The short-tailed fruit bat Carollia perspicillata: a model for studies in reproduction and development

Infection Studies with Airway Organoids from Carollia perspicillata Indicate That the Respiratory Epithelium Is Not a Barrier for Interspecies Transmission of Influenza Viruses

Bats are a natural reservoir for many viruses and are considered to play an important role in the interspecies transmission of viruses. To analyze the susceptibility of bat airway cells to infection by viruses of other mammalian species, we developed an airway organoid culture model derived from airways of Carollia perspicillata. Application of specific antibodies for fluorescent staining indicated that the cell composition of organoids resembled those of bat trachea and lungs as determined by immunohistochemistry. Infection studies indicated that Carollia perspicillata bat airway organoids (AOs) from the trachea or the lung are highly susceptible to infection by two different porcine influenza A viruses. The bat AOs were also used to develop an air-liquid interface (ALI) culture system of filter-grown epithelial cells. Infection of these cells showed the same characteristics, including lower virulence and enhanced replication and release of the H1N1/2006 virus compared to infection with H3N2/2007. These observations agreed with the results obtained by infection of porcine ALI cultures with these two virus strains. Interestingly, lectin staining indicated that bat airway cells only contain a small amount of alpha 2,6-linked sialic acid, the preferred receptor determinant for mammalian influenza A viruses. In contrast, large amounts of alpha 2,3-linked sialic acid, the preferred receptor determinant for avian influenza viruses, are present in bat airway epithelial cells. Therefore, bat airway cells may be susceptible not only to mammalian but also to avian influenza viruses. Our culture models, which can be extended to other parts of the airways and to other species, provide a promising tool to analyze virus infectivity and the transmission of viruses both from bats to other species and from other species to bats. IMPORTANCE We developed an organoid culture system derived from the airways of the bat species Carollia perspicillata. Using this cell system, we showed that the airway epithelium of these bats is highly susceptible to infection by influenza viruses of other mammalian species and thus is not a barrier for interspecies transmission. These organoids provide an almost unlimited supply of airway epithelial cells that can be used to generate well-differentiated epithelial cells and perform infection studies. The establishment of the organoid model required only three animals, and can be extended to other epithelia (nose, intestine) as well as to other species (bat and other animal species). Therefore, organoids promise to be a valuable tool for future zoonosis research on the interspecies transmission of viruses (e.g., bat → intermediate host → human).

Carollia perspicillata: A Small Bat with Tremendous Translational Potential for Studies of Brain Aging and Neurodegeneration

As the average human lifespan lengthens, the impact of neurodegenerative disease increases, both on the individual suffering neurodegeneration and on the community that supports those individuals. Studies aimed at understanding the mechanisms of neurodegeneration have relied heavily on observational studies of humans and experimental studies in animals, such as mice, in which aspects of brain structure and function can be manipulated to target mechanistic steps. An animal model whose brain is structurally closer to the human brain, that lives much longer than rodents, and whose husbandry is practical may be valuable for mechanistic studies that cannot readily be conducted in rodents. To demonstrate that the long-lived Seba’s short-tailed fruit bat, Carollia perspicillata, may fit this role, we used immunohistochemical labeling for NeuN and three calcium-binding proteins, calretinin, parvalbumin, and calbindin, to define hippocampal formation anatomy. Our findings demonstrate patterns of principal neuron organization that resemble primate and human hippocampal formation and patterns of calcium-binding protein distribution that help to define subregional boundaries. Importantly, we present evidence for a clear prosubiculum in the bat brain that resembles primate prosubiculum. Based on the similarities between bat and human hippocampal formation anatomy, we suggest that Carollia has unique advantages for the study of brain aging and neurodegeneration. A captive colony of Carollia allows age tracking, diet and environment control, pharmacological manipulation, and access to behavioral, physiological, anatomical, and molecular evaluation.

Characteristics of the endometrium in menstruating species: lessons learned from the animal kingdom†

Here we have summarized what is currently known about menstruating animal species with special emphasis on non-primate species: length of their menstrual cycle, ovulation, implantation, placentation, decidualization, and endometrial characteristics. Having an overview of all the possible animal models that can be used to study menstruation and the menstrual cycle could be useful to select the one that better matches the needs of the individual research projects. The most promising species to study menstruation seems to be the spiny mouse Acomys cahirinus. It is a rodent that could be easily held in the existing laboratory facilities for rats and mice but with the great advantage of having spontaneous menstruation and several human-like menstrual cycle characteristics. Among the species of menstruating bats, the black mastiff bat Molossus ater and wild fulvous fruit bat Rousettus leschenaultii are the ones presenting the most human-like characteristics. The elephant shrew seems to be the less suitable species among the ones analyzed. The induced mouse model of menstruation is also presented as an adaptable alternative to study menstruation.

Differential cellular proliferation underlies heterochronic generation of cranial diversity in phyllostomid bats

Background

Skull diversity in the neotropical leaf-nosed bats (Phyllostomidae) evolved through a heterochronic process called peramorphosis, with underlying causes varying by subfamily. The nectar-eating (subfamily Glossophaginae) and blood-eating (subfamily Desmondontinae) groups originate from insect-eating ancestors and generate their uniquely shaped faces and skulls by extending the ancestral ontogenetic program, appending new developmental stages and demonstrating peramorphosis by hypermorphosis. However, the fruit-eating phyllostomids (subfamilies Carollinae and Stenodermatinae) adjust their craniofacial development by speeding up certain developmental processes, displaying peramorphosis by acceleration. We hypothesized that these two forms of peramorphosis detected by our morphometric studies could be explained by differential growth and investigated cell proliferation during craniofacial morphogenesis.

Results

We obtained cranial tissues from four wild-caught bat species representing a range of facial diversity and labeled mitotic cells using immunohistochemistry. During craniofacial development, all bats display a conserved spatiotemporal distribution of proliferative cells with distinguishable zones of elevated mitosis. These areas were identified as modules by the spatial distribution analysis. Ancestral state reconstruction of proliferation rates and patterns in the facial module between species provided support, and a degree of explanation, for the developmental mechanisms underlying the two models of peramorphosis. In the long-faced species, Glossophaga soricina, whose facial shape evolved by hypermorphosis, cell proliferation rate is maintained at lower levels and for a longer period of time compared to the outgroup species Miniopterus natalensis. In both species of studied short-faced fruit bats, Carollia perspicillata and Artibeus jamaicensis, which evolved under the acceleration model, cell proliferation rate is increased compared to the outgroup.

Conclusions

This is the first study which links differential cellular proliferation and developmental modularity with heterochronic developmental changes, leading to the evolution of adaptive cranial diversity in an important group of mammals.

Characterization of Experimental Oro-Nasal Inoculation of Seba's Short-Tailed Bats (Carollia perspicillata) with Bat Influenza A Virus H18N11

In 2012 and 2013, the genomic sequences of two novel influenza A virus (IAV) subtypes, designated H17N10 and H18N11, were identified via next-generation sequencing in the feces of the little yellow-shouldered fruit bat (Sturnira lilium) and the flat-faced fruit-eating bat (Artibeus planirostris), respectively. The pathogenesis caused by these viruses in their respective host species is currently insufficiently understood, which is primarily due to the inability to obtain and keep these bat species under appropriate environmental and biosafety conditions. Seba’s short-tailed bats (Carollia perspicillata), in contrast, are close relatives and a natural H18N11 reservoir species, with the advantage of established animal husbandry conditions in academic research. To study viral pathogenesis in more detail, we here oro-nasally inoculated Seba’s short-tailed bats with the bat IAV H18N11 subtype. Following inoculation, bats appeared clinically healthy, but the histologic examination of tissues revealed a mild necrotizing rhinitis. Consistently, IAV-matrix protein and H18-RNA positive cells were seen in lesioned respiratory and olfactory nasal epithelia, as well as in intestinal tissues. A RT-qPCR analysis confirmed viral replication in the conchae and intestines as well as the presence of viral RNA in the excreted feces, without horizontal transmission to naïve contact animals. Moreover, all inoculated animals seroconverted with low titers of neutralizing antibodies.

Individual asymmetry as a predictor of fitness in the bat Carollia perspicillata

The measurement of fitness in wild populations is a challenging task, and a number of proxies have been proposed with different degrees of success. Developmental instability/stability (DI) is an organismal property associated with variance in bilateral asymmetry (fluctuating asymmetry-FA) and a correlated effect on fitness. This study provides evidence to corroborate the hypothesis that asymmetry partly reflects DI and is correlated with a reduction in fitness measured by survival and reproduction in bats. We studied two colonies of the bat Carollia perspicillata in southeastern Brazil over 5 years, marking and recapturing individuals. Gaussian mixture models for signed Forearm Asymmetry (ForA) distribution indicated that ~20% of asymmetry variation was due to DI heterogeneity among individuals. ForA, body condition (Scaled Mass Index-SMI) and Forearm Length (ForL) were used as predictors of survival probability in Cormack-Jolly-Seber models. Asymmetry was negatively associated with survival, whereas SMI and ForL were positively associated. The male C. perspicillata defend sites within the roost that are favoured by female harems, but there are mating opportunities for bachelor males, leading to both territorial disputes and sperm competition. As predicted by sexual selection, ForA was negatively associated with relative Testicle Length, a measure of reproductive potential. In females, ForA was negatively associated with the probability of two pregnancies (as opposed to one) in a given breeding season. The effect magnitudes and directions of associations suggest that asymmetry, even though not perfectly reflecting DI variation, is a useful predictor for fitness components in C. perspicillata.

The Bat as a New Model of Cortical Development

The organization of the mammalian cerebral cortex shares fundamental features across species. However, while the radial thickness of grey matter varies within one order of magnitude, the tangential spread of the cortical sheet varies by orders of magnitude across species. A broader sample of model species may provide additional clues for understanding mechanisms that drive cortical expansion. Here, we introduce the bat Carollia perspicillata as a new model species. The brain of C. perspicillata is similar in size to that of mouse but has a cortical neurogenic period at least 5 times longer than mouse, and nearly as long as that of the rhesus macaque, whose brain is 100 times larger. We describe the development of laminar and regional structures, neural precursor cell identity and distribution, immune cell distribution, and a novel population of Tbr2+ cells in the caudal ganglionic eminence of the developing neocortex of C. perspicillata. Our data indicate that unique mechanisms guide bat cortical development, particularly concerning cell cycle length. The bat model provides new perspective on the evolution of developmental programs that regulate neurogenesis in mammalian cerebral cortex, and offers insight into mechanisms that contribute to tangential expansion and gyri formation in the cerebral cortex.

Ovulation, fertilization, and early embryonic development in the menstruating fruit bat, Carollia perspicillata

To characterize periovulatory events, reproductive tracts were collected at 12 hr intervals from captive-bred, short-tailed fruit bats, Carollia perspicillata, on days 1-3 post coitum and examined histologically. Most bats bred readily. Graafian follicles developed large antra and exhibited preovulatory expansion of the cumulus oophorus. Ovulation had occurred in some on the morning, and in most by the evening, of day 1. The single ovum was released as a secondary oocyte and fertilized in the oviductal ampulla. Ovulated secondary oocytes were loosely associated with their cumulus cells, which were lost around the initiation of fertilization. Supernumerary spermatozoa were occasionally noted attached to the zonae pellucidae of oviductal ova, but never within the perivitelline space. By day 2, most ova had reached the pronuclear stage and by day 3, early cleavage stages. Several lines of evidence indicate that C. perspicillata is a spontaneous ovulator with a functional luteal phase. Most newly mated females had recently formed, but regressing corpora lutea, and thickened (albeit menstrual) uteri despite having been housed with males only for brief periods (<23 days). Menstruation is usually periovulatory in this species. Furthermore, the interval between successive estrus periods in most mated females that failed to establish ongoing pregnancies at the first was 21-27 days. Menstruation involved substantial endometrial desquamation, plus associated bleeding, and generally extended to the evening of day 3, the last time point studied. In nearly all females with a recent corpus luteum (n = 24 of 25; 96%), the preovulatory or newly ruptured follicle was in the opposite ovary.

Generating timed pregnancies in fruit bats (Carollia perspicillata)

When female short-tailed fruit bats (Carollia perspicillata) are bred, they are first kept sexually segregated for some months to adapt to captivity (in the case of recently captured animals) and to ensure that none are already pregnant. In the case of captive-reared females that had previously been housed with males, 4 mo should be sufficient. In the case of wild-caught females, 7 or 8 mo may not be too long, because introduction into captivity can substantially prolong existing early pregnancies (i.e., at or earlier than the primitive streak stage). Wild-caught females are also much more prone than captive-reared females to take pregnancies into delay after captive breeding. It is important to note that females should not be housed in sexual isolation for prolonged periods, because this can eventually lead to the development of markedly hyperplastic uteri and reduced fertility. Although this is a very serious problem for zoos maintaining all-female colonies of Carollia, it is not the case with our captive colony because the adult females are regularly bred, both to replenish the colony and to inhibit the development of hyperplastic uteri. The generation of timed pregnancies is described in this protocol. For breeding purposes, a stud male with prominent testes is introduced into each cage of females. Vaginal aspirates are then checked each morning thereafter for the presence of spermatozoa.

Collection of short-tailed fruit bats (Carollia perspicillata) from the wild

Adult female short-tailed fruit bats (Carollia perspicillata) exhibit a relatively high degree of reproductive synchronization in populations sampled carefully in Central America and on Trinidad. On the basis of these studies and temporal data for pregnancies in captive-bred animals, one may be able to sample adult female Carollia from other populations and, during much of the year, predict when different embryonic stages might be prevalent. Most adult female Carollia on Trinidad seem to carry two pregnancies each year, based on the observation that more than 90% are typically pregnant when sampled around the middle of each pregnancy period. For many females, the first pregnancy appears to be established between September and early November, includes a period of post-implantational developmental delay at the primitive streak stage, and is completed in March or April. A peak in births has been observed around April 1. Most parous females then conceive again at a post-partum estrus. In captive animals, this estrus usually occurs between 3 and 6 d after parturition, but sometimes, it is several days later. Using the available temporal data on pregnancies in both captive and wild Carollia, it is possible to predict when embryos at particular stages of development are most likely to be carried by females in the wild population on Trinidad. A similar approach might be used to collect embryos from another population, as outlined in this protocol.

Alcian blue/alizarin red staining of cartilage and bone of short-tailed fruit bat (Carollia perspicillata)

This protocol is used to stain embryo skeleton with alcian blue and alizarin red at later stages of development, when there is significant replacement of the cartilaginous early skeleton with ossified bone. It has been used with good results on the short-tailed fruit bat Carollia perspicillata and other bat species from CS 20 through neonatal stages.