Conditional gene recombination by adenovirus-driven Cre in the mouse uterus

SMAD2/3 signaling in the uterine epithelium controls endometrial cell homeostasis and regeneration

The regenerative potential of the endometrium is attributed to endometrial stem cells; however, the signaling pathways controlling its regenerative potential remain obscure. In this study, genetic mouse models and endometrial organoids are used to demonstrate that SMAD2/3 signaling controls endometrial regeneration and differentiation. Mice with conditional deletion of SMAD2/3 in the uterine epithelium using Lactoferrin-iCre develop endometrial hyperplasia at 12-weeks and metastatic uterine tumors by 9-months of age. Mechanistic studies in endometrial organoids determine that genetic or pharmacological inhibition of SMAD2/3 signaling disrupts organoid morphology, increases the glandular and secretory cell markers, FOXA2 and MUC1, and alters the genome-wide distribution of SMAD4. Transcriptomic profiling of the organoids reveals elevated pathways involved in stem cell regeneration and differentiation such as the bone morphogenetic protein (BMP) and retinoic acid signaling (RA) pathways. Therefore, TGFβ family signaling via SMAD2/3 controls signaling networks which are integral for endometrial cell regeneration and differentiation.

Uterine Prx2 restrains decidual differentiation through inhibiting lipolysis in mice

Uterine decidualization, characterized as extensive stromal cell proliferation, differentiation and polyploidization, is a crucial event for successful pregnancy and is tightly regulated by many different molecules and pathways. Prx2, an evolutionarily conserved homeobox transcription factor expressed in both embryos and adults, plays an important role during mesenchymal cell differentiation. However, it remains unclear what the exact function of Prx2 is in the uterine stromal cells, one type of mesenchymal cells. In the present study, employing in vivo and in vitro stromal cell decidualization models, combining adenovirus-mediated overexpression of Prx2, we found that the expression of Prx2 is initiated in the uterine stromal cells once the blastocyst attached to the epithelium and is always detected around the differentiated decidual zone in the anti-mesometrium of the uterus during post-implantation uterine development. Also, overexpression of Prx2 disturbed stromal-decidual differentiation, which is reflected by the decreased expression of decidual/trophoblast prolactin-related protein (Dtprp), the marker for uterine decidualization in mice. Further, we demonstrate that Prx2 overexpression disturbs lipolysis, leading to lipid droplets accumulation in uterine stromal cells, partially mediated by downregulated expression of adipocyte triglyceride lipase. Collectively, these data indicate that uterine Prx2 restrains uterine decidual differentiation through regulating lipid metabolism.

Generation of brain tumours in mice by Cre-mediated recombination of neural progenitors in situ with the tamoxifen metabolite endoxifen

Targeted cell- or region-specific gene recombination is widely used in the functional analysis of genes implicated in development and disease. In the brain, targeted gene recombination has become a mainstream approach to study neurodegeneration or tumorigenesis. The use of the Cre-loxP system to study tumorigenesis in the adult central nervous system (CNS) can be limited, when the promoter (such as GFAP) is also transiently expressed during development, which can result in the recombination of progenies of different lineages. Engineering of transgenic mice expressing Cre recombinase fused to a mutant of the human oestrogen receptor (ER) allows the circumvention of transient developmental Cre expression by inducing recombination in the adult organism. The recombination of loxP sequences occurs only in the presence of tamoxifen. Systemic administration of tamoxifen can, however, exhibit toxicity and might also recombine unwanted cell populations if the promoter driving Cre expression is active at the time of tamoxifen administration. Here, we report that a single site-specific injection of an active derivative of tamoxifen successfully activates Cre recombinase and selectively recombines tumour suppressor genes in neural progenitor cells of the subventricular zone in mice, and we demonstrate its application in a model for the generation of intrinsic brain tumours.

Development and Characterization of Uterine Glandular Epithelium Specific Androgen Receptor Knockout Mouse Model

While estrogen action is the major driver of uterine development, androgens acting via the androgen receptor (AR) may also promote uterine growth as suggested by uterine phenotypes in global AR knockout (ARKO) female mice. Because AR is expressed in uterine endometrial glands, we generated (Cre/loxP) uterine gland epithelium-specific ARKO (ugeARKO) to determine the role of endometrial gland-specific androgen actions. However, AR in uterine gland epithelium may not be required for normal uterine development and function because ugeARKO females had normal uterine development and fertility. To determine if exogenous androgens acting via AR can fully support uterine growth in the absence of estrogens, the ARKO and ugeARKO females were ovariectomized and treated with supraphysiological doses of testosterone or dihydrotestosterone (nonaromatizable androgen). Both dihydrotestosterone and testosterone supported full uterine regrowth in wild-type females while ARKO females had no regrowth (comparable to ovariectomized only). These findings suggest that androgens acting via AR can promote full uterine regrowth in the absence of estrogens. The ugeARKO had 50% regrowth when compared to intact uterine glands, and histomorphologically, both the endometrial and myometrial areas were significantly (P < 0.05) reduced, suggesting glandular epithelial AR located in the endometrium may indirectly modify myometrial development. Additionally, to confirm Cre function in endometrial glands, we generated uge-specific PTEN knockout mouse model. The ugePTEN knockout females developed severe endometrial hyperplasia and therefore present a novel model for future research.

Endometrial VEGF induces placental sFLT1 and leads to pregnancy complications

There is strong evidence that overproduction of soluble fms-like tyrosine kinase-1 (sFLT1) in the placenta is a major cause of vascular dysfunction in preeclampsia through sFLT1-dependent antagonism of VEGF. However, the cause of placental sFLT1 upregulation is not known. Here we demonstrated that in women with preeclampsia, sFLT1 is upregulated in placental trophoblasts, while VEGF is upregulated in adjacent maternal decidual cells. In response to VEGF, expression of sFlt1 mRNA, but not full-length Flt1 mRNA, increased in cultured murine trophoblast stem cells. We developed a method for transgene expression specifically in mouse endometrium and found that endometrial-specific VEGF overexpression induced placental sFLT1 production and elevated sFLT1 levels in maternal serum. This led to pregnancy losses, placental vascular defects, and preeclampsia-like symptoms, including hypertension, proteinuria, and glomerular endotheliosis in the mother. Knockdown of placental sFlt1 with a trophoblast-specific transgene caused placental vascular changes that were consistent with excess VEGF activity. Moreover, sFlt1 knockdown in VEGF-overexpressing animals enhanced symptoms produced by VEGF overexpression alone. These findings indicate that sFLT1 plays an essential role in maintaining vascular integrity in the placenta by sequestering excess maternal VEGF and suggest that a local increase in VEGF can trigger placental overexpression of sFLT1, potentially contributing to the development of preeclampsia and other pregnancy complications.

Overexpression of cyclin D3 improves decidualization defects in Hoxa-10(-/-) mice

Uterine decidualization, a crucial process for implantation, is a tightly regulated process encompassing proliferation, differentiation, and polyploidization of uterine stromal cells. Hoxa (Homeobox A)-10, a homeobox transcription factor, is highly expressed in decidualizing stromal cells. Targeted gene deletion experiments have demonstrated marked infertility resulting from severely compromised decidualization in Hoxa-10(-/-) mice. However, the underlying mechanism by which Hoxa-10 regulates stromal cell differentiation remains poorly understood. Cyclin D3, a G(1) phase cell-cycle regulatory protein involved in stromal cell proliferation and decidualization, is significantly reduced in Hoxa-10(-/-) mice. The expression of cyclin D3 in the pregnant mouse uterus parallels stromal cell decidualization. Here, we show that adenovirus-driven cyclin D3 replacement in Hoxa-10(-/-) mice improves stromal cell decidualization. To address our question of whether cyclin D3 replacement in Hoxa-10(-/-) mice can improve decidualization, both in vitro and in vivo studies were completed after the addition of cyclin D3 or empty (control) viral vectors. Immunostaining demonstrated increased proliferation and decidualization in both in vitro and in vivo studies, and in situ hybridization confirmed increased expression of decidualization markers in vivo. Placentation was demonstrated as well in vivo in the cyclin D3-replaced animals. However, fertility was not restored in Hoxa-10(-/-) mice after d 10 of pregnancy. Finally, we identified several downstream targets of cyclin D3 during decidualization in vitro via proteomics experiments, and these were confirmed using in situ hybridization in vivo. Collectively, these results demonstrate that cyclin D3 expression influences a host of genes involved in decidualization and can improve decidualization in Hoxa-10(-/-) mice.

Adenovirus-mediated genetic removal of signaling molecules in cultured primary mouse embryonic fibroblasts

The ability to genetically remove specific components of various cell signalling cascades has been an integral tool in modern signal transduction analysis. One particular method to achieve this conditional deletion is via the use of the Cre-loxP system. This method involves flanking the gene of interest with loxP sites, which are specific recognition sequences for the Cre recombinase protein. Exposure of the so-called floxed (flanked by loxP site) DNA to this enzyme results in a Cre-mediated recombination event at the loxP sites, and subsequent excision of the intervening gene³. Several different methods exist to administer Cre recombinase to the site of interest. In this video, we demonstrate the use of an adenovirus containing the Cre recombinase gene to infect primary mouse embryonic fibroblasts (MEFs) obtained from embryos containing a floxed Rac1 allele¹. Our rationale for selecting Rac1 MEFs for our experiments is that clear morphological changes can be seen upon deletion of Rac1, due to alterations in the actin cytoskeleton^2,5. 72 hours following viral transduction and Cre expression, cells were stained using the actin dye phalloidin and imaged using confocal laser scanning microscopy. It was observed that MEFs which had been exposed to the adeno-Cre virus appeared contracted and elongated in morphology compared to uninfected cells, consistent with previous reports^2,5. The adenovirus method of Cre recombinase delivery is advantageous as the adeno-Cre virus is easily available, and gene deletion via Cre in nearly 100% of the cells can be achieved with optimized adenoviral infection.

Cell cycle regulatory control for uterine stromal cell decidualization in implantation

Uterine stromal cell decidualization is integral to successful embryo implantation, which is a gateway to pregnancy establishment. This process is characterized by stromal cell proliferation and differentiation into decidual cells with polyploidy. The molecular mechanisms that are involved in these events remain poorly understood. The current concept is that locally induced factors with the onset of implantation influence uterine stromal cell proliferation and/or differentiation through modulation of core cell cycle regulators. This review will aim to address the currently available knowledge on interaction between growth factor/homeobox and cell cycle regulatory signaling in the progression of various aspects of decidualization.

Optimized adeno-associated virus 8 produces hepatocyte-specific Cre-mediated recombination without toxicity or affecting liver regeneration

Engineering viral vectors to produce liver-specific protein expression may help advance understanding of hepatic regeneration and disease states. In addition to introducing genes of interest to the liver, these vectors can be adapted for gene deletion when designed to express Cre recombinase. The ability to use this system requires high, liver-restricted expression, low toxicity, and no effect on the process of interest. We developed an adeno-associated virus 8 (AAV8) with a codon-optimized Cre recombinase under a hepatocyte-specific major urinary protein (MUP) promoter (MUP-iCre-AAV8) that fulfills these requirements. A single intravenous injection of ROSA26R reporter mice, which express lacZ after Cre-mediated recombination, demonstrated homogeneous beta-galactosidase expression limited to hepatocytes after only 7 days. Cre protein expression remained strong for at least 31 days. Serum liver function tests and histology demonstrated minimal liver toxicity. The presence of MUP-iCre-AAV8 did not affect hepatocyte proliferation after partial hepatectomy as measured by Ki67 staining.

CONCLUSION

AAV8 with the MUP promoter, by virtue of its lack of hepatic toxicity or effect on liver regeneration, may be an efficient alternative to complex transgenic methodologies for studies of the mouse liver.