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Michael J Ryan

Publications and source records attributed to Michael J Ryan.

At least 19 recordsLinked to original sources
PubMed2026

MADCAP: isolation of novel nAb-naïve AAV capsids from metagenomic data.

UNLABELLED: Gene therapy using adeno-associated virus (AAV) vectors offers promising treatment for genetic disorders, but significant limitations restrict clinical application. Current AAV serotypes exhibit strong liver tropism and require high doses for extra-hepatic targeting, and pre-existing antibodies (NAbs) exclude up to 50% of potential patients. Evolutionarily distant isolates can evade neutralization but typically transduce human tissues poorly and require extensive engineering. We developed MADCAP (Metagenomic AAV Discovery and Capsid Annotation Pipeline) to systematically mine metagenomic data for functional, clinically relevant AAV capsids. We hypothesized that these sources might contain capsids that do not circulate widely in humans, can transduce human cells, and avoid neutralization. We screened 4.2 million metagenomic samples and identified 139 novel AAV capsid isolates which were tested for viral capsid assembly, viability, neutralization evasion, and tissue transduction in non-human primates. While natural serotypes (AAV1, AAV2, AAV9) were neutralized at low dilutions of pooled human immunoglobulin (IVIG), 68% of tested MADCAP capsids exhibited minimal to undetectable neutralization even at supra-physiological IVIG concentrations. Systemically delivered MADCAP capsids effectively transduced multiple clinically relevant tissues in non-human primates. Two capsids, MC46 and MC55, demonstrated improved CNS tropism compared to AAV9 while maintaining comparable production yields. In passive transfer studies, MC46 retained full transduction efficiency in the presence of human antibodies, while AAV9 transduction was completely lost. This work establishes metagenomic mining as a powerful tool for accelerating AAV capsid discovery, identifying isolates with favorable tissue tropisms and resistance to broadly neutralizing antibodies. IMPORTANCE: This work provides proof of concept that potentially clinically relevant AAVs can be isolated from metagenomic data. Our findings lay the groundwork for accelerated discovery of AAV capsids which could potentially increase the accessibility and effectiveness of AAV gene therapy.

AAV↗
PubMed2007

Sexual selection drives speciation in an Amazonian frog.

One proposed mechanism of speciation is divergent sexual selection, whereby divergence in female preferences and male signals results in behavioural isolation. Despite the appeal of this hypothesis, evidence for it remains inconclusive. Here, we present several lines of evidence that sexual selection is driving behavioural isolation and speciation among populations of an Amazonian frog (Physalaemus petersi). First, sexual selection has promoted divergence in male mating calls and female preferences for calls between neighbouring populations, resulting in strong behavioural isolation. Second, phylogenetic analysis indicates that populations have become fixed for alternative call types several times throughout the species' range, and coalescent analysis rejects genetic drift as a cause for this pattern, suggesting that this divergence is due to selection. Finally, gene flow estimated with microsatellite loci is an average of 30 times lower between populations with different call types than between populations separated by a similar geographical distance with the same call type, demonstrating genetic divergence and incipient speciation. Taken together, these data provide strong evidence that sexual selection is driving behavioural isolation and speciation, supporting sexual selection as a cause for speciation in the wild.

Animals↗
PubMed2007

Cues for eavesdroppers: do frog calls indicate prey density and quality?

Predators and parasites that eavesdrop on the mating signals of their prey often preferentially select individuals within a prey/host species that produce specific cues. Mechanisms driving such signal preferences are poorly understood. In the tungara frog Physalaemus pustulosus, conspecific females, frog-eating bats, and blood-sucking flies all prefer complex to simple mating calls. In this study we assess the natural signal variation in choruses in the wild and test two hypotheses for why eavesdroppers prefer complex calls: (1) prey quality: complex calls indicate better quality of prey/host, and (2) prey density: complex calls indicate higher prey/host density. Call complexity is not correlated with frog length, mass, or body condition, but it does signal higher abundance of prey/host. Thus, increased effectiveness of attack may have played a role favoring the preference for complex calls in eavesdropping heterospecifics.

Animals↗
PubMed2006

Insulin resistance and obesity in a mouse model of systemic lupus erythematosus.

Accumulating data indicate that metabolic syndrome is an inflammatory condition. Systemic lupus erythematosus (SLE) is an autoimmune disorder associated with nephritis and cardiovascular disease. Evidence suggests that individuals with SLE are at risk for developing insulin resistance; however, this has not been directly examined. Using an established mouse strain with SLE (NZBWF1), we examined whether SLE is associated with increased body weight and fat deposition. Mean arterial pressure was significantly increased (140+/-4 versus 114+/-2 mm Hg; n > or = 5) in SLE mice by 36 weeks of age compared with control mice (NZW/LacJ). Body weight in SLE mice was higher at each age compared with controls by 12%, 22%, and 34% (n > 30). Visceral adipose tissue weight was increased in SLE by 44%, 74%, and 117% at 8, 20, and 36 weeks, respectively (n > or = 12). Plasma leptin was increased in SLE mice (8.6+/-1.0 versus 24.7+/-2.2 ng/mL; n = 5), and renal and adipose tissue exhibited macrophage infiltration. Fasted insulin was higher in SLE mice (0.6+/-0.1 versus 1.4+/-0.3 ng/mL; n > or = 10), but fasted glucose was not different (94+/-5 versus 80+/-9; n > or = 9). A glucose tolerance test caused a significantly greater and longer increase in blood glucose from mice with SLE compared with control mice. Food intake was not different between control and SLE mice. However, mice with SLE demonstrated lower levels of nighttime activity than controls. These data show that the NZBWF1 strain may be an important model to study the effects of obesity and insulin resistance on SLE-associated hypertension.

Animals↗
PubMed2006

Hypertension and impaired vascular function in a female mouse model of systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a chronic autoimmune inflammatory disease that predominantly affects women during their reproductive years. Although women with SLE have hypertension, the underlying mechanisms for this have not been examined. Despite the fact that inflammation is associated with altered endothelial and vascular function, the role of altered vascular function in the development of hypertension during SLE is unclear. In the present study, we tested whether a mouse model of SLE (NZBWF1) develops hypertension and examined whether increased blood pressure was associated with impaired endothelial-dependent relaxation. Female NZBWF1 mice were studied at 8, 20, and 36 wk of age. By 36 wk, urinary albumin and antinuclear antibodies were increased in SLE compared with control mice. Mean arterial pressure, measured by radiotelemetry, was significantly increased in SLE mice (124 +/- 4 mmHg, n = 10) compared with control NZW/LacJ mice (111 +/- 3 mmHg, n = 7) at 36 wk. Isolated carotid arteries from NZBWF1 mice, precontracted with U-46619 for assessment of endothelial-dependent relaxation, demonstrated a progressively impaired relaxation to ACh with age, although endothelial nitric oxide synthase mRNA expression was not different. Maximal tension generated by 5-hydroxytryptamine was increased in carotid arteries from NZBWF1 mice compared with controls at 8, 20, and 36 wk of age, suggesting a role for altered vascular function early on in the progression of SLE. Taken together, our data support a role for altered endothelial function as a contributing factor to the development of hypertension during SLE.

Acetylcholine↗
PubMed2006

The two novel CETP mutations Gln87X and Gln165X in a compound heterozygous state are associated with marked hyperalphalipoproteinemia and absence of significant coronary artery disease.

High levels of high-density lipoprotein cholesterol (HDL-C) occur with cholesteryl ester transfer protein (CETP) deficiency. However, the extent to which CETP deficiency states may be associated with protection against coronary artery disease (CAD) has been controversial. We evaluated a Greek pedigree with high levels of HDL-C and no history of premature CAD. The proband, a 45-year-old male with an HDL-C of 194 mg/dl with absent CETP activity, was heterozygous for two novel CETP mutations (Q87X and Q165X). A 64-slice multidetector CT scan revealed minimal (<10%) narrowing of the proximal left anterior descending artery without any other evidence of coronary atherosclerosis. In contrast to previous studies, these data suggest that complete CETP deficiency does not promote premature atherosclerosis. However, it remains unclear as to whether the relative lack of coronary atherosclerosis was the direct consequence of CETP deficiency and/or the lack of traditional CAD risk factors.

Adolescent↗
PubMed2006

The role of model female quality in the mate choice copying behaviour of sailfin mollies.

Female mate choice copying is a socially mediated mate choice behaviour, in which a male's attractiveness to females increases if he was previously chosen by another female as a mate. Although copying has been demonstrated in numerous species, little is known about the specific benefits it confers to copying females. Here we demonstrate that the mate choice behaviour of female sailfin mollies (Poecilia latipinna) is influenced by the phenotypic quality of model females with whom males are observed consorting. Test females choosing between two males of similar body length were found to significantly increase time spent with previously non-preferred males after having observed them with a relatively high-quality female. Conversely, females were found to significantly decrease time spent with previously preferred males after having observed them with a relatively low-quality female. Female mate choice copying might be maintained by selection based on the heuristic value it provides females choosing between males whose quality differences are not easily distinguishable.

Animals↗
PubMed2006

Social transmission of novel foraging behavior in bats: frog calls and their referents.

The fringe-lipped bat, Trachops cirrhosus, uses prey-emitted acoustic cues (frog calls) to assess prey palatability . Previous experiments show that wild T. cirrhosus brought into the laboratory are flexible in their ability to reverse the associations they form between prey cues and prey quality . Here we asked how this flexibility can be achieved in nature. We quantified the rate at which bats learned to associate the calls of a poisonous toad species with palatable prey by placing bats in three groups: (a) social learning, in which a bat inexperienced with the novel association was allowed to observe an experienced bat; (b) social facilitation, in which two inexperienced bats were presented with the experimental task together; and (c) trial-and-error, in which a single inexperienced bat was presented with the experimental task alone. In the social-learning group, bats rapidly acquired the novel association in an average of 5.3 trials. In the social-facilitation and trial-and-error groups, most bats did not approach the call of the poisonous species after 100 trials. Thus, once acquired, novel associations between prey cue and prey quality could spread rapidly through the bat population by cultural transmission. This is the first case to document predator social learning of an acoustic prey cue.

Animals↗
PubMed2006

Reproductive character displacement generates reproductive isolation among conspecific populations: an artificial neural network study.

When interactions with heterospecifics prevent females from identifying conspecific mates, natural selection can promote the evolution of mating behaviours that minimize such interactions. Consequently, mating behaviours may diverge among conspecific populations in sympatry and in allopatry with heterospecifics. This divergence in conspecific mating behaviours-reproductive character displacement-can initiate speciation if mating behaviours become so divergent as to generate reproductive isolation between sympatric and allopatric conspecifics. We tested these ideas by using artificial neural networks to simulate the evolution of conspecific mate recognition in populations sympatric and allopatric with different heterospecifics. We found that advertisement calls diverged among the different conspecific populations. Consequently, networks strongly preferred calls from their own population to those from foreign conspecific populations. Thus, reproductive character displacement may promote reproductive isolation and, ultimately, speciation among conspecific populations.

Animal Communication↗
PubMed2006

Renal vascular responses to CORM-A1 in the mouse.

CORM-A1 is a newly described water-soluble carbon monoxide (CO) releasing molecule (CORM) that can deliver CO to various vascular beds in the absence of dramatic changes in blood carboxy-hemoglobin (COHb) levels. We tested the in vivo and in vitro renal vascular effects of CORM-A1 administration using anesthetized mice instrumented with a renal flow probe as well as in isolated, pressurized renal interlobar arteries. Administration of CORM-A1 (0.96 micromol) resulted in a significant increase in renal blood flow (RBF) of 33 +/- 6% as compared to control. Administration of acetylcholine (50 pmol) caused a similar increase in RBF (25 +/- 4%). In order to determine if the vasodilatory effect of CORM-A1 in vivo was mediated through activation of soluble guanylate cyclase (sGC), mice were pretreated with the sGC inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 1 nmolkg(-1)min(-1)) for 30min. Pretreatment with ODQ significantly reduced the CORM-A1 mediated increase in RBF to 9 +/- 5% of control. In isolated pressurized renal interlobar arteries, CORM-A1 caused dose dependent vasodilatation of phenylephrine constricted arteries. The CORM-A1 mediated vasodilatation was significantly attenuated by ODQ to similar levels as observed in vivo. Inhibition of calcium activated potassium channels (Kca) with iberiotoxin resulted in a complete blockade of the CORM-A1 mediated vasodilatation in pressurized renal interlobar arteries. We conclude that CO released from CORM-A1 causes an increase in RBF and a decrease in vascular resistance through activation of sGC and opening of Kca channels in the kidney of the mouse.

Animals↗
PubMed2006

Ketopiperazine-based renin inhibitors: optimization of the "C" ring.

A systematic investigation of the S3 sub-pocket activity requirements was conducted. It was observed that linear and sterically small side chain substituents are preferred in the S3 sub-pocket for optimal renin inhibition. Polar groups in the S3-sub-pocket were not well tolerated and caused a reduction in renin inhibitory activity. Further, compounds with clog P's < or = 3 demonstrated a dramatic reduction in CYP3A4 inhibitory activity.

Crystallography, X-Ray↗
PubMed2006

Cerebral vascular effects of angiotensin II: new insights from genetic models.

Very little is known regarding the mechanisms of action of angiotensin II (Ang II) or the consequences of Ang II-dependent hypertension in the cerebral circulation. We tested the hypothesis that Ang II produces constriction of cerebral arteries that is mediated by activation of AT1A receptors and Rho-kinase. Basilar arteries (baseline diameter approximately 130 microm) from mice were isolated, cannulated and pressurized to measure the vessel diameter. Angiotensin II was a potent constrictor in arteries from male, but not female, mice. Vasoconstriction in response to Ang II was prevented by an inhibitor of Rho-kinase (Y-27632) in control mice, and was reduced by approximately 85% in mice deficient in expression of AT1A receptors. We also examined the chronic effects of Ang II using a model of Ang II-dependent hypertension, mice which overexpress human renin (R+) and angiotensinogen (A+). Responses to the endothelium-dependent agonist acetylcholine were markedly impaired in R+A+ mice (P<0.01) compared with controls, but were restored to normal by a superoxide scavenger (PEG-SOD). A-23187 (another endothelium-dependent agonist) produced vasodilation in control mice, but no response or vasoconstriction in R+A+ mice. In contrast, dilation of the basilar artery in response to a NO donor (NONOate) was similar in R+A+ mice and controls. Thus, Ang II produces potent constriction of cerebral arteries via activation of AT1A receptors and Rho-kinase. There are marked gender differences in cerebral vascular responses to Ang II. Endothelial function is greatly impaired in a genetic model of Ang II-dependent hypertension via a mechanism that involves superoxide.

Angiotensin II↗
PubMed2006

Geographic variation of genetic and behavioral traits in northern and southern tüngara frogs.

We use a combination of microsatellite marker analysis and mate-choice behavior experiments to assess patterns of reproductive isolation of the túngara frog Physalaemus pustulosus along a 550-km transect of 25 populations in Costa Rica and Panama. Earlier studies using allozymes and mitochondrial DNA defined two genetic groups of túngara frogs, one ranging from Mexico to northern Costa Rica (northern group), the second ranging from Panama to northern South America (southern group). Our more fine-scale survey also shows that the northern and southern túngara frogs are genetically different and geographically separated by a gap in the distribution in central Pacific Costa Rica. Genetic differences among populations are highly correlated with geographic distances. Temporal call parameters differed among populations as well as between genetic groups. Differences in calls were explained better by geographic distance than by genetic distance. Phonotaxis experiments showed that females preferred calls of males from their own populations over calls of males from other populations in about two-thirds to three-fourths of the contrasts tested. In mating experiments, females and males from the same group and females from the north with males from the south produced nests and tadpoles. In contrast, females from the south did not produce nests or tadpoles with males from the north. Thus, northern and southern túngara frogs have diverged both genetically and bioacoustically. There is evidence for some prezygotic isolation due to differences in mate recognition and fertilization success, but such isolation is hardly complete. Our results support the general observation that significant differences in sexual signals are often not correlated with strong genetic differentiation.

Animals↗
PubMed2005

Hormonal state influences aspects of female mate choice in the Túngara Frog (Physalaemus pustulosus).

Females alter their mate choices as they transition through different reproductive stages; however, the proximal mechanisms for such behavioral fluctuation are unclear. In many taxa, as females transition through different reproductive stages, there is an associated change in hormone levels; therefore, we examined whether fluctuation in hormone levels serves as a proximal mechanism for within-individual variation in mate choice in female túngara frogs (Physalaemus pustulosus). We manipulated hormone levels of females by administering 0, 10, 100, 500 or 1,000 IU of human chorionic gonadotropin (HCG), which is a ligand for luteinizing hormone (LH) receptors and will therefore cause increased gonadal hormone production. Phonotaxis assays were conducted to measure three aspects of mate choice behavior before and after HCG administration; receptivity (response to a conspecific mate signal), permissiveness (response to a signal that is less attractive than conspecific signals) and discrimination (ability to discern signal differences). The probability of response to a conspecific and an artificial hybrid signal significantly increased at the highest HCG doses. The difference in mean response time between pre- and post-HCG tests was significantly different for both the receptivity and permissiveness tests among the five doses. Increased permissiveness, however, was not due to decreased discrimination because females could discriminate between calls even at the highest HCG doses. These hormonal manipulations caused the same behavioral pattern we reported in females as they transitioned through different reproductive stages (Lynch, K.S., Rand, A.S., Ryan, M.J., Wilczynski, W., 2005. Plasticity in female mate choice associated with changing reproductive states. Anim. Behav. 69, 689-699), suggesting that changes in hormone levels can influence the female's mate choice behavior.

Animals↗
PubMed2005

A cognitive framework for mate choice and species recognition.

Mating decisions contribute to both the fitness of individuals and the emergence of evolutionary diversity, yet little is known about their cognitive architecture. We propose a simple model that describes how preferences are translated into decisions and how seemingly disparate patterns of preference can emerge from a single perceptual process. The model proposes that females use error-prone estimates of attractiveness to select mates based on a simple decision rule: choose the most attractive available male that exceeds some minimal criterion. We test the model in the tungara frog, a well-characterized species with an apparent dissociation between mechanisms of mate choice and species recognition. As suggested by our model results, we find that a mate attraction feature alters assessments of species status. Next, we compare female preferences in one-choice and two-choice tests, contexts thought to emphasize species recognition and mate choice, respectively. To do so, we use the model to generate maximum-likelihood estimators of preference strengths from empirical data. We find that a single representation of preferences is sufficient to explain response probabilities in both contexts across a wide range of stimuli. In this species, mate choice and species recognition are accurately and simply summarized by our model. While the findings resolve long-standing anomalies, they also illustrate how models of choice can bridge theoretical and empirical treatments of animal decisions. The data demonstrate a remarkable congruity of perceptual processes across contexts, tasks, and taxa.

Animals↗
PubMed2005

The effects of time, space and spectrum on auditory grouping in túngara frogs.

Male túngara frogs (Physalaemus pustulosus) produce complex calls consisting of two components, a approximately 350 ms FM sweep called the "whine" followed by up to seven approximately 40 ms harmonic bursts called "chucks". In order to choose and locate a calling male, females attending to choruses must group call components into auditory streams to correctly assign calls to their sources. Previously we showed that spatial cues play a limited role in grouping: calls with normal spectra and temporal structure are grouped over wide angular separations (< or =135 degrees ). In this study we again use phonotaxis to first test whether an alternative cue, the sequence of call components, plays a role in auditory grouping and second, whether grouping is mediated by peripheral or central mechanisms. We found that while grouping is not limited to the natural call sequence, it does vary with the relative onset times of the two calls. To test whether overlapping stimulation in the periphery is required for grouping, the whine and chuck were filtered to restrict their spectra to the sensitivity ranges of the amphibian and basilar papillae, respectively. For these dichotic-like stimuli, grouping still occurred (albeit only to 45 degrees separation), suggesting that stream formation is mediated by central mechanisms.

Animals↗