Efficient restricted gene expression in beta cells by lentivirus-mediated gene transfer into pancreatic stem/progenitor cells

AIMS/HYPOTHESIS

Gene transfer into pancreatic beta cells, which produce and secrete insulin, is a promising strategy to protect such cells against autoimmune destruction and also to generate beta cells in mass, thereby providing a novel therapeutic approach to treat diabetic patients. Until recently, exogenous DNA has been directly transferred into mature beta cells with various levels of success. We investigated whether exogenous DNA could be stably transferred into pancreatic stem/progenitor cells, which would subsequently differentiate into mature beta cells expressing the transgene.

METHODS

We designed transplantation and tissue culture procedures to obtain ex vivo models of pancreatic development. We next constructed recombinant lentiviruses expressing enhanced green fluorescent protein (eGFP) under the control of either the rat insulin promoter or a ubiquitous promoter, and performed viral infection of rat embryonic pancreatic tissue.

RESULTS

Embryonic pancreas infected with recombinant lentiviruses resulted in endocrine cell differentiation and restricted cell type expression of the transgene according to the specificity of the promoter used in the viral construct. We next demonstrated that the efficiency of infection could be further improved upon infection of embryonic pancreatic epithelia, followed by their in vitro culture, using conditions that favour endocrine cell differentiation. Under these conditions, endocrine stem/progenitor cells expressing neurogenin 3 are efficiently transduced by recombinant lentiviral vectors. Moreover, when eGFP was placed under the control of the insulin promoter, 70.4% of the developed beta cells were eGFP-expressing cells. All of the eGFP-positive cells were insulin-producing cells.

CONCLUSIONS/INTERPRETATION

We have demonstrated that mature rat pancreatic beta cells can be stably modified by infecting pancreatic stem/progenitor cells that undergo endocrine differentiation.

Evidence for muon neutrino oscillation in an accelerator-based experiment

We present results for nu(mu) oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced nu(mu) beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of nu(mu), which we presume have oscillated to nu(tau). The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0 sigma).

Suicide attempts in an African schizophrenia population: an assessment of demographic risk factors

This study investigated demographic variables, including affected sibling pair status, as risk factors for suicidal behavior in schizophrenia patients of African (Xhosa) descent. Xhosa subjects with schizophrenia were interviewed with the Diagnostic Interview for Genetic Studies (DIGS) and then stratified into two groups: those with ( n = 90) and those without ( n = 364) a history of previous suicide attempts. Demographic parameters (including gender, age, and social circumstances, sib ship) were then compared across these groups. Demographic predictors of suicide included sib ship status ( p = 0.038; OR = 1.7) and age of onset of illness ( p = 0.008; OR = 2.5). On further analysis of suicide in siblings, only a minority of sib pairs was found to be concordant for a lifetime history of suicide attempts (3%). These findings raise the possibility that affected sib pair status may be protective in nature. Given the counter-intuitive nature of this finding, further work is needed to replicate it, and to explore possible underlying mechanisms.

An application of the Theory of Planned Behaviour to blood donation: the importance of self-efficacy

Given that self-efficacy has emerged as a key construct in health psychology, this study set out to explore its utility in the context of blood donation as defined within the Theory of Planned Behaviour (TPB). An Ajzen and Fishbein-type questionnaire was administered to 100 undergraduate students at the University of Ulster, Coleraine. A hierarchical multiple regression analysis provided strong support for the role of self-efficacy as a major determinant of intention. It not only helped to explain some 73% of the variance, but also made a greater contribution to the prediction of intention than the other main independent variables of the model-past behaviour and self-identity. Demonstrating the utility of self-efficacy in the context of blood donor behaviour not only has several important practical implications, but serves to further highlight its importance within the TPB.

Multicenter linkage study of schizophrenia loci on chromosome 22q

The hypothesis of the existence of one or more schizophrenia susceptibility loci on chromosome 22q is supported by reports of genetic linkage and association, meta-analyses of linkage, and the observation of elevated risk for psychosis in people with velocardiofacial syndrome, caused by 22q11 microdeletions. We tested this hypothesis by evaluating 10 microsatellite markers spanning 22q in a multicenter sample of 779 pedigrees. We also incorporated age at onset and sex into the analysis as covariates. No significant evidence for linkage to schizophrenia or for linkage associated with earlier age at onset, gender, or heterogeneity across sites was observed. We interpret these findings to mean that the population-wide effects of putative 22q schizophrenia susceptibility loci are too weak to detect with linkage analysis even in large samples.

Examination of IMPA1 and IMPA2 genes in manic-depressive patients: association between IMPA2 promoter polymorphisms and bipolar disorder

Manic-depressive (bipolar) illness is a serious psychiatric disorder with a strong genetic predisposition. The disorder is likely to be multifactorial and etiologically complex, and the causes of genetic susceptibility have been difficult to unveil. Lithium therapy is a widely used pharmacological treatment of manic-depressive illness, which both stabilizes the ongoing episodes and prevents relapses. A putative target of lithium treatment has been the inhibition of the myo-inositol monophosphatase (IMPase) enzyme, which dephosphorylates myo-inositol monophosphate in the phosphatidylinositol signaling system. Two genes encoding human IMPases have so far been isolated, namely myo-inositol monophosphatase 1 (IMPA1) on chromosome 8q21.13-21.3 and myo-inositol monophosphatase 2 (IMPA2) on chromosome 18p11.2. In the present study, we have scanned for DNA variants in the human IMPA1 and IMPA2 genes in a pilot sample of Norwegian manic-depressive patients, followed by examination of selected polymorphisms and haplotypes in a family-based bipolar sample of Palestinian Arab proband-parent trios. Intriguingly, two frequent single-nucleotide polymorphisms (-461C>T and -207T>C) in the IMPA2 promoter sequence and their corresponding haplotypes showed transmission disequilibrium in the Palestinian Arab trios. No association was found between the IMPA1 polymorphisms and bipolar disorder, neither with respect to disease susceptibility nor with variation in lithium treatment response. The association between manic-depressive illness and IMPA2 variants supports several reports on the linkage of bipolar disorder to chromosome 18p11.2, and sustains the possible role of IMPA2 as a susceptibility gene in bipolar disorder.

Delivery of GDNF by an E1,E3/E4 deleted adenoviral vector and driven by a GFAP promoter prevents dopaminergic neuron degeneration in a rat model of Parkinson's disease

A new adenoviral vector (Ad-GFAP-GDNF) (Ad=adenovirus, GFAP=glial fibrillary acidic protein, GDNF=glial cell line-derived neurotrophic factor) was constructed in which (i) the E1,E3/E4 regions of Ad5 were deleted and (ii) the GDNF transgene is driven by the GFAP promoter. We verified, in vitro, that the recombinant GDNF was expressed in primary cultures of astrocytes. In vivo, the Ad-GFAP-GDNF was injected into the striatum of rats 1 week before provoking striatal 6-OHDA lesion. After 1 month, the striatal GDNF levels were 37 pg/microg total protein. This quantity was at least 120-fold higher than in nontransduced striatum or after injection of the empty adenoviral vector. At 3 months after viral injection, GDNF expression decreased, whereas the viral DNA remained unchanged. Furthermore, around 70% of the dopaminergic (DA) neurons were protected from degeneration up to 3 months as compared to about 45% in the control groups. In addition, the amphetamine-induced rotational behavior was decreased. The results obtained in this study on DA neuron protection and rotational behavior are similar to those previously reported using vectors with viral promoters. In addition to these results, we established that a high level of GDNF was present in the striatum and that the period of GDNF expression was prolonged after injection of our adenoviral vector.

Host choice promotes reproductive isolation between host races of the larch budmoth Zeiraphera diniana

The chances for sympatric speciation are improved if ecological divergence leads to assortative mating as a by-product. This effect is known in parasites that find mates using host cues, but studies of larch- and pine-feeding races of the larch budmoth (Zeiraphera diniana, Lepidoptera: Tortricidae) suggest it may also occur when mate attraction is via sex pheromones that are independent of habitat. We have previously shown that females releasing pheromones on or near their own host attract more males of their own race than if placed on the alternative host. This host effect would enhance assortative mating provided adults preferentially alight on their native hosts. Here we investigate alighting preferences in natural mixed forest using a novel likelihood analysis of genotypic clusters based on three semidiagnostic allozyme loci. Both larch and pine females show a realized alighting preference for their own host of 86%. The equivalent preferences of males were 79% for the larch race and 85% for the pine race. These preferences are also detectable in small-scale laboratory experiments, where alighting preferences of larch and pine races towards their own hosts were, respectively, 67 and 66% in females and 69 and 63% in males. Pure larch race moths reared in the laboratory had alighting choice similar to moths from natural populations, while hybrids were intermediate, showing that alighting preferences were heritable and approximately additive. The field estimates of alighting preference, coupled with earlier work on mate choice, yield an estimated rate of natural hybridization between sympatric host races of 2.2-3.8% per generation. Divergent alighting choice enhances pheromone-mediated assortative mating today, and is likely to have been an important cause of assortative mating during initial divergence in host use. Because resources are normally 'coarse-grained' in space and time, assortative mating due to ecological divergence may be a more important catalyst of sympatric speciation than generally realized.

LTP but not seizure is associated with up-regulation of AKAP-150

We have used differential display to profile and compare the mRNAs expressed in the hippocampus of freely moving animals after the induction of long-term potentiation (LTP) at the perforant path-dentate gyrus synapse with control rats receiving low-frequency stimulation. We have combined this with in situ hybridization and have identified A-kinase anchoring protein of 150 kDa (AKAP-150) as a gene selectively up-regulated during the maintenance phase of LTP. AKAP-150 mRNA has a biphasic modulation in the dentate gyrus following the induction of LTP. The expression of AKAP-150 was 29% lower than stimulated controls 1 h after the induction of LTP. Its expression was enhanced 3 (50%), 6 (239%) and 12 h (210%) after induction, returning to control levels by 24 h postinduction. The NMDA receptor antagonist CPP blocked the tetanus-induced modulation of AKAP-150 expression. Interestingly, strong generalized stimulation produced by electroconvulsive shock did not increase the expression of AKAP-150. This implies that the AKAP-150 harbours a novel property of selective responsiveness to the stimulation patterns that trigger NMDA-dependent LTP in vivo. Its selective up-regulation during LTP and its identified functions as a scaffold for protein kinase A, protein kinase C, calmodulin, calcineurin and ionotropic glutamate receptors suggest that AKAP-150 encodes is an important effector protein in the expression of late LTP.

Controlled transgene expression by E1-E4-defective adenovirus vectors harbouring a "tet-on" switch system

BACKGROUND

The "tet switch system" was originally described under the tet-off configuration with its components encoded by two separate plasmids. Since then, many virus vectors harbouring tet-off components have been designed and their regulation by tetracycline is widely reported. On the contrary, tet-on regulation by viral vectors is poorly documented.

METHODS

E1-E4-defective adenoviruses harbouring either rtTA or the luciferase gene under a minimal inducible promoter (TK* or CMV*) or both components in a single genome were produced. Using either a double or a single virus strategy, induction of luciferase expression was investigated in various cell lines, in mice muscle and in rat brain.

RESULTS

Over 400-fold induction can be reached with PC12 and NHA cells using a double virus strategy. Comparison of the background activity of different minimal inducible promoters revealed a significant difference between TK* and CMV* promoters both with the cell culture and the in vivo experiments. Interestingly, a single virus strategy permitted an induction exceeding 600-fold with human astrocyte primary cells. Moreover, the E1-E4-defective adenovirus-mediated tet-on system can be quickly switched off and turned back on again. Depending on the cell line, the level of rtTA derived by the single virus strategy differed, resulting in different efficiencies. Experiments performed in rat striatum and mouse muscle confirmed the importance of rtTA expression and minimal promoter used on both doxycycline-independent expression and induction efficiency. Under appropriated rtTA expression, a 32-fold induction is observed in mouse muscle.

CONCLUSIONS

In the recombinant adenovirus context, the CMV* but not the TK* promoter is sensitive to transcriptional interference resulting in high doxycycline-independent expression. By paying attention to the rtTA expression, moderate and high induction can be obtained in vivo and in vitro accordingly.

Age-dependent differential regulation of genes encoding APP and alpha-synuclein in hippocampal synaptic plasticity

We investigated the modulation of the messenger RNA encoding the amyloid precursor protein (APP) and alpha-synuclein following induction of long-term potentiation (LTP) in the dentate gyrus of young and aged rats. Three hours after tetanic stimulation, LTP induced in the young rats was maintained; the aged rats, however, fell into two subgroups: those in which LTP was maintained, and those in which LTP had declined to basal levels. In young rats, the global expression of mRNAs of all isoforms of APP and in particular that of the isoform lacking the KPI domain were significantly upregulated. In aged rats, the global expression of mRNAs of all isoforms of APP was not modified, regardless of whether LTP was maintained or not. The level of mRNA encoding the Kunitz protease-inhibitory (KPI)-minus isoform of APP, however, was increased in aged rats in which LTP was maintained, suggesting that the gene of this isoform may be more specifically regulated by synaptic plasticity. In contrast, we found that the gene encoding alpha-synuclein showed a trend towards being downregulated at the mRNA level in young rats following LTP, and significantly so in aged rats in which LTP was maintained, whereas it was not downregulated in aged rats with decremental LTP. These data suggest that the regulated expression of APP isoforms is part of the tanscriptional response associated with the enduring forms of synaptic plasticity and is altered with age. Whereas the level of alpha-synuclein mRNA is not apparently modified in normal LTP, it may reflect a mechanism of apoptotic cell death in aging that is in part responsible for decremental synaptic plasticity.

Viral and non-viral gene therapy partially prevents experimental cisplatin-induced neuropathy

Sensory neuropathies are a frequent and dose-limiting complication resulting from treatment with cisplatin. Neurotrophin-3 (NT-3) promotes the survival of the large fiber sensory neurones that are impaired in cisplatin-induced neuropathy, and may therefore serve as a preventive agent. However, the short half-life of recombinant NT-3 after systemic administration limits its clinical applications. We compared two muscle-based gene transfer strategies for the continuous delivery of NT-3 to the bloodstream in an experimental model of cisplatin-induced neuropathy. Electrophysiological studies showed that the intramuscular injection of an adenovirus encoding NT-3 partially prevented the cisplatin-induced increase in sensory distal latencies. Similar effects were observed in cisplatin-treated mice that received intramuscular injections of a plasmid encoding NT-3 associated with in vivo electroporation. The two techniques were well tolerated and induced only slight muscle toxicity. Measurement of renal function, weight and survival showed that neither technique increased the toxicity of cisplatin. Our study shows that gene therapy, using either a viral or a non-viral vector, is a promising strategy for the prevention of cisplatin-induced neuropathy.

Spatio-temporal heterogeneity and cell-specificity of long-term potentiation-induced mRNA expression in the dentate gyrus in vivo

Gene expression in neurones can vary in response to neuronal activation. In this study, to analyse the spatio-temporal dynamics of the transcriptional response of three genes following the induction of long-term potentiation within the entire dentate gyrus in vivo, two new complementary approaches based on in situ hybridisation were developed: three-dimensional reconstruction of the pattern of mRNA expression within the entire dentate gyrus; and radioactive co-detection of two mRNA species allowing quantification of two different mRNAs in the same brain section. Zif268, Homer and syntaxin 1B genes were studied, and their regulated expression was examined three times after the induction of long-term potentiation. Constitutive expression of each gene under control conditions was homogeneous, but the spatial distribution of mRNA was heterogeneous along the rostro-caudal axis of the dentate gyrus following the induction of long-term potentiation, and different for each gene. In addition, the intensity of each gene-specific pattern of expression varied over time following the induction of long-term potentiation. Our results reveal that long-term potentiation differentially modulates the expression of mRNA species in cells of the dentate gyrus depending on their position along the rostro-caudal axis, on the gene and on time. We suggest that there are several molecular mechanisms of long-term potentiation, differing from one cluster of cells of the dentate gyrus to another, or that the different signaling pathways involved in long-term potentiation are used with varying efficiencies by different cells.

Involvement of NF-Y and Sp1 in basal and cAMP-stimulated transcriptional activation of the tryptophan hydroxylase (TPH ) gene in the pineal gland

The expression of the tryptophan hydroxylase (TPH) gene, encoding the rate-limiting enzyme of serotonin biosynthesis, is tightly regulated both at the transcriptional and at the post-transcriptional levels. In the pineal gland, transcription of the gene is activated in response to an intracellular circadian increase of the cAMP concentration. We have previously shown that transcription of a 2.1-kb fragment of the human TPH promoter is induced by cAMP, although it lacks the canonical cAMP responsive element, CRE. The minimal promoter (-73/+29) has only weak transcriptional activity but is responsive to cAMP. It contains an inverted CCAAT box, which was demonstrated to be involved in this response. Here, we have extended our investigation to the functional features of the inverted CCAAT box in the -252/+29 TPH promoter, which has a higher basal activity. We show that an additional cis -acting sequence, the adjacent GC-rich region, cooperates with the inverted CCAAT box for the full activation of basal transcription, and that both elements are essential for the full cAMP response. We also show that in pinealocytes, NF-Y and Sp1 transactivators bind the inverted CCAAT box and GC-rich-region, respectively. These factors participate in a novel pathway for the cAMP-mediated response of the TPH promoter, which is independent of the canonical CRE-mediated response.

A novel sensitive microarray approach for differential screening using probes labelled with two different radioelements

We have developed a novel microarray approach for differential screening using probes labelled with two different radioelements. The complementary DNAs from the reverse transcription of mRNAs from two different biological samples were labelled with radioelements of significantly different energies (3H and 35S or 33P). Radioactive images corresponding to the expressed genes were acquired with a MicroImager, a real time, high resolution digital autoradiography system. An algorithm was used to process the data such that the initially acquired radioactive image was filtered into two subimages, each representative of the hybridisation result specific for one probe. The simultaneous screening of gene expression in two different biological samples requires <100 ng mRNA without any amplification. In such conditions, the technique is sensitive enough to directly quantify the amount of mRNA even when present in small amounts: 10(7) molecules in the probe as assessed with an added control sequence and 2 x 10(5) molecules with an endogenous tyrosine hydroxylase mRNA. This novel technique of double radioactive labelling on a microarray is thus suitable for the comparison of gene expression in two different biological samples available in only small quantities. Consequently, it has great potential for various biological fields, such as neuroscience.

Regulated expression of the neuronal calcium sensor-1 gene during long-term potentiation in the dentate gyrus in vivo

Neuronal calcium sensor-1 (NCS-1), the mammalian homologue of frequenin, is a member of a highly conserved family of neuron-specific calcium-binding proteins which has been implicated in exocytosis and in multiple calcium-signalling pathways, suggesting a potential involvement in mechanisms of neuronal plasticity. Here, using in situ hybridization, we report an increased induction of the mRNA encoding NCS-1 in dentate granule cells following the induction of long-term potentiation in the awake rat. We show that NCS-1 mRNA levels are increased 1 and 3 h after long-term potentiation in an N-methyl-D-aspartate receptor-dependent manner, returning to baseline expression levels by 6 h. Electroconvulsive stimulation also induced NCS-1 mRNA transcription in the dentate gyrus, but at the different time of 6 h post-seizure, returning to baseline by 12 h. These results show that regulated expression of the NCS-1 gene is part of the transcriptional response associated with activity-dependent neuronal plasticity in vivo and suggest a molecular mechanism capable of mediating a functional change in synapse sensitivity to calcium and calcium-signalling pathways after long-term potentiation.

Continuous delivery of neurotrophin 3 by gene therapy has a neuroprotective effect in experimental models of diabetic and acrylamide neuropathies

Neurotrophic factors (NFs) are promising agents for the treatment of peripheral neuropathies such as diabetic neuropathy. However, the value of treatment with recombinant NF is limited by the short half-lives of these molecules, which reduces efficiency, and by their potential toxicity. We explored the use of intramuscular injection of a recombinant adenovirus encoding NT-3 (AdNT-3) to deliver sustained low doses of NT-3. We assessed its effect in two rat models: streptozotocin (STZ)-induced diabetes, a model of early diabetic neuropathy characterized by demyelination, and acrylamide experimental neuropathy, a model of diffuse axonal neuropathy which, like late-onset human diabetic neuropathy, results in a diffuse sensorimotor neuropathy with dysautonomy. Treatment of STZ-diabetic rats with AdNT-3 partially prevented the slowing of motor and sensory nerve conduction velocities (p < 0.01 and p < 0.0001, respectively). Treatment with AdNT-3 of acrylamide-intoxicated rats prevented the slowing of motor and nerve conduction velocities (p < 0.001 and p < 0.0001, respectively) and the decrease in amplitude of compound muscle potentials (p < 0.0001), an index of denervation. Acrylamide-intoxicated rats treated with NT-3 had higher than control levels of muscle choline acetyltransferase activity (p < 0.05), suggesting greater muscle innervation. In addition, treatment of acrylamide-intoxicated rats with AdNT-3 significantly improved behavioral test results. Treatment with AdNT-3 was well tolerated with minimal muscle inflammation and no detectable general side effects. Therefore, our results suggest that NT-3 delivery by adenovirus-based gene therapy is a promising strategy for the prevention of both early diabetic neuropathy and axonal neuropathies, especially late axonal diabetic neuropathy.

Selective cardiorespiratory and catecholaminergic areas express the hypoxia-inducible factor-1alpha (HIF-1alpha) under in vivo hypoxia in rat brainstem

Under severe oxygen deprivation, all cells are able to express the transcription factor HIF-1, which activates a wide range of genes. Under tolerable hypoxia, chemosensory inputs are integrated in brainstem areas, which control cardiorespiratory responses. However, the molecular mechanisms of this functional acclimatization are unknown. We investigated when and where the inducible HIF-1alpha subunit is expressed in the rat brainstem in vivo, under physiological hypoxia. The regional localization of HIF-1alpha mRNA and protein was determined by in situ hybridization and immunocytochemistry in adult male rats exposed to moderate hypoxia (10% O2) for 1-6 h. HIF-1alpha protein was found in cell types identified by immunocytochemistry as catecholaminergic neurons. Hypoxia induced HIF-1alpha mRNA and protein in only some parts of the brainstem located dorsomedially and ventrolaterally, which are those involved in the cardiorespiratory control. No labelling was detected under normoxia. The protein was detected in glia and neurons after 1 and 6 h of hypoxia, respectively. A subset of A2C2 and A1C1 catecholaminergic neurons colocalized tyrosine hydroxylase and HIF-1alpha proteins under hypoxia, but no HIF-1alpha was detected in more rostral catecholaminergic areas. In contrast to cardiorespiratory areas, HIF-1alpha protein was already present under normoxia in glial cells of brainstem tracts but was not overexpressed under hypoxia, although HIF-1alpha mRNA was up-regulated. In conclusion, there appear to be two regulatory mechanisms for HIF-1alpha expression in the brainstem: hypoxic induction of HIF-1alpha protein in cardiorespiratory-related areas and constitutive protein expression unaffected by hypoxia in brainstem tracts.

Sciatica caused by epidural gas. Four case reports

We report four cases of sciatica caused by gas in the epidural space with no other abnormality. Only 21 similar cases have been reported. Clinical features are identical to those of common sciatica, and plain radiographs are often uninformative. Computed tomography shows a low-density epidural collection displacing the nerve root.

Host-induced assortative mating in host races of the larch budmoth

The likelihood of sympatric speciation is enhanced when assortative mating is a by-product of adaptation to different habitats. Pleiotropy of this kind is recognized as important in parasites that use their hosts as a long-range cue for finding mates, but is generally assumed to have limited applicability for most other organisms. In the larch budmoth, Zeiraphera diniana (Lepidoptera: Tortricidae), sympatric host races feed on larch or pine. Zeiraphera diniana females attract males (call) by releasing host-independent long-range pheromones. Pheromone composition differs strongly between host races, but we show in an experimental field study that cross-attraction can occur at a rate of 0.03-0.38. Cross-attraction to larch females increases when they call from neighborhoods (8-m radius) rich in pine or from pine trees. Cross-attraction to pine females similarly increases when calling from neighborhoods rich in larch, but there is no significant effect of calling substrate. Males, as well as females, of this species preferentially alight on their own host, and in neighborhoods where their own host is common. This effect of tree species and host neighborhood on assortative mating is therefore due, at least in part, to the numbers of males of each host race present within approximately 200 m2 surrounding the female. This proximity effect is enhanced by the clumped distributions of the hosts themselves. Host chemistry might also affect pheromone production and/or response directly, but we have evidence neither for nor against this. This work provides empirical evidence that host adaptation has a pleiotropic effect on assortative mating in a species with host-independent long-range mating signals. Sympatric speciation via pleiotropy between ecological traits and assortative mating may thus be more common than generally supposed: Clumped resource distributions and habitat choice by adults are widespread.

Disruptive sexual selection against hybrids contributes to speciation between Heliconius cydno and Heliconius melpomene

Understanding the fate of hybrids in wild populations is fundamental to understanding speciation. Here we provide evidence for disruptive sexual selection against hybrids between Heliconius cydno and Heliconius melpomene. The two species are sympatric across most of Central and Andean South America, and coexist despite a low level of hybridization. No-choice mating experiments show strong assortative mating between the species. Hybrids mate readily with one another, but both sexes show a reduction in mating success of over 50% with the parental species. Mating preference is associated with a shift in the adult colour pattern, which is involved in predator defence through Müllerian mimicry, but also strongly affects male courtship probability. The hybrids, which lie outside the curve of protection afforded by mimetic resemblance to the parental species, are also largely outside the curves of parental mating preference. Disruptive sexual selection against F(1) hybrids therefore forms an additional post-mating barrier to gene flow, blurring the distinction between pre-mating and post-mating isolation, and helping to maintain the distinctness of these hybridizing species.

Quantitative effects on gene silencing by allelic variation at a tetranucleotide microsatellite

Microsatellites are common repeated sequences, which are useful as genetic markers and lack any clearly established function. In a previous study we suggested that an intronic polymorphic TCAT repeat in the tyrosine hydroxylase (TH) gene, the microsatellite HUMTH01, may regulate transcription. The TH gene encodes the rate-limiting enzyme in the synthesis of catecholamines, and the microsatellite HUMTH01 has been used in genetic studies of neuropsychiatric and cardiovascular diseases, in which disturbances of catecholaminergic neurotransmission have been implicated. HUMTH01 alleles associated with these diseases act as transcriptional enhancers when linked to a minimal promoter and are recognized by specific nuclear factors. Here we show that allelic variations of HUMTH01 commonly found in humans have a quantitative silencing effect on TH gene expression. Two specific proteins, ZNF191, a zinc finger protein, and HBP1, an HMG box transcription factor, which bind the TCAT motif, were then cloned. Finally, allelic variations of HUMTH01 correlate with quantitative and qualitative changes in the binding by ZNF191. Thus, this repeated sequence may contribute to the control of expression of quantitative genetic traits. As the HUMTH01 core motif is ubiquitous in the genome, this phenomenon may be relevant to the quantitative expression of many genes in addition to TH.

Sex-linked hybrid sterility in a butterfly

Recent studies, primarily in Drosophila, have greatly advanced our understanding of Haldane's rule, the tendency for hybrid sterility or inviability to affect primarily the heterogametic sex (Haldane 1922). Although dominance theory (Turelli and Orr 1995) has been proposed as a general explanation of Haldane's rule, this remains to be tested in female-heterogametic taxa, such as the Lepidoptera. Here we describe a novel example of Haldane's rule in Heliconius melpomene (Lepidoptera; Nymphalidae). Female F1 offspring are sterile when a male from French Guiana is crossed to a female from Panama, but fertile in the reciprocal cross. Male F1s are fertile in both directions. Similar female F1 sterility occurs in crosses between French Guiana and eastern Colombian populations. Backcrosses and linkage analysis show that sterility results from an interaction between gene(s) on the Z chromosome of the Guiana race with autosomal factors in the Panama genome. Large X (or Z) effects are commonly observed in Drosophila, but to our knowledge have not been previously demonstrated for hybrid sterility in Lepidoptera. Differences in the abundance of male versus female or Z-linked versus autosomal sterility factors cannot be ruled out in our crosses as causes of Haldane's rule. Nonetheless, the demonstration that recessive Z-linked loci cause hybrid sterility in a female heterogametic species supports the contention that dominance theory provides a general explanation of Haldane's rule (Turelli and Orr 2000).