In vivo virtual histology of mouse embryogenesis by ultrasound biomicroscopy and magnetic resonance imaging

Three-dimensional label-free imaging of mammalian yolk sac vascular remodeling with optical resolution photoacoustic microscopy

Vessel development in the yolk sac is important for the embryo development and the malfunction of which can lead to cardiac dysfunction, embryonic malformation and miscarriage. Although substantial emphasis has been placed on the yolk sac vascular remodeling, no detailed three-dimensional (3D) imaging and quantitative analysis of this process has been described. Herein, we explored the development of the vascular system in the visceral yolk sac (VYS) on E11.5, E12.5 and E13.5 mouse embryos using a home-built large field-of-view (FOV) optical-resolution photoacoustic microscopy (OR-PAM). The results showed that OR-PAM can be used as a label-free imaging tool for studying the 2D/3D morphology changes of the vascular system during organogenesis. In addition, after a quantitative analysis the results showed that the microvascular density in the VYS gradually reduced along with the embryo growth. Vascular density in the VYS of E11.5 mouse embryos was almost 6-fold than that of E13.5. Hovever, the averaged vessel diameter of the entire VYS membrane increased gradually with the development of embryos. This study suggests that OR-PAM is a potential tool for acquiring the hemodynamic parameters of mammalian embryos, which could be further used for studying diseases related with the vascular remodeling such as vascular malformations and heart defects.

Modelling the immunopathophysiology of Brucella melitensis and its lipopolysaccharide in mice infected via oral route of exposure

Brucella melitensis is one of the leading zoonotic pathogens with significant economic implications in animal industry worldwide. Lipopolysaccharide, however, remains by far the major virulence with substantial role in diseases pathogenesis. Nonetheless, the effect of B. melitensis and its lipopolysaccharide on immunopathophysiological aspects largely remains an enigma. This study examines the effect of B.melitensis and its lipopolysaccharide on immunopathophysiological parameters following experimental infection using mouse model. Eighty four (n = 84) mice, BALB/c, both sexes with equal gender distribution and 6-8 weeks-old were randomly assigned into three groups. Group 1-2 (n = 72) were orally inoculated with 0.4 mL containing 10⁹ CFU/mL of B. melitensis and its LPS, respectively. Group 3 (n = 12) was challenged orally with phosphate buffered saline and served as a control group. Animals were observed for clinical signs, haematological and histopathological analysis for a period of 24 days post-infection. We hereby report that B.melitensis infected group demonstrated significant clinical signs and histopathological changes than LPS infected group. However, both infected groups showed elevated levels of interleukins (IL-1β and IL-6) and antibody levels (IgM and IgG) with varying degrees of predominance in LPS infected group than B. melitensis infected group. For hormone analysis, low levels of progesterone, estradiol and testosterone were observed in both B. melitensis and LPS groups throughout the study period. Moreover, in B. melitensis infected group, the organism was re-isolated from the organs and tissues of gastrointestinal, respiratory and reproductive systems thereby confirming the infection and transmission dynamics. This report is the first detailed investigation comparing the infection progression and host responses in relation to the immunopathophysiological aspects in a mouse model after oral inoculation with B. melitensis and its lipopolysaccharide.

In Vivo Imaging With Confirmation by Histopathology for Increased Rigor and Reproducibility in Translational Research: A Review of Examples, Options, and Resources

Preclinical noninvasive imaging can be an indispensable tool for studying animal models of disease. In vivo imaging to assess anatomical, functional, and molecular features requires verification by a comparison to the macroscopic and microscopic morphological features, since all noninvasive in vivo imaging methods have much lower resolution than standard histopathology. Comprehensive pathological evaluation of the animal model is underutilized; yet, many institutions have veterinary or human pathologists with necessary comparative pathology expertise. By performing a rigorous comparison to gross or histopathology for image interpretation, these trained individuals can assist scientists with the development of the animal model, experimental design, and evaluation of the in vivo imaging data. These imaging and pathology corroboration studies undoubtedly increase scientific rigor and reproducibility in descriptive and hypothesis-driven research. A review of case examples including ultrasound, nuclear, optical, and MRI is provided to illustrate how a wide range of imaging modalities data can be confirmed by gross or microscopic pathology. This image confirmation and authentication will improve characterization of the model and may contribute to decreasing costs and number of animals used and to more rapid translation from preclinical animal model to the clinic.

Detection of Successful and Unsuccessful Pregnancies in Mice within Hours of Pairing through Frequency Analysis of High Temporal Resolution Core Body Temperature Data

Many controllable factors negatively impact fetal development, underscoring the importance of early pregnancy detection and identification of events that reliably predict potential complications. Clinically, core body temperature (CBT) is used to aid family planning and pregnancy detection. However, such temperature data typically are gathered in single, daily measurements. In animal studies, interventions or cell/tissue harvesting at defined stages of fetal development are arduous, requiring timed mating by trained observers. The value of continuous temperature measurements remains largely unexplored, but the advent of small, inexpensive, and increasingly ubiquitous, accurate sensor devices makes continuous measures feasible. Here, using a mouse model, we show that continuous, 1-min resolution CBT measurements reliably allow for the earliest and most accurate detection of pregnancy (100%, within 14 h of initial pairing), without requiring interaction with the animal for data collection. This method also reveals a subset of females that exhibit a pregnancy-like response following pairing that persists for a variable number of days. Application of wavelet analysis that permits frequency analysis while preserving temporal resolution, uncovers significant differences in ultradian frequencies of CBT; these rhythms are significantly increased in the 12 h after the day of pairing for pregnancies carried to term compared to apparent pregnancies that failed. High temporal resolution CBT and wavelet analysis permit strikingly early detection and separation of successful pregnancies and pregnancy-like events.

Optical coherence tomography for embryonic imaging: a review

Embryogenesis is a highly complex and dynamic process, and its visualization is crucial for understanding basic physiological processes during development and for identifying and assessing possible defects, malformations, and diseases. While traditional imaging modalities, such as ultrasound biomicroscopy, micro-magnetic resonance imaging, and micro-computed tomography, have long been adapted for embryonic imaging, these techniques generally have limitations in their speed, spatial resolution, and contrast to capture processes such as cardiodynamics during embryogenesis. Optical coherence tomography (OCT) is a noninvasive imaging modality with micrometer-scale spatial resolution and imaging depth up to a few millimeters in tissue. OCT has bridged the gap between ultrahigh resolution imaging techniques with limited imaging depth like confocal microscopy and modalities, such as ultrasound sonography, which have deeper penetration but poorer spatial resolution. Moreover, the noninvasive nature of OCT has enabled live imaging of embryos without any external contrast agents. We review how OCT has been utilized to study developing embryos and also discuss advances in techniques used in conjunction with OCT to understand embryonic development.

Full-length human placental sFlt-1-e15a isoform induces distinct maternal phenotypes of preeclampsia in mice

OBJECTIVE

Most anti-angiogenic preeclampsia models in rodents utilized the overexpression of a truncated soluble fms-like tyrosine kinase-1 (sFlt-1) not expressed in any species. Other limitations of mouse preeclampsia models included stressful blood pressure measurements and the lack of postpartum monitoring. We aimed to 1) develop a mouse model of preeclampsia by administering the most abundant human placental sFlt-1 isoform (hsFlt-1-e15a) in preeclampsia; 2) determine blood pressures in non-stressed conditions; and 3) develop a survival surgery that enables the collection of fetuses and placentas and postpartum (PP) monitoring.

METHODS

Pregnancy status of CD-1 mice was evaluated with high-frequency ultrasound on gestational days (GD) 6 and 7. Telemetry catheters were implanted in the carotid artery on GD7, and their positions were verified by ultrasound on GD13. Mice were injected through tail-vein with adenoviruses expressing hsFlt-1-e15a (n = 11) or green fluorescent protein (GFP; n = 9) on GD8/GD11. Placentas and pups were delivered by cesarean section on GD18 allowing PP monitoring. Urine samples were collected with cystocentesis on GD6/GD7, GD13, GD18, and PPD8, and albumin/creatinine ratios were determined. GFP and hsFlt-1-e15a expression profiles were determined by qRT-PCR. Aortic ring assays were performed to assess the effect of hsFlt-1-e15a on endothelia.

RESULTS

Ultrasound predicted pregnancy on GD7 in 97% of cases. Cesarean section survival rate was 100%. Mean arterial blood pressure was higher in hsFlt-1-e15a-treated than in GFP-treated mice (∆MAP = 13.2 mmHg, p = 0.00107; GD18). Focal glomerular changes were found in hsFlt-1-e15a -treated mice, which had higher urine albumin/creatinine ratios than controls (109.3 ± 51.7 μg/mg vs. 19.3 ± 5.6 μg/mg, p = 4.4 x 10(-2); GD18). Aortic ring assays showed a 46% lesser microvessel outgrowth in hsFlt-1-e15a-treated than in GFP-treated mice (p = 1.2 x 10(-2)). Placental and fetal weights did not differ between the groups. One mouse with liver disease developed early-onset preeclampsia-like symptoms with intrauterine growth restriction (IUGR).

CONCLUSIONS

A mouse model of late-onset preeclampsia was developed with the overexpression of hsFlt-1-e15a, verifying the in vivo pathologic effects of this primate-specific, predominant placental sFlt-1 isoform. HsFlt-1-e15a induced early-onset preeclampsia-like symptoms associated with IUGR in a mouse with a liver disease. Our findings support that hsFlt-1-e15a is central to the terminal pathway of preeclampsia, and it can induce the full spectrum of symptoms in this obstetrical syndrome.

Imaging techniques for visualizing and phenotyping congenital heart defects in murine models

Mouse model is ideal for investigating the genetic and developmental etiology of congenital heart disease. However, cardiovascular phenotyping for the precise diagnosis of structural heart defects in mice remain challenging. With rapid advances in imaging techniques, there are now high throughput phenotyping tools available for the diagnosis of structural heart defects. In this review, we discuss the efficacy of four different imaging modalities for congenital heart disease diagnosis in fetal/neonatal mice, including noninvasive fetal echocardiography, micro-computed tomography (micro-CT), micro-magnetic resonance imaging (micro-MRI), and episcopic fluorescence image capture (EFIC) histopathology. The experience we have gained in the use of these imaging modalities in a large-scale mouse mutagenesis screen have validated their efficacy for congenital heart defect diagnosis in the tiny hearts of fetal and newborn mice. These cutting edge phenotyping tools will be invaluable for furthering our understanding of the developmental etiology of congenital heart disease.

Techniques for visualization of cell-cell contact at the fetal-maternal interface

Historically, several in vitro/ex vivo microscopy imaging techniques have been used to study cellular interactions within the uterus and the placenta. As these experimental methods have revealed compelling facts about the biologic phenomena of cell-cell contacts in these organs, they cannot be used to study complex dynamic behavior of living cells inside their physiologic environment. For this, recent advances in intravital imaging techniques, together with two-photon microscopy, offer an exciting opportunity to study such dynamic immunologic processes at the cellular level in the complex uterine and placental tissues. In this article, we review experimental imaging techniques that have been used for studying the uterus and placenta. In particular, we describe the advantages of intravital techniques and discuss novel procedures that can be used in reproductive immunology. We also describe several technical details involved in image sequence post-processing required to extract useful data. Finally, we conclude by discussing how the reproductive immunology field may benefit from the broad use of these intravital techniques.

Quantitative three-dimensional imaging of live avian embryonic morphogenesis via micro-computed tomography

Many clinically relevant congenital malformations arise during mid to late embryonic stages. This period is challenging to image quantitatively in live embryos, necessitating the use of multiple specimens with increased experimental variability. Here we establish X-ray and blood-pool computed tomography (CT) contrast agent toxicity and teratogenesis thresholds for 3D Micro-CT imaging of live avian embryos. Day 4 chick embryos micro-injected with Visipaque™ (VP) developed for an additional 6 days without defect. X-ray radiation up to 798 mGy was nontoxic. Peak average contrast of 1,060 HU occurred within 1 hr of imaging at 50 μm resolution. VP-enhanced contrast persisted past 24 hr with delayed accumulation in the allantois. Regional volumes of VP-injected embryos were statistically identical to those of fixed embryos perfused with osmium tetroxide. We further quantified longitudinal volumetric morphogenesis of the allantois over 30 hr. These results demonstrate the safety and efficacy of contrast enhanced quantitative micro-CT imaging for live embryos.

3-dimensional imaging modalities for phenotyping genetically engineered mice

A variety of 3-dimensional (3D) digital imaging modalities are available for whole-body assessment of genetically engineered mice: magnetic resonance microscopy (MRM), X-ray microcomputed tomography (microCT), optical projection tomography (OPT), episcopic and cryoimaging, and ultrasound biomicroscopy (UBM). Embryo and adult mouse phenotyping can be accomplished at microscopy or near microscopy spatial resolutions using these modalities. MRM and microCT are particularly well-suited for evaluating structural information at the organ level, whereas episcopic and OPT imaging provide structural and functional information from molecular fluorescence imaging at the cellular level. UBM can be used to monitor embryonic development longitudinally in utero. Specimens are not significantly altered during preparation, and structures can be viewed in their native orientations. Technologies for rapid automated data acquisition and high-throughput phenotyping have been developed and continually improve as this exciting field evolves.

Optical Coherence Tomography for live imaging of mammalian development

Understanding the nature and mechanism of congenital defects of the different organ systems in humans has heavily relied on the analysis of the corresponding mutant phenotypes in rodent models. Optical Coherence Tomography (OCT) has recently emerged as a powerful tool to study early embryonic development. This non-invasive optical methodology does not require labeling and allows visualization of embryonic tissues with single cell resolution. Here, we will discuss how OCT can be applied for structural imaging of early mouse and rat embryos in static culture, cardiodynamic and blood flow analysis, and in utero embryonic imaging at later stages of gestation, demonstrating how OCT can be used to assess structural and functional birth defects in mammalian models.

Micro-ultrasound for preclinical imaging

Over the past decade, non-invasive preclinical imaging has emerged as an important tool to facilitate biomedical discovery. Not only have the markets for these tools accelerated, but the numbers of peer-reviewed papers in which imaging end points and biomarkers have been used have grown dramatically. High frequency 'micro-ultrasound' has steadily evolved in the post-genomic era as a rapid, comparatively inexpensive imaging tool for studying normal development and models of human disease in small animals. One of the fundamental barriers to this development was the technological hurdle associated with high-frequency array transducers. Recently, new approaches have enabled the upper limits of linear and phased arrays to be pushed from about 20 to over 50 MHz enabling a broad range of new applications. The innovations leading to the new transducer technology and scanner architecture are reviewed. Applications of preclinical micro-ultrasound are explored for developmental biology, cancer, and cardiovascular disease. With respect to the future, the latest developments in high-frequency ultrasound imaging are described.

Optical coherence tomography for high-resolution imaging of mouse development in utero

Although the mouse is a superior model to study mammalian embryonic development, high-resolution live dynamic visualization of mouse embryos remain a technical challenge. We present optical coherence tomography as a novel methodology for live imaging of mouse embryos through the uterine wall thereby allowing for time lapse analysis of developmental processes and direct phenotypic analysis of developing embryos. We assessed the capability of the proposed methodology to visualize structures of the living embryo from embryonic stages 12.5 to 18.5 days postcoitus. Repetitive in utero embryonic imaging is demonstrated. Our work opens the door for a wide range of live, in utero embryonic studies to screen for mutations and understand the effects of pharmacological and toxicological agents leading to birth defects.

Imaging modalities to assess structural birth defects in mutant mouse models

Assessment of structural birth defects (SBDs) in animal models usually entails conducting detailed necropsy for anatomical defects followed by histological analysis for tissue defects. Recent advances in new imaging technologies have provided the means for rapid phenotyping of SBDs, such as using ultra-high frequency ultrasound biomicroscopy, optical coherence tomography, micro-CT, and micro-MRI. These imaging modalities allow the detailed assessment of organ/tissue structure, and with ultrasound biomicroscopy, structure and function of the cardiovascular system also can be assessed noninvasively, allowing the longitudinal tracking of the fetus in utero. In this review, we briefly discuss the application of these state-of-the-art imaging technologies for phenotyping of SBDs in rodent embryos and fetuses, showing how these imaging modalities may be used for the detection of a wide variety of SBDs.

Screening for embryonic loss during in utero development of mice with a human 1.5 Tesla clinical MRI scanner

PURPOSE

To establish in utero MRI-scanning of mouse implantation sites in a 1.5 Tesla whole-body human clinical scanner for evaluation of impaired implantation, placental or developmental defects due to genetic alterations.

MATERIALS AND METHODS

Pregnant C57Bl/6 wild-type and Cx31-deficient mice revealing placental defects were analyzed in utero using a 1.5 Tesla whole-body clinical scanner in combination with a 3-cm-diameter single loop (slice thickness: 1.2 mm). Imaging of implantation sites was evaluated from 6.5-13.5 dpc and amount of implantation sites and in vivo development was analyzed during the critical phase of placentation from 10.5-13.5 dpc.

RESULTS

This method provided high resolution in plane images permitting confident identification of all implantation sites from 6.5 dpc onward. A loss of 60% of Cx31-deficient embryos was demonstrated compared with controls. Repeated anesthesia as well as imaging protocols produced no gross malformations in the surviving mice.

CONCLUSION

Using a human clinical MRI scanner high resolution imaging of the entire uterus of the mice and all the embryos inside could be performed. This method is well suited to noninvasively monitor and quantify embryo implantation and to follow this dynamic process in vivo without compromising pregnancy progression and embryonic development.

Ovarian imaging in the mouse using ultrasound biomicroscopy (UBM): a validation study

The mouse is a well accepted model for studies of human reproduction despite little being known about follicle dynamics in this species. Longitudinal studies of mouse folliculogenesis have been hampered by the lack of an appropriate imaging tool. Ultrasound biomicroscopy (UBM) may overcome this obstacle as it confers near-microscopic resolution through the use of high-frequency ultrasound waves. The objective of the present study was to determine whether UBM could be used to count and measure ovarian follicles and corpora lutea (CL) reliably in mice. Ovaries of 25 adult CD-1 mice were imaged using a 55-MHz transducer and then excised and processed for histology. Follicles and CL were counted and measured from digitally stored UBM cine-loops and photographed histological sections. Differences between techniques were assessed by Bland-Altman agreement analyses. Follicle counts yielded by the two techniques varied by only +/-1 follicle when follicles ranged between 300 and 499 microm. Perfect agreement among counts was evident when follicles were >500 microm. The total number of CL was accurately estimated using UBM; however, the number of 350-699 microm CL was underestimated and the number of CL>or=700 microm was overestimated. In conclusion, UBM can be used reliably to count and measure follicles in mice.