Blind Mole Rat Spalax Research Articles

Local Adaptation of Bitter Taste and Ecological Speciation in a Wild Mammal.

Sensory systems are attractive evolutionary models to address how organisms adapt to local environments that can cause ecological speciation. However, tests of these evolutionary models have focused on visual, auditory, and olfactory senses. Here, we show local adaptation of bitter taste receptor genes in two neighboring populations of a wild mammal—the blind mole rat Spalax galili—that show ecological speciation in divergent soil environments. We found that basalt-type bitter receptors showed higher response intensity and sensitivity compared with chalk-type ones using both genetic and cell-based functional analyses. Such functional changes could help animals adapted to basalt soil select plants with less bitterness from diverse local foods, whereas a weaker reception to bitter taste may allow consumption of a greater range of plants for animals inhabiting chalk soil with a scarcity of food supply. Our study shows divergent selection on food resources through local adaptation of bitter receptors, and suggests that taste plays an important yet underappreciated role in speciation.

Comparative Neurology of Circadian Photoreception: The Retinohypothalamic Tract (RHT) in Sighted and Naturally Blind Mammals.

The mammalian eye contains two systems for light perception: an image detecting system constituted primarily of the classical photoreceptors, rods and cones, and a non-image forming system (NIF) constituted of a small group of intrinsically photosensitive retinal ganglion cells driven by melanopsin (mRGCs). The mRGCs receive input from the outer retina and NIF mediates light entrainment of circadian rhythms, masking behavior, light induced inhibition of nocturnal melatonin secretion, pupillary reflex (PLR), and affect the sleep/wake cycle. This review focuses on the mammalian NIF and its anatomy in the eye as well as its neuronal projection to the brain. This pathway is known as the retinohypothalamic tract (RHT). The development and functions of the NIF as well as the knowledge gained from studying gene modified mice is highlighted. Furthermore, the similarities of the NIF between sighted (nocturnal and diurnal rodent species, monkeys, humans) and naturally blind mammals (blind mole rats Spalax ehrenbergi and the Iberian mole, Talpa occidentalis) are discussed in relation to a changing world where increasing exposure to artificial light at night (ALAN) is becoming a challenge for humans and animals in the modern society.

Presumed ecological speciation in blind mole rats: does soil type influence mate preferences?

Reproductive isolation is a fundamental part of speciation processes. The establishing of reproductive isolation in speciation with ongoing gene flow is unlikely unless divergent selection is overruling gene flow homogenization, which seems to be most effective when combined with non-random mating. We explored whether assortative mating via female mate-choice contributes to reproductive isolation between populations of the blind mole rat Spalax galili inhabiting abutting rendzina-soil and basaltic-soil areas in a microsite similar to one in which ecological speciation has recently been suggested as a possible model driving the divergence between mole rats from the different soils. We performed T-maze experiments with mole rats captured in early winter (i.e. premating season) of 2 consecutive years and found no existence of females from either soil type preferring males originating from their own soils based on olfactory cues. In addition, inconsistent preferences for males based on soil type in tests with females that were tested twice were found. This suggests that female mate choice based on olfactory cues is unlikely to be an isolating barrier between the mole rats from the two soil types. In such circumstances, ecological speciation would have to occur through other mechanisms of divergent selection, such as reproductive isolation due to strong habitat (soil) preferences, vocalisation or seismic communication.

Hypoxia tolerance, longevity and cancer-resistance in the mole rat Spalax \u2013 a liver transcriptomics approach

The blind subterranean mole rat Spalax shows a remarkable tolerance to hypoxia, cancer-resistance and longevity. Unravelling the genomic basis of these adaptations will be important for biomedical applications. RNA-Seq gene expression data were obtained from normoxic and hypoxic Spalax and rat liver tissue. Hypoxic Spalax broadly downregulates genes from major liver function pathways. This energy-saving response is likely a crucial adaptation to low oxygen levels. In contrast, the hypoxia-sensitive rat shows massive upregulation of energy metabolism genes. Candidate genes with plausible connections to the mole rat’s phenotype, such as important key genes related to hypoxia-tolerance, DNA damage repair, tumourigenesis and ageing, are substantially higher expressed in Spalax than in rat. Comparative liver transcriptomics highlights the importance of molecular adaptations at the gene regulatory level in Spalax and pinpoints a variety of starting points for subsequent functional studies.

Soil preference in blind mole rats in an area of supposed sympatric speciation: do they choose the fertile or the familiar?

AbstractAnimals become adapted to different habitats, which, under some circumstances, may lead to speciation. Such speciation can possibly take place even in sympatry, as has recently been suggested in the blind mole rat Spalax galili surveyed at a microsite where two soil types of ecologically contrasting characteristics, basaltic soil and rendzina soil, abut each other. Such speciation would be possible if mole rats developed reproductive isolation, for example, by means of habitat choice. In our study, we quantified food supply and soil characteristics of 20 blind mole rat burrow systems in both soils at a new microsite and tested the mole rat's soil preference in a T‐maze. The basaltic soil was harder and heavier than the rendzina soil, and had higher density and biomass of food, which is comparable to the published data from the only other studied microsite 3.7 km apart. Mole rats preferred to burrow in their familiar soil, when the tested soils were moist. After the soils were dried, both groups of mole rats tended to burrow preferentially in the rendzina soil, nevertheless, this preference was only significant in rendzina‐soil mole rats. We propose that after the suppression of olfactory cues mole rats preferred to burrow in soil with lower energetic costs of burrowing. We suggest that soil preference by mole rats is effective mainly in moist soil that releases specific odorous cues, which coincides with mating season and natal dispersal. This preference could also play an important causative role in reproductive isolation of the two blind mole rat populations.

Adaptive methylation regulation of p53 pathway in sympatric speciation of blind mole rats, Spalax

Epigenetic modifications play significant roles in adaptive evolution. The tumor suppressor p53, well known for controlling cell fate and maintaining genomic stability, is much less known as a master gene in environmental adaptation involving methylation modifications. The blind subterranean mole rat Spalax eherenbergi superspecies in Israel consists of four species that speciated peripatrically. Remarkably, the northern Galilee species Spalax galili (2n = 52) underwent adaptive ecological sympatric speciation, caused by the sharply divergent chalk and basalt ecologies. This was demonstrated by mitochondrial and nuclear genomic evidence. Here we show that the expression patterns of the p53 regulatory pathway diversified between the abutting sympatric populations of S. galili in sharply divergent chalk-basalt ecologies. We identified higher methylation on several sites of the p53 promoter in the population living in chalk soil (chalk population). Site mutagenesis showed that methylation on these sites linked to the transcriptional repression of p53 involving Cut-Like Homeobox 1 (Cux1), paired box 4 (Pax 4), Pax 6, and activator protein 1 (AP-1). Diverse expression levels of p53 between the incipiently sympatrically speciating chalk-basalt abutting populations of S. galili selectively affected cell-cycle arrest but not apoptosis. We hypothesize that methylation modification of p53 has adaptively shifted in supervising its target genes during sympatric speciation of S. galili to cope with the contrasting environmental stresses of the abutting divergent chalk-basalt ecologies.

Molecular evolution of antioxidant and hypoxia response in long-lived, cancer-resistant blind mole rats: The Nrf2–Keap1 pathway

The Nrf2–Keap1 pathway is crucial for the cellular antioxidant and hypoxia response in vertebrates. Deciphering its modifications in hypoxia-adapted animals will help understand its functionality under environmental stress and possibly allow for knowledge transfer into biomedical research. The blind mole rat Spalax, a long-lived cancer-resistant rodent, lives in burrows underground and is adapted to severely hypoxic conditions. Here we have conducted a bioinformatical survey of Spalax core genes from the Nrf2–Keap1 pathway on the coding sequence level in comparison to other hypoxia-tolerant and -sensitive rodents. We find strong sequence conservation across all genes, illustrating the pathway's importance. One of the central players however, Spalax Keap1, shows a non-conservative amino acid substitution from tyrosine to cysteine in its intervening region (IVR) domain. Cysteines in this location have been shown to be of high functional relevance to the binding and degradation of Nrf2. Therefore, this peculiar substitution could influence the cellular Nrf2 levels in Spalax and, thereby, downstream gene expression in the antioxidant pathway, contributing to the special adaptive phenotype of the blind mole rat.

Sympatric speciation revealed by genome-wide divergence in the blind mole rat Spalax

Sympatric speciation (SS), i.e., speciation within a freely breeding population or in contiguous populations, was first proposed by Darwin [Darwin C (1859) On the Origins of Species by Means of Natural Selection] and is still controversial despite theoretical support [Gavrilets S (2004) Fitness Landscapes and the Origin of Species (MPB-41)] and mounting empirical evidence. Speciation of subterranean mammals generally, including the genus Spalax, was considered hitherto allopatric, whereby new species arise primarily through geographic isolation. Here we show in Spalax a case of genome-wide divergence analysis in mammals, demonstrating that SS in continuous populations, with gene flow, encompasses multiple widespread genomic adaptive complexes, associated with the sharply divergent ecologies. The two abutting soil populations of S. galili in northern Israel habituate the ancestral Senonian chalk population and abutting derivative Plio-Pleistocene basalt population. Population divergence originated ∼0.2-0.4 Mya based on both nuclear and mitochondrial genome analyses. Population structure analysis displayed two distinctly divergent clusters of chalk and basalt populations. Natural selection has acted on 300+ genes across the genome, diverging Spalax chalk and basalt soil populations. Gene ontology enrichment analysis highlights strong but differential soil population adaptive complexes: in basalt, sensory perception, musculature, metabolism, and energetics, and in chalk, nutrition and neurogenetics are outstanding. Population differentiation of chemoreceptor genes suggests intersoil population's mate and habitat choice substantiating SS. Importantly, distinctions in protein degradation may also contribute to SS. Natural selection and natural genetic engineering [Shapiro JA (2011) Evolution: A View From the 21st Century] overrule gene flow, evolving divergent ecological adaptive complexes. Sharp ecological divergences abound in nature; therefore, SS appears to be an important mode of speciation as first envisaged by Darwin [Darwin C (1859) On the Origins of Species by Means of Natural Selection].

Habitat and Burrow System Characteristics of the Blind Mole Rat Spalax galili in an Area of Supposed Sympatric Speciation.

A costly search for food in subterranean rodents resulted in various adaptations improving their foraging success under given ecological conditions. In Spalax ehrenbergi superspecies, adaptations to local ecological conditions can promote speciation, which was recently supposed to occur even in sympatry at sites where two soil types of contrasting characteristics abut each other. Quantitative description of ecological conditions in such a site has been, nevertheless, missing. We measured characteristics of food supply and soil within 16 home ranges of blind mole rats Spalax galili in an area subdivided into two parts formed by basaltic soil and pale rendzina. We also mapped nine complete mole rat burrow systems to compare burrowing patterns between the soil types. Basaltic soil had a higher food supply and was harder than rendzina even under higher moisture content and lower bulk density. Population density of mole rats was five-times lower in rendzina, possibly due to the lower food supply and higher cover of Sarcopoterium shrubs which seem to be avoided by mole rats. A combination of food supply and soil parameters probably influences burrowing patterns resulting in shorter and more complex burrow systems in basaltic soil.

519: Fibroblasts isolated from the cancer resistant blind mole rat Spalax exert an extraordinary anticancer activity towards human cancer cells by triggering mitochondrial-dependent apoptosis

519: Fibroblasts isolated from the cancer resistant blind mole rat Spalax exert an extraordinary anticancer activity towards human cancer cells by triggering mitochondrial-dependent apoptosis

Genome-wide adaptive complexes to underground stresses in blind mole rats Spalax.

The blind mole rat (BMR), Spalax galili, is an excellent model for studying mammalian adaptation to life underground and medical applications. The BMR spends its entire life underground, protecting itself from predators and climatic fluctuations while challenging it with multiple stressors such as darkness, hypoxia, hypercapnia, energetics and high pathonecity. Here we sequence and analyse the BMR genome and transcriptome, highlighting the possible genomic adaptive responses to the underground stressors. Our results show high rates of RNA/DNA editing, reduced chromosome rearrangements, an over-representation of short interspersed elements (SINEs) probably linked to hypoxia tolerance, degeneration of vision and progression of photoperiodic perception, tolerance to hypercapnia and hypoxia and resistance to cancer. The remarkable traits of the BMR, together with its genomic and transcriptomic information, enhance our understanding of adaptation to extreme environments and will enable the utilization of BMR models for biomedical research in the fight against cancer, stroke and cardiovascular diseases.

They live in the land down under: thyroid function and basal metabolic rate in the Blind Mole Rat, Spalax

The Israeli blind subterranean mole rat (Spalax ehrenbergi superspecies) lives in sealed underground burrows under extreme, hypoxic conditions. The four Israeli Spalax allospecies have adapted to different climates, the cool–humid (Spalax galili, 2 n = 52 chromosomes), semihumid (S. golani, 2 n = 54) north regions, warm–humid (S. carmeli, 2 n = 58) central region and the warm–dry S. judaei, 2 n = 60) southern regions. A dramatic interspecies decline in basal metabolic rate (BMR) from north to south, even after years of captivity, indicates a genetic basis for this BMR trait. We examined the possibility that the genetically-conditioned interspecies BMR difference was expressed via circulating thyroid hormone. An unexpected north to south increase in serum free thyroxine (FT4) and total 3, 5, 3′-triiodo-L-thyronine (T3) (p < 0.02) correlated negatively with previously published BMR measurements. The increases in serum FT4 and T3 were symmetrical, so that the T3:FT4 ratio – interpretable as an index of conversion of T4 to T3 in nonthyroidal tissues – did not support relative decrease in production of T3 as a contributor to BMR. Increased north-to-south serum FT4 and T3 levels also correlated negatively with hemoglobin/hematocrit. North-to-south adaptations in spalacids include decreased BMR and hematocrit/hemoglobin in the face of increasing thyroid hormone levels, arguing for independent control of hormone secretion and BMR/hematocrit/hemoglobin. But the significant inverse relationship between thyroid hormone levels and BMR/hematocrit/hemoglobin is also consistent with a degree of cellular resistance to thyroid hormone action that protects against hormone-induced increase in oxygen consumption in a hostile, hypoxic environment.

Mitochondrial genome of bamboo rat Rhizomys pruinosus

Bamboo rats are a group of subterranean rodents some of which feed on the roots and shoots of bamboo and other plants. In this study, we sequence the mitochondrial genome of a hoary bamboo rat Rhizomys pruinosus from the south of China. The genome is 16,575 bp in length, and had a gene content of 13 protein coding, 22 tRNAs and 2 rRNAs. The overall base composition is 30.94% T, 24.83% C, 32.21% A and 12.02% G, with an A + T bias of 63.15%. The cytochrome genes were the most conservative genes compared with plateau zokor (Eospalax baileyi) and blind mole rats (Spalax carmeli) in the family Spalacidae. These mitochondrial data are potentially important for the study of molecular evolution, conservation genetics, agricultural technology and epidemiology.

Bukovina blind mole rat Spalax graecus revisited: phylogenetics, morphology, taxonomy, habitat associations and conservation

Abstract The Bukovina blind mole rat Spalax graecus is the westernmost representative of the genus and one of the least known European mammals. As currently understood, the species contains three isolates on both sides of the south‐eastern Carpathian Mountains. Our focus was on Bukovina blind mole rats from north‐eastern Romania and adjacent Ukraine, i.e. on the nominal subspecies Spalax graecus graecus Topachevskii 1976. Phylogenetic reconstruction based on 1140‐bp‐long cytochrome b sequence revealed a sister position of Spalax graecus against the genus Nannospalax. Pairwise Kimura two‐parameter genetic divergences were evidently higher between Spalax graecus and the three species of Nannospalax (mean distances ± standard errors between 0.177 ± 0.014 and 0.197 ± 0.016) than between the three species of Nannospalax (up to 0.128 ± 0.010). The two genera were separated by 178 mutational steps. The Bukovina blind mole rat is so far known from 13 localities in north‐eastern Romania and adjacent Ukraine. The most influential environmental factors in the Spalax graecus habitat model were seasonality in precipitation, type of soil and altitude. The elevational range of suitable habitats is 39–848 m. The area occupied is estimated at 15581 km2, but patches with high habitat suitability cover only 1604 km2. The main habitat for the Bukovina blind mole rat is likely to degrade and the conservation needs of the species will soon have to be taken into account. We recommend the inclusion of the species on Annex II or IV of the European Union's Habitats Directive on grounds of its (i) narrow endemism, (ii) small range of occupancy, (iii) small overall population size and (iv) vulnerability to changes in agricultural land use.

Transcriptome analysis of the spalax hypoxia survival response includes suppression of apoptosis and tight control of angiogenesis

BackgroundThe development of complex responses to hypoxia has played a key role in the evolution of mammals, as inadequate response to this condition is frequently associated with cardiovascular diseases, developmental disorders, and cancers. Though numerous studies have used mice and rats in order to explore mechanisms that contribute to hypoxia tolerance, these studies are limited due to the high sensitivity of most rodents to severe hypoxia. The blind subterranean mole rat Spalax is a hypoxia tolerant rodent, which exhibits unique longevity and therefore has invaluable potential in hypoxia and cancer research.ResultsUsing microarrays, transcript abundance was measured in brain and muscle tissues from Spalax and rat individuals exposed to acute and chronic hypoxia for varying durations. We found that Spalax global gene expression response to hypoxia differs from that of rat and is characterized by the activation of functional groups of genes that have not been strongly associated with the response to hypoxia in hypoxia sensitive mammals. Using functional enrichment analysis of Spalax hypoxia induced genes we found highly significant overrepresentation of groups of genes involved in anti apoptosis, cancer, embryonic/sexual development, epidermal growth factor receptor binding, coordinated suppression and activation of distinct groups of transcription factors and membrane receptors, in addition to angiogenic related processes. We also detected hypoxia induced increases of different critical Spalax hub gene transcripts, including antiangiogenic genes associated with cancer tolerance in Down syndrome human individuals.ConclusionsThis is the most comprehensive study of Spalax large scale gene expression response to hypoxia to date, and the first to use custom Spalax microarrays. Our work presents novel patterns that may underlie mechanisms with critical importance to the evolution of hypoxia tolerance, with special relevance to medical research.

Cancer resistance in the blind mole rat is mediated by concerted necrotic cell death mechanism

Blind mole rats Spalax (BMR) are small subterranean rodents common in the Middle East. BMR is distinguished by its adaptations to life underground, remarkable longevity (with a maximum documented lifespan of 21 y), and resistance to cancer. Spontaneous tumors have never been observed in spalacids. To understand the mechanisms responsible for this resistance, we examined the growth of BMR fibroblasts in vitro of the species Spalax judaei and Spalax golani. BMR cells proliferated actively for 7-20 population doublings, after which the cells began secreting IFN-β, and the cultures underwent massive necrotic cell death within 3 d. The necrotic cell death phenomenon was independent of culture conditions or telomere shortening. Interestingly, this cell behavior was distinct from that observed in another long-lived and cancer-resistant African mole rat, Heterocephalus glaber, the naked mole rat in which cells display hypersensitivity to contact inhibition. Sequestration of p53 and Rb proteins using SV40 large T antigen completely rescued necrotic cell death. Our results suggest that cancer resistance of BMR is conferred by massive necrotic response to overproliferation mediated by p53 and Rb pathways, and triggered by the release of IFN-β. Thus, we have identified a unique mechanism that contributes to cancer resistance of this subterranean mammal extremely adapted to life underground.

Methionine sulfoxide reductases and methionine sulfoxide in the subterranean mole rat (Spalax): Characterization of expression under various oxygen conditions

The blind subterranean mole rat (Spalax ehrenbergi) exhibits a relatively long life span, which is attributed to an efficient antioxidant defense affording protection against accumulation of oxidative modifications of proteins. Methionine residues can be oxidized to methionine sulfoxide (MetO) and then enzymatically reduced by the methionine sulfoxide reductase (Msr) system. In the current study we have isolated the cDNA sequences of the Spalax Msr genes as well as 23 additional selenoproteins and monitored the activities of Msr enzymes in liver and brain of rat (Rattus norvegicus), Spalax galili, and Spalax judaei under normoxia, hypoxia, and hyperoxia. Under normoxia, the Msr activity was lower in S. galili in comparison to S. judaei and R. norvegicus especially in the brain. The pattern of Msr activity of the three species was similar throughout the tested conditions. However, exposure of the animals to hypoxia caused a significant enhancement of Msr activity, especially in S. galili. Hyperoxic exposure showed a highly significant induction of Msr activity compared with normoxic conditions for R. norvegicus and S. galili brain. It was concluded that among all species examined, S. galili appears to be more responsive to oxygen tension changes and that the Msr system is upregulated mainly by severe hypoxia.

Cellular adaptation to hypoxia and p53 transcription regulation

Tumor suppressor p53 is the most frequently mutated gene in human tumors. Meanwhile, under stress conditions, p53 also acts as a transcription factor, regulating the expression of a series of target genes to maintain the integrity of genome. The target genes of p53 can be classified into genes regulating cell cycle arrest, genes involved in apoptosis, and genes inhibiting angiogenesis. p53 protein contains a transactivation domain, a sequence-specific DNA binding domain, a tetramerization domain, a non-specific DNA binding domain that recognizes damaged DNA, and a later identified proline-rich domain. Under stress, p53 proteins accumulate and are activated through two mechanisms. One, involving ataxia telangiectasia-mutated protein (ATM), is that the interaction between p53 and its down-regulation factor murine double minute 2 (MDM2) decreases, leading to p53 phosphorylation on Ser15, as determined by the post-translational mechanism; the other holds that p53 increases and is activated through the binding of ribosomal protein L26 (RPL26) or nucleolin to p53 mRNA 5( untranslated region (UTR), regulating p53 translation. Under hypoxia, p53 decreases transactivation and increases transrepression. The mutations outside the DNA binding domain of p53 also contribute to tumor progress, so further studies on p53 should also be focused on this direction. The subterranean blind mole rat Spalax in Israel is a good model for hypoxia-adaptation. The p53 of Spalax mutated in residue 172 and residue 207 from arginine to lysine, conferring it the ability to survive hypoxic conditions. This model indicates that p53 acts as a master gene of diversity formation during evolution.

Cloning andin vivoexpression of vascular endothelial growth factor receptor 2(Flkl)in the naturally hypoxia‐tolerant subterranean mole rat

Vascular endothelial growth factor receptor (VEGF) plays a critical role in blood vessel formation and affects nerve growth and survival. VEGF receptor 2 (Flk1) functions as the major signal transducer of angiogenesis, mediating VEGF induction of endothelial tubulogenesis. We have cloned and analyzed expression of Flk1 in the blind subterranean mole rat Spalax ehrenbergi. Spalax experience abrupt and sharp changes in oxygen supply in their sealed underground niche and, hence, are genetically adapted to hypoxia and serve as a unique, natural mammalian model organism for hypoxia tolerance. Spalax Flk1 is relatively conserved at the nucleic acid and amino acid level compared to human, mouse, and rat orthologs. Reverse transcription-quantitative polymerase chain reaction was used to analyze Flk1 expression in muscle and brain of animals exposed to ambient or variant hypoxic oxygen levels at multiple stages of development. Transcript levels were compared with those obtained from Rattus, a primary model for human physiology. Our findings demonstrate that under normoxic conditions Flk1 patterns of expression correlate well with our previous investigations of VEGF expression. Exposure to hypoxic conditions resulted in divergent patterns of Flk1 expression between Spalax and Rattus and between muscle and brain. It appears that the regulatory mechanisms differentiating expression between the species and between tissues are most likely unique, suggesting that Flk1 expression may be regulated by multiple processes, including both angiogenesis and neurogenesis.

Antioxidant activity in Spalax ehrenbergi: a possible adaptation to underground stress

The blind subterranean mole rat Spalax ehrenbergi superspecies has evolved adaptive strategies to cope with underground stress. Hypoxia is known to stimulate reactive oxygen species generation; however, mechanisms by which Spalax counteracts oxidative damage have not been investigated before. We studied in Spalax the oxidative status of the Harderian gland (HG), an organ which is particularly vulnerable to oxidative stress in many rodents. With regard to the sexual dimorphism found in this gland, differences between males and females were determined and compared to the surface-dwelling Syrian hamster. Our results show, for the first time, that Spalax exhibits remarkably low biomolecular damage, which implies the existence of physiological strategies to avoid oxidative damage under fluctuating O(2) and CO(2) levels existing in the mole rat's subterranean niche. Correspondingly, main antioxidant enzymes, such as superoxide dismutase (SOD), catalase, and glutathione reductase (GR), exhibited high activities in both genders; in particular, remarkably high levels were measured in SOD. SOD and GR activities showed statistically significant differences between sexes. Melatonin, an important circadian agent is also a very important antioxidant molecule and is synthesized in the Harderian glands (HGs) of Spalax. Therefore, the possible interaction between antioxidant enzymes and melatonin is suggested.