An organism-wide atlas of hormonal signaling based on the mouse lemur single-cell transcriptome

Hormones mediate long-range cell communication and play vital roles in physiology, metabolism, and health. Traditionally, endocrinologists have focused on one hormone or organ system at a time. Yet, hormone signaling by its very nature connects cells of different organs and involves crosstalk of different hormones. Here, we leverage the organism-wide single cell transcriptional atlas of a non-human primate, the mouse lemur (Microcebus murinus), to systematically map source and target cells for 84 classes of hormones. This work uncovers previously-uncharacterized sites of hormone regulation, and shows that the hormonal signaling network is densely connected, decentralized, and rich in feedback loops. Evolutionary comparisons of hormonal genes and their expression patterns show that mouse lemur better models human hormonal signaling than mouse, at both the genomic and transcriptomic levels, and reveal primate-specific rewiring of hormone-producing/target cells. This work complements the scale and resolution of classical endocrine studies and sheds light on primate hormone regulation.

Molecular Liver Fingerprint Reflects the Seasonal Physiology of the Grey Mouse Lemur (Microcebus murinus) during Winter

Grey mouse lemurs (Microcebus murinus) are primates that respond to environmental energetic constraints through strong physiological seasonality. They notably fatten during early winter (EW), and mobilize their lipid reserves while developing glucose intolerance during late winter (LW), when food availability is low. To decipher how the hepatic mechanisms may support such metabolic flexibility, we analyzed the liver proteome of adult captive male mouse lemurs, whose seasonal regulations are comparable to their wild counterparts. We highlight profound hepatic changes that reflect fat accretion in EW at the whole-body level, without triggering an ectopic storage of fat in the liver, however. Moreover, molecular regulations are consistent with the decrease in liver glucose utilization in LW, and therefore with reduced tolerance to glucose. However, no major regulation was seen in insulin signaling/resistance pathways. Fat mobilization in LW appeared possibly linked to the reactivation of the reproductive system while enhanced liver detoxification may reflect an anticipation to return to summer levels of food intake. Overall, these results show that the physiology of mouse lemurs during winter relies on solid molecular foundations in liver processes to adapt fuel partitioning while opposing the development of a pathological state despite large lipid fluxes.

Primate Torpor: Regulation of Stress-activated Protein Kinases During Daily Torpor in the Gray Mouse Lemur, Microcebus murinus

Very few selected species of primates are known to be capable of entering torpor. This exciting discovery means that the ability to enter a natural state of dormancy is an ancestral trait among primates and, in phylogenetic terms, is very close to the human lineage. To explore the regulatory mechanisms that underlie primate torpor, we analyzed signal transduction cascades to discover those involved in coordinating tissue responses during torpor. The responses of mitogen-activated protein kinase (MAPK) family members to primate torpor were compared in six organs of control (aroused) versus torpid gray mouse lemurs, Microcebus murinus. The proteins examined include extracellular signal-regulated kinases (ERKs), c-jun NH₂-terminal kinases (JNKs), MAPK kinase (MEK), and p38, in addition to stress-related proteins p53 and heat shock protein 27 (HSP27). The activation of specific MAPK signal transduction pathways may provide a mechanism to regulate the expression of torpor-responsive genes or the regulation of selected downstream cellular processes. In response to torpor, each MAPK subfamily responded differently during torpor and each showed organ-specific patterns of response. For example, skeletal muscle displayed elevated relative phosphorylation of ERK1/2 during torpor. Interestingly, adipose tissues showed the highest degree of MAPK activation. Brown adipose tissue displayed an activation of ERK1/2 and p38, whereas white adipose tissue showed activation of ERK1/2, p38, MEK, and JNK during torpor. Importantly, both adipose tissues possess specialized functions that are critical for torpor, with brown adipose required for non-shivering thermogenesis and white adipose utilized as the primary source of lipid fuel for torpor. Overall, these data indicate crucial roles of MAPKs in the regulation of primate organs during torpor.

Characterization of blood biochemical markers during aging in the Grey Mouse Lemur (Microcebus murinus): impact of gender and season

BACKGROUND

Hematologic and biochemical data are needed to characterize the health status of animal populations over time to determine the habitat quality and captivity conditions. Blood components and the chemical entities that they transport change predominantly with sex and age. The aim of this study was to utilize blood chemistry monitoring to establish the reference levels in a small prosimian primate, the Grey Mouse Lemur (Microcebus murinus).

METHOD

In the captive colony, mouse lemurs may live 10-12 years, and three age groups for both males and females were studied: young (1-3 years), middle-aged (4-5 years) and old (6-10 years). Blood biochemical markers were measured using the VetScan Comprehensive Diagnostic Profile. Because many life history traits of this primate are highly dependent on the photoperiod (body mass and reproduction), the effect of season was also assessed.

RESULTS

The main effect of age was observed in blood markers of renal functions such as creatinine, which was higher among females. Additionally, blood urea nitrogen significantly increased with age and is potentially linked to chronic renal insufficiency, which has been described in captive mouse lemurs. The results demonstrated significant effects related to season, especially in blood protein levels and glucose rates; these effects were observed regardless of gender or age and were likely due to seasonal variations in food intake, which is very marked in this species.

CONCLUSION

These results were highly similar with those obtained in other primate species and can serve as references for future research of the Grey Mouse Lemur.

Torpor use during gestation and lactation in a primate

Torpor is an energy-saving mechanism that allows endotherms to overcome energetic challenges. Torpor should be avoided during reproduction because of potential incompatibility with offspring growth. To test if torpor can be used during gestation and lactation to compensate for food shortage, we exposed reproductive female grey mouse lemurs (Microcebus murinus), a heterothermic primate, to different levels of food availability. Torpor use was characterised by daily skin temperature profiles, and its energetic outcome was assessed from changes in body mass. Food shortage triggered torpor during the end of the gestation period (n = 1), ranging from shallow in response to 40% food restriction to deep daily torpor in response to 80% restriction. During the early period of lactation, females fed ad libitum (n = 2) or exposed to a 40% restriction (n = 4) remained normothermic; but 80% food restricted females (n = 5) gave priority to energy saving, increasing the frequency and depth of torpor bouts. The use of torpor was insufficient to compensate for 80% energetic shortage during lactation resulting in loss of mass from the mother and delayed growth in the pups. This study provides the first evidence that a heterothermic primate can use torpor to compensate for food shortages even during reproduction. This physiological flexibility likely evolved as a response to climate-driven fluctuations in food availability in Madagascar.

The development of small primate models for aging research

Nonhuman primate (NHP) aging research has traditionally relied mainly on the rhesus macaque. But the long lifespan, low reproductive rate, and relatively large body size of macaques and related Old World monkeys make them less than ideal models for aging research. Manifold advantages would attend the use of smaller, more rapidly developing, shorter-lived NHP species in aging studies, not the least of which are lower cost and the ability to do shorter research projects. Arbitrarily defining "small" primates as those weighing less than 500 g, we assess small, relatively short-lived species among the prosimians and callitrichids for suitability as models for human aging research. Using the criteria of availability, knowledge about (and ease of) maintenance, the possibility of genetic manipulation (a hallmark of 21st century biology), and similarities to humans in the physiology of age-related changes, we suggest three species--two prosimians (Microcebus murinus and Galago senegalensis) and one New World monkey (Callithrix jacchus)--that deserve scrutiny for development as major NHP models for aging studies. We discuss one other New World monkey group, Cebus spp., that might also be an effective NHP model of aging as these species are longer-lived for their body size than any primate except humans.

Distinct transcriptome expression of the temporal cortex of the primate Microcebus murinus during brain aging versus Alzheimer's disease-like pathology

Aging is the primary risk factor of neurodegenerative disorders such as Alzheimer's disease (AD). However, the molecular events occurring during brain aging are extremely complex and still largely unknown. For a better understanding of these age-associated modifications, animal models as close as possible to humans are needed. We thus analyzed the transcriptome of the temporal cortex of the primate Microcebus murinus using human oligonucleotide microarrays (Affymetrix). Gene expression profiles were assessed in the temporal cortex of 6 young adults, 10 healthy old animals and 2 old, “AD-like” animals that presented ß-amyloid plaques and cortical atrophy, which are pathognomonic signs of AD in humans. Gene expression data of the 14,911 genes that were detected in at least 3 samples were analyzed. By SAM (significance analysis of microarrays), we identified 47 genes that discriminated young from healthy old and “AD-like” animals. These findings were confirmed by principal component analysis (PCA). ANOVA of the expression data from the three groups identified 695 genes (including the 47 genes previously identified by SAM and PCA) with significant changes of expression in old and “AD-like” in comparison to young animals. About one third of these genes showed similar changes of expression in healthy aging and in “AD-like” animals, whereas more than two thirds showed opposite changes in these two groups in comparison to young animals. Hierarchical clustering analysis of the 695 markers indicated that each group had distinct expression profiles which characterized each group, especially the “AD-like” group. Functional categorization showed that most of the genes that were up-regulated in healthy old animals and down-regulated in “AD-like” animals belonged to metabolic pathways, particularly protein synthesis. These data suggest the existence of compensatory mechanisms during physiological brain aging that disappear in “AD-like” animals. These results open the way to new exploration of physiological and “AD-like” aging in primates.

The grey mouse lemur uses season-dependent fat or protein sparing strategies to face chronic food restriction

During moderate calorie restriction (CR) the heterotherm Microcebus murinus is able to maintain a stable energy balance whatever the season, even if only wintering animals enter into torpor. To understand its energy saving strategies to respond to food shortages, we assessed protein and energy metabolisms associated with wintering torpor expression or summering torpor avoidance. We investigated body composition, whole body protein turnover, and daily energy expenditure (DEE), during a graded (40 and 80%) 35-day CR in short-days (winter; SD40 and SD80, respectively) and long-days (summer; LD40 and LD80, respectively) acclimated animals. LD40 animals showed no change in fat mass (FM) but a 12% fat free mass (FFM) reduction. Protein balance being positive after CR, the FFM loss was early and rapid. The 25% DEE reduction, in LD40 group was mainly explained by FFM changes. LD80 animals showed a steady body mass loss and were excluded from the CR trial at day 22, reaching a survival-threatened body mass. No data were available for this group. SD40 animals significantly decreased their FM level by 21%, but maintained FFM. Protein sparing was achieved through a 35 and 39% decrease in protein synthesis and catabolism (protein turnover), respectively, overall maintaining nitrogen balance. The 21% reduction in energy requirement was explained by the 30% nitrogen flux drop but also by torpor as DEE FFM-adjusted remained 13% lower compared to ad-libitum. SD80 animals were unable to maintain energy and nitrogen balances, losing both FM and FFM. Thus summering mouse lemurs equilibrate energy balance by a rapid loss of active metabolic mass without using torpor, whereas wintering animals spare protein and energy through increased torpor expression. Both strategies have direct fitness implication: 1) to maintain activities at a lower body size during the mating season and 2) to preserve an optimal wintering muscle mass and function.

Age effects on pheromone induced Fos expression in olfactory bulbs of a primate

In the gray mouse lemur, a prosimian primate, aging is associated with a reduction of olfactory behaviors and sexual stimulation. To assess the effect of aging on the central response to pheromone stimulation in this primate, we measured the c-fos expression in the main and accessory olfactory bulbs of adult and aged male mouse lemurs, following exposure to the volatile phase of urine from proestrous females. In adults, pheromone exposure increased the number of Fos-positive neurons in the main olfactory bulb without changes in the accessory olfactory bulb. Fos expression was not increased by the odorant stimulation in aged mouse lemurs. Our results may explain the age-related decrease in behaviors associated with olfactory stimulation in this primate.

Melatonin and methimazole mimic short-day-induced fattening in gray mouse lemurs

Short-day-induced fattening was investigated in the small nocturnal primate Microcebus murinus. Animals were either transferred from long photoperiod (LP) to short photoperiod (SP) or maintained in LP and submitted to various treatments. Animals fed daily on 40 microg of melatonin (MEL) at two different times showed a significant increase in body mass compared to LP-exposed animals. This weight gain was more marked in animals fed with MEL 2 h before night onset, suggesting a critical period around the first hours of the night. The MEL-induced fattening was associated with an increase in food intake and a decrease in plasma thyroxin (T4) levels. On the other hand, a decrease in T4 plasma levels induced by two doses of methimazole (MET) led to either an increase (3 mg/day) or a decrease (10 mg/day) of body mass, suggesting a role of thyroid hormones in the photoperiodic regulation of body mass. The MET-induced fattening did not involve any change in food intake. These findings suggest that autumn fattening in the gray mouse lemur proceeds from two distinct mechanisms. First, an increase of food intake may result in the SP-induced increase in MEL secretion. Second, a decrease of energy expenditure may be due to the MEL-induced hypothyroidism.

Calpain 3 is expressed in astrocytes of rat and Microcebus brain

The calcium-dependent protease calpain is involved in numerous functions, including the control of cell survival, plasticity and motility. Whereas the isoforms calpain 1 and 2 have been described as ubiquitously expressed enzymes, calpain 3 has been called "muscle-specific", although trace amounts of calpain 3 mRNA have been detected by Northern blot in brain homogenates. In this study, we validated antibodies raised either against the peptides that were specific for a given isoform or the peptides present in all the three isoforms. We then used the anti-calpain 3 antibodies together with antibodies directed against cell-type-specific proteins to determine by double- and triple-labelling immunocytochemistry if the protease is expressed in specific cell populations of rat as well as lesser mouse lemur (Microcebus murinus) brain. Calpain 3 was almost exclusively found in cells displaying astrocyte morphology. These cells, most of which co-expressed glial fibrillary acidic protein, were particularly numerous close to the striatal subventricular zone (where numerous neurones forming the rostral migratory stream (RMS) towards the olfactory bulbs are generated) and the RMS itself. Other immunoreactive cells were found close to the pial surface of the forebrain, in the corpus callosum and in the dentate gyrus. Calpain 3 may be involved in astrocyte plasticity and/or motility.

Artificially accelerated aging by shortened photoperiod alters early gene expression (Fos) in the suprachiasmatic nucleus and sulfatoxymelatonin excretion in a small primate, Microcebus murinus

In mammals, a number of anatomical and functional changes occur in the circadian timing system with aging. In certain species, aging can be modified by various factors which induce a number of pathological changes. In a small primate, the gray mouse lemur (Microcebus murinus), long-term acceleration of seasonal rhythms by exposing the animals to a shortened photoperiodic regime (up to 2.5 times the natural photoperiodic regime) alters longevity, based on survival curves and morphological changes. This provides a model for challenging the idea that modifications of the circadian pacemaker are related to chronological (years) versus biological (photoperiodic cycles) age. To assess the effect of aging and accelerated aging on the circadian pacemaker of this primate, we measured body weight variations, the daily rhythm in urine 6-sulfatoxymelatonin and the light-induced expression of the immediate early gene (Fos) in the suprachiasmatic nucleus of mouse lemurs that had been exposed to different photoperiodic cycles. Urine samples were collected throughout the day and urine 6-sulfatoxymelatonin levels were measured by radioimmunoassay. Light-induced Fos expression in the suprachiasmatic nucleus was studied by exposing the animals to a 15-min monochromatic pulse of light (500 nm) at saturating or sub-saturating levels of irradiance (10(11) or 10(14) photons/cm(2)/s) during the dark phase. The classical pattern of 6-sulfatoxymelatonin excretion was significantly altered in aged mouse lemurs which failed to show a nocturnal peak. Fos expression following exposure to low levels of irradiance was reduced by 88% in the suprachiasmatic nucleus of aged mouse lemurs. Exposure to higher irradiance levels showed similar results, with a reduction of 66% in Fos expression in the aged animals. Animals subjected to artificially accelerated aging demonstrated the same alterations in melatonin production and Fos response to light as animals that had been maintained in a routine photoperiodic cycle. Our data indicate that there are dramatic changes in melatonin production and in the cellular response to photic input in the suprachiasmatic nucleus of aged mouse lemurs, and that these alterations depend on the number of expressed seasonal cycles rather than on a fixed chronological age. These results provide new insights into the mechanisms underlying artificial accelerated aging at the level of the molecular mechanisms of the biological clock.

Short and mid-wavelength cone distribution in a nocturnal Strepsirrhine primate (Microcebus murinus)

Strepsirrhines are of considerable interest for understanding the evolution of cone photoreceptors because they represent the most ancestral living primates. The retina of nocturnal Strepsirrhines is reported to contain a single population of medium/long wavelength (MW/LW) cones whereas short wavelength (SW) cones are totally absent. The area centralis of nocturnal Strepsirrhines also lacks the degree of central specialization seen in the fovea of diurnal primates. In this study of a nocturnal Strepsirrhine, the gray mouse lemur (Microcebus murinus), we used specific antibodies that recognize SW and MW/LW opsins to determine the presence of different cone subtypes and their distribution in relation to that of rods and ganglion cells. The results are compared to two diurnal Haplorhine species, a New World (Callithrix jacchus) and an Old World (Macaca fascicularis) monkey. In the mouse lemur, both antibodies to MW/LW cone opsin (COS-1 and CERN956) label the same population of cones. A small proportion of SW cones is only stained by the JH455 antiserum whereas the monoclonal OS-2 antibody shows negative staining. These two antibodies label the same SW cone population in other primates. The extracellular matrix of all cones is also labeled by the peanut agglutinin (PNA) lectin. In mouse lemur retinal wholemounts, peak cone density is localized at the area centralis and ranged from 7,500 to 8,000 cones/mm(2). SW cones represent less than 0.2 % of the total cone population and are mainly located in the nasal part of the retina. SW cones show an irregular distribution and densities never exceed 49 cones/mm(2). The distribution of neurons in the ganglion cell layer shows a distinct centroperipheral gradient with a peak of 28,000 cells/mm(2) at the area centralis. Rod distribution shows a centroperipheral gradient with the peak (850,000 rods/mm(2)) including and extending slightly dorsal to the area centralis. The theoretical spatial resolution of the mouse lemur (4.9 cycles/degree) is slightly lower to that of other nocturnal primates. The densities of rods, cones, and ganglion cell layer neurons represent a compromise between spatial resolution and sensitivity for both photopic and scotopic vision.

Daily energy expenditure of the grey mouse lemur (Microcebus murinus): a small primate that uses torpor

We aimed to investigate the pattern of utilisation of torpor and its impact on energy budgets in free-living grey mouse lemurs (Microcebus murinus), a small nocturnal primate endemic to Madagascar. We measured daily energy expenditure (DEE) and water turnover using doubly labelled water, and we used temperature-sensitive radio collars to measure skin temperature (Tsk) and home range. Our results showed that male and female mouse lemurs in the wild enter torpor spontaneously over a wide range of ambient temperatures (Ta) during the dry season, but not during the rainy season. Mouse lemurs remained torpid between 1.7-8.9 h with a daily mean of 3.4 h, and their Tsk s fell to a minimum of 18.8 degrees C. Mean home ranges of mouse lemurs which remained normothermic were similar in the rainy and dry season. During the dry season, the mean home range of mouse lemurs showing daily torpor was significantly smaller than that of animals remaining normothermic. The DEE of M. murinus remaining normothermic in the rainy season (122 +/- 65.4 kJ x day(-1)) was about the same of that of normothermic mouse lemurs in the dry season (115.5 +/- 27.3 kJ x day(-1)). During the dry season, the mean DEE of M. murinus that utilised daily torpor was 103.4 +/- 32.7 kJ x day(-1) which is not significantly different from the mean DEE of animals remaining normothermic. We found that the DEE of mouse lemurs using daily torpor was significantly correlated with the mean temperature difference between Tsk and Ta (r2 = 0.37) and with torpor bout length (r2 = 0.46), while none of these factors explained significant amounts of variation in the DEE of the mouse lemurs remaining normothermic. The mean water flux rate of mouse lemurs using daily torpor (13.0 +/- 4.1 ml x day(-1)) was significantly lower than that of mouse lemurs remaining normothermic (19.4 +/- 3.8 ml x day(-1)), suggesting the lemurs conserve water by entering torpor. Thus, this first study on the energy budget of free-ranging M. murinus demonstrates that torpor may not only reflect its impact on the daily energy demands, but involve wider adaptive implications such as water requirements.

Photoperiod-induced changes in energy balance in gray mouse lemurs

To cope with the 6-month dry winter occurring in its natural habitat, the gray mouse lemur (Microcebus murinus), a Malagasy prosimian primate, exhibits a pre-wintering fattening phase that has been previously demonstrated to be dependent on the photoperiod. To assess early changes in energy balance following a photoperiodic shift, food intake (FI), resting metabolic rate (RMR), plasma triglycerides, plasma thyroxine and urinary excretion of cortisol were measured in 12 males and 12 females for 8 weeks following a shift from short (SP: 10 h light/day) to long (LP: 14 h light/day) photoperiod or from LP to SP. Shift from LP to SP led to a high, linear body mass (BM) increase in both sexes, concomitant to an increase in plasma triglycerides and a decrease in plasma thyroxine, while no change in RMR occurred. FI significantly increased from 30 to 40 kcal/day as early as the first week following SP exposure but spontaneously decreased after 4 weeks, reaching minimal values (10 kcal/day) after 14 weeks of SP exposure. Shift from SP to LP led to a decrease in BM and an increase in FI, but both were slow and different between males and females. No change in RMR was observed except a significant increase in males during the first week of LP exposure. However, plasma thyroxine levels and cortisol excretion similarly increased in both sexes following LP exposure. These results suggest that autumnal fattening mainly proceed from changes in FI and in thyroxine secretion triggered by exposure to SP. In contrast, BM loss following LP exposure would be related to seasonal sexual activation rather than to a direct control by photoperiod.

Comparative morphology and histochemistry of glands associated with the vomeronasal organ in humans, mouse lemurs, and voles

The vomeronasal organ (VNO) is a chemosensory structure of the vertebrate nasal septum that has been recently shown to exist in nearly all adult humans. Although its link to reproductive behaviors has been shown in some primates, its functionality in humans is still debated. Some authors have suggested that the human VNO has the capacity to detect pheromones, while others described it as little more than a glandular pit. However, no studies have utilized histochemical techniques that would reveal whether the human VNO functions as a generalized gland duct or a specialized chemosensory organ. Nasal septal tissue from 13 humans (2-86 years old) were compared to that of two adult lemurs (Microcebus murinus) and eight adult voles (four Microtus pennsylvanicus and four Microtus ochrogaster). Sections at selected intervals of the VNO were stained with periodic acid-Schiff (PAS), alcian blue (AB), AB-PAS, and PAS-hematoxylin procedures. Results revealed typical well-developed VNOs with tubuloacinar glands in Microtus and Microcebus. VNO glands were AB-negative and PAS-positive in voles and mouse lemurs. Homo differed from Microtus and Microcebus in having more branched, AB and PAS-positive glands that emptied into the VNO lumen. Furthermore, the human VNO epithelium had unicellular mucous glands (AB and PAS-positive) and cilia, similar to respiratory epithelia. These results demonstrate unique characteristics of the human VNO which at once differs from glandular ducts (e.g., cilia) and also from the VNOs of mammals possessing demonstrably functional VNO.

Topographical localization of iron in brains of the aged fat-tailed dwarf lemur (Cheirogaleus medius) and gray lesser mouse lemur (Microcebus murinus)

Iron deposits in the human brain are characteristic of normal aging but have also been implicated in various neurodegenerative diseases. Among nonhuman primates, strepsirhines are of particular interest because hemosiderosis has been consistently observed in captive aged animals. In particular, the cheirogaleids, because of their small size, rapid maturity, fecundity, and relatively short life expectancy, are a useful model system for the study of normal and pathological cerebral aging. This study was therefore undertaken to explore iron localization in the brain of aged cheirogaleids (mouse and dwarf lemurs) with histochemistry and magnetic resonance microscopy. Results obtained with both techniques were comparable. There was no difference between old animals in the two species. The young animals (3 years old) showed no iron deposits. In the old animals (8-15 years old), iron pigments were mainly localized in the globus pallidus, the substantia nigra, the neocortical and cerebellar white matter, and anterior forebrain structures, including the nucleus basalis of Meynert. This distribution agrees with previous findings in monkeys and humans. In addition, we observed iron in the thalamus of these aged non-human primates. Microscopic NMR images clearly reveal many features seen with the histochemical procedure, and magnetic resonance microscopy is a powerful method for visualizing age-related changes in brain iron.

Magnetic resonance microscopy of iron in the basal forebrain cholinergic structures of the aged mouse lemur

Increased non-heme iron levels in the brain of Alzheimer's disease (AD) patients are higher than the levels observed in age matched normal subjects. Iron level in structures that are highly relevant for AD, such as the basal forebrain, can be detected post mortem with histochemistry. Because of the small size of these structures, in vivo MR detection is very difficult at conventional field magnets (1.5 and 4 T). In this study, we observed iron deposits with histochemistry and MR microscopy at 11.7 T in the brain of the mouse lemur, a strepsirhine primate which is the only known animal model of aging presenting both senile plaques and neurofibrillary degeneration. We also examined a related species, the dwarf lemur. Iron distribution in aged animals (8 to 15 years old) agrees with previous findings in humans. In addition, the high iron levels of the globus pallidus is paralleled by a comparable contrast in basal forebrain cholinergic structures. Because of the enhancement of iron-dependent contrast with increasing field strength, microscopic magnetic resonance imaging of the mouse lemur appears to be an ideal model system for studying in vivo iron changes in the basal forebrain in relation to aging and neurodegeneration.

Cloning of the presenilin 2 cDNA and its distribution in brain of the primate, Microcebus murinus: coexpression with betaAPP and Tau proteins

A 1340-bp cDNA fragment encoding the lemurian presenilin 2 protein (PS2) was isolated from a Microcebus murinus brain cDNA library by PCR using oligonucleotide primers based on the nucleotide sequence of the human gene. Analysis of five isolated clones showed that the sequence encoded a 448-amino-acid open reading frame, 95.5% identical to the human and 93.5% identical to the mouse presenilin 2 sequences. However, neither the localization of the 2 positions in PS2 nor that of the 43 positions in PS1 associated with early onset Alzheimer's disease were changed. Expression of the presenilin 2 was detected by RT-PCR and compared with that of presenilin 1 and betaAPP in the brain and in peripheral tissues (liver, kidney, and spleen). Immunohistochemistry with a specific polyclonal antiserum raised against a synthetic peptide from the N-terminal part of the human PS2 showed that the protein is distributed throughout the microcebe brain, in vascular and nerve structures. In cortical and in subcortical areas, PS2 labeling was weak and granular in appearance and was scattered throughout the cytoplasm of many neurones, extending into neurites. The gene expression of PS2 increased with age but was not affected by the presence of numerous amyloid plaques. Double labeling immunocytochemistry detected very few neurones with combined immunoreactivity PS2 and APP, or PS2 and Tau.

Influence of daylength on metabolic rate and daily water loss in the male prosimian primate Microcebus murinus

In its natural habitat, Microcebus murinus, a small malagasy prosimian primate, is exposed to seasonal shortage of water and resources. During the winter dry season, animals enter a pronounced fattening period with concurrent decrease in behavioural/physiological activities, whereas the breeding season is restricted to the rainy summer months. To determine the role of daylength on metabolic rate and water loss in this nocturnal primate, we measured body mass, oxygen consumption at 25 degrees C (RMR), circadian water loss through urine output (UO) and evaporation (EWL) in eight males exposed to either short days (8L:16D SD) or long days (14L:10D LD), under controlled captive conditions. Exposure to SD led to a ponderal increase (maximal body mass: 125 +/- 4 g, N = 8), and to significant changes in RMR and water loss, both reaching lowest values after 3 months under SD (0.84 +/- 0.04 ml O2 h-1 g-1 and 38 +/- 0.3 mg H2O g-1 day-1, respectively). Following exposure to LD, body mass decreased to 77 +/- 3 g (N = 8), whereas both RMR and water loss, mainly through EWL, significantly increased (P < 0.001), the highest value occurring after 2 months (1.51 +/- 0.08 ml O2 h-1 g-1 and 87 +/- 7 mgH2O g-1 day-1, respectively). Moreover, independent of daylength, circadian changes in EWL were characterized by significantly reduced values during the diurnal rest. The results demonstrate that daylength variations affect the physiology of this tropical primate, allowing anticipatory adaptation to seasonal environmental constraints.

Cerebral T2-weighted signal decrease during aging in the mouse lemur primate reflects iron accumulation

4.7 Tesla T2-weighted magnetic resonance images showed a highly significant signal decrease in the pallidum, substantia nigra, putamen, and a less significant decrease in the thalamus and the caudate of aging mouse lemurs (Microcebus murinus). We evaluated the contribution of iron deposits to the signal decrease comparing Perls' stained histological sections of six mouse lemurs brains aged 1 to 10 years to magnetic resonance images. In young animals, none of the brain structures was stained. A large number of iron deposits were visible in the pallidum and substantia nigra of aged animals and a moderate number in the middle aged ones. In the putamen, few iron deposits were visible in aged and middle-aged animals. The thalamus and the caudate appeared unstained with Perls' technique; iron was too low to be detected. The intensification of the reaction by diaminobenzidine revealed iron deposits in the thalamus of aging animals. This study suggests that in mouse lemurs, iron deposits are responsible for T2-weighted signal decrease in the central gray nuclei.

Prion immunoreactivity in brain, tonsil, gastrointestinal epithelial cells, and blood and lymph vessels in lemurian zoo primates with spongiform encephalopathy

We report on two animals of a non-human primate species Eulemur fulvus mayottensis, housed in the local zoo and fed over a number of years with a food containing cattle meat, that developed serious neurological symptoms associated with prion immunoreactivity in brain and various viscera. Microscopy of the brains showed neuronal vacuolation with patchy/perivacuolar immunolabelling with an abnormal isoform of prion protein (IR-PrP), an important characteristic of spongiform encephalopathy. For the first time, we report the presence in the same severely ill animals of IR-PrP in the gastrointestinal tract, detected by immunocytochemistry with mono- and polyclonal antibodies directed against various parts of the PrP. Strong PrP labelling was observed in the epithelial cells lining the pharyngeal and gastrointestinal lumen. The tonsils and the walls of the lymph and blood vessels below the intestinal epithelium were also labelled. There were no such immunoreactions in healthy lemurians killed as controls, i.e. a younger congener of the same species housed under the same conditions, and others belonging to the smaller species Microcebus murinus, reared in the laboratory and never fed on commercial food products containing cattle meat. These results demonstrate a strong PrP accumulation in the brain, the gastrointestinal tract and underlying lymphoreticular structures in these primates living in a zoological park and suffering from a spongiform encephalopathy.

beta-Amyloid protein precursor in Microcebus murinus: genotyping and brain localization

Senile plaques characterized by beta-amyloid protein (A beta) deposits around dystrophic neurites and glial cells are more abundant in the cerebral cortical parenchyma of Alzheimer's disease (AD) patients than in the aged population. Four different mutations in the amyloid precursor protein (APP) gene have been directly involved in a few cases of familial AD with early onset (before 60 years). Previous studies have shown that Microcebus murinus, a nonhuman primate, also develops analogous deposits of A beta in the cortical parenchyma and blood vessel walls in the brain. Sequence analysis of exons 16 and 17 of the APP gene, encoding for A beta, revealed that even if nucleotide divergences occurred, the resulting peptide is completely homologous with the human A beta. The systematic comparison of the A beta nucleotide sequence in microcebus with or without amyloid deposits revealed that neither the presence of mutations involved in some cases of early onset familial AD nor the presence of a mutational founder effect can explain the amyloidosis observed in some old microcebus of our breeding. Localization of the APP was performed by immunocytochemistry in the brains of adult microcebus (1 to 11 years of age) using two antibodies raised against the C-terminus and N-terminus portions of APP. Microscopic examinations revealed that in the microcebus the APP distribution was similar to that observed in the human: (1) A beta and its precursor were simultaneously observed in amyloid plaques (AP) of the cortical parenchyma; (2) APP was localized in cell bodies and proximal dendrites of neurons, in astrocytes and oligodendrocytes, and in blood vessel and capillary walls; (3) labeling of APP in these structures was correlated with the presence of AP; and (4) labeling of APP increased with the age of the animal.

Immunocytochemical characterization of Tau proteins during cerebral aging of the lemurian primate Microcebus murinus

The immunocytochemistry of Tau proteins in the cortical pyramidal neurons of the adult microcebes has been studied, using antibodies against human normal and pathological Tau proteins. Some changes related to the age and to some pathologies were observed. In fact, during the adult life, Tau proteins appeared as very thin granulations scattered in the whole neuronal cytoplasm. With age, a part of these proteins aggregated and became like thick granules at the neuron periphery; the distribution was not uniform, and numerous neurons with aggregated Tau proteins were observed in amyloid plaque-containing brains. Abnormally phosphorylated Tau proteins were also observed in some aged animals, using an absorbed anti-PHF recognizing the pathological Tau proteins characteristic of Alzheimer's disease. This present work confirms that the microcebe is a good model for studying disfunctions involved in the normal cerebral aging and in some neurodegenerative disorders which affect humans.

Biochemical characterization of Tau proteins during cerebral aging of the lemurian primate Microcebus murinus

Tau proteins extracted from the brain of 12 adult microcebes ranging from 2 to 9 years old were characterized by Western blots, using immunological probes against normal and pathological human Tau proteins. In microcebes, the molecular weight of Tau proteins increases during aging, with variants of 52-54, 64, 67 kDa in the young adult and variants of 60 and 70 kDa in the oldest animal studied. The increase of the apparent molecular weight is due to a change of conformation and a stabilization in the "hyperphosphorylated" state, as revealed with phosphorylation-dependent monoclonal antibodies Tau-1 and AD2. Furthermore, AD1 specifically detected Alzheimer-type epitopes on the 60 kDa Tau isoform from a very old microcebe. These results suggest that Microcebus murinus is an interesting model for the study of the biochemical dysfunctions that occur in the human brain during aging and Alzheimer disease.

Immunocytochemical characterization of Tau proteins during cerebral aging of the lemurian primate Microcebus murinus

The immunocytochemistry of Tau proteins in the cortical pyramidal neurons of the adult microcebes has been studied, using antibodies against human normal and pathological Tau proteins. Some changes related to the age and to some pathologies were observed. In fact, during the adult life, Tau proteins appeared as very thin granulations scattered in the whole neuronal cytoplasm. With age, a part of these proteins aggregated and became like thick granules at the neuron periphery; the distribution was not uniform, and numerous neurons with aggregated Tau proteins were observed in amyloid plaque-containing brains. Abnormally phosphorylated Tau proteins were also observed in some aged animals, using an absorbed anti-PHF recognizing the pathological Tau proteins characteristic of Alzheimer's disease. This present work confirms that the microcebe is a good model for studying disfunctions involved in the normal cerebral aging and in some neurodegenerative disorders which affect humans.

Identification of amyloid beta protein in the brain of the small, short-lived lemurian primate Microcebus murinus

The deposition of amyloid beta (A beta) protein in the brain has been demonstrated immunocytochemically in the small Lemurian primate Microcebus murinus. Both meningocerebral vascular deposits and cortical parenchymal deposits occur. All eight aged (> 8 years old) Microcebus examined showed vascular amyloid deposits, whereas only four exhibited parenchymal plaques. The vascular amyloid infiltrated the tunica media of the leptomeningeal and cortical arteries and arterioles and was also found in capillaries. A beta was observed to be deposited in three general forms in the cortical neuropil: round or elliptical plaques that were thioflavin-negative but sometimes showed a central concentration of A beta immunoreactivity; round plaques with a densely immunoreactive core that was thioflavin-positive; extensive ribbon-like infiltrations enclosing multiple cortical blood vessels. These observations, taken together with previous descriptions of age-related neurodegenerative changes in Microcebus, indicate that this species undergoes a beta-amyloid-associated neuropathology highly similar to that seen in Alzheimer's disease. We conclude that this lemurian primate of small size and relatively short life expectancy, provides a compelling animal model of some principal features of Alzheimer's disease.