Path Of Differentiation Research Articles

The Bile Acid Nuclear Receptor FXRα Is a Critical Regulator of Mouse Germ Cell Fate.

SummarySpermatogenesis is the process by which spermatozoa are generated from spermatogonia. This cell population is heterogeneous, with self-renewing spermatogonial stem cells (SSCs) and progenitor spermatogonia that will continue on a path of differentiation. Only SSCs have the ability to regenerate and sustain spermatogenesis. This makes the testis a good model to investigate stem cell biology. The Farnesoid X Receptor alpha (FXRα) was recently shown to be expressed in the testis. However, its global impact on germ cell homeostasis has not yet been studied. Here, using a phenotyping approach in Fxrα−/− mice, we describe unexpected roles of FXRα on germ cell physiology independent of its effects on somatic cells. FXRα helps establish and maintain an undifferentiated germ cell pool and in turn influences male fertility. FXRα regulates the expression of several pluripotency factors. Among these, in vitro approaches show that FXRα controls the expression of the pluripotency marker Lin28 in the germ cells.

Characterisation of cell cycle arrest and terminal differentiation in a maximally proliferative human epithelial tissue: Lessons from the human hair follicle matrix

Human hair follicle (HF) growth and hair shaft formation require terminal differentiation-associated cell cycle arrest of highly proliferative matrix keratinocytes. However, the regulation of this complex event remains unknown. CIP/KIP family member proteins (p21CIP1, p27KIP1 and p57KIP2) regulate cell cycle progression/arrest, endoreplication, differentiation and apoptosis. Since they have not yet been adequately characterized in the human HF, we asked whether and where CIP/KIP proteins localise in the human hair matrix and pre-cortex in relation to cell cycle activity and HF-specific epithelial cell differentiation that is marked by keratin 85 (K85) protein expression. K85 expression coincided with loss or reduction in cell cycle activity markers, including in situ DNA synthesis (EdU incorporation), Ki-67, phospho-histone H3 and cyclins A and B1, affirming a post-mitotic state of pre-cortical HF keratinocytes. Expression of CIP/KIP proteins was found abundantly within the proliferative hair matrix, concomitant with a role in cell cycle checkpoint control. p21CIP1, p27KIP1 and cyclin E persisted within post-mitotic keratinocytes of the pre-cortex, whereas p57KIP2 protein decreased but became nuclear. These data imply a supportive role for CIP/KIP proteins in maintaining proliferative arrest, differentiation and anti-apoptotic pathways, promoting continuous hair bulb growth and hair shaft formation in anagen VI. Moreover, post-mitotic hair matrix regions contained cells with enlarged nuclei, and DNA in situ hybridisation showed cells that were >2N in the pre-cortex. This suggests that CIP/KIP proteins might counterbalance cyclin E to control further rounds of DNA replication in a cell population that has a propensity to become tetraploid. These data shed new light on the in situ-biography of human hair matrix keratinocytes on their path of active cell cycling, arrest and terminal differentiation, and showcase the human HF as an excellent, clinically relevant model system for cell cycle physiology research of human epithelial cells within their natural tissue habitat.

Immune Response Regulation has Therapeutic Potential in the Treatment of Cancer


 
 
 
 Background: Depending on their path of differentiation, immune cells can have opposing roles in tumour progression. As a result, during growth, tumours undergo selective pressure to produce immunosuppressive factors that contribute to tumour growth, angiogenesis, and metastasis. This review discusses the contribution of different macrophages and T cells to tumour progression, as well as their role in current cancer immunotherapies.
 Methods: We searched for articles online through McGill Library with search terms including the names of different immune cells along with “polarity”, “tumour progression”, or “cancer immunotherapy”. Cancer therapies “CTLA-4 blockade”, “Ipilimumab”, “adoptive cell transfer”, and “PD1 inhibition” were also used as search terms.
 Summary: Depending on the cell types involved, crosstalk between different immune cells in the tumour stroma can contribute to either the development or the inhibition of tumour growth. Certain therapies such as adoptive cytotoxic T lymphocyte (CTLs) transfer and CTLA-4 & PD1 inhibition work by enhancing CTL tumoricidal responses, and have produced durable responses in a small but significant group of patients. Other therapies work by skewing the phenotype of tumour associated macrophages from pro-tumorigenic to anti-tumorigenic. However, disrupting the balance between immune cell functions risks triggering inflammatory disorders such as autoimmunity. Therefore, future directions in cancer immunotherapy include targeting potential responders and restricting therapeutic mechanisms to the tumour microenvironment.
 
 
 

MHCI and CD8 lineage commitment. Prolonged access to thymic epithelial MHCI seals CD8⁺ lineage commitment.

The stage of thymocyte maturation when commitment to the CD8+ lineage is consolidated by recognition of major histocompatibility complex class I (MHCI) on thymic epithelial cells has been elucidated in a study published in Immunology and Cell Biology...

Unlocking epigenetic codes in neurogenesis.

During embryonic and adult neurogenesis, neuronal stem cells follow a highly conserved path of differentiation to give rise to functional neurons at various developmental stages. Epigenetic regulation--including DNA modifications, histone modifications, and noncoding regulatory RNAs, such as microRNA (miRNA) and long noncoding RNA (lncRNA)--plays a pivotal role in embryonic and adult neurogenesis. Here we review the latest in our understanding of the epigenetic regulation in neurogenesis, with a particular focus on newly identified cytosine modifications and their dynamics, along with our perspective for future studies.

MOBILIZATION OF WORLD FLOWERING PLANTS SUPPLIES BASED ON DEVELOPMENT OF SYSTEMATIZED GENETIC COLLECTION OF ADAPTIVE AND AGRONOMIC VALUABLE TRAITS

The problems of study and utilization of plant germplasm collections and arrangement of genetic resources based on botanical, functional, morphological, biochemical, and genetical principles are underlined in the article. The types of identified and systemized germplasm collections and genetic resources of flowering plants are described. The search path and methods of identification, differentiation, arrangement, and selection of genetic donors and germplasm collections of traits of ontogenetic and phylogenetic adaptation are shown in the article.

Increased Membrane Cholesterol in Lymphocytes Diverts T-Cells toward an Inflammatory Response

Cell signaling for T-cell growth, differentiation, and apoptosis is initiated in the cholesterol-rich microdomains of the plasma membrane known as lipid rafts. Herein, we investigated whether enrichment of membrane cholesterol in lipid rafts affects antigen-specific CD4 T-helper cell functions. Enrichment of membrane cholesterol by 40–50% following squalene administration in mice was paralleled by an increased number of resting CD4 T helper cells in periphery. We also observed sensitization of the Th1 differentiation machinery through co-localization of IL-2Rα, IL-4Rα, and IL-12Rβ2 subunits with GM1 positive lipid rafts, and increased STAT-4 and STAT-5 phosphorylation following membrane cholesterol enrichment. Antigen stimulation or CD3/CD28 polyclonal stimulation of membrane cholesterol-enriched, resting CD4 T-cells followed a path of Th1 differentiation, which was more vigorous in the presence of increased IL-12 secretion by APCs enriched in membrane cholesterol. Enrichment of membrane cholesterol in antigen-specific, autoimmune Th1 cells fostered their organ-specific reactivity, as confirmed in an autoimmune mouse model for diabetes. However, membrane cholesterol enrichment in CD4+ Foxp3 + T-reg cells did not alter their suppressogenic function. These findings revealed a differential regulatory effect of membrane cholesterol on the function of CD4 T-cell subsets. This first suggests that membrane cholesterol could be a new therapeutic target to modulate the immune functions, and second that increased membrane cholesterol in various physiopathological conditions may bias the immune system toward an inflammatory Th1 type response.

Interplay Between Local Versus Soluble Transforming Growth Factor-Beta and Fibrin Scaffolds: Role of Cells and Impact on Human Mesenchymal Stem Cell Chondrogenesis

Structural extracellular matrix molecules gain increasing attention as scaffolds for cartilage tissue engineering owing to their natural role as a growth factor repository. We recently observed that a collagen-type I/III (Col-I/III) matrix, human recombinant transforming growth factor-beta (TGF-β) protein, and fibrin hydrogel (FG) combined to a biphasic construct provided sufficient long-term TGF-β support to drive in vitro chondrogenesis of human mesenchymal stem cells (hMSC). Here we ask whether FG and Col-I/III can both retain TGF-β, describe the influence of cell seeding on TGF-β release, and compare the molecular path of hMSC chondrogenic differentiation under soluble versus local TGF-β supply. Release of growth factor from scaffolds augmented with increasing amounts of TGF-β was analyzed over 7 days and chondrogenesis was assessed over 42 days. Low TGF-β release rates from Col-I/III as opposed to higher release from FG indicated that both molecules retained TGF-β, with Col-I/III being the superior storage component. Cell seeding enhanced TGF-β retention in FG by about threefold and almost stopped release beyond 24 h. TGF-β remained bioactive and supported MSC chondrogenesis without impairing the amount of proteoglycan and collagen-type II deposition per cell and per construct compared to standard scaffold-free MSC pellets supplied with soluble TGF-β. Local TGF-β, however, mediated lower cell content, less collagen-type X relative to collagen-type II deposition and no matrix metalloproteinase-13 up-regulation. In conclusion, cells quickly halted release of local TGF-β from FG, turning FG and Col-I/III into attractive TGF-β repositories capable to drive full hMSC chondrogenesis, but via a modulated differentiation pathway. Since only part of the changes was reproduced by transient soluble TGF-β supply, release kinetics alone could not explain the molecular differences, suggesting that local TGF-β acts distinct from its soluble counterpart.

A new genus Acupipora gen. nov. from the upper carboniferous of the East European platform and problem of classification of bryozoans of the order Fenestellida

The species composition of the bryozoan genus Paucipora Termier et Termier, 1971 is revised. A new species, Paucipora akishinensis sp. nov., and a new genus, Acupipora gen. nov., with the type species Polypora subborealis Schulga-Nesterenko, 1951, are described. The problems of classification of the order Fenestellida are discussed. Criteria for the division of the order into families and subfamilies are developed. The evolution of fenestellids is shown to proceed along the path of morphological differentiation of structural elements of colonies, polymerization of autozooecia, and formation of heterozooecia. It was accompanied by morphological parallelisms. A scheme of the phylogenetic relationships between the families and subfamilies of the order is presented.

Stem cells as bone marrow residents

In addition to being a source of hematopoietic and mesenchymal stromal cells, bone marrow is known to be the source of stem cell populations, which express pluripotential markers and are capable of differentiating into cells of three blastophyllums (ectoderm, mesoderm, and endoderm). Recently, a new population of so-called "very small embryonic like cells" (VSELs) has been identified in the bone marrow in addition to well-known pluripotential cells, such as MIAMI, MSC, and MAPS. The presence of stem cells with a wide spectrum of differentiation capacities in the bone marrow allows an alternative interpretation of the phenomenon of plasticity and the possibility of their switch from a canonical to a nontrivial path of differentiation. The phenotypic features of VSELs, their differentiation capacities, ontogenetic origins, and relationships with other types of stem cells are studied. The role of bone marrow stem cells and induced pluripotential stem cells in regeneration processes and their possible therapeutic application are discussed.

Quantifying the Waddington landscape and biological paths for development and differentiation

We developed a theoretical framework to prove the existence and quantify the Waddington landscape as well as chreode-biological paths for development and differentiation. The cells can have states with the higher probability ones giving the different cell types. Different cell types correspond to different basins of attractions of the probability landscape. We study how the cells develop from undifferentiated cells to differentiated cells from landscape perspectives. We quantified the Waddington landscape through construction of underlying probability landscape for cell development. We show the developmental process proceeds as moving from undifferentiated to the differentiated basins of attractions. The barrier height of the basins of attractions correlates with the escape time that determines the stability of cell types. We show that the developmental process can be quantitatively described and uncovered by the biological paths on the quantified Waddington landscape from undifferentiated to the differentiated cells. We found the dynamics of the developmental process is controlled by a combination of the gradient and curl force on the landscape. The biological paths often do not follow the steepest descent path on the landscape. The landscape framework also quantifies the possibility of reverse differentiation process such as cell reprogramming from differentiated cells back to the original stem cell. We show that the biological path of reverse differentiation is irreversible and different from the one for differentiation process. We found that the developmental process described by the underlying landscape and the associated biological paths is relatively stable and robust against the influences of environmental perturbations.

New T-Helper Subsets Controlling the Immune System and Tissue Cells

Th2 cells [6], but also appears to be valid for other T-cell subsets. It is known, for example, that Th2 differentiation inhibits Th1 commitment and vice versa. Specifically, the IL-4-induced transcription factors STAT-6 and GATA-3 inhibit differentiation into Th1 cells in the early phase of commitment [7,8]. Recently, it was shown that the Th1 transcription factor T-bet directly regulates GATA-3 function, suggesting that transcription factors compete in the early differentiation phase of T cells, potentially integrating environmental signals in order to finally imprint the T-cell phenotype [9,10]. The imprinted phenotype is thought to be based on epigenetic modification that provides a stable phenotype even upon multiple cell divisions, which explains how clonal expansion can be realized after phenotypic T-cell differentiation. Therefore, immunomodulation on the path of T-cell differentiation is likely to generate sustained treatment effects, but is always dependent on effective antigen stimulation or vaccination.

Modelling hematopoiesis in health and disease

Hematopoiesis is the process responsible for maintaining the number of circulating blood cells that are undergoing continuous turnover. At the root of this process are the hematopoietic stem cells (HSC), that replicate slowly to self-renew and give rise to progeny cells that proceed along the path of differentiation. The process is complex, with the cells responding to a wide variety of cytokines and growth factors. We discuss the mathematics of hematopoiesis based on stochastic cell behavior. Multiple compartments are introduced to keep track of each cell division process and increasing differentiation. The same mathematical model that describes normal hematopoiesis across mammals as a stable steady state of a hierarchical stochastic process is also used to understand the detailed dynamics of various disorders both in humans and in animal models. The microecology of the multitude of cell lineages that constitute what we call troubled hematopoiesis evolves in time under mutation and selection, the paradigmatic components of Darwinian evolution. Thus, the present approach provides a novel perspective for looking at cancer progression and cure.

Suppressing Glioblastoma Stem Cell Function by Aldehyde Dehydrogenase Inhibition with Chloramphenicol or Disulfiram as a New Treatment Adjunct: A Hypothesis

Strong expression of aldehyde dehydrogenase is a prominent feature of both normal and cancer stem cells, including the stem cell sub-population of glioblastoma. Aldehyde dehydrogenase function is used by cancer stem cells to repopulate a tumor mass after chemotherapy cytoreduction. Cancer stem cells tend to be chemotherapy compared to the non-stem cell majority cell population in several common human cancers. Such has been demonstrated specifically in glioblastoma. In normal hematopoietic stem cells with unimpaired high levels of aldehyde dehydrogenase, stem cells divide rarely and then asymmetrically to a daughter stem cell and a daughter cell on a path of differentiation or symmetrically with both daughter cells on a differentiated path. If a parallel situation obtains in glioblastoma stem cells, the migrating, far flung paucicellular extensions will be stem cell rich and use aldehyde dehydrogenase to generate the characteristic multiple metastases made up of mostly non-stem cells. With inhibition of aldehyde dehydrogenase, stem cell division to non-stem daughter cells tends to become blocked. We have three old yet potent aldehyde dehydrogenase inhibitors on the market- chloral hydrate, chloramphenicol, and disulfiram- they should be investigated as adjuncts in glioblastoma chemotherapy. If GBM stem cell function can be thwarted by potent aldehyde dehydrogenase inhibition, they will be less able to regenerate a stem cell derived tumor mass after primary resection or chemotherapy.

Modeling the architecture and dynamics of hematopoiesis

Hematopoiesis is a multistep process that results in the production of a variety of blood cells with different morphologies and diverse functions. All of these cells have their origin in hematopoietic stem cells Hematopoietic Stem Cells (HSCs) that replicate slowly to self-renew and give rise to progeny cells that proceed along the path of differentiation. The process is complex with the cells responding to a wide variety of cytokines and growth factors. We discuss a model of hematopoiesis based on stochastic cell behavior. Multiple compartments are introduced to keep track of each cell division process and increasing differentiation. Despite its simplicity, the model is able to account for the salient features of hematopoiesis and is compatible with considerable and independent experimental data. The model is applicable to hematopoiesis across mammals and can be used to understand the dynamics of various disorders both in humans and in animal models.

Phyllotactic pattern is altered in the transition to flowering in the early ears of Zea mays landrace chapalote (Poaceae)

The origin of polystichy in the maize ear and central tassel spike continues to challenge our understanding of evolution in this important crop species. In this paper we tested the hypothesis that the change in phyllotaxy occurs in the region of husk leaf production before the transition to reproductive growth. Young ear or presumptive ear primordia were dissected to examine the transition from distichous husk leaves below the ear through spiral phyllotaxy to the polystichous arrangement of spikelet pair primordia in the young ear. Serial transverse sections were used to document the thickness of successive disks of insertion of lateral primordia and to reconstruct the path of procambial differentiation. The transition in phyllotaxy, though variable, typically occurs in the vegetative zone and is associated with periodic heterogeneity in the thickness of leaf bases and a delay in the development of waves of procambial differentiation into the base of the young ear.

Exogenous collagen-enhanced recruitment of mesenchymal stem cells during rabbit articular cartilage repair

Background Despite the well-known effect of type-I collagen in promoting cartilage repair, the mechanism still remains unknown. In this study we investigated this mechanism using a rabbit model of cartilage defects.Animals and methods 5-mm-diameter full-thickness defects were created on both patellar grooves of 53 Japanese white rabbits (approximately 13 weeks old). The left defect was filled with collagen gel and the right defect was left empty. The rabbits were killed and examined morphometrically until the twenty-fourth postoperative week, by (1) evaluation of matrix production, (2) enumeration of the total number of cells engaged in cartilage repair, (3) enumeration of the proliferating cells, (4) localization of mesenchymal stem cells, and (v) localization of apoptotic cells.Results We found that type-I collagen enhances cell recruitment, and thereby increases the number of proliferating cells. A considerable proportion of the proliferating cells were identified as bone marrow-derived mesenchymal stem cells. However, type-I collagen does not prevent the chondrocyte precursors from undergoing apoptotic disengagement from the chondrogenic lineage.Interpretation Type-I collagen promotes cartilage repair by enhancing recruitment of bone marrowderived mesenchymal stem cells. Additional use of agent(s) that sustain mesenchymal stem cells along the chondrogenic path of differentiation may constitute an appropriate environment for cartilage repair.

Complex Translocation (8;16;21); a New Variant of t(8;21), with t(13;22) in Acute Myeloid Leukemia.

The translocation (8;21)(q22;q22) is a common recurrent chromosome aberration present in 10% to 15% of all acute myeloid leukemias. In approximately 3% of all cases with t(8;21), a variant of t(8;21) involving chromosomes 8,21 and other chromosomes is present. We report here a case of AML-M2 with a new complex translocation (8;16;21)(q22;p16.3;q22) associated with additional abnormality t(13;22)(q22;q13) not described before. Fluorescent in-situ hybridization analysis with probes for ETO and AML1 genes, and probes for the subtelomeric regions of chromosome 16 demonstrated an ETO-AML1 fusion signal on der(8). The 5′ region of ETO gene with chromosome arm distal to translocation breakpoint had moves to der(16) while region of AML1 probe proximal to translocation brealpoint stayed on der(21). The signal for the subtelomeric probe for 16p was present on der(21). Use of painting probe for chromosome 13 confirmed t(13;22). In a hematopoietic cell the expression of chimeric AML1- ETO protein resulting from t(8;21) plays a key role in leukemic transformation by targeting AML1-CBFB transcription factor complex, an essential regulator of genes required for normal hematopoietic cell development, by dominant negative effect on normal AML1 protein. However, the expression of AML1- ETO does not block normal differentiation of stem cells. Additional mutational events must occur in hematopoietic progenitor cell to block normal path of differentiation. Although clinical features of variant translocation is same as cases with conventional t(8;21), prognostic implications of variant (8;21) are yet to be established. Chromosome region 16p13 has been involved in clinically important translocations with poor prognosis such as t(8;16)(p11;p13) and t(11;16)(q23;p13) and may have similar implications. Translocation (8;21) is frequently accompanied by additional chromosome abnormalities i.e. loss of sex chromosome, trisomy 8 and structural abnormalities of 9q. Additional reports on secondary genetic alterations accompanying t(8;21) are needed to understand their cumulative effect. Chromosome region 16p13, 13q22 and 22q13 may harbor putative genes influencing normal path of differentiation.

Isochores and tissue-specificity.

The housekeeping (ubiquitously expressed) genes in the mammal genome were shown here to be on average slightly GC-richer than tissue-specific genes. Both housekeeping and tissue-specific genes occupy similar ranges of GC content, but the former tend to concentrate in the upper part of the range. In the human genome, tissue-specific genes show two maxima, GC-poor and GC-rich. The strictly tissue-specific human genes tend to concentrate in the GC-poor region; their distribution is left-skewed and thus reciprocal to the distribution of housekeeping genes. The intermediately tissue-specific genes show an intermediate GC content and the right-skewed distribution. Both in the human and mouse, genes specific for some tissues (e.g., parts of the central nervous system) have a higher average GC content than housekeeping genes. Since they are not transcribed in the germ line (in contrast to housekeeping genes), and therefore have a lower probability of inheritable gene conversion, this finding contradicts the biased gene conversion (BGC) explanation for elevated GC content in the heavy isochores of mammal genome. Genes specific for germ-line tissues (ovary, testes) show a low average GC content, which is also in contradiction to the BGC explanation. Both for the total data set and for the most part of tissues taken separately, a weak positive correlation was found between gene GC content and expression level. The fraction of ubiquitously expressed genes is nearly 1.5-fold higher in the mouse than in the human. This suggests that mouse tissues are comparatively less differentiated (on the molecular level), which can be related to a less pronounced isochoric structure of the mouse genome. In each separate tissue (in both species), tissue-specific genes do not form a clear-cut frequency peak (in contrast to housekeeping genes), but constitute a continuum with a gradually increasing degree of tissue-specificity, which probably reflects the path of cell differentiation and/or an independent use of the same protein in several unrelated tissues.

Chromatin elimination – an oddity or a common mechanism in differentiation and development?

Over many decades, a great number of exceptions from the rule of equal segregation of the chromosomes during cell division have been found in different animal species. The most diversified is the process of chromosome re-arrangement that takes place during the specification of soma versus germ-line cell fate in the embryos from the whole spectrum of animal phyla. In nematodes, copepodes, insects, hagfish, and marsupials, the chromatin/chromosome elimination is a common path of normal cell differentiation and development. This also raises the question of the mechanisms and factors that promote elimination in pre-somatic cell lines and/or inhibit the elimination in the prospective germ cells. We will discuss the possible role of the germ plasm in this process.