Deletion of Wt1 during early gonadogenesis leads to differences of sex development in male and female adult mice

Assessing the role of the WT1 transcription factor (WT1) during early gonad differentiation and its impact on adult sex development has been difficult due to the complete gonadal agenesis and embryonic lethality exhibited by Wt1KO mouse models. Here, we generated Wt1LoxP/GFP;Wt1Cre mice, the first Wt1KO mouse model that reaches adulthood with a dramatically reduced Wt1 expression during early gonadogenesis. Wt1LoxP/GFP;Wt1Cre mice lacked mature gonads and displayed genital tracts containing both male and female genital structures and ambiguous genitalia. We found that WT1 is necessary for the activation of both male and female sex-determining pathways, as embryonic mutant gonads failed to upregulate the expression of the genes specific for each genetic programme. The gonads of Wt1LoxP/GFP;Wt1Cre mice showed a lack of production of Sertoli and pre-granulosa cells and a reduced number of germ cells. NR5A1 and the steroidogenic genes expression was modulated differently in XY and XX Wt1LoxP/GFP;Wt1Cre gonads, explaining the mutant phenotypes. Further studies of the XX Wt1LoxP/GFP;Wt1Cre gonads revealed that deletion of WT1 at an early stage impaired the differentiation of several cell types including somatic cells and the ovarian epithelium. Through the characterisation of this Wt1KO mouse model, we show that the deletion of Wt1 during early gonadogenesis produces dramatic defects in adult sex development

Wt1 is required for cardiovascular progenitor cell formation through transcriptional control of Snail and E-cadherin

Epicardial epithelial-mesenchymal transition (EMT) is hypothesized to generate cardiovascular progenitor cells that differentiate into various cell types, including coronary smooth muscle and endothelial cells, perivascular and cardiac interstitial fibroblasts and cardiomyocytes. Here we show that an epicardial-specific knockout of Wt1 leads to a reduction of mesenchymal progenitor cells and their derivatives. We demonstrate that Wt1 is essential for repression of the epithelial phenotype in epicardial cells and during Embryonic Stem (ES) cell differentiation, through direct transcriptional regulation of Snail (Snai1) and E-cadherin (Cdh1), two of the major mediators of EMT. Some mesodermal lineages fail to form in Wt1 null embryoid bodies but this effect is rescued by the expression of Snai1, underlining the importance of EMT in generating these differentiated cells. These new insights into the molecular mechanisms regulating cardiovascular progenitor cells and EMT will shed light on the pathogenesis of heart diseases and may help the development of cell based therapies

A Wt1-Controlled Chromatin Switching Mechanism Underpins Tissue-Specific Wnt4 Activation and Repression

SummaryWt1 regulates the epithelial-mesenchymal transition (EMT) in the epicardium and the reverse process (MET) in kidney mesenchyme. The mechanisms underlying these reciprocal functions are unknown. Here, we show in both embryos and cultured cells that Wt1 regulates Wnt4 expression dichotomously. In kidney cells, Wt1 recruits Cbp and p300 as coactivators; in epicardial cells it enlists Basp1 as a corepressor. Surprisingly, in both tissues, Wt1 loss reciprocally switches the chromatin architecture of the entire Ctcf-bounded Wnt4 locus, but not the flanking regions; we term this mode of action “chromatin flip-flop.” Ctcf and cohesin are dispensable for Wt1-mediated chromatin flip-flop but essential for maintaining the insulating boundaries. This work demonstrates that a developmental regulator coordinates chromatin boundaries with the transcriptional competence of the flanked region. These findings also have implications for hierarchical transcriptional regulation in development and disease

Visceral and subcutaneous fat have different origins and evidence supports a mesothelial source

International audience: Fuelled by the obesity epidemic, there is considerable interest in the developmental origins of white adipose tissue (WAT) and the stem and progenitor cells from which it arises. Whereas increased visceral fat mass is associated with metabolic dysfunction, increased subcutaneous WAT is protective. There are six visceral fat depots: perirenal, gonadal, epicardial, retroperitoneal, omental and mesenteric, and it is a subject of much debate whether these have a common developmental origin and whether this differs from that for subcutaneous WAT. Here we show that all six visceral WAT depots receive a significant contribution from cells expressing Wt1 late in gestation. Conversely, no subcutaneous WAT or brown adipose tissue arises from Wt1-expressing cells. Postnatally, a subset of visceral WAT continues to arise from Wt1-expressing cells, consistent with the finding that Wt1 marks a proportion of cell populations enriched in WAT progenitors. We show that all visceral fat depots have a mesothelial layer like the visceral organs with which they are associated, and provide several lines of evidence that Wt1-expressing mesothelium can produce adipocytes. These results reveal a major ontogenetic difference between visceral and subcutaneous WAT, and pinpoint the lateral plate mesoderm as a major source of visceral WAT. They also support the notion that visceral WAT progenitors are heterogeneous, and suggest that mesothelium is a source of adipocytes

Synaptic Activity Regulates Mitochondrial Iron Metabolism to Enhance Neuronal Bioenergetics

Synaptic activity is the main energy-consuming process in the central nervous system. We are beginning to understand how energy is supplied and used during synaptic activity by neurons. However, the long-term metabolic adaptations associated with a previous episode of synaptic activity are not well understood. Herein, we show that an episode of synaptic activity increases mitochondrial bioenergetics beyond the duration of the synaptic activity by transcriptionally inducing the expression of iron metabolism genes with the consequent enhancement of cellular and mitochondrial iron uptake. Iron is a necessary component of the electron transport chain complexes, and its chelation or knockdown of mitochondrial iron transporter Mfrn1 blocks the activity-mediated bioenergetics boost. We found that Mfrn1 expression is regulated by the well-known regulator of synaptic plasticity CREB, suggesting the coordinated expression of synaptic plasticity programs with those required to meet the associated increase in energetic demands

Mitochondrial fragmentation in excitotoxicity requires ROCK activation

Mitochondria morphology constantly changes through fission and fusion processes that regulate mitochondrial function, and it therefore plays a prominent role in cellular homeostasis. Cell death progression is associated with mitochondrial fission. Fission is mediated by the mainly cytoplasmic Drp1, which is activated by different post-translational modifications and recruited to mitochondria to perform its function. Our research and other studies have shown that in the early moments of excitotoxic insult Drp1 must be nitrosylated to mediate mitochondrial fragmentation in neurons. Nonetheless, mitochondrial fission is a multistep process in which filamentous actin assembly/disassembly and myosin-mediated mitochondrial constriction play prominent roles. Here we establish that in addition to nitric oxide production, excitotoxicity-induced mitochondrial fragmentation also requires activation of the actomyosin regulator ROCK. Although ROCK1 has been shown to phosphorylate and activate Drp1, experiments using phosphor-mutant forms of Drp1 in primary cortical neurons indicate that in excitotoxic conditions, ROCK does not act directly on Drp1 to mediate fission, but may act on the actomyosin complex. Thus, these data indicate that a wider range of signaling pathways than those that target Drp1 are amenable to be inhibited to prevent mitochondrial fragmentation as therapeutic optio

WT1 regulates the expression of inhibitory chemokines during heart development

The embryonic epicardium is an important source of cardiovascular precursor cells and paracrine factors that are required for adequate heart formation. Signaling pathways regulated by WT1 that promote heart development have started to be described; however, there is little information on signaling pathways regulated by WT1 that could act in a negative manner. Transcriptome analysis of Wt1KO epicardial cells reveals an unexpected role for WT1 in repressing the expression of interferon-regulated genes that could be involved in a negative regulation of heart morphogenesis. Here, we showed that WT1 is required to repress the expression of the chemokines Ccl5 and Cxcl10 in epicardial cells. We observed an inverse correlation of Wt1 and the expression of Cxcl10 and Ccl5 during epicardium development. Chemokine receptor analyses of hearts from Wt1(gfp/+) mice demonstrate the differential expression of their chemokine receptors in GFP(+) epicardial enriched cells and GFP(-) cells. Functional assays demonstrate that CXCL10 and CCL5 inhibit epicardial cells migration and the proliferation of cardiomyocytes respectively. WT1 regulates the expression levels of Cxcl10 and Ccl5 in epicardial cells directly and indirectly through increasing the levels of IRF7. As epicardial cell reactivation after a myocardial damage is linked with WT1 expression, the present work has potential implications in adult heart repair