FGF-induced Pea3 transcription factors program the genetic landscape for cell fate determination

ETVs dictate hPSC differentiation by tuning biophysical properties

Stem cells maintain a dynamic dialog with their niche, integrating biochemical and biophysical cues to modulate cellular behavior. Yet, the transcriptional networks that regulate cellular biophysical properties remain poorly defined. Here, we leverage human pluripotent stem cells (hPSCs) and two morphogenesis models - gastruloids and pancreatic differentiation - to establish ETV transcription factors as critical regulators of biophysical parameters and lineage commitment. Genetic ablation of ETV1 or ETV1/ETV4/ETV5 in hPSCs enhances cell-cell and cell-ECM adhesion, leading to aberrant multilineage differentiation including disrupted germ-layer organization, ectoderm loss, and extraembryonic cell overgrowth in gastruloids. Furthermore, ETV1 loss abolishes pancreatic progenitor formation. Single-cell RNA sequencing and follow-up assays reveal dysregulated mechanotransduction via the PI3K/AKT signaling. Our findings highlight the importance of transcriptional control over cell biophysical properties and suggest that manipulating these properties may improve in vitro cell and tissue engineering strategies.

The capicua-ataxin-1-like complex regulates Notch-driven marginal zone B cell development and sepsis progression

Follicular B (FOB) and marginal zone B (MZB) cells are pivotal in humoral immune responses against pathogenic infections. MZB cells can exacerbate endotoxic shock via interleukin-6 secretion. Here we show that the transcriptional repressor capicua (CIC) and its binding partner, ataxin-1-like (ATXN1L), play important roles in FOB and MZB cell development. CIC deficiency reduces the size of both FOB and MZB cell populations, whereas ATXN1L deficiency specifically affects MZB cells. B cell receptor signaling is impaired only in Cic-deficient FOB cells, whereas Notch signaling is disrupted in both Cic-deficient and Atxn1l-deficient MZB cells. Mechanistically, ETV4 de-repression leads to inhibition of Notch1 and Notch2 transcription, thereby inhibiting MZB cell development in B cell-specific Cic-deficient (Cicf/f;Cd19-Cre) and Atxn1l-deficient (Atxn1lf/f;Cd19-Cre) mice. In Cicf/f;Cd19-Cre and Atxn1lf/f; Cd19-Cre mice, humoral immune responses and lipopolysaccharide-induced sepsis progression are attenuated but are restored upon Etv4-deletion. These findings highlight the importance of the CIC-ATXN1L complex in MZB cell development and may provide proof of principle for therapeutic targeting in sepsis.

Phospholipase Cγ regulates lacrimal gland branching by competing with PI3K in phosphoinositide metabolism

Although the regulation of branching morphogenesis by spatially distributed cues is well established, the role of intracellular signaling in determining the branching pattern remains poorly understood. In this study, we investigated the regulation and function of phospholipase C gamma (PLCγ) in Fibroblast Growth Factor (FGF) signaling in lacrimal gland development. We showed that deletion of PLCγ1 in the lacrimal gland epithelium leads to ectopic branching and acinar hyperplasia, which was phenocopied by either mutating the PLCγ1 binding site on Fgfr2 or disabling any of its SH2 domains. PLCγ1 inactivation did not change the level of Fgfr2 or affect MAPK signaling, but instead led to sustained AKT phosphorylation due to increased PIP3 production. Consistent with this, PLCγ1 mutant phenotype can be reproduced by elevation of PI3K signaling in Pten knockout and attenuated by blocking AKT signaling. This study demonstrated that PLCγ modulates PI3K signaling by shifting phosphoinositide metabolism, revealing an important role of signaling dynamics in conjunction with spatial cues in shaping branching morphogenesis.

Crk mediates Csk-Hippo signaling independently of Yap tyrosine phosphorylation to induce cell extrusion

Src family kinases (SFKs), including Src, Fyn and Yes, play important roles in development and cancer. Despite being first discovered as the Yes-associated protein, the regulation of Yap by SFKs remains poorly understood. Here, through single-cell analysis and genetic lineage tracing, we show that the pan-epithelial ablation of C-terminal Src kinase (Csk) in the lacrimal gland unleashes broad Src signaling but specifically causes extrusion and apoptosis of acinar progenitors at a time when they are shielded by myoepithelial cells from the basement membrane. Csk mutants can be phenocopied by constitutively active Yap and rescued by deleting Yap or Taz, indicating a significant functional overlap between Src and Yap signaling. Although Src-induced tyrosine phosphorylation has long been believed to regulate Yap activity, we find that mutating these tyrosine residues in both Yap and Taz fails to perturb mouse development or alleviate the Csk lacrimal gland phenotype. In contrast, Yap loses Hippo signaling-dependent serine phosphorylation and translocates into the nucleus in Csk mutants. Further chemical genetics studies demonstrate that acute inhibition of Csk enhances Crk/CrkL phosphorylation and Rac1 activity, whereas removing Crk/CrkL or Rac1/Rap1 ameliorates the Csk mutant phenotype. These results show that Src controls Hippo-Yap signaling through the Crk/CrkL-Rac/Rap axis to promote cell extrusion.

Neuronal-epithelial cross-talk drives acinar specification via NRG1-ERBB3-mTORC2 signaling

Acinar cells are the principal secretory units of multiple exocrine organs. A single-cell, layered, lumenized acinus forms from a large cohort of epithelial progenitors that must initiate and coordinate three cellular programs of acinar specification, namely, lineage progression, secretion, and polarization. Despite this well-known outcome, the mechanism(s) that regulate these complex programs are unknown. Here, we demonstrate that neuronal-epithelial cross-talk drives acinar specification through neuregulin (NRG1)-ERBB3-mTORC2 signaling. Using single-cell and global RNA sequencing of developing murine salivary glands, we identified NRG1-ERBB3 to precisely overlap with acinar specification during gland development. Genetic deletion of Erbb3 prevented cell lineage progression and the establishment of lumenized, secretory acini. Conversely, NRG1 treatment of isolated epithelia was sufficient to recapitulate the development of secretory acini. Mechanistically, we found that NRG1-ERBB3 regulates each developmental program through an mTORC2 signaling pathway. Thus, we reveal that a neuronal-epithelial (NRG1/ERBB3/mTORC2) mechanism orchestrates the creation of functional acini.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Postnatal regulation of B-1a cell development and survival by the CIC-PER2-BHLHE41 axis

B-1 cell development mainly occurs via fetal and neonatal hematopoiesis and is suppressed in adult bone marrow hematopoiesis. However, little is known about the factors inhibiting B-1 cell development at the adult stage. We report that capicua (CIC) suppresses postnatal B-1a cell development and survival. CIC levels are high in B-1a cells and gradually increase in transitional B-1a (TrB-1a) cells with age. B-cell-specific Cic-null mice exhibit expansion of the B-1a cell population and a gradual increase in TrB-1a cell frequency with age but attenuated B-2 cell development. CIC deficiency enhances B cell receptor (BCR) signaling in transitional B cells and B-1a cell viability. Mechanistically, CIC-deficiency-mediated Per2 derepression upregulates Bhlhe41 levels by inhibiting CRY-mediated transcriptional repression for Bhlhe41, consequently promoting B-1a cell formation in Cic-null mice. Taken together, CIC is a key transcription factor that limits the B-1a cell population at the adult stage and balances B-1 versus B-2 cell formation.

Jack of all trades, master of each: the diversity of fibroblast growth factor signalling in eye development

A central question in development biology is how a limited set of signalling pathways can instruct unlimited diversity of multicellular organisms. In this review, we use three ocular tissues as models of increasing complexity to present the astounding versatility of fibroblast growth factor (FGF) signalling. In the lacrimal gland, we highlight the specificity of FGF signalling in a one-dimensional model of budding morphogenesis. In the lens, we showcase the dynamics of FGF signalling in altering functional outcomes in a two-dimensional space. In the retina, we present the prolific utilization of FGF signalling from three-dimensional development to homeostasis. These examples not only shed light on the cellular basis for the perfection and complexity of ocular development, but also serve as paradigms for the diversity of FGF signalling.

Identification of Biomarkers Controlling Cell Fate In Blood Cell Development

A blood cell lineage consists of several consecutive developmental stages starting from the pluri- or multipotent stem cell to a state of terminal differentiation. Despite their importance for human biology, the regulatory pathways and gene networks that govern these differentiation processes are not yet fully understood. This is in part due to challenges associated with delineating the interactions between transcription factors (TFs) and their corresponding target genes. A possible step forward in this case is provided by the increasing amount of expression data, as a basis for linking differentiation stages and gene activities. Here, we present a novel hierarchical approach to identify characteristic expression peak patterns that global regulators excert along the differentiation path of cell lineages. Based on such simple patterns, we identified cell state-specific marker genes and extracted TFs that likely drive their differentiation. Integration of the mean expression values of stage-specific “key player” genes yielded a distinct peaking pattern for each lineage that was used to identify further genes in the dataset which behave similarly. Incorporating the set of TFs that regulate these genes led to a set of stage-specific regulators that control the biological process of cell fate. As proof of concept, we considered two expression datasets covering key differentiation events in blood cell formation of mice.

Lacrimal gland budding requires PI3K-dependent suppression of EGF signaling

The patterning of epithelial buds is determined by the underlying signaling network. Here, we study the cross-talk between phosphoinositide 3-kinase (PI3K) and Ras signaling during lacrimal gland budding morphogenesis. Our results show that PI3K is activated by both the p85-mediated insulin-like growth factor (IGF) and Ras-mediated fibroblast growth factor (FGF) signaling. On the other hand, PI3K also promotes extracellular signal-regulated kinase (ERK) signaling via a direct interaction with Ras. Both PI3K and ERK are upstream regulators of mammalian target of rapamycin (mTOR), and, together, they prevent expansion of epidermal growth factor (EGF) receptor expression from the lacrimal gland stalk to the bud region. We further show that this suppression of EGF signaling is necessary for induction of lacrimal gland buds. These results reveal that the interplay between PI3K, mitogen-activated protein kinase, and mTOR mediates the cross-talk among FGF, IGF, and EGF signaling in support of lacrimal gland development.

JAK3 is a potential biomarker and associated with immune infiltration in kidney renal clear cell carcinoma

Kidney renal clear cell carcinoma (KIRC) is one of the most common cancers globally, with an overall poor prognosis. The Janus kinase (JAK) family plays an essential role in cellular mechanisms such as proliferation, metastasis, invasion, and immunity. In our study, various web-portals were used to explore the expression and clinical significance of JAK3 in KIRC. JAK3 expression was significantly up-regulated in KIRC tissues. Patients with KIRC having high JAK3 levels displayed a substantially decreased disease-free survival rate and overall survival rate. Significant correlations were obtained between JAK3 expression and the abundance of immune cells and immune biomarker sets. Enrichment function analysis revealed that gene function significantly correlated with JAK3, which was primarily associated with the immune response, JAK-STAT signaling pathway, Ras signaling pathway via several cancer-related kinases, miRNAs, and transcription factors. Moreover, we also identified several kinase, miRNA or transcription factor targets of JAK3 in KIRC. The hub genes (JAK3, FCHO1, INSl3, DEF6, and GPR132) were associated with the activation or inhibition of several famous cancer related pathways. Our results demonstrated that JAK3 is a potential biomarker and associated with immune infiltration in KIRC.

Etv transcription factors functionally diverge from their upstream FGF signaling in lens development

The signal regulated transcription factors (SRTFs) control the ultimate transcriptional output of signaling pathways. Here, we examined a family of FGF-induced SRTFs - Etv1, Etv 4, and Etv 5 - in murine lens development. Contrary to FGF receptor mutants that displayed loss of ERK signaling and defective cell differentiation, Etv deficiency augmented ERK phosphorylation without disrupting the normal lens fiber gene expression. Instead, the transitional zone for lens differentiation was shifted anteriorly as a result of reduced Jag1-Notch signaling. We also showed that Etv proteins suppresses mTOR activity by promoting Tsc2 expression, which is necessary for the nuclei clearance in mature lens. These results revealed the functional divergence between Etv and FGF in lens development, demonstrating that these SRTFs can operate outside the confine of their upstream signaling.

Characterization of Tg(Etv4-GFP) and Etv5 RFP Reporter Lines in the Context of Fibroblast Growth Factor 10 Signaling During Mouse Embryonic Lung Development

Members of the PEA3 transcription factors are emerging as bone fide targets for fibroblast growth factor (FGF) signaling. Among them, ETV4 and ETV5 appear to mediate FGF10 signaling during early embryonic lung development. In this paper, recently obtained Tg(Etv4-GFP) and Etv5^{CreERT2−RFP} fluorescent reporter lines were generally characterized during early embryonic development and in the context of FGF10 signaling, in particular. We found that both Tg(Etv4-GFP) and Etv5^{CreERT2−RFP} were primarily expressed in the epithelium of the lung during embryonic development. However, the expression of Etv5^{CreERT2−RFP} was much higher than that of Tg(Etv4-GFP), and continued to increase during development, whereas Tg(Etv4-GFP) decreased. The expression patterns of the surrogate fluorescent protein GFP and RFP for ETV4 and ETV5, respectively, agreed with known regions of FGF10 signaling in various developing organs, including the lung, where ETV4-GFP was seen primarily in the distal epithelium and to a lesser extent in the surrounding mesenchyme. As expected, ETV5-RFP was restricted to the lung epithelium, showing a decreasing expression pattern from distal buds to proximal conducting airways. FGF10 inhibition experiments confirmed that both Etv4 and Etv5 are downstream of FGF10 signaling. Finally, we also validated that both fluorescent reporters responded to FGF10 inhibition in vitro. In conclusion, these two reporter lines appear to be promising tools to monitor FGF10/FGFR2b signaling in early lung development. These tools will have to be further validated at later stages and in other organs of interest.

Oncogenic ETS Factors in Prostate Cancer

Prostate cancer is unique among carcinomas in that a fusion gene created by a chromosomal rearrangement is a common driver of the disease. The TMPRSS2/ERG rearrangement drives aberrant expression of the ETS family transcription factor ERG in 50% of prostate tumors. Similar rearrangements promote aberrant expression of the ETS family transcription factors ETV1 and ETV4 in another 10% of cases. Together, these three ETS factors are thought to promote tumorigenesis in the majority of prostate cancers. A goal of precision medicine is to be able to apply targeted therapeutics that are specific to disease subtypes. ETS gene rearrangement positive tumors represent the largest molecular subtype of prostate cancer, but to date there is no treatment specific to this marker. In this chapter we will review the latest findings regarding the molecular mechanisms of ETS factor function in the prostate. These molecular details may provide a path towards new therapeutic targets for this subtype of prostate cancer. Further, we will describe efforts to target the oncogenic functions of ETS family transcription factors directly as well as indirectly.