Investigating the evolutionary dynamics of diploid number variation in Ctenomys (Ctenomyidae, Rodentia)

Contrary to predictions from classical hybrid sterility models of chromosomal speciation, some organisms display high rates of karyotype variation. Ctenomys are the current mammals with the greatest interspecific and intraspecific chromosomal variation. A large number of species have been studied cytogenetically. The diploid numbers of chromosomes range from 2n = 10 to 2n = 70. Here, we analyzed karyotype evolution in Ctenomys using comparative phylogenetic methods. We found a strong phylogenetic signal with chromosome number. This refutes the chromosomal megaevolution model, which proposes the independent accumulation of multiple chromosomal rearrangements in each closely related species. We found that Brownian motion (BM) described the observed characteristic changes more thoroughly than the Ornstein-Uhlenbeck and Early-Burst models. This suggests that the evolution of chromosome numbers occurs by a random walk along phylogenetic clades. However, our data indicate that the BM model alone does not fully characterize the chromosomal evolution of Ctenomys.

Integrated Proteomics Unveils Nuclear PDE3A2 as a Regulator of Cardiac Myocyte Hypertrophy

BACKGROUND

Signaling by cAMP is organized in multiple distinct subcellular nanodomains regulated by cAMP-hydrolyzing PDEs (phosphodiesterases). Cardiac β-adrenergic signaling has served as the prototypical system to elucidate cAMP compartmentalization. Although studies in cardiac myocytes have provided an understanding of the location and properties of a handful of cAMP subcellular compartments, an overall view of the cellular landscape of cAMP nanodomains is missing.

METHODS

Here, we combined an integrated phosphoproteomics approach that takes advantage of the unique role that individual PDEs play in the control of local cAMP, with network analysis to identify previously unrecognized cAMP nanodomains associated with β-adrenergic stimulation. We then validated the composition and function of one of these nanodomains using biochemical, pharmacological, and genetic approaches and cardiac myocytes from both rodents and humans.

RESULTS

We demonstrate the validity of the integrated phosphoproteomic strategy to pinpoint the location and provide critical cues to determine the function of previously unknown cAMP nanodomains. We characterize in detail one such compartment and demonstrate that the PDE3A2 isoform operates in a nuclear nanodomain that involves SMAD4 (SMAD family member 4) and HDAC-1 (histone deacetylase 1). Inhibition of PDE3 results in increased HDAC-1 phosphorylation, leading to inhibition of its deacetylase activity, derepression of gene transcription, and cardiac myocyte hypertrophic growth.

CONCLUSIONS

We developed a strategy for detailed mapping of subcellular PDE-specific cAMP nanodomains. Our findings reveal a mechanism that explains the negative long-term clinical outcome observed in patients with heart failure treated with PDE3 inhibitors.

Embracing Heterogeneity in The Multicenter Stroke Preclinical Assessment Network (SPAN) Trial

The Stroke Preclinical Assessment Network (SPAN) is a multicenter preclinical trial platform using rodent models of transient focal cerebral ischemia to address translational failure in experimental stroke. In addition to centralized randomization and blinding and large samples, SPAN aimed to introduce heterogeneity to simulate the heterogeneity embodied in clinical trials for robust conclusions. Here, we report the heterogeneity introduced by allowing the 6 SPAN laboratories to vary most of the biological and experimental model variables and the impact of this heterogeneity on middle cerebral artery occlusion (MCAo) performance. We included the modified intention-to-treat population of the control mouse cohort of the first SPAN trial (n=421) and examined the biological and procedural independent variables and their covariance. We then determined their impact on the dependent variables cerebral blood flow drop during MCAo, time to achieve MCAo, and total anesthesia duration using multivariable analyses. We found heterogeneity in biological and procedural independent variables introduced mainly by the site. Consequently, all dependent variables also showed heterogeneity among the sites. Multivariable analyses with the site as a random effect variable revealed filament choice as an independent predictor of cerebral blood flow drop after MCAo. Comorbidity, sex, use of laser Doppler flow to monitor cerebral blood flow, days after trial onset, and maintaining anesthesia throughout the MCAo emerged as independent predictors of time to MCAo. Total anesthesia duration was predicted by most independent variables. We present with high granularity the heterogeneity introduced by the biological and model selections by the testing sites in the first trial of cerebroprotection in rodent transient filament MCAo by SPAN. Rather than trying to homogenize all variables across all sites, we embraced the heterogeneity to better approximate clinical trials. Awareness of the heterogeneity, its sources, and how it impacts the study performance may further improve the study design and statistical modeling for future multicenter preclinical trials.

Leishmaniosis in Rodents Caused by Leishmania infantum: A Review of Studies in the Mediterranean Area

Leishmaniosis infection begins when a phlebotomine sand fly vector inoculates pathogenic protozoan parasites of the genus Leishmania into a mammalian host. In the case of Leishmania infantum, the domestic dog is considered to be the main parasite reservoir, and canine leishmaniosis (CanL) has a high mortality rate in untreated dogs. Hundreds of cases of human leishmaniosis (HL) are reported in the world each year, the incidence in Europe being relatively low. Leishmaniosis control is primarily focused on the dog, combining methods that prevent sand fly bites and boost host resistance to infection. However, these measures are only partially effective and new solutions need to be found. One of the main factors limiting CanL and HL control is the existence of a sylvatic Leishmania transmission cycle that interacts with the domestic cycle maintained by dogs. It is suspected that the main reservoir of infection in wildlife are rodents, whose expansion and rapid population growth worldwide is increasing the risk of human and zoonotic pathogen transfer. The aim of this review is therefore to analyze reports in the literature that may shed light on the potential role of rodents in the leishmaniosis transmission cycle in the Mediterranean area. Following the general methodology recommended for reviews, six databases (Google Scholar, Ovid, PubMed, Science Direct, Scopus and Web of Science) were explored for the period January 1995 to December 2020. The results extracted from 39 publications that met the established inclusion criteria were analyzed. It was found that 23 species of rodents have been studied in nine countries of the Mediterranean basin. Of the 3,643 specimens studied, 302 tested positive for L. infantum infection by serology, microscopy and/or molecular techniques.

Molecular Survey and Genetic Diversity of Hemoplasmas in Rodents from Chile

Even though hemotrophic mycoplasma (hemoplasma) infections are well documented in a wide variety of hosts worldwide, there is a gap in the knowledge aobut hemoplasmas in rodents. This study aimed to molecularly survey and investigate the genetic diversity of hemoplasmas in rodents from Chile. Synanthropic and wild rodents (n = 74) were captured in the southern province of Valdivia (Corral, Valdivia, Riñihue, and Reumén localities). Spleen samples were submitted to a conventional PCR for hemotrophic Mycoplasma spp. targeting the 16S rRNA gene (800 bp), followed by sequencing, phylogenetic, and genetic diversity analyses. The overall occurrence of hemotrophic mycoplasmas in rodents from Valdivia was 24.5% (18/74) [95% CI (14.5; 34.1)]. Hemoplasmas were detected in Mus musculus (1/4), Rattus norvegicus (1/16), Abrothrix longipilis (7/13), A. olivaceo (6/8), and Oligoryzomys longicaudatus (3/10). The nucleotide polymorphism analysis of the targeted 16S rRNA region showed low diversity, with two genotypes and a high identity to the variants detected in wild rodents from Brazil. Hemoplasmas are described for the first time in rodents from Chile with a moderate occurrence and low 16S rDNA genetic diversity within the sampled rodent population. The detected hemoplasma genotypes were specific to rodents and were not shared with other mammals.

Blowing up Neural Repair for Stroke Recovery: Preclinical and Clinical Trial Considerations

The repair and recovery of the brain after stroke is a field that is emerging in its preclinical science and clinical trials. However, recent large, multicenter clinical trials have been negative, and conflicting results emerge on biological targets in preclinical studies. The coalescence of negative clinical translation and confusion in preclinical studies raises the suggestion that perhaps the field of stroke recovery faces a fate similar to stroke neuroprotection, with interesting science ultimately proving difficult to translate to the clinic. This review highlights improvements in 4 areas of the stroke neural repair field that should reorient the field toward successful clinical translation: improvements in rodent genetic models of stroke recovery, consideration of the biological target in stroke recovery, stratification in clinical trials, and the use of appropriate clinical trial end points.

HIMF (Hypoxia-Induced Mitogenic Factor) Signaling Mediates the HMGB1 (High Mobility Group Box 1)-Dependent Endothelial and Smooth Muscle Cell Crosstalk in Pulmonary Hypertension

OBJECTIVE

HIMF (hypoxia-induced mitogenic factor; also known as FIZZ1 [found in inflammatory zone-1] or RELM [resistin-like molecule-α]) is an etiological factor of pulmonary hypertension (PH) in rodents, but its underlying mechanism is unclear. We investigated the immunomodulatory properties of HIMF signaling in PH pathogenesis. Approach and Results: Gene-modified mice that lacked HIMF (KO [knockout]) or overexpressed HIMF human homolog resistin (hResistin) were used for in vivo experiments. The pro-PH role of HIMF was verified in HIMF-KO mice exposed to chronic hypoxia or sugen/hypoxia. Mechanistically, HIMF/hResistin activation triggered the HMGB1 (high mobility group box 1) pathway and RAGE (receptor for advanced glycation end products) in pulmonary endothelial cells (ECs) of hypoxic mouse lungs in vivo and in human pulmonary microvascular ECs in vitro. Treatment with conditioned medium from hResistin-stimulated human pulmonary microvascular ECs induced an autophagic response, BMPR2 (bone morphogenetic protein receptor 2) defects, and subsequent apoptosis-resistant proliferation in human pulmonary artery (vascular) smooth muscle cells in an HMGB1-dependent manner. These effects were confirmed in ECs and smooth muscle cells isolated from pulmonary arteries of patients with idiopathic PH. HIMF/HMGB1/RAGE-mediated autophagy and BMPR2 impairment were also observed in pulmonary artery (vascular) smooth muscle cells of hypoxic mice, effects perhaps related to FoxO1 (forkhead box O1) dampening by HIMF. Experiments in EC-specific hResistin-overexpressing transgenic mice confirmed that EC-derived HMGB1 mediated the hResistin-driven pulmonary vascular remodeling and PH.

CONCLUSIONS

In HIMF-induced PH, HMGB1-RAGE signaling is pivotal for mediating EC-smooth muscle cell crosstalk. The humanized mouse data further support clinical implications for the HIMF/HMGB1 signaling axis and indicate that hResistin and its downstream pathway may constitute targets for the development of novel anti-PH therapeutics in humans.

Standards and Methodological Rigor in Pulmonary Arterial Hypertension Preclinical and Translational Research

Despite advances in our understanding of the pathophysiology and the management of pulmonary arterial hypertension (PAH), significant therapeutic gaps remain for this devastating disease. Yet, few innovative therapies beyond the traditional pathways of endothelial dysfunction have reached clinical trial phases in PAH. Although there are inherent limitations of the currently available models of PAH, the leaky pipeline of innovative therapies relates, in part, to flawed preclinical research methodology, including lack of rigour in trial design, incomplete invasive hemodynamic assessment, and lack of careful translational studies that replicate randomized controlled trials in humans with attention to adverse effects and benefits. Rigorous methodology should include the use of prespecified eligibility criteria, sample sizes that permit valid statistical analysis, randomization, blinded assessment of standardized outcomes, and transparent reporting of results. Better design and implementation of preclinical studies can minimize inherent flaws in the models of PAH, reduce the risk of bias, and enhance external validity and our ability to distinguish truly promising therapies form many false-positive or overstated leads. Ideally, preclinical studies should use advanced imaging, study several preclinical pulmonary hypertension models, or correlate rodent and human findings and consider the fate of the right ventricle, which is the major determinant of prognosis in human PAH. Although these principles are widely endorsed, empirical evidence suggests that such rigor is often lacking in pulmonary hypertension preclinical research. The present article discusses the pitfalls in the design of preclinical pulmonary hypertension trials and discusses opportunities to create preclinical trials with improved predictive value in guiding early-phase drug development in patients with PAH, which will need support not only from researchers, peer reviewers, and editors but also from academic institutions, funding agencies, and animal ethics authorities.

Comparing the Superficial Vasculature of the Central Nervous System in Six Laboratory Animals: A Hypothesis About the Role of the "Circle of Willis"

We provide images of the entire central nervous system vasculature, and compare the anatomical findings in six different laboratory animals. A detailed understanding of the specific anatomy for each is important in the design of experimental modeling and for understanding the specific function of each target organ. Six different types of animals, the Korean wild mouse, C57BL/6J mouse, F344 rat, mongolian gerbil, Syrian hamsters, and guinea pigs, were included. To stain the blood vessels in each of the animals, Alcian blue reagent was used to perfuse each species. The bifurcation and anastomotic patterns of the anterior cerebral arteries differed in each species. The vascular supply to the olfactory nerve was visualized as a single artery supplying both olfactory nerves, and arteries supplying the lateral portion of the olfactory nerves originating from the olfactory bulb area. The posterior communicating arteries of the six animals demonstrated unique morphologies. The shape of the hypophyseal portal system varied by species. Most animals used in this study had a hexagonal Circle of Willis, except for the Korean wild mouse. Using this approach, we successfully mapped the brain vascular system in six different species of animals. This information and the images created can guide other researchers as they design research studies and create experimental models for new surgical procedures and approaches. Anat Rec, 2019. © 2019 Wiley Periodicals, Inc. Anat Rec, 302:2049-2061, 2019. © 2019 American Association for Anatomy.

Molecular Survey of Tularemia and Plague in Small Mammals From Iran

Introduction: Plague and tularemia are zoonoses and their causative bacteria are circulating in certain regions of Iran. This study was conducted to investigate potential disease reservoirs amongst small wildlife species in different regions of Iran.

Methods: Rodents, insectivores and hares from 17 different provinces of the country were collected in 2014 and 2015. Samples were taken from the spleens of the animals and Real-time PCR was applied to detect nucleic acid sequences that are specific to Francisella tularensis and Yersinia pestis, respectively.

Results: Among 140 collected rodents, 25 distinct species were identified out of which five were the most common: Microtus paradoxus (21% out of 140 rodents), Apodemus witherbyi (12%), Microtus irani (11%), Mus musculus (11%) and Microtus socialis (10%). Seventeen insectivores were collected and identified as Crocidura suaveolens (82%) and C. leucodon (18%). Fifty-one hares were collected and identified as Lepus europaeus (57%), Lepus tolai (14%) and Lepus sp. (29%). Three out of 140 explored rodents (1.91%) were positive for F. tularensis, an A. witherbyi, a Mus musculus domesticus, and a Chionomys nivalis collected from Golestan, Khuzestan and Razavi Khorasan provinces, respectively. Two hares (3.92%) were F. tularensis-positive, a L. europaeus from Khuzestan and a Lepus sp. from the Sistan and Baluchistan province. None of the tested animals were positive for Y. pestis.

Conclusion: This is the first report of direct detection of F. tularensis in mammals of Iran and the first-time observation of the agent in a snow vole, C. nivalis worldwide. The results indicate that tularemia is more widespread in Iran than previously reported including the Northeast and Southwestern parts of the country. Future studies should address genetic characterization of F. tularensis positive DNA samples from Iran to achieve molecular subtyping and rule out assay cross-reactivity with near neighbor Francisella species.

Comparing the Organs and Vasculature of the Head and Neck in Five Murine Species

BACKGROUND/AIM

The purpose of the present study was to delineate the cervical and facial vascular and associated anatomy in five murine species, and compare them for optimal use in research studies focused on understanding the pathology and treatment of diseases in humans.

MATERIALS AND METHODS

The specific adult male animals examined were mice (C57BL/6J), rats (F344), mongolian gerbils (Merionesunguiculatus), hamsters (Syrian), and guinea pigs (Hartley). To stain the vasculature and organs, of the face and neck, each animal was systemically perfused using the vital stain, Trypan Blue. Following this step, the detailed anatomy of the head and neck could be easily visualized in all species.

RESULTS

Unique morphological characteristics were demonstrated by comparing the five species, including symmetry of the common carotid origin bilaterally in the Mongolian Gerbil, a large submandibular gland in the hamster and an enlarged buccal branch in the Guinea Pig. In reviewing the anatomical details, this staining technique proves superior for direct surgical visualization and identification.

CONCLUSION

The anatomical details provided through these five species atlas will help experimental researchers in the future to select the most appropriate animal model for specific laboratory studies aimed to improve our understanding and treatment of diseases in patients.

Complete mitochondrial genomes of the Laotian Rock Rat (Laonastes aenigmamus) confirm deep divergence within the species

Mitochondrial genomes of five Laotian Rock Rat (Laonastes aenigmamus) samples from Vietnam and Laos were sequenced using an Illumina platform. After de novo assembly, 13 protein-coding genes and two rRNA (12S and 16S) of the five genomes were aligned and analyzed with those from other related species under maximum likelihood and Bayesian inferences. Both methods revealed congruent tree topologies, which support two independently evolving clades of L. aenigmamus from Laos and Vietnam. The relaxed time calibration analysis showed that the two major lineages of the Laotian Rock Rat split about 8 million years ago, which was consistent with the results from previous studies using only cytochrome b sequences. Such a deep divergence time suggests the recognition of two rock rat species, but further nuclear DNA and morphological data are needed to solve the taxonomy of this taxon.

Selective Sphingosine 1-Phosphate Receptor 1 Agonist Is Protective Against Ischemia/Reperfusion in Mice

BACKGROUND AND PURPOSE

Growing evidence supports that the immunomodulatory drug fingolimod is protective in stroke. Fingolimod binds to 4 of 5 sphingosine-1-phosphate (S1P) receptors and, among other actions, it induces lymphopenia. In this study, we investigated whether a selective S1P1 agonist is protective in experimental stroke.

METHODS

Drug selectivity was studied in vitro in cells overexpressing the human S1P receptors. Mice (n=54) received different doses of LASW1238 (3 or 10 mg/kg), fingolimod (1 mg/kg), or the vehicle intraperitoneal, and lymphopenia was studied at different time points. After intraluminal middle cerebral artery occlusion for 45 minutes and immediately after reperfusion, mice (n=56) received the drug treatment. At 24 hours, a neurological test was performed and infarct volume was measured. Treatment and all the analyses were performed in a blind fashion.

RESULTS

In vitro functional assays showed that LASW1238 is a selective agonist of the S1P1 receptor. At 10 mg/kg, this compound induced sustained lymphopenia in mice comparable with fingolimod, whereas at 3 mg/kg it induced short-lasting lymphopenia. After ischemia, both LASW1238 (10 mg/kg) and fingolimod reduced infarct volume, but only LASW1238 (10 mg/kg) showed statistically significant differences versus the vehicle. The neurological function and plasma cytokine levels were not different between groups.

CONCLUSIONS

The selective S1P1 agonist LASW1238 reduces infarct volume after ischemia/reperfusion in mice, but only when lymphopenia is sustained for at least 24 hours. S1P1 and lymphocytes are potential targets for drug treatment in stroke. Defining the best drug dosing regimens to control the extent and duration of lymphopenia is critical to achieve the desired effects.

A Review of Applied Aspects of Dealing with Gut Microbiota Impact on Rodent Models

The gut microbiota (GM) affects numerous human diseases, as well as rodent models for these. We will review this impact and summarize ways to handle this challenge in animal research. The GM is complex, with the largest fractions being the gram-positive phylum Firmicutes and the gram-negative phylum Bacteroidetes. Other important phyla are the gram-negative phyla Proteobacteria and Verrucomicrobia, and the gram-positive phylum Actinobacteria. GM members influence models for diseases, such as inflammatory bowel diseases, allergies, autoimmunity, cancer, and neuropsychiatric diseases. GM characterization of all individual animals and incorporation of their GM composition in data evaluation may therefore be considered in future protocols. Germfree isolator-housed rodents or rodents made virtually germ free by antibiotic cocktails can be used to study diverse microbial influences on disease expression. Through subsequent inoculation with selected strains or cocktails of microbes, new "defined flora" models can yield valuable knowledge on the impact of the GM, and of specific GM members and their interactions, on important disease phenotypes and mechanisms. Rodent husbandry and microbial quality assurance practices will be important to ensure and confirm appropriate and research relevant GM.

Serologic evidence for Borrelia hermsii infection in rodents on federally owned recreational areas in California

Tick-borne relapsing fever (TBRF) is endemic in mountainous regions of the western United States. In California, the principal agent is the spirochete Borrelia hermsii, which is transmitted by the argasid tick Ornithodoros hermsi. Humans are at risk of TBRF when infected ticks leave an abandoned rodent nest in quest of a blood meal. Rodents are the primary vertebrate hosts for B. hermsii. Sciurid rodents were collected from 23 sites in California between August, 2006, and September, 2008, and tested for serum antibodies to B. hermsii by immunoblot using a whole-cell sonicate and a specific antigen, glycerophosphodiester phosphodiesterase (GlpQ). Antibodies were detected in 20% of rodents; seroprevalence was highest (36%) in chipmunks (Tamias spp). Seroprevalence in chipmunks was highest in the Sierra Nevada (41%) and Mono (43%) ecoregions and between 1900 and 2300 meters elevation (43%). The serological studies described here are effective in implicating the primary vertebrate hosts involved in the maintenance of the ticks and spirochetes in regions endemic for TBRF.

Immune reconstitution and graft-versus-host reactions in rat models of allogeneic hematopoietic cell transplantation

Allogeneic hematopoietic cell transplantation (alloHCT) extends the lives of thousands of patients who would otherwise succumb to hematopoietic malignancies such as leukemias and lymphomas, aplastic anemia, and disorders of the immune system. In alloHCT, different immune cell types mediate beneficial graft-versus-tumor (GvT) effects, regulate detrimental graft-versus-host disease (GvHD), and are required for protection against infections. Today, the “good” (GvT effector cells and memory cells conferring protection) cannot be easily separated from the “bad” (GvHD-causing cells), and alloHCT remains a hazardous medical modality. The transplantation of hematopoietic stem cells into an immunosuppressed patient creates a delicate environment for the reconstitution of donor blood and immune cells in co-existence with host cells. Immunological reconstitution determines to a large extent the immune status of the allo-transplanted host against infections and the recurrence of cancer, and is critical for long-term protection and survival after clinical alloHCT. Animal models continue to be extremely valuable experimental tools that widen our understanding of, for example, the dynamics of post-transplant hematopoiesis and the complexity of immune reconstitution with multiple ways of interaction between host and donor cells. In this review, we discuss the rat as an experimental model of HCT between allogeneic individuals. We summarize our findings on lymphocyte reconstitution in transplanted rats and illustrate the disease pathology of this particular model. We also introduce the rat skin explant assay, a feasible alternative to in vivo transplantation studies. The skin explant assay can be used to elucidate the biology of graft-versus-host reactions, which are known to have a major impact on immune reconstitution, and to perform genome-wide gene expression studies using controlled combinations of minor and major histocompatibility between the donor and the recipient.

Chromosomal evolution in Rodentia

Rodentia is the most species-rich mammalian order and includes several important laboratory model species. The amount of new information on karyotypic and phylogenetic relations within and among rodent taxa is rapidly increasing, but a synthesis of these data is currently lacking. Here, we have integrated information drawn from conventional banding studies, recent comparative painting investigations and molecular phylogenetic reconstructions of different rodent taxa. This permitted a revision of several ancestral karyotypic reconstructions, and a more accurate depiction of rodent chromosomal evolution.

Using ecology to guide the study of cognitive and neural mechanisms of different aspects of spatial memory in food-hoarding animals

Understanding the survival value of behaviour does not tell us how the mechanisms that control this behaviour work. Nevertheless, understanding survival value can guide the study of these mechanisms. In this paper, we apply this principle to understanding the cognitive mechanisms that support cache retrieval in scatter-hoarding animals. We believe it is too simplistic to predict that all scatter-hoarding animals will outperform non-hoarding animals on all tests of spatial memory. Instead, we argue that we should look at the detailed ecology and natural history of each species. This understanding of natural history then allows us to make predictions about which aspects of spatial memory should be better in which species. We use the natural hoarding behaviour of the three best-studied groups of scatter-hoarding animals to make predictions about three aspects of their spatial memory: duration, capacity and spatial resolution, and we test these predictions against the existing literature. Having laid out how ecology and natural history can be used to predict detailed cognitive abilities, we then suggest using this approach to guide the study of the neural basis of these abilities. We believe that this complementary approach will reveal aspects of memory processing that would otherwise be difficult to discover.

Granulated metrial gland cells and interstitial trophoblast in the uterine wall of the bank vole, Clethrionomys glareolus, in early pregnancy

The morphology and distribution of granulated metrial gland cells and of interstitial trophoblast cells in the uterine wall was studied in the first half of pregnancy in the bank vole, Clethrionomys glareolus. The morphology and distribution of granulated metrial gland cells was generally similar to that found in other members of the Rodentia, although they were absent from the walls of the arterial vessels passing through the decidua basalis. Interstitial trophoblast invaded the decidualising endometrium mesometrial to, and antimesometrial to, the implanted embryos. There was no apparent spatiotemporal relationship between the distribution of granulated metrial gland cells and interstitial trophoblast cells.