Widespread but tissue-specific patterns of interferon-induced transmembrane protein 3 (IFITM3, FRAGILIS, MIL-1) in the mouse gastrula

The mouse allantois: new insights at the embryonic-extraembryonic interface

During the early development of Placentalia, a distinctive projection emerges at the posterior embryonic-extraembryonic interface of the conceptus; its fingerlike shape presages maturation into the placental umbilical cord, whose major role is to shuttle fetal blood to and from the chorion for exchange with the mother during pregnancy. Until recently, the biology of the cord's vital vascular anlage, called the body stalk/allantois in humans and simply the allantois in rodents, has been largely unknown. Here, new insights into the development of the mouse allantois are featured, from its origin and mechanism of arterial patterning through its union with the chorion. Key to generating the allantois and its critical functions are the primitive streak and visceral endoderm, which together are sufficient to create the entire fetal-placental connection. Their newly discovered roles at the embryonic-extraembryonic interface challenge conventional wisdom, including the physical limits of the primitive streak, its function as sole purveyor of mesoderm in the mouse, potency of visceral endoderm, and the putative role of the allantois in the germ line. With this working model of allantois development, understanding a plethora of hitherto poorly understood orphan diseases in humans is now within reach. This article is part of the theme issue 'Extraembryonic tissues: exploring concepts, definitions and functions across the animal kingdom'.

Interferon-Induced Transmembrane Protein 3 Expression Upregulation Is Involved in Progression of Hepatocellular Carcinoma

Purpose

Interferon-induced transmembrane protein 3 (IFITM3) is a key signaling molecule regulating cell growth in some tumors, but its function and mechanism in hepatocellular carcinoma (HCC) remain unknown. Our study investigated the relationship between the expression of IFITM3 and HCC development. Material and Methods. IFITM3 expression was identified via multiple gene expression databases and investigated in HCC tissue samples. Then, PLC/PRF/5 cells were transfected with lentivirus to knock down and overexpress the expression of IFITM3. IFITM3 expression, cell proliferation, and migration were detected by qRT-PCR, western blotting, QuantiGene Plex 2.0 assay, immunohistochemistry, CCK-8, and wound healing tests. RNA-seq technology identified the PI3K/AKT/mTOR pathway as an IFITM3-related signaling pathway for investigation.

Results

IFITM3 expression was higher in HCC tissues than in adjacent normal tissues, and the level of IFITM3 was higher in HCC tissues with low differentiation and metastatic potential than in those with high/medium differentiation and without metastatic potential. A higher RNA level of IFITM3 was found in samples with IFITM3 rs12252-CC genotype rather than the TT genotype. Knockdown of IFITM3 in PLC/PRF/5 cells inhibited cell proliferation and migration, blocked the expression of the PI3K/AKT/mTOR signaling pathway, and decreased the expression of vimentin. The results were opposite with the overexpression of IFITM3.

Conclusion

Upregulation of IFITM3 plays a role in the development of HCC. Possibly through regulating HCC cell proliferation and migration, these effects are associated with the PI3K/AKT/mTOR signaling pathway. Upregulation of IFITM3 is also associated with the IFITM3 rs12252-CC genotype.

EVs Containing Host Restriction Factor IFITM3 Inhibited ZIKV Infection of Fetuses in Pregnant Mice through Trans-placenta Delivery

Zika virus (ZIKV) infection can lead to neurological complications and fetal defects, and it has attracted global public health concerns. Effective treatment for ZIKV infection remains elusive, and a preventative vaccine is not yet available. Therapeutics for fetuses need to overcome placenta barriers to reach the fetuses and require higher safety standards. In the present study, we engineered mammalian extracellular vesicles (EVs) to deliver a host restriction factor, interferon-induced transmembrane protein 3 (IFITM3), for the treatment of ZIKV infection. Our results demonstrated that the IFITM3-containing EVs (IFITM3-Exos) suppressed ZIKV viremia by a 2-log reduction in pregnant mice. Moreover, the engineered EVs effectively delivered IFITM3 protein across the placental barrier and suppressed ZIKV in the fetuses with significant reduction of viremia in key fetal organs as measured by quantitative real-time PCR. Mechanistic study showed that IFITM3 was delivered to late endosomes/lysosomes where it inhibited viral entry into the host cells. Our study demonstrated that EVs could act as a cross-placenta drug delivery vehicle to the fetus, and IFITM3, an endogenous restriction factor, is a potential treatment for ZIKV infection during pregnancy.

Malignancy and IFITM3: Friend or Foe?

The prevalence and incidence of cancers has risen over the last decade. Available treatments have improved outcomes, yet mortality and morbidity remain high, creating an urgent demand for personalized and new therapy targets. Interferon induced transmembrane protein (IFITM3) is highly expressed in cancers and is a marker of poor prognosis. In this review, we discuss recent advances in IFITM3 biology, the regulatory pathways, and its function within cancer as part of immunity and maintaining stemness. Overexpression of IFITM3 is likely an indirect effect of ongoing inflammation, immune and cancer epithelial-to-mesenchymal (EMT) related pathways i.e., interferons, TGF-β, WNT/β-catenin, etc. However, IFITM3 also influences tumorigenic phenotypes, such as cell proliferation, migration and invasion. Furthermore, IFITM3 plays a key role in cancer growth and maintenance. Silencing of IFITM3 reduces these phenotypes. Therefore, targeting of IFITM3 will likely have implications for potential cancer therapies.

Is extra-embryonic endoderm a source of placental blood cells?

The extra-embryonic hypoblast/visceral endoderm of Placentalia carries out a variety of functions during gestation, including hematopoietic induction. Results of decades-old and recent experiments have provided compelling evidence that, in addition to its inducing properties, hypoblast/visceral endoderm itself is a source of placental blood cells. Those observations that highlight extra-embryonic endoderm's role as an overlooked source of placental blood cells across species are briefly discussed here, with suggestions for future exploration.

Characterization of migratory primordial germ cells in the aorta-gonad-mesonephros of a 4.5-week-old human embryo: a toolbox to evaluate in vitro early gametogenesis

STUDY QUESTION

Which set of antibodies can be used to identify migratory and early post-migratory human primordial germ cells (hPGCs)?

STUDY FINDING

We validated the specificity of 33 antibodies for 31 markers, including POU5F1, NANOG, PRDM1 and TFAP2C as specific markers of hPGCs at 4.5 weeks of development of Carnegie stage (CS12–13), whereas KIT and SOX17 also marked the intra-aortic hematopoietic stem cell cluster in the aorta-gonad-mesonephros (AGM).

WHAT IS KNOWN ALREADY

The dynamics of gene expression during germ cell development in mice is well characterized and this knowledge has proved crucial to allow the development of protocols for the in vitro derivation of functional gametes. Although there is a great interest in generating human gametes in vitro, it is still unclear which markers are expressed during the early stages of hPGC development and many studies use markers described in mouse to benchmark differentiation of human PGC-like cells (hPGCLCs). Early post-implantation development differs significantly between mice and humans, and so some germ cells markers, including SOX2, SOX17, IFITM3 and ITGA6 may not identify mPGCs and hPGCs equally well.

STUDY DESIGN, SIZE, DURATION

This immunofluorescence study investigated the expression of putative hPGC markers in the caudal part of a single human embryo at 4.5 weeks of development.

PARTICIPANTS/MATERIALS, SETTING, METHODS

We have investigated by immunofluorescence the expression of a set of 33 antibodies for 31 markers, including pluripotency, germ cell, adhesion, migration, surface, mesenchymal and epigenetic markers on paraffin sections of the caudal part, including the AGM region, of a single human embryo (CS12–13). The human material used was anonymously donated with informed consent from elective abortions without medical indication.

MAIN RESULTS AND THE ROLE OF CHANCE

We observed germ cell specific expression of NANOG, TFAP2C and PRDM1 in POU5F1+ hPGCs in the AGM. The epigenetic markers H3K27me3 and 5mC were sufficient to distinguish hPGCs from the surrounding somatic cells. Some mPGC-markers were not detected in hPGCs, but marked other tissues; whereas other markers, such as ALPL, SOX17, KIT, TUBB3, ITGA6 marked both POU5F1+ hPGCs and other cells in the AGM. We used a combination of multiple markers, immunostaining different cellular compartments when feasible, to decrease the chance of misidentifying hPGCs.

LARGE SCALE DATA

Non-applicable.

LIMITATIONS REASONS FOR CAUTION

Material to study early human development is unique and very rare thus restricting the sample size. We have used a combination of antibodies limited by the number of paraffin sections available.

WIDER IMPLICATIONS OF THE FINDINGS

Most of our knowledge on early gametogenesis has been obtained from model organisms such as mice and is extrapolated to humans. However, since there is a dedicated effort to produce human artificial gametes in vitro, it is of great importance to determine the expression and specificity of human-specific germ cell markers. We provide a systematic analysis of the expression of 31 different markers in paraffin sections of a CS12–13 embryo. Our results will help to set up a toolbox of markers to evaluate protocols to induce hPGCLCs in vitro.

STUDY FUNDING AND COMPETING INTEREST(S)

M.G.F. was funded by Fundação para a Ciência e Tecnologia (FCT) [SFRH/BD/78689/2011] and S.M.C.S.L. was funded by the Interuniversity Attraction Poles (IAP, P7/07) and the European Research Council Consolidator (ERC-CoG-725722-OVOGROWTH). The authors declare no conflict of interest.

Interferon-induced transmembrane protein-3 rs12252-CC is associated with low differentiation and progression of hepatocellular carcinoma

Interferon-induced transmembrane protein 3 (IFITM3) is a component of ISG (Interferon-Stimulated Gene) family. The association between IFITM3 and hepatocellular carcinoma (HCC) has been reported. While the relationship between this genetic variation and the progress of HCC remains unclear. To address this issue, we explore the relationship between the IFITM3-rs12252 genetic variants and the progression of HCC in this study.A total of 336 candidates were enrolled in the study, including 156 patients with HBV related HCC and 180 patients with chronic Hepatitis B infections or liver cirrhosis. Liver cirrhosis or chronic hepatitis B were diagnosed with clinical characteristics and staging, laboratory testing, and imaging results of viral infection and hepatic damage. Polymerase chain reaction (PCR) was employed to determine the gene polymorphism of IFITM3, and analyzed with the GraphPad Prism v 5.The patients with HCC had a significantly higher proportion of IFITM3 rs12252-CC as compared with the patients with chronic HBV infection or liver cirrhosis. Moreover, the distribution of CC genotype in HCC patients with low differentiation was significantly higher than that in those with high differentiation. Furthermore, the patients with CC genotype were found with bigger tumor size, higher percentage of vascular thrombosis, higher distribution of low differentiation and higher 5-year relapse rate than those with CT/TT genotypes.This study indicates a correlation between the IFITM3-rs12252 CC genotype and the progression of HCC.

Visceral endoderm and the primitive streak interact to build the fetal-placental interface of the mouse gastrula

Hypoblast/visceral endoderm assists in amniote nutrition, axial positioning and formation of the gut. Here, we provide evidence, currently limited to humans and non-human primates, that hypoblast is a purveyor of extraembryonic mesoderm in the mouse gastrula. Fate mapping a unique segment of axial extraembryonic visceral endoderm associated with the allantoic component of the primitive streak, and referred to as the "AX", revealed that visceral endoderm supplies the placentae with extraembryonic mesoderm. Exfoliation of the AX was dependent upon contact with the primitive streak, which modulated Hedgehog signaling. Resolution of the AX's epithelial-to-mesenchymal transition (EMT) by Hedgehog shaped the allantois into its characteristic projectile and individualized placental arterial vessels. A unique border cell separated the delaminating AX from the yolk sac blood islands which, situated beyond the limit of the streak, were not formed by an EMT. Over time, the AX became the hindgut lip, which contributed extensively to the posterior interface, including both embryonic and extraembryonic tissues. The AX, in turn, imparted antero-posterior (A-P) polarity on the primitive streak and promoted its elongation and differentiation into definitive endoderm. Results of heterotopic grafting supported mutually interactive functions of the AX and primitive streak, showing that together, they self-organized into a complete version of the fetal-placental interface, forming an elongated structure that exhibited A-P polarity and was composed of the allantois, an AX-derived rod-like axial extension reminiscent of the embryonic notochord, the placental arterial vasculature and visceral endoderm/hindgut.

STELLA collaborates in distinct mesendodermal cell subpopulations at the fetal-placental interface in the mouse gastrula

The allantois-derived umbilical component of the chorio-allantoic placenta shuttles fetal blood to and from the chorion, thereby ensuring fetal-maternal exchange. The progenitor populations that establish and supply the fetal-umbilical interface lie, in part, within the base of the allantois, where the germ line is claimed to segregate from the soma. Results of recent studies in the mouse have reported that STELLA (DPPA-3, PGC7) co-localizes with PRDM1 (BLIMP1), the bimolecular signature of putative primordial germ cells (PGCs) throughout the fetal-placental interface. Thus, if PGCs form extragonadally within the posterior region of the mammal, they cannot be distinguished from the soma on the basis of these proteins. We used immunohistochemistry, immunofluorescence, and confocal microscopy of the mouse gastrula to co-localize STELLA with a variety of gene products, including pluripotency factor OCT-3/4, mesendoderm-associated T and MIXl1, mesendoderm- and endoderm-associated FOXa2 and hematopoietic factor Runx1. While a subpopulation of cells localizing OCT-3/4 was always found independently of STELLA, STELLA always co-localized with OCT-3/4. Despite previous reports that T is involved in specification of the germ line, co-localization of STELLA and T was detected only in a small subset of cells in the base of the allantois. Slightly later in the hindgut lip, STELLA+/(OCT-3/4+) co-localized with FOXa2, as well as with RUNX1, indicative of definitive endoderm and hemangioblasts, respectively. STELLA was never found with MIXl1. On the basis of these and previous results, we conclude that STELLA identifies at least five distinct cell subpopulations within the allantois and hindgut, where they may be involved in mesendodermal differentiation and hematopoiesis at the posterior embryonic-extraembryonic interface. These data provide a new point of departure for understanding STELLA's potential roles in building the fetal-placental connection.

Brachyury drives formation of a distinct vascular branchpoint critical for fetal-placental arterial union in the mouse gastrula

How the fetal-placental arterial connection is made and positioned relative to the embryonic body axis, thereby ensuring efficient and directed blood flow to and from the mother during gestation, is not known. Here we use a combination of genetics, timed pharmacological inhibition in living mouse embryos, and three-dimensional modeling to link two novel architectural features that, at present, have no status in embryological atlases. The allantoic core domain (ACD) is the extraembryonic extension of the primitive streak into the allantois, or pre-umbilical tissue; the vessel of confluence (VOC), situated adjacent to the ACD, is an extraembryonic vessel that marks the site of fetal-placental arterial union. We show that genesis of the fetal-placental connection involves the ACD and VOC in a series of steps, each one dependent upon the last. In the first, Brachyury (T) ensures adequate extension of the primitive streak into the allantois, which in turn designates the allantoic-yolk sac junction. Next, the streak-derived ACD organizes allantoic angioblasts to the axial junction; upon signaling from Fibroblast Growth Factor Receptor-1 (FGFR1), these endothelialize and branch, forming a sprouting VOC that unites the umbilical and omphalomesenteric arteries with the fetal dorsal aortae. Arterial union is followed by the appearance of the medial umbilical roots within the VOC, which in turn designate the correct axial placement of the lateral umbilical roots/common iliac arteries. In addition, we show that the ACD and VOC are conserved across Placentalia, including humans, underscoring their fundamental importance in mammalian biology. We conclude that T is required for correct axial positioning of the VOC via the primitive streak/ACD, while FGFR1, through its role in endothelialization and branching, further patterns it. Together, these genetic, molecular and structural elements safeguard the fetus against adverse outcomes that can result from vascular mispatterning of the fetal-placental arterial connection.

PRDM1/BLIMP1 is widely distributed to the nascent fetal-placental interface in the mouse gastrula

BACKGROUND

PRDM1 is a transcriptional repressor that contributes to primordial germ cell (PGC) development. During early gastrulation, epiblast-derived PRDM1 is thought to be restricted to a lineage-segregated germ line in the allantois. However, given recent findings that PGCs overlap an allantoic progenitor pool that contributes widely to the fetal-umbilical interface, posterior PRDM1 may also contribute to soma.

RESULTS

Within the posterior mouse gastrula (early streak, 12-s stages, embryonic days ∼6.75-9.0), PRDM1 localized to all tissues containing putative PGCs; however, PRDM1 was also found in all three primary germ layers, their derivatives, and two presumptive growth centers, the allantoic core domain and ventral ectodermal ridge. While PRDM1 and STELLA colocalized predominantly within the hindgut, where putative PGCs reside, other colocalizing cells were found in non-PGC sites. Additional PRDM1 and STELLA cells were found independent of each other throughout the posterior region, including the hindgut. The Prdm1-Cre-driven reporter supported PRDM1 localization in the majority of sites; however, some Prdm1 descendants were found in sites independent of PRDM1 protein, including allantoic mesothelium and hindgut endoderm.

CONCLUSIONS

Posterior PRDM1 contributes more broadly to the developing fetal-maternal connection than previously recognized, and PRDM1 and STELLA, while overlapping in putative PGCs, also co-localize in several other tissues. Developmental Dynamics 246:50-71, 2017. © 2016 Wiley Periodicals, Inc.

Mouse primordial germ cells: a reappraisal

Current dogma is that mouse primordial germ cells (PGCs) segregate within the allantois, or source of the umbilical cord, and translocate to the gonads, differentiating there into sperm and eggs. In light of emerging data on the posterior embryonic-extraembryonic interface, and the poorly studied but vital fetal-umbilical connection, we have reviewed the past century of experiments on mammalian PGCs and their relation to the allantois. We demonstrate that, despite best efforts and valuable data on the pluripotent state, what is and is not a PGC in vivo is obscure. Furthermore, sufficient experimental evidence has yet to be provided either for an extragonadal origin of mammalian PGCs or for their segregation within the posterior region. Rather, most evidence points to an alternative hypothesis that PGCs in the mouse allantois are part of a stem/progenitor cell pool that exhibits all known PGC "markers" and that builds/reinforces the fetal-umbilical interface, common to amniotes. We conclude by suggesting experiments to distinguish the mammalian germ line from the soma.

Umbilical cord accidents and legal implications

Umbilical cord accidents (UCA) are a significant cause of stillbirth. Although infrequent, litigation may occur when there is a poor outcome associated with UCA. With advances in imaging, the ability to identify UCA by ultrasound and magnetic resonance imaging raises awareness of the risk of a poor outcome. Management of a pregnancy with an identified UCA may require more fetal surveillance by both the mother and caregiver. This is especially important if there is a previous history of UCA with or without stillbirth. UCA should be an acknowledged risk which is part of prenatal screening. In the event of a poor outcome associated with UCA, it is recommended that the patient be fully informed of all prenatal information including images. Excellent communication with parents who are looking for answers after a tragic outcome may help to decrease litigation risk.

Expression profile and histological distribution of IFITM1 and IFITM3 during H9N2 avian influenza virus infection in BALB/c mice

The H9N2 avian influenza virus is a pandemic threat which has repeatedly caused infection in humans and shows enhanced replication and transmission in mice. Previous reports showed that host factors, the interferon-inducible transmembrane (IFITM) protein, can block the replication of pathogens and affect their pathogenesis. BALB/c mice are routine laboratory animals used in influenza virus research, but the effects of H9N2 influenza virus on tissue distribution and expression pattern of IFITM in these mice are unknown. Here, we investigated the expression patterns and tissue distribution of IFITM1 and IFITM3 in BALB/c mice by infection with H9N2 AIV strains with only a PB2 residue 627 difference. The results showed that the expression patterns of ITITM1 and IFITM3 differ in various tissues of BALB/c mice at different time points after infection. IFITM1 and IFITM3 showed cell- and tissue-specific distribution in the lung, heart, liver, spleen, kidney and brain. Notably, the epithelial and neuronal cells all expressed the proteins of IFITM1 and IFITM3. Our results provide the first look at differences in IFITM1 and IFITM3 expression patterns in BALB/c mice infected by H9N2 influenza viruses. This will enhance research on the interaction between AIV and host and further will elucidate the pathogenesis of influenza virus infection based on the interferon-inducible transmembrane (IFITM) protein.

Mixl1 localizes to putative axial stem cell reservoirs and their posterior descendants in the mouse embryo

Mixl1 is thought to play important roles in formation of mesoderm and endoderm. Previously, Mixl1 expression was reported in the posterior primitive streak and allantois, but the precise spatiotemporal whereabouts of Mixl1 protein throughout gastrulation have not been elucidated. To localize Mixl1 protein, immunohistochemistry was carried out at 2-4 h intervals on mouse gastrulae between primitive streak and 16-somite pair (s) stages (~E6.5-9.5). Mixl1 localized to the entire primitive streak early in gastrulation. However, by headfold stages (~E7.75-8.0), Mixl1 diminished within the mid-streak but remained concentrated at either end of the streak, and localized throughout midline posterior visceral endoderm. At the streak's anterior end, Mixl1 was confined to the posterior crown cells of Hensen's node, which contribute to dorsal hindgut endoderm, and the posterior notochord. In the posterior streak, Mixl1 localized to the Allantoic Core Domain (ACD), which is the source of most of the allantois and contributes to the posterior embryonic-extraembryonic interface. In addition, Mix1 co-localized with the early hematopoietic marker, Runx1, in the allantois and visceral yolk sac blood islands. During hindgut invagination (4-16s, ~E8.5-9.5), Mixl1 localized to the hindgut lip, becoming concentrated within the midline anastomosis of the splanchnopleure, which appears to create the ventral component of the hindgut and omphalomesenteric artery. Surrounding the distal hindgut, Mixl1 identified midline cells within tailbud mesoderm. Mixl1 was also found in the posterior notochord. These findings provide a critical systematic, and tissue-level understanding of embryonic Mixl1 localization, and support its role in regulation of crucial posterior axial mesendodermal stem cell niches during embryogenesis.

Defining the neighborhoods that escort the oocyte through its early life events and into a functional follicle

The ovary functions to chaperone the most precious cargo for female individuals, the oocyte, thereby allowing the passage of genetic material to subsequent generations. Within the ovary, single oocytes are surrounded by a legion of granulosa cells inside each follicle. These two cell types depend upon one another to support follicle formation and oocyte survival. The infrastructure and events that work together to ultimately form these functional follicles within the ovary are unprecedented, given that the oocyte originates as a cell like all other neighboring cells within the embryo prior to gastrulation. This review discusses the journey of the germ cell in the context of the developing female mouse embryo, with a focus on specific signaling events and cell-cell interactions that escort the primordial germ cell as it is specified into the germ cell fate, migrates through the hindgut into the gonad, differentiates into an oocyte, and culminates upon formation of the primordial and then primary follicle.