FOXN1: A Master Regulator Gene of Thymic Epithelial Development Program

Thymic Carcinoma: Unraveling Neuroendocrine Differentiation and Epithelial Cell Identity Loss

BACKGROUND

The histogenesis of thymic epithelial tumors (TETs) has been a subject of debate. Recent technological advancements have revealed that thymic carcinomas often exhibit a phenotype akin to tuft cells, which is a subset of medullary TECs. Here, we further explored the gene expression signatures of thymic carcinomas in relation to tuft cells and their kinships-ionocytes and neuroendocrine cells (neuroendocrine group).

METHODS

We analyzed a single-cell RNA sequencing dataset from the normal human thymus. Concurrently, we examined publicly available datasets on the mRNA expression and methylation status of TECs and lung cancers. Real-time quantitative PCR was also conducted with our tissue samples.

RESULTS

Thymic carcinomas displayed a neuroendocrine phenotype biased toward tuft cells and ionocytes. When exploring the possible regulators of this phenotype, we discovered that HDAC9 and NFATC1 were characteristically expressed in the neuroendocrine group in adult TECs and thymic carcinomas. Additionally, the pan-thymic epithelium markers, exemplified by PAX9 and SIX1, were significantly suppressed in thymic carcinomas.

CONCLUSIONS

Thymic carcinomas might be characterized by unique neuroendocrine differentiation and loss of identity as thymic epithelial cells. Future studies investigating the role of HDAC9 and NFATC1 in thymic epithelium are warranted to explore their potential as therapeutic targets in TETs.

Comprehensive phenotypic analysis of diverse FOXN1 variants

BACKGROUND

Thymus hypoplasia due to stromal cell problems has been linked to mutations in several transcription factors, including Forkhead box N1 (FOXN1). FOXN1 supports T-cell development by regulating the formation and expansion of thymic epithelial cells (TECs). While autosomal recessive FOXN1 mutations result in a nude and severe combined immunodeficiency phenotype, the impact of single-allelic or compound heterozygous FOXN1 mutations is less well-defined.

OBJECTIVE

With more than 400 FOXN1 mutations reported, their impact on protein function and thymopoiesis remains unclear for most variants. We developed a systematic approach to delineate the functional impact of diverse FOXN1 variants.

METHODS

Selected FOXN1 variants were tested with transcriptional reporter assays and imaging studies. Thymopoiesis was assessed in mouse lines genocopying several human FOXN1 variants. Reaggregate thymus organ cultures were used to compare the thymopoietic potential of the FOXN1 variants.

RESULTS

FOXN1 variants were categorized into benign, loss- or gain-of-function, and/or dominant-negatives. Dominant negative activities mapped to frameshift variants impacting the transactivation domain. A nuclear localization signal was mapped within the DNA binding domain. Thymopoiesis analyses with mouse models and reaggregate thymus organ cultures revealed distinct consequences of particular Foxn1 variants on T-cell development.

CONCLUSIONS

The potential effect of a FOXN1 variant on T-cell output from the thymus may relate to its effects on transcriptional activity, nuclear localization, and/or dominant negative functions. A combination of functional assays and thymopoiesis comparisons enabled a categorization of diverse FOXN1 variants and their potential impact on T-cell output from the thymus.

Comprehensive Transcriptomic Analysis for Thymic Epithelial Cells of Aged Mice and Humans

Thymic epithelial cells (TECs) play a critical role in thymic development and thymopoiesis. As individuals age, TECs undergo various changes that impact their functions, leading to a reduction in cell numbers and impaired thymic selection. These age-related alterations have been observed in both mice and humans. However, the precise mechanisms underlying age-related TEC dysfunction remain unclear. Furthermore, there is a lack of a comprehensive study that connects mouse and human biological processes in this area. To address this gap, we conducted an extensive transcriptome analysis of young and old TECs in mice, complemented by further analysis of publicly available human TEC single-cell RNA sequencing data. Our analysis revealed alterations in both known and unknown pathways that potentially contribute to age-related TEC dysfunction. Specifically, we observed downregulation of pathways related to cell proliferation, T cell development, metabolism, and cytokine signaling in old age TECs. Conversely, TGF-β, BMP, and Wnt signaling pathways were upregulated, which have been known to be associated with age-related TEC dysfunctions or newly discovered in this study. Importantly, we found that these age-related changes in mouse TECs were consistently present in human TECs as well. This cross-species validation further strengthens the significance of our findings. In conclusion, our comprehensive analysis provides valuable insight into the biological and immunological characteristics of aged TECs in both mice and humans. These findings contribute to a better understanding of thymic involution and age-induced immune dysfunction.

Histogenetic and disease-relevant phenotypes in thymic epithelial tumors (TETs): The potential significance for future TET classification

Thymic epithelial tumors (TETs) encompass morphologically various subtypes. Thus, it would be meaningful to explore the expression phenotypes that delineate each TET subtype or overarching multiple subtypes. If these profiles are related to thymic physiology, they will improve our biological understanding of TETs and may contribute to the establishment of a more rational TET classification. Against this background, pathologists have attempted to identify histogenetic features in TETs for a long time. As part of this work, our group has reported several TET expression profiles that are histotype-dependent and related to the nature of thymic epithelial cells (TECs). For example, we found that beta5t, a constituent of thymoproteasome unique to cortical TECs, is expressed mainly in type B thymomas, for which the nomenclature of cortical thymoma was once considered. Another example is the discovery that most thymic carcinomas, especially thymic squamous cell carcinomas, exhibit expression profiles similar to tuft cells, a recently discovered special type of medullary TEC. This review outlines the currently reported histogenetic phenotypes of TETs, including those related to thymoma-associated myasthenia gravis, summarizes their genetic signatures, and provides a perspective for the future direction of TET classification.

Foxn1 overexpression promotes thymic epithelial progenitor cell proliferation and mTEC maintenance, but does not prevent thymic involution

The transcription factor FOXN1 is essential for fetal thymic epithelial cell (TEC) differentiation and proliferation. Postnatally, Foxn1 levels vary widely between TEC subsets, from low/undetectable in putative TEC progenitors to highest in differentiated TEC subsets. Correct Foxn1 expression is required to maintain the postnatal microenvironment; premature downregulation of Foxn1 causes a rapid involution-like phenotype, and transgenic overexpression can cause thymic hyperplasia and/or delayed involution. We investigated a K5.Foxn1 transgene that drives overexpression in mouse TECs, but causes neither hyperplasia nor delay or prevention of aging-related involution. Similarly, this transgene cannot rescue thymus size in Foxn1lacZ/lacZ mice, which undergo premature involution as a result of reduced Foxn1 levels. However, TEC differentiation and cortico-medullary organization are maintained with aging in both K5.Foxn1 and Foxn1lacZ/lacZ mice. Analysis of candidate TEC markers showed co-expression of progenitor and differentiation markers as well as increased proliferation in Plet1+ TECs associated with Foxn1 expression. These results demonstrate that the functions of FOXN1 in promoting TEC proliferation and differentiation are separable and context dependent, and suggest that modulating Foxn1 levels can regulate the balance of proliferation and differentiation in TEC progenitors.

Thymus transplantation regulates blood pressure and alleviates hypertension-associated heart and kidney damage via transcription factors FoxN1 pathway

Previous studies have found that thymus is involved in the process of hypertension. However, whether thymus transplantation alleviates target organ damage in hypertensive mice remains unknown. The aim of this study was to evaluate the effects of thymus transplantation on blood pressure and target organ changes in mice with hypertension. Mice were randomly divided into normal control group (Con), hypertensive group (HTN) and thymus transplantation group (HTN + Trans). Thymus of neonatal mice was transplanted into the renal capsule of the transplantation group. After transplantation, the mouse tail noninvasive pressure was measured and heart function was evaluated weekly. Then mice were euthanized and organs or tissues were harvested at 4 weeks post-transplantation. The blood pressure of HTN + Trans group was lower than that in the HTN group. The expression of FoxN1, Aire, ATRAP, thymosin β4 and the content of sjTREC in thymus of HTN group was decreased and the number of naïve T cells in HTN group was lower compared with other two groups. The ratio of cTEC/mTEC in HTN group was higher than that in Con group and lower than that in HTN + Trans group. Cardiac pathology showed cardiac hypertrophy and fibrosis in HTN group whereas thymus transplantation improved heart function and structure. Altogether, our findings demonstrated thymus transplantation could improve thymus function of hypertensive mice, which increased the expression of thymus transcription factor FoxN1, affected the proportion of T cell subsets, and increased thymosin β4 thereby reducing blood pressure and reversing the progression of target organ damage.

Pathological complete remission of relapsed tumor by photo-activating antibody-mimetic drug conjugate treatment

Antibody-mimetic drug conjugate is a novel noncovalent conjugate consisting of an antibody-mimetic recognizing a target molecule on the cancer cell surface and low-molecular-weight payloads that kill the cancer cells. In this study, the efficacy of a photo-activating antibody-mimetic drug conjugate targeting HER2-expressing tumors was evaluated in mice, by using the affibody that recognize HER2 (Z_HER2:342 ) as a target molecule and an axially substituted silicon phthalocyanine (a novel potent photo-activating compound) as a payload. The first treatment with the photo-activating antibody-mimetic drug conjugates reduced the size of all HER2-expressing KPL-4 xenograft tumors macroscopically. However, during the observation period, relapsed tumors gradually appeared in approximately 50% of the animals. To evaluate the efficacy of repeated antibody-mimetic drug conjugate treatment, animals with relapsed tumors were treated again with the same regimen. After the second observation period, the mouse tissues were examined histopathologically. Unexpectedly, all relapsed tumors were eradicated, and all animals were diagnosed with pathological complete remission. After the second treatment, skin wounds healed rapidly, and no significant side effects were observed in other organs, except for occasional microscopic granulomatous tissues beneath the serosa of the liver in a few mice. Repeated treatments seemed to be well tolerated. These results indicate the promising efficacy of the repeated photo-activating antibody-mimetic drug conjugate treatment against HER2-expressing tumors.

Limits to in vivo fate changes of epithelia in thymus and parathyroid by ectopic expression of transcription factors Gcm2 and Foxn1

The development of the parathyroid and the thymus from the third pharyngeal pouch depends on the activities of the Gcm2 and Foxn1 transcription factors, respectively, whose expression domains sharply demarcate two regions in the developing third pharyngeal pouch. Here, we have generated novel mouse models to examine whether ectopic co-expression of Gcm2 in the thymic epithelium and of Foxn1 in the parathyroid perturbs the establishment of organ fates in vivo. Expression of Gcm2 in the thymic rudiment does not activate a parathyroid-specific expression programme, even in the absence of Foxn1 activity. Co-expression of Foxn1 in the parathyroid fails to impose thymopoietic capacity. We conclude that the actions of Foxn1 and Gcm2 transcription factors are cell context-dependent and that they each require permissive transcription factor landscapes in order to successfully interfere with organ-specific cell fate.

Thymus Functionality Needs More Than a Few TECs

The thymus, a primary lymphoid organ, produces the T cells of the immune system. Originating from the 3^rd pharyngeal pouch during embryogenesis, this organ functions throughout life. Yet, thymopoiesis can be transiently or permanently damaged contingent on the types of systemic stresses encountered. The thymus also undergoes a functional decline during aging, resulting in a progressive reduction in naïve T cell output. This atrophy is evidenced by a deteriorating thymic microenvironment, including, but not limited, epithelial-to-mesenchymal transitions, fibrosis and adipogenesis. An exploration of cellular changes in the thymus at various stages of life, including mouse models of in-born errors of immunity and with single cell RNA sequencing, is revealing an expanding number of distinct cell types influencing thymus functions. The thymus microenvironment, established through interactions between immature and mature thymocytes with thymus epithelial cells (TEC), is well known. Less well appreciated are the contributions of neural crest cell-derived mesenchymal cells, endothelial cells, diverse hematopoietic cell populations, adipocytes, and fibroblasts in the thymic microenvironment. In the current review, we will explore the contributions of the many stromal cell types participating in the formation, expansion, and contraction of the thymus under normal and pathophysiological processes. Such information will better inform approaches for restoring thymus functionality, including thymus organoid technologies, beneficial when an individuals’ own tissue is congenitally, clinically, or accidentally rendered non-functional.

In vitro and in vivo functions of T cells produced in complemented thymi of chimeric mice generated by blastocyst complementation

Blastocyst complementation is an intriguing way of generating humanized animals for organ preparation in regenerative medicine and establishing novel models for drug development. Confirming that complemented organs and cells work normally in chimeric animals is critical to demonstrating the feasibility of blastocyst complementation. Here, we generated thymus-complemented chimeric mice, assessed the efficacy of anti-PD-L1 antibody in tumor-bearing chimeric mice, and then investigated T-cell function. Thymus-complemented chimeric mice were generated by injecting C57BL/6 (B6) embryonic stem cells into Foxn1^nu/nu morulae or blastocysts. Flow cytometry data showed that the chimeric mouse thymic epithelial cells (TECs) were derived from the B6 cells. T cells appeared outside the thymi. Single-cell RNA-sequencing analysis revealed that the TEC gene-expression profile was comparable to that in B6 mice. Splenic T cells of chimeric mice responded very well to anti-CD3 stimulation in vitro; CD4⁺ and CD8⁺ T cells proliferated and produced IFNγ, IL-2, and granzyme B, as in B6 mice. Anti-PD-L1 antibody treatment inhibited MC38 tumor growth in chimeric mice. Moreover, in the chimeras, anti-PD-L1 antibody restored T-cell activation by significantly decreasing PD-1 expression on T cells and increasing IFNγ-producing T cells in the draining lymph nodes and tumors. T cells produced by complemented thymi thus functioned normally in vitro and in vivo. To successfully generate humanized animals by blastocyst complementation, both verification of the function and gene expression profiling of complemented organs/cells in interspecific chimeras will be important in the near future.

Protection against autoimmunity is driven by thymic epithelial cell-mediated regulation of Treg development

Medullary thymic epithelial cells (mTECs) are key antigen-presenting cells mediating T cell tolerance to prevent harmful autoimmunity. mTECs both negatively select self-reactive T cells and promote the development of thymic regulatory T cells (tTregs) that mediate peripheral tolerance. The relative importance of these two mechanisms of thymic education to prevent autoimmunity is unclear. We generated a mouse model to specifically target the development and function of mTECs by conditional ablation of the NF-κB–inducing kinase (NIK) in the TEC compartment. In contrast to germline-deficient NIK−/− mice, Foxn1CreNIKfl/fl mice rapidly developed fatal T cell–dependent multiorgan autoimmunity shortly after birth. Thymic transplantation and adoptive transfer experiments demonstrated that autoimmunity arises specifically from the emergence of dysfunctional tTregs. Thus, Treg function, rather than negative selection, enforces the protection of peripheral tissues from autoimmune attack.

Human stem cell-derived thymic epithelial cells enhance human T-cell development in a xenogeneic thymus

BACKGROUND

Generation of thymic tissue from pluripotent stem cells would provide therapies for acquired and congenital thymic insufficiency states.

OBJECTIVES

This study aimed to generate human thymic epithelial progenitors from human embryonic stem cells (hES-TEPs) and to assess their thymopoietic function in vivo.

METHODS

This study differentiated hES-TEPs by mimicking developmental queues with FGF8, retinoic acid, SHH, Noggin, and BMP4. Their function was assessed in reaggregate cellular grafts under the kidney capsule and in hybrid thymi by incorporating them into swine thymus (SwTHY) grafts implanted under the kidney capsules of immunodeficient mice that received human hematopoietic stem and progenitor cells (hHSPCs) intravenously.

RESULTS

Cultured hES-TEPs expressed FOXN1 and formed colonies expressing EPCAM and both cortical and medullary thymic epithelial cell markers. In thymectomized immunodeficient mice receiving hHSPCs, hES-TEPs mixed with human thymic mesenchymal cells supported human T-cell development. Hypothesizing that support from non-epithelial thymic cells might allow long-term function of hES-TEPs, the investigators injected them into SwTHY tissue, which supports human thymopoiesis in NOD severe combined immunodeficiency IL2Rγ^null mice receiving hHSPCs. hES-TEPs integrated into SwTHY grafts, enhanced human thymopoiesis, and increased peripheral CD4⁺ naive T-cell reconstitution.

CONCLUSIONS

This study has developed and demonstrated in vivo thymopoietic function of hES-TEPs generated with a novel differentiation protocol. The SwTHY hybrid thymus model demonstrates beneficial effects on human thymocyte development of hES-TEPs maturing in the context of a supportive thymic structure.

Ectopic cervical thymi and no thymic involution until midlife in naked mole rats

Immunosenescence is a hallmark of aging and manifests as increased susceptibility to infection, autoimmunity, and cancer in the elderly. One component of immunosenescence is thymic involution, age-associated shrinkage of the thymus, observed in all vertebrates studied to date. The naked mole rat (Heterocephalus glaber) has become an attractive animal model in aging research due to its extreme longevity and resistance to disease. Here, we show that naked mole rats display no thymic involution up to 11 years of age. Furthermore, we found large ectopic cervical thymi in addition to the canonical thoracic thymus, both being identical in their cell composition. The developmental landscape in naked mole rat thymi revealed overt differences from the murine T-cell compartment, most notably a decrease of CD4+ /CD8+ double-positive cells and lower abundance of cytotoxic effector T cells. Our observations suggest that naked mole rats display a delayed immunosenescence. Therapeutic interventions aimed at reversing thymic aging remain limited, underscoring the importance of understanding the cellular and molecular mechanisms behind a sustained immune function in the naked mole rat.

The New "Wholly Trinity" in the Diagnosis and Management of Inborn Errors of Immunity

The field of immunology has a rich and diverse history, and the study of inborn errors of immunity (IEIs) represents both the "cake" and the "icing on top of the cake," as it has enabled significant advances in our understanding of the human immune system. This explosion of knowledge has been facilitated by a unique partnership, a triumvirate formed by the physician who gathers detailed immunological and clinical phenotypic information from, and shares results with, the patient; the laboratory scientist/immunologist who performs diagnostic testing, as well as advanced functional correlative studies; and the genomics scientist/genetic counselor, who conducts and interprets varied genetic analyses, all of which are essential for dissecting constitutional genetic disorders. Although the basic principles of clinical care have not changed in recent years, the practice of clinical immunology has changed to reflect the prodigious advances in diagnostics, genomics, and therapeutics. An "omic/tics"-centric approach to IEI reflects the tremendous strides made in the field in the new millennium with recognition of new disorders, characterization of the molecular underpinnings, and development and implementation of personalized treatment strategies. This review brings renewed attention to bear on the indispensable "trinity" of phenotypic, genomic, and immunological analyses in the diagnosis, management, and treatment of IEIs.

Current and Future Therapeutic Approaches for Thymic Stromal Cell Defects

Inborn errors of thymic stromal cell development and function lead to impaired T-cell development resulting in a susceptibility to opportunistic infections and autoimmunity. In their most severe form, congenital athymia, these disorders are life-threatening if left untreated. Athymia is rare and is typically associated with complete DiGeorge syndrome, which has multiple genetic and environmental etiologies. It is also found in rare cases of T-cell lymphopenia due to Nude SCID and Otofaciocervical Syndrome type 2, or in the context of genetically undefined defects. This group of disorders cannot be corrected by hematopoietic stem cell transplantation, but upon timely recognition as thymic defects, can successfully be treated by thymus transplantation using cultured postnatal thymic tissue with the generation of naïve T-cells showing a diverse repertoire. Mortality after this treatment usually occurs before immune reconstitution and is mainly associated with infections most often acquired pre-transplantation. In this review, we will discuss the current approaches to the diagnosis and management of thymic stromal cell defects, in particular those resulting in athymia. We will discuss the impact of the expanding implementation of newborn screening for T-cell lymphopenia, in combination with next generation sequencing, as well as the role of novel diagnostic tools distinguishing between hematopoietic and thymic stromal cell defects in facilitating the early consideration for thymus transplantation of an increasing number of patients and disorders. Immune reconstitution after the current treatment is usually incomplete with relatively common inflammatory and autoimmune complications, emphasizing the importance for improving strategies for thymus replacement therapy by optimizing the current use of postnatal thymus tissue and developing new approaches using engineered thymus tissue.

Structure, Dynamics and Function of the 26S Proteasome

The 26S proteasome is the most complex ATP-dependent protease machinery, of ~2.5 MDa mass, ubiquitously found in all eukaryotes. It selectively degrades ubiquitin-conjugated proteins and plays fundamentally indispensable roles in regulating almost all major aspects of cellular activities. To serve as the sole terminal "processor" for myriad ubiquitylation pathways, the proteasome evolved exceptional adaptability in dynamically organizing a large network of proteins, including ubiquitin receptors, shuttle factors, deubiquitinases, AAA-ATPase unfoldases, and ubiquitin ligases, to enable substrate selectivity and processing efficiency and to achieve regulation precision of a vast diversity of substrates. The inner working of the 26S proteasome is among the most sophisticated, enigmatic mechanisms of enzyme machinery in eukaryotic cells. Recent breakthroughs in three-dimensional atomic-level visualization of the 26S proteasome dynamics during polyubiquitylated substrate degradation elucidated an extensively detailed picture of its functional mechanisms, owing to progressive methodological advances associated with cryogenic electron microscopy (cryo-EM). Multiple sites of ubiquitin binding in the proteasome revealed a canonical mode of ubiquitin-dependent substrate engagement. The proteasome conformation in the act of substrate deubiquitylation provided insights into how the deubiquitylating activity of RPN11 is enhanced in the holoenzyme and is coupled to substrate translocation. Intriguingly, three principal modes of coordinated ATP hydrolysis in the heterohexameric AAA-ATPase motor  were discovered to regulate intermediate functional steps of the proteasome, including ubiquitin-substrate engagement, deubiquitylation, initiation of substrate translocation and processive substrate degradation. The atomic dissection of the innermost working of the 26S proteasome opens up a new era in our understanding of the ubiquitin-proteasome system and has far-reaching implications in health and disease.

Inborn errors of thymic stromal cell development and function

As the primary site for T cell development, the thymus is responsible for the production and selection of a functional, yet self-tolerant T cell repertoire. This critically depends on thymic stromal cells, derived from the pharyngeal apparatus during embryogenesis. Thymic epithelial cells, mesenchymal and vascular elements together form the unique and highly specialised microenvironment required to support all aspects of thymopoiesis and T cell central tolerance induction. Although rare, inborn errors of thymic stromal cells constitute a clinically important group of conditions because their immunological consequences, which include autoimmune disease and T cell immunodeficiency, can be life-threatening if unrecognised and untreated. In this review, we describe the molecular and environmental aetiologies of the thymic stromal cell defects known to cause disease in humans, placing particular emphasis on those with a propensity to cause thymic hypoplasia or aplasia and consequently severe congenital immunodeficiency. We discuss the principles underpinning their diagnosis and management, including the use of novel tools to aid in their identification and strategies for curative treatment, principally transplantation of allogeneic thymus tissue.

Combined transient ablation and single-cell RNA-sequencing reveals the development of medullary thymic epithelial cells

Medullary thymic epithelial cells (mTECs) play a critical role in central immune tolerance by mediating negative selection of autoreactive T cells through the collective expression of the peripheral self-antigen compartment, including tissue-specific antigens (TSAs). Recent work has shown that gene-expression patterns within the mTEC compartment are heterogenous and include multiple differentiated cell states. To further define mTEC development and medullary epithelial lineage relationships, we combined lineage tracing and recovery from transient in vivo mTEC ablation with single-cell RNA-sequencing in Mus musculus. The combination of bioinformatic and experimental approaches revealed a non-stem transit-amplifying population of cycling mTECs that preceded Aire expression. We propose a branching model of mTEC development wherein a heterogeneous pool of transit-amplifying cells gives rise to Aire- and Ccl21a-expressing mTEC subsets. We further use experimental techniques to show that within the Aire-expressing developmental branch, TSA expression peaked as Aire expression decreased, implying Aire expression must be established before TSA expression can occur. Collectively, these data provide a roadmap of mTEC development and demonstrate the power of combinatorial approaches leveraging both in vivo models and high-dimensional datasets.

Specialized cells in the immune system known as T cells protect the body from infection by destroying disease-causing microbes, such as bacteria or viruses. T cells use proteins on their surface called receptors to stick to infectious microbes and remove them from the body. Some newly developed T-cells, however, contain receptors that recognize and bind to cells that belong in the body. If these faulty T cells are released, they can attack healthy tissues and cause an autoimmune disease.

After a new T cell is developed, it gets carried to a gland in the chest known as the thymus. Cells in the thymus called mTECs screen T cells for receptors that may bind to the body’s tissues. mTECs do this by presenting T cells with proteins that are commonly found on the surface of healthy cells in the body. If a T cell recognizes any of these ‘tissue specific proteins’, it is destroyed or given a new role in the body. Some faulty T cells, however, still manage to evade detection. One way to uncover why this might happen is to investigate how mTECs develop. Previous work showed that mTECs transition through various stages before reaching their final form. However, the order in which these events occur remained unclear.

To gain a better understanding of these developmental steps, Wells, Miller et al. extracted mTECs from the thymus of mice and analyzed the genetic make-up of individual cells. This uncovered a missing link in mTEC development: a new type of cell that is the immediate predecessor of the final mTEC. These ‘predecessor’ cells were actively growing, highlighting that mTECs can be constantly generated in the body. By probing the genes that generate tissue-specific proteins in mTECs, Wells, Miller et al. revealed that these proteins were only produced for short periods and in the late stages of mTEC development.

These findings contribute to our understanding of how mTECs develop to screen T cells. Mapping these developmental stages will make it easier to identify when faulty T cells are able to evade mTECs. This will lead to earlier detection of autoimmune diseases which could result in better treatments.

Pleiotropic Functions of FoxN1: Regulating Different Target Genes during Embryogenesis and Nymph Molting in the Brown Planthopper

FoxN1 gene belongs to the forkhead box gene family that comprises a diverse group of “winged helix” transcription factors that have been implicated in a variety of biochemical and cellular processes. In the brown planthopper (BPH), FoxN1 is highly expressed in the ovaries and newly laid eggs, where it acted as an indispensable gene through its molecular targets to regulate early embryonic development. Moreover, the results of the RNAi experiments indicated that Nilaparvata lugensFoxN1 (NlFoxN1) exhibited pleiotropism: they not only affected the embryogenesis, but also played an important role in molting. RNA-seq and RNAi were further used to reveal potential target genes of NlFoxN1 in different stages. In the eggs, ten downregulated genes were defined as potential target genes of NlFoxN1 because of the similar expression patterns and functions with NlFoxN1. Knockdown of NlFoxN1 or any of these genes prevented the development of the eggs, resulting in a zero hatchability. In the nymphs, NlFoxN1 regulated the expression of a keratin gene, type I cytoskeletal keratin 9 (NlKrt9), to participate in the formation of an intermediate filament framework. Depletion of NlFoxN1 or NlKrt9 in nymphs, BPHs failed to shed their old cuticle during nymph-to-nymph or nymph-to-adult molting and the mortality was almost 100%. Altogether, the pleiotropic roles of NlFoxN1 during embryogenesis and nymph molting were supported by the ability to coordinate the temporal and spatial gene expression of their target genes.

Molecular Insights Into the Causes of Human Thymic Hypoplasia With Animal Models

22q11.2 deletion syndrome (DiGeorge), CHARGE syndrome, Nude/SCID and otofaciocervical syndrome type 2 (OTFCS2) are distinct clinical conditions in humans that can result in hypoplasia and occasionally, aplasia of the thymus. Thymic hypoplasia/aplasia is first suggested by absence or significantly reduced numbers of recent thymic emigrants, revealed in standard-of-care newborn screens for T cell receptor excision circles (TRECs). Subsequent clinical assessments will often indicate whether genetic mutations are causal to the low T cell output from the thymus. However, the molecular mechanisms leading to the thymic hypoplasia/aplasia in diverse human syndromes are not fully understood, partly because the problems of the thymus originate during embryogenesis. Rodent and Zebrafish models of these clinical syndromes have been used to better define the underlying basis of the clinical presentations. Results from these animal models are uncovering contributions of different cell types in the specification, differentiation, and expansion of the thymus. Cell populations such as epithelial cells, mesenchymal cells, endothelial cells, and thymocytes are variably affected depending on the human syndrome responsible for the thymic hypoplasia. In the current review, findings from the diverse animal models will be described in relation to the clinical phenotypes. Importantly, these results are suggesting new strategies for regenerating thymic tissue in patients with distinct congenital disorders.

Identification and functional study of immortalized mouse thymic epithelial cells

As the key cells in a three-dimensional scaffold within the thymus, Thymic epithelial cells (TECs) play critical roles in the homing, migration and differentiation of T cell precursors through adhesive interactions and the release of various cytokines. In this study, primary cultures of mouse TECs were isolated and identified with TEC-specific antibodies CK5 and CK8. These TECs were immortalized by retroviral transduction of simian virus (SV) 40 large T antigen. We then compared the functions of TECs and immortalized TECs (iTECs). Cell morphology and the proliferative capacity of TECs and iTECs were observed by inverted microscope photography and crystal violet assay after passage. A soft agar assay was then performed to observe their clone formation ability. The expression levels of epithelial cell related factors, such as IL-7, Lptin, Pax-9, Sema3A and et al., were detected by IF and qPCR. TECs were co-cultured with human acute monocytic leukemia cells (THP-1), and the effect of TECs on promoting THP-1 proliferation was observed with flow cytometry and CFSE labeling. Senescence-associated β-galactosidase assay was measured to detect the anti-aging capabilities of the cells. Cell cycle distribution was analyzed by propidium iodide (PI) staining, and paclitaxel (PTX)-induced apoptosis was detected by Annexin V-PI staining to evaluate the anti-apoptotic ability of the cells. Throughout, we found that the immortalized TECs still retain the characteristics of primary TECs, such as the morphology, function and epithelial characteristics; however, iTECs have stronger capabilities in proliferation and anti-aging. Our research suggests that the iTECs were successfully immortalized by SV40 large T antigen, and that the biological characteristics and functions of iTECs were similar to the original TECs. This immortalized cell can be used as an efficient cell model in functional research of the thymus substituting primary TECs with iTECs.

Estrogen, estrogen-like molecules and autoimmune diseases

In western countries, the slope of autoimmune disease (AD) incidence is increasing and affects 5-8% of the population. Mainly prevalent in women, these pathologies are due to thymic tolerance processes breakdown. The female sex hormone, estrogen, is involved in this AD female susceptibility. However, predisposition factors have to act in concert with unknown triggering environmental factors (virus, microbiota, pollution) to initiate AD. Individuals are exposed to various environmental compounds that display endocrine disruption abilities. The cellular effects of some of these molecules may be mediated through the aryl hydrocarbon receptor (AhR). Here, we review the effects of these molecules on the homeostasis of the thymic cells, the immune tolerance intrinsic factors (transcription factors, epigenetic marks) and on the immune tolerance extrinsic factors (microbiota, virus sensibility). This review highlights the contribution of estrogen and endocrine disruptors on the dysregulation of mechanisms sustaining AD development.

FOXN1 compound heterozygous mutations cause selective thymic hypoplasia in humans

We report on 2 patients with compound heterozygous mutations in forkhead box N1 (FOXN1), a transcription factor essential for thymic epithelial cell (TEC) differentiation. TECs are critical for T cell development. Both patients had a presentation consistent with T-/loB+NK+ SCID, with normal hair and nails, distinct from the classic nude/SCID phenotype in individuals with autosomal-recessive FOXN1 mutations. To understand the basis of this phenotype and the effects of the mutations on FOXN1, we generated mice using CRISPR-Cas9 technology to genocopy mutations in 1 of the patients. The mice with the Foxn1 compound heterozygous mutations had thymic hypoplasia, causing a T-B+NK+ SCID phenotype, whereas the hair and nails of these mice were normal. Characterization of the functional changes due to the Foxn1 mutations revealed a 5-amino acid segment at the end of the DNA-binding domain essential for the development of TECs but not keratinocytes. The transcriptional activity of this Foxn1 mutant was partly retained, indicating a region that specifies TEC functions. Analysis of an additional 9 FOXN1 mutations identified in multiple unrelated patients revealed distinct functional consequences contingent on the impact of the mutation on the DNA-binding and transactivation domains of FOXN1.

Anephrogenic phenotype induced by SALL1 gene knockout in pigs

To combat organ shortage in transplantation medicine, a novel strategy has been proposed to generate human organs from exogenous pluripotent stem cells utilizing the developmental mechanisms of pig embryos/foetuses. Genetically modified pigs missing specific organs are key elements in this strategy. In this study, we demonstrate the feasibility of using a genome-editing approach to generate anephrogenic foetuses in a genetically engineered pig model. SALL1 knockout (KO) was successfully induced by injecting genome-editing molecules into the cytoplasm of pig zygotes, which generated the anephrogenic phenotype. Extinguished SALL1 expression and marked dysgenesis of nephron structures were observed in the rudimentary kidney tissue of SALL1-KO foetuses. Biallelic KO mutations of the target gene induced nephrogenic defects; however, biallelic mutations involving small in-frame deletions did not induce the anephrogenic phenotype. Through production of F1 progeny from mutant founder pigs, we identified mutations that could reliably induce the anephrogenic phenotype and hence established a line of fertile SALL1-mutant pigs. Our study lays important technical groundwork for the realization of human kidney regeneration through the use of an empty developmental niche in pig foetuses.

Dynamic Regulation of Proteasome Expression

The 26S proteasome is a multisubunit complex that catalyzes the degradation of ubiquitinated proteins. The proteasome comprises 33 distinct subunits, all of which are essential for its function and structure. Proteasomes are necessary for various biological processes in cells; therefore, precise regulation of proteasome expression and activity is essential for maintaining cellular health and function. Two decades of research revealed that transcription factors such as Rpn4 and Nrf1 control expression of proteasomes. In this review, we focus on the current understanding and recent findings on the mechanisms underlying the regulation of proteasome expression, as well as the translational regulation of proteasomes.

Transgenic Exosomes for Thymus Regeneration

During senescence, Wnt4 expression is down-regulated (unlike their Frizzled receptors), while PPARgamma expression increases in the thymus. Together, these changes allow for thymic degeneration to occur, observed as adipose involution. However, when restored, Wnt4 can efficiently counteract PPARgamma and prevent thymic senescence from developing. The Wnt-pathway activator miR27b has also been reported to inhibit PPARgamma. Our goal was to evaluate the Wnt4 and miR27b levels of Wnt4-transgenic thymic epithelial cell (TEC)-derived exosomes, show their regenerative potential against age-related thymic degeneration, and visualize their binding and distribution both in vitro and in vivo. First, transgenic exosomes were harvested from Wnt4 over-expressing TECs and analyzed by transmission electron microscopy. This unveiled exosomes ranging from 50 to 100 nm in size. Exosomal Wnt4 protein content was assayed by ELISA, while miR27b levels were measured by TaqMan qPCR, both showing elevated levels in transgenic exosomes relative to controls. Of note, kit-purified TEI (total exosome isolate) outperformed UC (ultracentrifugation)-purified exosomes in these parameters. In addition, a significant portion of exosomal Wnt4 proved to be displayed on exosomal surfaces. For functional studies, steroid (Dexamethasone or DX)-induced TECs were used as cellular aging models in which DX-triggered cellular aging was efficiently prevented by transgenic exosomes. Finally, DiI lipid-stained exosomes were applied on the mouse thymus sections and also iv-injected into mice, for in vitro binding and in vivo tracking, respectively. We have observed distinct staining patterns using DiI lipid-stained transgenic exosomes on sections of young and aging murine thymus samples. Moreover, in vivo injected DiI lipid-stained transgenic exosomes showed detectable homing to the thymus. Of note, Wnt4-transgenic exosome homing outperformed control (Wnt5a-transgenic) exosome homing. In summary, our findings indicate that exosomal Wnt4 and miR27b can efficiently counteract thymic adipose involution. Although extrapolation of mouse results to the human setting needs caution, our results appoint transgenic TEC exosomes as promising tools of immune rejuvenation and contribute to the characterization of the immune-modulatory effects of extracellular vesicles in the context of regenerative medicine.

Medullary thymic epithelial cells: Deciphering the functional diversity beyond promiscuous gene expression

Within the thymus, cortical and medullary thymic epithelial cells (cTECs and mTECs, respectively) provide unique microenvironments for the development of T cells that are responsive to diverse foreign antigens while self-tolerant. Essential for tolerance induction, mTECs play a critical role in negative selection and T regulatory cell differentiation. In this article, we review the current knowledge on the functional diversity within mTECs and discuss how these novel subsets contribute to tolerance induction and are integrated in the complex blueprint of mTEC differentiation.

Cultured Human Thymic-Derived Cells Display Medullary Thymic Epithelial Cell Phenotype and Functionality

Thymic epithelial cells are one of the main components of the thymic microenvironment required for T-cell development. In this work, we describe an efficient method free of enzymatic and Facs-sorted methods to culture human medullary thymic epithelial cells without affecting the cell phenotypic, physiologic and functional features. Human medulla thymic epithelial cells (mTECs) are obtained by culturing thymic biopsies explants. After 7 days of primo-culture, mTECs keep their ability to express key molecules involved in immune tolerance processes such as autoimmune regulator, tissue-specific antigens, chemokines, and cytokines. In addition, the cells sensor their cultured environment and consequently adjust their gene expression network. Therefore, we describe and provide a human mTEC model that may be used to test the effect of various molecules on thymic epithelial cell homeostasis and physiology. This method should allow the investigations of the specificities and the knowledge of human mTECs in normal or pathological conditions and therefore discontinue the extrapolations done on the murine models.

EphB receptors, mainly EphB3, contribute to the proper development of cortical thymic epithelial cells

EphB and their ligands ephrin-B are an important family of protein tyrosine kinase receptors involved in thymocyte-thymic epithelial cell interactions known to be key for the maturation of both thymic cell components. In the present study, we have analyzed the maturation of cortical thymic epithelium in EphB-deficient thymuses evaluating the relative relevance of EphB2 and EphB3 in the process. Results support a relationship between the epithelial hypocellularity of mutant thymuses and altered development of thymocytes, lower proportions of cycling thymic epithelial cells and increased epithelial cell apoptosis. Together, these factors induce delayed development of mutant cortical TECs, defined by the expression of different cell markers, i.e. Ly51, CD205, MHCII, CD40 and β5t. Furthermore, although both EphB2 and EphB3 are necessary for cortical thymic epithelial maturation, the relevance of EphB3 is greater since EphB3-/- thymic cortex exhibits a more severe phenotype than that of EphB2-deficient thymuses.

Transcriptional profiling analysis of Zearalenone-induced inhibition proliferation on mouse thymic epithelial cell line 1

Zearalenone (ZEA) was a mycotoxin biosynthesized by a variety of Fusarium fungi via a polypeptide pathway. ZEA has significant toxic reaction on immune cells. Thymic epithelial cells (TECs) as a crucial constituent of thymic stroma can provide unique microenvironment for thymocyte maturation, but the mechanism of ZEA affecting the TECs is poorly understood. The basic data about gene expression differences for the ZEA on thymic epithelial cell line 1 (MTEC1) will help us to elucidate this mechanism. Here, cell viability and proliferation assay and transcriptome sequencing on MTEC1 treated with ZEA were performed. 4188 differentially expressed genes (DEGs) between ZEA treated and control groups were identified, confirmed and analyzed. Our results showed that 10-50μg/ml ZEA significantly inhibited MTEC1 proliferation and arrested cell cycle at G2/M phase. Gene ontology and KEGG pathway analysis revealed that Chemokine, JAK-STAT and Toll-like receptor signaling pathway, were involved in the cell cycle pathway. 16 key genes involved in the cell cycle processes were validated and the results suggested that Mitotic catastrophe (MC) may take part in ZEA inhibition of METC1 cell proliferation. These data highlighted the importance of cell cycle pathway in MTEC1 treated with ZEA, and will contribute to get the molecular mechanisms of ZEA inhibition of MTEC1 cell proliferation.

Molecular Classification of Primary Immunodeficiencies of T Lymphocytes

Proper regulation of the immune system is required for protection against pathogens and preventing autoimmune disorders. Inborn errors of the immune system due to inherited or de novo germline mutations can lead to the loss of protective immunity, aberrant immune homeostasis, and the development of autoimmune disease, or combinations of these. Forward genetic screens involving clinical material from patients with primary immunodeficiencies (PIDs) can vary in severity from life-threatening disease affecting multiple cell types and organs to relatively mild disease with susceptibility to a limited range of pathogens or mild autoimmune conditions. As central mediators of innate and adaptive immune responses, T cells are critical orchestrators and effectors of the immune response. As such, several PIDs result from loss of or altered T cell function. PID-associated functional defects range from complete absence of T cell development to uncontrolled effector cell activation. Furthermore, the gene products of known PID causal genes are involved in diverse molecular pathways ranging from T cell receptor signaling to regulators of protein glycosylation. Identification of the molecular and biochemical cause of PIDs can not only guide the course of treatment for patients, but also inform our understanding of the basic biology behind T cell function. In this chapter, we review PIDs with known genetic causes that intrinsically affect T cell function with particular focus on perturbations of biochemical pathways.

Chd7 Is Critical for Early T-Cell Development and Thymus Organogenesis in Zebrafish

Coloboma, heart defect, atresia choanae, retarded growth and development, genital hypoplasia, ear anomalies/deafness (CHARGE) syndrome is a congenital disorder affecting multiple organs and mainly caused by mutations in CHD7, a gene encoding a chromatin-remodeling protein. Immunodeficiency and reduced T cells have been noted in CHARGE syndrome. However, the mechanisms underlying T lymphopenia are largely unexplored. Herein, we observed dramatic decrease of T cells in both chd7knockdown and knockout zebrafish embryos. Unexpectedly, hematopoietic stem and progenitor cells and, particularly, lymphoid progenitor cells were increased peripherally in nonthymic areas in chd7-deficient embryos, unlikely to contribute to the T-cell decrease. Further analysis demonstrated that both the organogenesis and homing function of the thymus were seriously impaired. Chd7 might regulate thymus organogenesis through modulating the development of both neural crest cell-derived mesenchyme and pharyngeal endoderm-derived thymic epithelial cells. The expression of foxn1, a central regulator of thymic epithelium, was remarkably down-regulated in the pharyngeal region in chd7-deficient embryos. Moreover, the T-cell reduction in chd7-deficient embryos was partially rescued by overexpressing foxn1, suggesting that restoring thymic epithelium may be a potential therapeutic strategy for treating immunodeficiency in CHARGE syndrome. Collectively, the results indicated that chd7 was critical for thymic development and T-lymphopenia in CHARGE syndrome may be mainly attributed to the defects of thymic organogenesis. The current finding may benefit the diagnosis and therapy of T lymphopenia and immunodeficiency in CHARGE syndrome.

MicroRNAs Regulate Thymic Epithelium in Age-Related Thymic Involution via Down- or Upregulation of Transcription Factors

Age-related thymic involution is primarily induced by defects in nonhematopoietic thymic epithelial cells (TECs). It is characterized by dysfunction of multiple transcription factors (TFs), such as p63 and FoxN1, and also involves other TEC-associated regulators, such as Aire. These TFs and regulators are controlled by complicated regulatory networks, in which microRNAs (miRNAs) act as a key player. miRNAs can either directly target the 3'-UTRs (untranslated regions) of the TFs to suppress TF expression or target TF inhibitors to reduce or increase TF inhibitor expression and thereby indirectly enhance or inhibit TF expression. Here, we review the current understanding and recent studies about how miRNAs are involved in age-related thymic involution via regulation of TEC-autonomous TFs. We also discuss potential strategies for targeting miRNAs to rejuvenate age-related declined thymic function.

FOXN1 Transcription Factor in Epithelial Growth and Wound Healing

FOXN1 is a prodifferentiation transcription factor in the skin epithelium. Recently, it has also emerged as an important player in controlling the skin wound healing process, as it actively participates in reepithelialization and is thought to be responsible for scar formation. FOXN1 positivity is also a feature of pigmented keratinocytes, including nevi, and FOXN1 is an attribute of benign epithelial tumors. The lack of FOXN1 favors the skin regeneration process displayed by nude mice, pointing to FOXN1 as a switch between regeneration and reparative processes. The stem cell niche provides a functional source of cells after the loss of tissue following wounding. The involvement of prodifferentiation factors in the regulation of this pool of stem cells is suggested. However, the exact mechanism is still under question, and we speculate that the FOXN1 transcription factor is involved in this process. This review analyzes the pleiotropic effects of FOXN1 in the skin, its function in the tumorigenesis process, and its potential role in depletion of the stem cell niche after injury, as well as its suggested mechanistic role, acting in a cell-autonomous and a non-cell-autonomous manner during skin self-renewal.

mTFkb: a knowledgebase for fundamental annotation of mouse transcription factors

Transcription factors (TFs) are well-known important regulators in cell biology and tissue development. However, in mouse, one of the most widely-used model species, currently the vast majority of the known TFs have not been functionally studied due to the lack of sufficient annotations. To this end, we collected and analyzed the whole transcriptome sequencing data from more than 30 major mouse tissues and used the expression profiles to annotate the TFs. We found that the expression patterns of the TFs are highly correlated with the histology of the tissue types thus can be used to infer the potential functions of the TFs. Furthermore, we found that as many as 30% TFs display tissue-specific expression pattern, and these tissue-specific TFs are among the key TFs in their corresponding tissues. We also observed signals of divergent transcription associated with many TFs with unique expression pattern. Lastly, we have integrated all the data, our analysis results as well as various annotation resources to build a web-based database named mTFkb freely accessible at http://www.myogenesisdb.org/mTFkb/. We believe that mTFkb could serve as a useful and valuable resource for TF studies in mouse.

Microbial lysate upregulates host oxytocin

Neuropeptide hormone oxytocin has roles in social bonding, energy metabolism, and wound healing contributing to good physical, mental and social health. It was previously shown that feeding of a human commensal microbe Lactobacillus reuteri (L. reuteri) is sufficient to up-regulate endogenous oxytocin levels and improve wound healing capacity in mice. Here we show that oral L. reuteri-induced skin wound repair benefits extend to human subjects. Further, dietary supplementation with a sterile lysate of this microbe alone is sufficient to boost systemic oxytocin levels and improve wound repair capacity. Oxytocin-producing cells were found to be increased in the caudal paraventricular nucleus [PVN] of the hypothalamus after feeding of a sterile lysed preparation of L. reuteri, coincident with lowered blood levels of stress hormone corticosterone and more rapid epidermal closure, in mouse models. We conclude that microbe viability is not essential for regulating host oxytocin levels. The results suggest that a peptide or metabolite produced by bacteria may modulate host oxytocin secretion for potential public or personalized health goals.

Dysfunction of the thymus in mice with hypertension

The aim of this study was to evaluate thymus function in mice with hypertension. A total of 60 C57BL/6J mice were randomized into control, sham surgery and two-kidney, one-clip groups (n=20 in each). At 4 or 8 weeks after surgery, mice were sacrificed, and blood, spleens, kidneys and thymuses were harvested. The results of reverse transcription-quantitative polymerase chain reaction analysis revealed that the mRNA levels of Forkhead box protein N1 (Foxn1) and autoimmune regulator (AIRE) in the thymus tissue of mice from the HTN group were significantly lower than those from the control group at 4 and 8 weeks (P<0.05). Foxn1 and AIRE expression was also reduced in the sham surgery group at 4 weeks after surgery, but had recovered 4 weeks later. Similar results were observed for the expression of signal-joint T cell receptor excision circles and the percentages of T cell subsets. The present study indicates that impaired thymus function is associated with hypertension in mice, which suggests that thymus function may be a novel target for the treatment of patients with hypertension.

FOXN1 deficient nude severe combined immunodeficiency

Nude severe combined immunodeficiency is a rare inherited disease caused by autosomal recessive loss-of-function mutations in FOXN1. This gene encodes a transcription factor essential for the development of the thymus, the primary lymphoid organ that supports T-cell development and selection. To date nine cases have been reported presenting with the clinical triad of absent thymus resulting in severe T-cell immunodeficiency, congenital alopecia universalis and nail dystrophy. Diagnosis relies on testing for FOXN1 mutations, which allows genetic counselling and guides therapeutic management. Options for treating the underlying immune deficiency include HLA-matched genoidentical haematopoietic cell transplantation containing mature donor T-cells or thymus tissue transplantation. Experience from other severe combined immune deficiency syndromes suggests that early diagnosis, supportive care and definitive management result in better patient outcomes. Without these the prognosis is poor due to early-onset life threatening infections.

Progress on thymic function from Maui

Maui, Hawaii, was the home for the latest Global Thymus Network meeting 5-9 June 2016. Participants gathered together to discuss how one little organ can have such huge effects.

MicroRNA-205 Maintains T Cell Development following Stress by Regulating Forkhead Box N1 and Selected Chemokines

The thymus, an organ responsible for T cell development, is one of the more stress-sensitive tissues in the body. Stress, in the form of infections, radiation exposure, and steroids, impairs thymic epithelial cell (TEC) functions and induces the programmed cell death of immature thymocytes. MicroRNAs are small noncoding RNAs involved in tissue repair and homeostasis, with several supporting T cell development. We report that miR-205, an epithelial-specific miR, maintains thymopoiesis following inflammatory perturbations. Thus, the activation of diverse pattern recognition receptors in mice causes a more severe thymic hypoplasia and delayed T cell recovery when miR-205 is conditionally ablated in TECs. Gene expression comparisons in the TECs with/without miR-205 revealed a significant differential regulation of chemokine/chemokine receptor pathways, antigen processing components, and changes in the Wnt signaling system. This was partly a consequence of reduced expression of the transcriptional regulator of epithelial cell function, Forkhead Box N1 (Foxn1), and its two regulated targets, stem cell factor and ccl25, following stress. miR-205 mimics supplemented into miR-205-deficient fetal thymic organ cultures restored Foxn1 expression along with ccl25 and stem cell factor A number of putative targets of miR-205 were up-regulated in TECs lacking miR-205, consistent with an important role for this miR in supporting T cell development in response to stress.

Eph/ephrin-B-mediated cell-to-cell interactions govern MTS20(+) thymic epithelial cell development

Thymus development is a complex process in which cell-to-cell interactions between thymocytes and thymic epithelial cells (TECs) are essential to allow a proper maturation of both thymic cell components. Although signals that control thymocyte development are well known, mechanisms governing TEC maturation are poorly understood, especially those that regulate the maturation of immature TEC populations during early fetal thymus development. In this study, we show that EphB2-deficient, EphB2LacZ and EphB3-deficient fetal thymuses present a lower number of cells and delayed maturation of DN cell subsets compared to WT values. Moreover, deficits in the production of chemokines, known to be involved in the lymphoid seeding into the thymus, contribute in decreased proportions of intrathymic T cell progenitors (PIRA/B(+)) in the mutant thymuses from early stages of development. These features correlate with increased proportions of MTS20(+) cells but fewer MTS20(-) cells from E13.5 onward in the deficient thymuses, suggesting a delayed development of the first epithelial cells. In addition, in vitro the lack of thymocytes or the blockade of Eph/ephrin-B-mediated cell-to-cell interactions between either thymocytes-TECs or TECs-TECs in E13.5 fetal thymic lobes coursed with increased proportions of MTS20(+) TECs. This confirms, for the first time, that the presence of CD45(+) cells, corresponding at these stages to DN1 and DN2 cells, and Eph/ephrin-B-mediated heterotypic or homotypic cell interactions between thymocytes and TECs, or between TECs and themselves, contribute to the early maturation of MTS20(+) TECs.

Beneficial bacteria inhibit cachexia

Muscle wasting, known as cachexia, is a debilitating condition associated with chronic inflammation such as during cancer. Beneficial microbes have been shown to optimize systemic inflammatory tone during good health; however, interactions between microbes and host immunity in the context of cachexia are incompletely understood. Here we use mouse models to test roles for bacteria in muscle wasting syndromes. We find that feeding of a human commensal microbe, Lactobacillus reuteri, to mice is sufficient to lower systemic indices of inflammation and inhibit cachexia. Further, the microbial muscle-building phenomenon extends to normal aging as wild type animals exhibited increased growth hormone levels and up-regulation of transcription factor Forkhead Box N1 [FoxN1] associated with thymus gland retention and longevity. Interestingly, mice with a defective FoxN1 gene (athymic nude) fail to inhibit sarcopenia after L. reuteri therapy, indicating a FoxN1-mediated mechanism. In conclusion, symbiotic bacteria may serve to stimulate FoxN1 and thymic functions that regulate inflammation, offering possible alternatives for cachexia prevention and novel insights into roles for microbiota in mammalian ontogeny and phylogeny.

Loss of Pten Disrupts the Thymic Epithelium and Alters Thymic Function

The thymus is the site of T cell development and selection. In addition to lymphocytes, the thymus is composed of several types of stromal cells that are exquisitely organized to create the appropriate environment and microenvironment to support the development and selection of maturing T cells. Thymic epithelial cells (TECs) are one of the more important cell types in the thymic stroma, and they play a critical role in selecting functional T cell clones and supporting their development. In this study, we used a mouse genetics approach to investigate the consequences of deleting the Pten tumor suppressor gene in the TEC compartment of the developing thymus. We found that PTEN deficiency in TECs results in a smaller thymus with significantly disordered architecture and histology. Accordingly, loss of PTEN function also results in decreased T cells with a shift in the distribution of T cell subtypes towards CD8+ T cells. These experiments demonstrate that PTEN is critically required for the development of a functional thymic epithelium in mice. This work may help better understand the effects that certain medical conditions or clinical interventions have upon the thymus and immune function.

Changing in lipid profile induced by the mutation of Foxn1 gene: A lipidomic analysis of Nude mice skin

Nude mice carry a spontaneous mutation affecting the gene Foxn1 mainly expressed in the epidermis. This gene is involved in several skin functions, especially in the proliferation and the differentiation of keratinocytes which are key cells of epithelial barrier. The skin, a protective barrier for the body, is essentially composed of lipids. Taking into account these factors, we conducted a lipidomic study to search for any changes in lipid composition of skin possibly related to Foxn1 mutation. Lipids were extracted from skin biopsies of Nude and BALB/c mice to be analyzed by liquid chromatography coupled to a high resolution mass spectrometer (HRMS). Multivariate and univariate data analyses were carried out to compare lipid extracts. Identification was performed using HRMS data, retention time and mass spectrometry fragmentation study. These results indicate that mutation of Foxn1 leads to significant modifications in the lipidome in Nude mice skin. An increase in cholesterol sulfate, phospholipids, sphingolipids and fatty acids associated with a decrease in glycerolipids suggest that the lipidome in mice skin is regulated by the Foxn1 gene.

Severe combined immunodeficiency--an update

Severe combined immunodeficiencies (SCIDs) are a group of inherited disorders responsible for severe dysfunctions of the immune system. These diseases are life-threatening when the diagnosis is made too late; they are the most severe forms of primary immunodeficiency. SCID patients often die during the first two years of life if appropriate treatments to reconstitute their immune system are not undertaken. Conventionally, SCIDs are classified according either to the main pathway affected by the molecular defect or on the basis of the specific immunologic phenotype that reflects the stage where the blockage occurs during the differentiation process. However, during the last few years many new causative gene alterations have been associated with unusual clinical and immunological phenotypes. Many of these novel forms of SCID also show extra-hematopoietic alterations, leading to complex phenotypes characterized by a functional impairment of several organs, which may lead to a considerable delay in the diagnosis. Here we review the biological and clinical features of SCIDs paying particular attention to the most recently identified forms and to their unusual or extra-immunological clinical features.

A deletion in FOXN1 is associated with a syndrome characterized by congenital hypotrichosis and short life expectancy in Birman cats

An autosomal recessive syndrome characterized by congenital hypotrichosis and short life expectancy has been described in the Birman cat breed (Felis silvestris catus). We hypothesized that a FOXN1 (forkhead box N1) loss-of-function allele, associated with the nude phenotype in humans, mice and rats, may account for the syndrome observed in Birman cats. To the best of our knowledge, spontaneous mutations in FOXN1 have never been described in non-human, non-rodent mammalian species. We identified a recessive c.1030_1033delCTGT deletion in FOXN1 in Birman cats. This 4-bp deletion was associated with the syndrome when present in two copies. Percentage of healthy carriers in our French panel of genotyped Birman cats was estimated to be 3.2%. The deletion led to a frameshift and a premature stop codon at position 547 in the protein. In silico, the truncated FOXN1 protein was predicted to lack the activation domain and critical parts of the forkhead DNA binding domain, both involved in the interaction between FOXN1 and its targets, a mandatory step to promote normal hair and thymic epithelial development. Our results enlarge the panel of recessive FOXN1 loss-of-function alleles described in mammals. A DNA test is available; it will help owners avoid matings at risk and should prevent the dissemination of this morbid mutation in domestic felines.