonly known ticks in the region. In summary, prevalence of TBPs in black-backed jackals from this semi-arid rangeland region was lower than in jackal populations in more mesic regions. These jackals were apparently not infected with B. rossi. While this study is one of the first investigations into the epidemiology of TBPs infecting jackals and adds to the sparse literature, further studies which span landscape uses, climate conditions and seasonality are encouraged.

Molecular detection of tick-borne pathogens in caracals (Caracal caracal) living in human-modified landscapes of South Africa

Background

Wild carnivores living alongside humans and domestic animals are vulnerable to changes in the infectious disease dynamics in their populations. The aims of this study were to determine the prevalence and diversity of selected tick-borne pathogens (TBPs) of veterinary and/or zoonotic concern in wild populations of caracals (Caracal caracal) occurring in human-modified landscapes in South Africa. Using molecular techniques, we screened 57 caracal blood samples for infection by rickettsial bacteria and piroplasms in three regions of South Africa: rangeland in the Central Karoo (n = 27) and Namaqualand (n = 14) as well as the urban edge of the Cape Peninsula (n = 16) of South Africa. To characterise pathogen identity, we sequenced the 18S rRNA and 16S rRNA genes from positive samples and analysed sequences within a phylogenetic framework. We also examine the diversity of potential tick vectors.

Results

All individuals tested were infected with at least one tick-borne pathogen. Pathogens included Hepatozoon felis, Babesia felis, Babesia leo and a potentially novel Babesia species. An Anaplasma species previously described in South African domestic dogs was also found in 88% of urban edge caracals. Higher rates of co-infection characterised urban edge caracals (81% vs 15% and 0% in the two rangeland populations), as well as a greater incidence of mixed infections. Host attached tick species include Haemaphysalis elliptica, an important pathogen vector among carnivore hosts.

Conclusions

This study confirms the occurrence of previously undocumented tick-borne pathogens infecting free-ranging caracals in human-modified landscapes. We identify clear differences in the pathogen profiles among our study populations and discuss the likely health costs to caracals living adjacent to urban areas.

Unsustainable anthropogenic mortality disrupts natal dispersal and promotes inbreeding in leopards

Anthropogenic mortality of wildlife is typically inferred from measures of the absolute decline in population numbers. However, increasing evidence suggests that indirect demographic effects including changes to the age, sex, and social structure of populations, as well as the behavior of survivors, can profoundly impact population health and viability. Specifically, anthropogenic mortality of wildlife (especially when unsustainable) and fragmentation of the spatial distribution of individuals (home-ranges) could disrupt natal dispersal mechanisms, with long-term consequences to genetic structure, by compromising outbreeding behavior and gene flow. We investigate this threat in African leopards (Panthera pardus pardus), a polygynous felid with male-biased natal dispersal. Using a combination of spatial (home-range) and genetic (21 polymorphic microsatellites) data from 142 adult leopards, we contrast the structure of two South African populations with markedly different histories of anthropogenically linked mortality. Home-range overlap, parentage assignment, and spatio-genetic autocorrelation together show that historical exploitation of leopards in a recovering protected area has disrupted and reduced subadult male dispersal, thereby facilitating opportunistic male natal philopatry, with sons establishing territories closer to their mothers and sisters. The resultant kin-clustering in males of this historically exploited population is comparable to that of females in a well-protected reserve and has ultimately led to localized inbreeding. Our findings demonstrate novel evidence directly linking unsustainable anthropogenic mortality to inbreeding through disrupted dispersal in a large, solitary felid and expose the genetic consequences underlying this behavioral change. We therefore emphasize the importance of managing and mitigating the effects of unsustainable exploitation on local populations and increasing habitat fragmentation between contiguous protected areas by promoting in situ recovery and providing corridors of suitable habitat that maintain genetic connectivity.

Comparative RNA-seq analysis of nickel hyperaccumulating and non-accumulating populations of Senecio coronatus (Asteraceae)

Most metal hyperaccumulating plants accumulate nickel, yet the molecular basis of Ni hyperaccumulation is not well understood. We chose Senecio coronatus to investigate this phenomenon as this species displays marked variation in shoot Ni content across ultramafic outcrops in the Barberton Greenstone Belt (South Africa), thus allowing an intraspecific comparative approach to be employed. No correlation between soil and shoot Ni contents was observed, suggesting that this variation has a genetic rather than environmental basis. This was confirmed by our observation that the accumulation phenotype of plants from two hyperaccumulator and two non-accumulator populations was maintained when the plants were grown on a soil mix from these four sites for 12 months. We analysed the genetic variation among 12 serpentine populations of S. coronatus, and used RNA-seq for de novo transcriptome assembly and analysis of gene expression in hyperaccumulator versus non-accumulator populations. Genetic analysis revealed the presence of hyperaccumulators in two well supported evolutionary lineages, indicating that Ni hyperaccumulation may have evolved more than once in this species. RNA-Seq analysis indicated that putative homologues of transporters associated with root iron uptake in plants are expressed at elevated levels in roots and shoots of hyperaccumulating populations of S. coronatus from both evolutionary lineages. We hypothesise that Ni hyperaccumulation in S. coronatus may have evolved through recruitment of these transporters, which play a role in the iron-deficiency response in other plant species.

Differential foraging success across a light level spectrum explains the maintenance and spatial structure of colour morphs in a polymorphic bird

Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution, may be driven by differential selective advantage via improved crypsis, under varying light conditions.

A review of the status and development of Kuwait's fisheries

The status of Kuwait's fisheries landings and relative abundance for major species was reviewed using research data from Kuwait Institute for Scientific Research and landing data from the Kuwait's Central Statistical Bureau. Landing data showed significant decreases for major commercial species such as zobaidy (Pampus argenteus), suboor (Tenualosa ilisha), hamoor (Epinephelus coioides), newaiby (Otolithes ruber) and hamra (Lutjanus malabaricus) while abundance data for the shrimp Penaeus semisulcatus showed significant reduction in the recent years mainly because of overfishing. The catch-rate data showed continuous decline for major species such as zobaidy, newaiby and hamoor, which indicate that stock abundances of these species are low. The reduction in stock abundance in context with changes in habitat quality, particularly the effects of reduced discharge of the Shatt Al-Arab, is discussed.

Development and characterization of 10 microsatellite markers in the Cape horseshoe bat, Rhinolophus capensis (Chiroptera, Rhinolophidae) and cross-amplification in southern African Rhinolophus species

Background

The Cape horseshoe bat, Rhinolophus capensis, is endemic to the Cape region of South Africa. Coalescent analysis of mitochondrial DNA sequence data suggests extensive historical gene flow between populations despite strong geographic variation of their echolocation call phenotype. Nevertheless the fine-scale genetic structure and evolutionary ecology of R. capensis remains poorly understood. Here we describe the development of 10 novel polymorphic microsatellite loci to investigate of the dispersal ecology of R. capensis and to facilitate taxonomic studies of Rhinolophus species in southern Africa.

Findings

We report 10 microsatellite primer pairs that consistently amplify scorable and polymorphic loci across 12 African rhinolophid species. Initial analysis of two populations of R. capensis from South Africa revealed moderate to high levels of allelic variation with 4–14 alleles per locus and observed heterozygosities of 0.450–0.900. No evidence of linkage disequilibrium was observed and eight of the loci showed no departure from Hardy–Weinberg equilibrium. Cross-species utility of these markers revealed consistently amplifiable polymorphic loci in eleven additional rhinolophid species.

Conclusions

The cross-amplification success of the microsatellites developed here provides a cost-effective set of population genetic marker for the study of rhinolophid evolutionary ecology and conservation in southern Africa.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1465-5) contains supplementary material, which is available to authorized users.

Pleistocene aridification cycles shaped the contemporary genetic architecture of Southern African baboons

Plio-Pleistocene environmental change influenced the evolutionary history of many animal lineages in Africa, highlighting key roles for both climate and tectonics in the evolution of Africa’s faunal diversity. Here, we explore diversification in the southern African chacma baboon Papio ursinus sensu lato and reveal a dominant role for increasingly arid landscapes during past glacial cycles in shaping contemporary genetic structure. Recent work on baboons (Papio spp.) supports complex lineage structuring with a dominant pulse of diversification occurring 1-2Ma, and yet the link to palaeoenvironmental change remains largely untested. Phylogeographic reconstruction based on mitochondrial DNA sequence data supports a scenario where chacma baboon populations were likely restricted to refugia during periods of regional cooling and drying through the Late Pleistocene. The two lineages of chacma baboon, ursinus and griseipes, are strongly geographically structured, and demographic reconstruction together with spatial analysis of genetic variation point to possible climate-driven isolating events where baboons may have retreated to more optimum conditions during cooler, drier periods. Our analysis highlights a period of continuous population growth beginning in the Middle to Late Pleistocene in both the ursinus and the PG2 griseipes lineages. All three clades identified in the study then enter a state of declining population size (Nef) through to the Holocene; this is particularly marked in the last 20,000 years, most likely coincident with the Last Glacial Maximum. The pattern recovered here conforms to expectations based on the dynamic regional climate trends in southern Africa through the Pleistocene and provides further support for complex patterns of diversification in the region’s biodiversity.

Transcription of the Rous sarcoma virus genome in vitro and in vivo

RNA-directed DNA synthesis by detergent-disrupted virions of Rous sarcoma virus (RSV) initiates by the covalent attachment of pdA to the 3'-terminal rA of a 4S RNA hydrogen-bonded to the 70S RNA template. This 4S "primer" has structural features of tRNA and can be aminoacylated with methionine. Synthesis and integration of provirus DNA can be monitored in both permissive (duck) and nonpermissive (mouse) cells acutely infected with RSV. The results of these studies, as well as data obtained with RSV-infected mammalian cells which have reverted from a transformed to a pheno-typically normal state, indicate that integration of viral genes into the host chromosome is not sufficient cause for transformation. Pertinent features of virus-specific RNA-directed DNA synthesis in vitro and in vivo are reviewed and compared.

Detection and characterization of RNA tumor virus-specific DNA in cells

RNA tumor virus-specific DNA in cells can be detected by its capacity to 1) alter the reassociation kinetics of labeled double-stranded product of viral RNA-directed DNA polymerase; 2) anneal single-stranded DNA (cDNA) synthesized by viral polymerase; or 3) hybridize labeled viral 70S (genomic) RNA. Duplexes formed with these procedures can be analyzed for fidelity of base pairing, and the integration of viral DNA into the host genome can be established with a simple but stringent technique. We illustrate this methodology as applied to detection of Rous sarcoma virus (RSV)-specific DNA in XC cells and of mouse mammary tumor virus (MMTV)-specific DNA in murine and human tissues.

Genetic signatures for enhanced olfaction in the African mole-rats

The Olfactory Receptor (OR) superfamily, the largest in the vertebrate genome, is responsible for vertebrate olfaction and is traditionally subdivided into 17 OR families. Recent studies characterising whole-OR subgenomes revealed a 'birth and death' model of evolution for a range of species, however little is known about fine-scale evolutionary dynamics within single-OR families. This study reports the first assessment of fine-scale OR evolution and variation in African mole-rats (Bathyergidae), a family of subterranean rodents endemic to sub-Saharan Africa. Because of the selective pressures of life underground, enhanced olfaction is proposed to be fundamental to the evolutionary success of the Bathyergidae, resulting in a highly diversified OR gene-repertoire. Using a PCR-sequencing approach, we analysed variation in the OR7 family across 14 extant bathyergid species, which revealed enhanced levels of functional polymorphisms concentrated across the receptors' ligand-binding region. We propose that mole-rats are able to recognise a broad range of odorants and that this diversity is reflected throughout their OR7 gene repertoire. Using both classic tests and tree-based methods to test for signals of selection, we investigate evolutionary forces across the mole-rat OR7 gene tree. Four well-supported clades emerged in the OR phylogeny, with varying signals of selection; from neutrality to positive and purifying selection. Bathyergid life-history traits and environmental niche-specialisation are explored as possible drivers of adaptive OR evolution, emerging as non-exclusive contributors to the positive selection observed at OR7 genes. Our results reveal unexpected complexity of evolutionary mechanisms acting within a single OR family, providing insightful perspectives into OR evolutionary dynamics.

Sensory trait variation in an echolocating bat suggests roles for both selection and plasticity

Background

Across heterogeneous environments selection and gene flow interact to influence the rate and extent of adaptive trait evolution. This complex relationship is further influenced by the rarely considered role of phenotypic plasticity in the evolution of adaptive population variation. Plasticity can be adaptive if it promotes colonization and survival in novel environments and in doing so may increase the potential for future population differentiation via selection. Gene flow between selectively divergent environments may favour the evolution of phenotypic plasticity or conversely, plasticity itself may promote gene flow, leading to a pattern of trait differentiation in the presence of gene flow. Variation in sensory traits is particularly informative in testing the role of environment in trait and population differentiation. Here we test the hypothesis of ‘adaptive differentiation with minimal gene flow’ in resting echolocation frequencies (RF) of Cape horseshoe bats (Rhinolophus capensis) across a gradient of increasingly cluttered habitats.

Results

Our analysis reveals a geographically structured pattern of increasing RF from open to highly cluttered habitats in R. capensis; however genetic drift appears to be a minor player in the processes influencing this pattern. Although Bayesian analysis of population structure uncovered a number of spatially defined mitochondrial groups and coalescent methods revealed regional-scale gene flow, phylogenetic analysis of mitochondrial sequences did not correlate with RF differentiation. Instead, habitat discontinuities between biomes, and not genetic and geographic distances, best explained echolocation variation in this species. We argue that both selection for increased detection distance in relatively less cluttered habitats and adaptive phenotypic plasticity may have influenced the evolution of matched echolocation frequencies and habitats across different populations.

Conclusions

Our study reveals significant sensory trait differentiation in the presence of historical gene flow and suggests roles for both selection and plasticity in the evolution of echolocation variation in R. capensis. These results highlight the importance of population level analyses to i) illuminate the subtle interplay between selection, plasticity and gene flow in the evolution of adaptive traits and ii) demonstrate that evolutionary processes may act simultaneously and that their relative influence may vary across different environments.

Phenotypic convergence in genetically distinct lineages of a Rhinolophus species complex (Mammalia, Chiroptera)

Phenotypes of distantly related species may converge through adaptation to similar habitats and/or because they share biological constraints that limit the phenotypic variants produced. A common theme in bats is the sympatric occurrence of cryptic species that are convergent in morphology but divergent in echolocation frequency, suggesting that echolocation may facilitate niche partitioning, reducing competition. If so, allopatric populations freed from competition, could converge in both morphology and echolocation provided they occupy similar niches or share biological constraints. We investigated the evolutionary history of a widely distributed African horseshoe bat, Rhinolophus darlingi, in the context of phenotypic convergence. We used phylogenetic inference to identify and date lineage divergence together with phenotypic comparisons and ecological niche modelling to identify morphological and geographical correlates of those lineages. Our results indicate that R. darlingi is paraphyletic, the eastern and western parts of its distribution forming two distinct non-sister lineages that diverged ~9.7 Mya. We retain R. darlingi for the eastern lineage and argue that the western lineage, currently the sub-species R. d. damarensis, should be elevated to full species status. R. damarensis comprises two lineages that diverged ~5 Mya. Our findings concur with patterns of divergence of other co-distributed taxa which are associated with increased regional aridification between 7-5 Mya suggesting possible vicariant evolution. The morphology and echolocation calls of R. darlingi and R. damarensis are convergent despite occupying different biomes. This suggests that adaptation to similar habitats is not responsible for the convergence. Furthermore, R. darlingi forms part of a clade comprising species that are bigger and echolocate at lower frequencies than R. darlingi, suggesting that biological constraints are unlikely to have influenced the convergence. Instead, the striking similarity in morphology and sensory biology are probably the result of neutral evolutionary processes, resulting in the independent evolution of similar phenotypes.

Abstract P1-04-01: Loss of Notch4 reduces mammary tumorigenesis by MYC and activated KRAS

Over-expression of Notch receptors and aberrant Notch signaling have been reported in both preinvasive ductal carcinoma in situ and invasive breast cancer. The Notch 4 receptor, in particular, is preferentially activated in human breast cancer stem cell-enriched populations, and inhibition of Notch 4 reduces tumor formation of human breast cancer cells in xenograft models (Harrison, 2010). Myc gene amplification has also been found in about 15% of breast tumors, and 22%–35% of tumors exhibit overexpression of Myc at the transcriptional level. Transgenic mice over-expressing MYC develop invasive adenocarcinomas and preferentially harbor secondary activating mutations in KRas. We examined whether Notch receptors were activated in mouse mammary tumors over-expressing MYC and activated KRAS (KRASV12) and found Notch 4 to be significantly activated in these tumors compared to normal mammary tissue. Furthermore, Notch 4 was localized to the nucleus in the tumors over-expressing MYC and KRASV12, but not in mammary glands over-expressing MYC or activated KRASV12 alone. To examine the requirement of Notch4 in mammary tumorigenesis by MYC and KRASV12, we transplanted mammary epithelial cells isolated from Notch4 knockout mice and wild-type mice that have been transduced with MYC and KRASV12 into the mammary glands of syngeneic mice. There was a significant reduction in the onset of tumorigenesis in mammary glands that had been transplanted with mammary epithelial cells lacking Notch4. These findings suggest that Notch4 is important in mammary tumorigenesis induced by cooperation of MYC and activated RAS. We are currently examining the relevance of Nocth4 activation in human breast cancers that over-express MYC and the mechanism by which Notch4 promotes tumorigenesis by Myc and activated RAS.

Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P1-04-01.

Morphological and molecular evidence reveals recent hybridization between gorilla taxa

Molecular studies have demonstrated a deep lineage split between the two gorilla species, as well as divisions within these taxa; estimates place this divergence in the mid-Pleistocene, with gene flow continuing until approximately 80,000 years ago. Here, we present analyses of skeletal data indicating the presence of substantial recent gene flow among gorillas at all taxonomic levels: between populations, subspecies, and species. Complementary analyses of DNA sequence variation suggest that low-level migration occurred primarily in a westerly-to-easterly direction. In western gorillas, the locations of hybrid phenotypes map closely to expectations based on population refugia and riverine barrier hypotheses, supporting the presence of significant vicariance-driven structuring and occasional admixture within this taxon. In eastern lowland gorillas, the high frequency of hybrid phenotypes is surprising, suggesting that this region represents a zone of introgression between eastern gorillas and migrants from the west, and underscoring the conservation priority of this critically endangered group. These results highlight the complex nature of evolutionary divergence in this genus, indicate that historical gene flow has played a major role in structuring gorilla diversity, and demonstrate that our understanding of the evolutionary processes responsible for shaping biodiversity can benefit immensely from consideration of morphological and molecular data in conjunction.

Mitochondrial DNA analysis reveals Plio-Pleistocene diversification within the chacma baboon

Modern baboons evolved as a distinct lineage prior to 2.5 Mya. Previous scenarios of diversification within this lineage have assessed the phylogenetic position of the chacma baboon of southern Africa relative to other baboons, but have not examined variation within this taxon. Here we provide a phylogenetic analysis of lineage diversity across the range of the chacma baboon, and show that: (1) chacma baboons diverged as a separate lineage at approximately 1.84 Mya; (2) the chacma lineage is characterised by a deep lineage split dividing chacmas into northeastern (1.52 Mya) and southwestern (1.22 Mya) clades; (3) ruacana baboons of Namibia form their own distinct monophyletic group within the southwestern clade, emerging approximately 0.68 Mya. These patterns likely result from a complex interplay of genetic drift and gene flow as the chacma lineage diversified across a broad geographic landscape during the climatically variable Plio-Pleistocene.

Social common mole-rats enhance outbreeding via extra-pair mating

Females in many species engage in matings with males that are not their social mates. These matings are predicted to increase offspring heterozygosity and fitness, and thereby prevent the deleterious effects of inbreeding. We tested this hypothesis in a cooperative breeding mammal, the common mole-rat Cryptomys hottentotus hottentotus. Laboratory-based studies suggested a system of strict social monogamy, while recent molecular studies indicate extensive extra-pair paternity despite colonies being founded by an outbred pair. Our data show that extra-pair and within-colony breeding males differed significantly in relatedness to breeding females, suggesting that females may gain genetic benefits from breeding with non-resident males. Extra-colony male mating success was not based on heterozygosity criteria at microsatellite loci; however, litters sired by extra-colony males exhibited increased heterozygosity. While we do not have the data that refute a relationship between individual levels of inbreeding (Hs) and fitness, we propose that a combination of both male and female factors most likely explain the adaptive significance of extra-pair mating whereby common mole-rats maximize offspring fitness by detecting genetic compatibility with extra-pair mates at other key loci, but it is not known which sex controls these matings.

Nestin-Cre transgenic mouse line Nes-Cre1 mediates highly efficient Cre/loxP mediated recombination in the nervous system, kidney, and somite-derived tissues

Here we describe the generation of the Nes-Cre1 transgenic mouse line in which Cre recombinase expression is controlled by the rat nestin promoter and intron 2 enhancer. This line has previously been used for conditional loss-of-function studies of various genes in the central nervous system and first branchial arch ectoderm. Here we report the detailed temporal and spatial recombination pattern of Nes-Cre1 using three different reporters of Cre-mediated recombination, ROSA26R (R26R), Z/AP, and Z/EG. Cre/loxP recombination was detected in embryos as early as the head-fold stage. By embryonic day (E)15.5 recombination occurred in virtually all cells of the nervous system and unexpectedly also in somite-derived tissues and kidneys. Tissues with little or no recombination included heart, liver, thymus, and lung. This study suggests that Nes-Cre1-mediated recombination occurs in progenitor cell types present in the neuroectoderm, the developing mesonephros, and the somites.

Genomic progression in mouse models for liver tumors

The principal cause of human liver cancer is infection with hepatitis viruses B and C, but tumor progression is fueled by ensuing perturbations that confer gain of function on proto-oncogenes or loss of function on tumor suppressor genes. Frequent among these perturbations is overexpression of the proto-oncogene MET. We have modeled the pathogenesis of liver tumors by expressing conditional transgenes of MET in the hepatocytes of inbred mice. The response to the MET transgene varied with both the magnitude and timing of its expression but included hyperplasia of hepatic progenitor cells, as well as benign and malignant tumors that display both phenotypic and genotypic resemblances to human counterparts. The results reveal MET to be a crucial switch in the development of the liver; dramatize how different cellular compartments within a developmental lineage can give rise to distinctive tumor stem cells; delineate rules of tumor progression; provide evidence that the experimental tumors in mice are authentic models for human tumors; and support a role for MET in the genesis of human liver tumors. The models should be useful in elucidating the mechanisms of tumorigenesis and in the preclinical testing of new therapeutics.

Exotic meson decay to omegapi0pi-

A partial-wave analysis of the mesons from the reaction pi(-)p --> pi(+)pi(-)pi(-)pi(0)pi(0)p has been performed. The data show b(1)pi decay of the spin-exotic states pi(1)(1600) and pi(1)(2000). Three isovector 2(-+) states were seen in the omegarho(-) decay channel. In addition to the well known pi(2)(1670), signals were also observed for pi(2)(1880) and pi(2)(1970).

Molecular insight into patterns of colony composition and paternity in the common mole-rat Cryptomys hottentotus hottentotus

We report the discovery of intraspecific variation in both colony composition and patterns of paternity in two populations of the social common mole-rat Cryptomys hottentotus hottentotus. These two populations represent the mesic and arid habitat extremes of the species' broad ecological range in South Africa. Until recently colonies of the common mole-rat were thought to consist of familial groups whereby all colony members were the offspring of a monogamous reproductive pair. The remaining colony members were thought to forego reproduction until both social and ecological conditions favoured dispersal and opportunities for independent outbreeding. Results from genetic assignment tests using microsatellite markers indicate that while colony composition is dominated by familial groups, colonies within both populations included both adult and subadult foreign conspecifics. Analysis of parentage reveals that the social organization of C. h. hottentotus is not that of strict monogamy; paternity of offspring was not assigned consistently to the largest, most dominant male within the colony. Moreover, a number of significantly smaller males were found to sire offspring, suggesting a sneak-mating strategy by subordinate within-colony males. Extra-colony extra-pair paternity (ECP) was also found to characterize C. h. hottentotus colonies, occurring with similar frequencies in both habitats. Both dominant established breeding males and subordinate males were identified as siring young in nonsource colonies. Furthermore, established breeding males were found to sire extra-colony young in the same season as siring young within their source colonies. We discuss the significance of these results within the context of the divergent ecological regimes characterizing the two sites and observe that our results revisit the accuracy of using behavioural and morphological characters, which have structured the basis of our understanding of the behavioural ecology of this species, as indicators of breeding status in mark-recapture studies.

Transcripts from the cellular homologs of retroviral oncogenes: distribution among chicken tissues

The oncogenes (v-onc genes) of rapidly transforming retroviruses have homologs (c-onc genes) in the genomes of normal cells. In this study, we characterized and quantitated transcription from four c-onc genes, c-myb, c-myc, c-erb, and c-src, in a variety of chicken cells and tissues. Electrophoretic analysis of polyadenylated RNA, followed by transfer to nitrocellulose and hybridization to cloned onc probes showed that c-myb, c-myc, and c-src each give rise to a single mature transcript, whereas c-erb gives rise to multiple transcripts (B. Vennstrom and J. M. Bishop, Cell, in press) which vary in abundance among different cells and tissues. Transcription from c-myb, c-myc, c-erb, and c-src was quantitated by a "dot-blot" hybridization assay. We found that c-myc, c-erb, and c-src transcription could be detected in nearly all cells and tissues examined, whereas c-myb transcription was detected only in some hemopoietic cells; these cells, however, belong to several different lineages. Thus, in no case was expression of a c-onc gene restricted to a single cell lineage. There appeared to be a correlation between levels of c-myb expression and hemopoietic activity of the tissues and cells examined, which suggests that c-myb may be expressed primarily in immature hemopoietic cells. An examination of c-onc RNA levels in target cells and tissues for viruses carrying the corresponding v-onc genes revealed no obvious correlation, direct or inverse, between susceptibility to transformation by a given v-onc gene and expression of the homologous c-onc gene.

Morbidity of tamoxifen–perceptions of patients and healthcare professionals

There is little published data comparing patients' and doctors' perceptions of tamoxifen-related morbidity and toxicity, in particular in terms of side-effects which are not medically serious but which disrupt quality of life. We undertook a questionnaire-based study of 210 randomly selected, disease-free pre- and post-menopausal breast cancer patients to assess perceived morbidity whilst taking tamoxifen. We also questioned 143 healthcare professionals, including nurses, GPs and oncologists, on their opinions of tamoxifen-related side-effects. This study suggests that patients experience significant morbidity while taking adjuvant tamoxifen but will tolerate this for the sake of anticipated benefits. Healthcare professionals particularly hospital-based doctors and specialist nurses tend to overestimate the prevalence and severity of tamoxifen-associated symptoms.

c-Myc regulates mammalian body size by controlling cell number but not cell size

Overexpression of the proto-oncogene c-myc has been implicated in the genesis of diverse human tumours. c-Myc seems to regulate diverse biological processes, but its role in tumorigenesis and normal physiology remains enigmatic. Here we report the generation of an allelic series of mice in which c-myc expression is incrementally reduced to zero. Fibroblasts from these mice show reduced proliferation and after complete loss of c-Myc function they exit the cell cycle. We show that Myc activity is not needed for cellular growth but does determine the percentage of activated T cells that re-enter the cell cycle. In vivo, reduction of c-Myc levels results in reduced body mass owing to multiorgan hypoplasia, in contrast to Drosophila c-myc mutants, which are smaller as a result of hypotrophy. We find that c-myc substitutes for c-myc in fibroblasts, indicating they have similar biological activities. This suggests there may be fundamental differences in the mechanisms by which mammals and insects control body size. We propose that in mammals c-Myc controls the decision to divide or not to divide and thereby functions as a crucial mediator of signals that determine organ and body size.

Activation of the Met receptor by cell attachment induces and sustains hepatocellular carcinomas in transgenic mice

Overexpression is the most common abnormality of receptor tyrosine kinases (RTKs) in human tumors. It is presumed that overexpression leads to constitutive activation of RTKs, but the mechanism of that activation has been uncertain. Here we show that overexpression of the Met RTK allows activation of the receptor by cell attachment and that this form of activation can be tumorigenic. Transgenic mice that overexpressed Met in hepatocytes developed hepatocellular carcinoma (HCC), one of the human tumors in which Met has been implicated previously. The tumorigenic Met was activated by cell attachment rather than by ligand. Inactivation of the transgene led to regression of even highly advanced tumors, apparently mediated by apoptosis and cessation of cellular proliferation. These results reveal a previously unappreciated mechanism by which the tumorigenic action of RTKs can be mediated, provide evidence that Met may play a role in both the genesis and maintenance of HCC, and suggest that Met may be a beneficial therapeutic target in tumors that overexpress the receptor.

Observation of exotic meson production in the reaction pi- p --> eta'pi- p at 18 GeV/c

An amplitude analysis of an exclusive sample of 5765 events from the reaction pi- p-->eta'pi- p at 18 GeV/c is described. The eta'pi- production is dominated by natural parity exchange and by three partial waves: those with J(PC) = 1(-+), 2(++), and 4(++). A mass-dependent analysis of the partial-wave amplitudes indicates the production of the a2(1320) meson as well as the a4(2040) meson, observed for the first time decaying to eta'pi-. The dominant, exotic (non- qq) 1(-+) partial wave is shown to be resonant with a mass of 1.597+/-0.010(+0.045)(-0.010) GeV/c2 and a width of 0.340+/-0.040+/-0.050 GeV/c2. This exotic state, the pi1(1600), is produced with a t dependence which is different from that of the a2(1320) meson, indicating differences between the production mechanisms for the two states.

BCL-2 cooperates with promyelocytic leukemia retinoic acid receptor alpha chimeric protein (PMLRARalpha) to block neutrophil differentiation and initiate acute leukemia

The promyelocytic leukemia retinoic acid receptor alpha (PMLRARalpha) chimeric protein is associated with acute promyelocytic leukemia (APL). PMLRARalpha transgenic mice develop leukemia only after several months, suggesting that PMLRARalpha does not by itself confer a fully malignant phenotype. Suppression of apoptosis can have a central role in tumorigenesis; therefore, we assessed whether BCL-2 influenced the ability of PMLRARalpha to initiate leukemia. Evaluation of preleukemic animals showed that whereas PMLRARalpha alone modestly altered neutrophil maturation, the combination of PMLRARalpha and BCL-2 caused a marked accumulation of immature myeloid cells in bone marrow. Leukemias developed more rapidly in mice coexpressing PMLRARalpha and BCL-2 than in mice expressing PMLRARalpha alone, and all mice expressing both transgenes succumbed to leukemia by 7 mo. Although both preleukemic, doubly transgenic mice and leukemic animals had abundant promyelocytes in the bone marrow, only leukemic mice exhibited thrombocytopenia and dissemination of immature cells. Recurrent gain of chromosomes 7, 8, 10, and 15 and recurrent loss of chromosome 2 were identified in the leukemias. These chromosomal changes may be responsible for the suppression of normal hematopoiesis and dissemination characteristic of the acute leukemias. Our results indicate that genetic changes that inhibit apoptosis can cooperate with PMLRARalpha to initiate APL.

Mercuric chloride activates the Src-family protein tyrosine kinase, Hck in myelomonocytic cells

Hck is a member of the Src-family of protein tyrosine kinases that appears to function in mature leukocytes to communicate a number of extracellular signals including various cytokines. In this study we show that the thiol-reactive heavy metal, mercuric chloride (HgCl2) induces rapid and robust activation of tyrosine phosphorylation within human myelomonocytic cells. This increase in tyrosine-phosphorylated proteins requires the activity of Hck because both kinase inactive alleles of Hck and pharmacological inhibitors selective for the Src-family kinases are able to abrogate the cellular response to HgCl2. Furthermore, ectopic expression of Hck in murine fibroblasts is able to confer HgCl2 responsiveness, as indicated by an increase in tyrosine-phosphorylated proteins to a normally nonresponsive cell line. Concomitant with the activation of Hck, there is a physical association of Hck with another cytoplasmic protein tyrosine kinase, Syk. The ability of HgCl2 to activate Src-family kinases such as Hck in hematopoietic cells may help explain why exposure to the heavy metal is associated with immune system dysfunction in rodents as well as humans.

Overexpression of MYC causes p53-dependent G2 arrest of normal fibroblasts

Overexpression of the proto-oncogene MYC has been implicated in the genesis of diverse human cancers. One explanation for the role of MYC in tumorigenesis has been that this gene might drive cells inappropriately through the division cycle, leading to the relentless proliferation characteristic of the neoplastic phenotype. Herein, we report that the overexpression of MYC alone cannot sustain the division cycle of normal cells but instead leads to their arrest in G(2). We used an inducible form of the MYC protein to stimulate normal human and rodent fibroblasts. The stimulated cells passed through G(1) and S but arrested in G(2) and frequently became aneuploid, presumably as a result of inappropriate reinitiation of DNA synthesis. Absence of the tumor suppressor gene p53 or its downstream effector p21 reduced the frequency of both G(2) arrest and aneuploidy, apparently by compromising the G(2) checkpoint control. Thus, relaxation of the G(2) checkpoint may be an essential early event in tumorigenesis by MYC. The loss of p53 function seems to be one mechanism by which this relaxation commonly occurs. These findings dramatize how multiple genetic events can collaborate to produce neoplastic cells.

Inducible chromosomal translocation of AML1 and ETO genes through Cre/loxP-mediated recombination in the mouse

Transgenic mice have been used to explore the role of chromosomal translocations in the genesis of tumors. But none of these efforts has actually involved induction of a translocation in vivo. Here we report the use of Cre recombinase to replicate in vivo the t(8;21) translocation found in human acute myeloid leukemia (AML). As in the human tumors, the murine translocation fuses the genes AML1 and ETO. We used homologous recombination to place loxP sites at loci that were syntenic with the break points for the human translocation. Cre activity was provided in mice by a transgene under the control of the Nestin promoter, or in cultured B cells by infecting with a retroviral vector encoding Cre. In both instances, Cre activity mediated interchromosomal translocations that fused the AML1 and ETO genes. Thus, reciprocal chromosomal translocations that closely resemble rearrangements found in human cancers can be achieved in mice.