A morphological and immunohistochemical comparison of mammary tissues from the short-tailed fruit bat (Carollia perspicillata) and the mouse

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).

Prenatal Mammary Gland Development in the Mouse: Research Models and Techniques for Its Study from Past to Present

Mammary gland development starts during prenatal life, when at designated positions along the ventrolateral boundary of the embryonic or fetal trunk, surface ectodermal cells coalesce to form primordia for mammary glands, instead of differentiating into epidermis. With the wealth of genetically engineered mice available as research models, our understanding of the prenatal phase of mammary development has recently greatly advanced. This understanding includes the recognition of molecular and mechanistic parallels between prenatal and postnatal mammary morphogenesis and even tumorigenesis, much of which can moreover be extrapolated to human. This makes the murine embryonic mammary gland a useful model for a myriad of questions pertaining to normal and pathological breast development. Hence, unless indicated otherwise, this review describes embryonic mammary gland development in mouse only, and lists mouse models that have been examined for defects in embryonic mammary development. Techniques that originated in the field of developmental biology, such as explant culture and tissue recombination, were adapted specifically to research on the embryonic mammary gland. Detailed protocols for these techniques have recently been published elsewhere. This review describes how the development and adaptation of these techniques moved the field forward from insights on (comparative) morphogenesis of the embryonic mammary gland to the understanding of tissue and molecular interactions and their regulation of morphogenesis and functional development of the embryonic mammary gland. It is here furthermore illustrated how generic molecular biology and biochemistry techniques can be combined with these older, developmental biology techniques, to address relevant research questions. As such, this review should provide a solid starting point for those wishing to familiarize themselves with this fascinating and important subdomain of mammary gland biology, and guide them in designing a relevant research strategy.

Differential expression of serotonin, tryptophan hydroxylase and monoamine oxidase A in the mammary gland of the Myotis velifer bat

The mammary gland has long drawn the attention of the scientific community due to the limited knowledge of some fundamental aspects involved in the control of its function. Myotis velifer, a microchiropteran species, provides an interesting model to study some of the regulatory factors involved in the control of the mammary gland cycle. Having an asynchronous, monoestrous reproductive pattern, female M. velifer bats undergo drastic morphological changes of the breast during the reproductive cycle. Current research on non-chiropteran mammals indicates that serotonin (5-HT) plays a major role in the intraluminal volume homeostasis of the mammary gland during lactation; however, an analysis of both the expression and localization of the main components of the serotonergic system in the bat mammary gland is lacking. Thus, the objectives of the present study were: to describe the gross and histological anatomy of the mammary gland of M. velifer to establish the lactation period for this species; to analyze the distribution and expression of the main serotonergic components in the mammary tissues of these bats under the physiological conditions of lactation, involution and the resting phase; and to provide information on the involvement of 5-HT in the regulation of the physiological function of this organ. To assess the expression and localization of serotonergic components, multiple immunofluorescence, Western blot and HPLC methods were used. 5-HT and the enzyme that catalyzes its synthesis (TPH) were located in both myoepithelial and luminal epithelial cells, while the enzyme responsible for the catabolism of this neurohormone (MAO A) was found in luminal epithelial cells as well as in secreted products. We also found an increased expression of serotonergic components during lactation, indicating that elements of the serotonergic system may play an important role in lactation in this species of bat in a way similar to that of other mammal species.

Wild Fulvous Fruit Bats (Rousettus leschenaulti) Exhibit Human-Like Menstrual Cycle1

We investigated the menstrual cycle of wild fulvous fruit bats (Rousettus leschenaulti), focusing on changes in the endometrial and ovarian structure and pituitary and steroid hormones. The menstrual cycle lasts for 33 days in bats studied in their natural habitat and in captivity. Vaginal bleeding was restricted to a single day (Day 1). A preovulatory follicle was found in the ovary on Day 18 when the levels of LH and FSH reached their maxima, accompanied by a thickened endometrium. On Day 24, serum levels of progesterone and estradiol-17 were also maximal, and uterine glands increased in size. After that, the levels of progesterone dropped precipitously, leading to menstrual bleeding. Both the morphologic and hormonal changes observed in fulvous fruit bats during the menstrual cycle resemble similar changes in humans. Fulvous fruit bats may be useful nonprimate laboratory models to study menstruation and menstrual dysfunction.

Development of bat flight: morphologic and molecular evolution of bat wing digits

The earliest fossil bats resemble their modern counterparts in possessing greatly elongated digits to support the wing membrane, which is an anatomical hallmark of powered flight. To quantitatively confirm these similarities, we performed a morphometric analysis of wing bones from fossil and modern bats. We found that the lengths of the third, fourth, and fifth digits (the primary supportive elements of the wing) have remained constant relative to body size over the last 50 million years. This absence of transitional forms in the fossil record led us to look elsewhere to understand bat wing evolution. Investigating embryonic development, we found that the digits in bats (Carollia perspicillata) are initially similar in size to those of mice (Mus musculus) but that, subsequently, bat digits greatly lengthen. The developmental timing of the change in wing digit length points to a change in longitudinal cartilage growth, a process that depends on the relative proliferation and differentiation of chondrocytes. We found that bat forelimb digits exhibit relatively high rates of chondrocyte proliferation and differentiation. We show that bone morphogenetic protein 2 (Bmp2) can stimulate cartilage proliferation and differentiation and increase digit length in the bat embryonic forelimb. Also, we show that Bmp2 expression and Bmp signaling are increased in bat forelimb embryonic digits relative to mouse or bat hind limb digits. Together, our results suggest that an up-regulation of the Bmp pathway is one of the major factors in the developmental elongation of bat forelimb digits, and it is potentially a key mechanism in their evolutionary elongation as well.