Biomedical subjects

Elaine Fuchs

Publications and source records attributed to Elaine Fuchs.

At least 37 records · Page 2Linked to original sources

PubMed2005

Defining the impact of beta-catenin/Tcf transactivation on epithelial stem cells.

Wnt signaling has been implicated in stem cell (SC) biology, but little is known about how stabilized beta-catenin functions within native SC niches. We address this by defining the impact of beta-catenin stabilization on maintenance, proliferation, and lineage commitment of multipotent follicle SCs when in their native niche and in culture. We employ gain of function mutations and inducible loss of function mutations to demonstrate that beta-catenin stabilization is essential for promoting the transition between SC quiescence and conversion to proliferating transit amplifying (TA) progeny. We transcriptionally profile purified SCs isolated directly from wild-type and elevated beta-catenin follicles in both resting and activated states to uncover the discrete set of genes whose expression in native SCs is dependent upon beta-catenin stabilization. Finally, we address the underlying mechanism and show that in the SC niche, Wnt signaling and beta-catenin stabilization transiently activate Lef1/Tcf complexes and promote their binding to target genes that promote TA cell conversion and proliferation to form the activated cells of the newly developing hair follicle. We also show that these changes precede subsequent Wnt signals that impact on the TA progeny to specify the differentiation lineages of the follicle.

Animals↗

PubMed2005

Mice in the world of stem cell biology.

The ability of embryos to diversify and of some adult tissues to regenerate throughout life is directly attributable to stem cells. These cells have the capacity to self-renew-that is, to divide and to create additional stem cells-and to differentiate along a specific lineage. The differentiation of pluripotent embryonic stem cells along specific cell lineages has been used to understand the molecular mechanisms involved in tissue development. The often endless capacity of embryonic stem cells to generate differentiated cell types positions the field of stem cells at the nexus between developmental biologists, who are fascinated by the properties of these cells, and clinicians, who are excited about the prospects of bringing stem cells from bench to bedside to treat degenerative disorders and injuries for which there are currently no cures. Here we highlight the importance of mice in stem cell biology and in bringing the world one step closer to seeing these cells brought to fruition in modern medicine.

Animals↗

PubMed2004

A signaling pathway involving TGF-beta2 and snail in hair follicle morphogenesis.

In a common theme of organogenesis, certain cells within a multipotent epithelial sheet exchange signals with their neighbors and develop into a bud structure. Using hair bud morphogenesis as a paradigm, we employed mutant mouse models and cultured keratinocytes to dissect the contributions of multiple extracellular cues in orchestrating adhesion dynamics and proliferation to shape the cluster of cells involved. We found that transforming growth factor beta2 signaling is necessary to transiently induce the transcription factor Snail and activate the Ras-mitogen-activated protein kinase (MAPK) pathway in the bud. In the epidermis, Snail misexpression leads to hyperproliferation and a reduction in intercellular adhesion. When E-cadherin is transcriptionally down-regulated, associated adhesion proteins with dual functions in signaling are released from cell-cell contacts, a process which we demonstrate leads to Ras-MAPK activation. These studies provide insights into how multipotent cells within a sheet are stimulated to undergo transcriptional changes that result in proliferation, junctional remodeling, and bud formation. This novel signaling pathway further weaves together the web of different morphogens and downstream transcriptional events that guide hair bud formation within the developing skin.

Animals↗

PubMed2004

Coordinating cytoskeletal tracks to polarize cellular movements.

For many years after the discovery of actin filaments and microtubules, it was widely assumed that their polymerization, organization, and functions were largely distinct. However, in recent years it has become increasingly apparent that coordinated interactions between microtubules and filamentous actin are involved in many polarized processes, including cell shape, mitotic spindle orientation, motility, growth cone guidance, and wound healing. In the past few years, significant strides have been made in unraveling the intricacies that govern these intertwined cytoskeletal rearrangements.

Actins↗

PubMed2004

Self-renewal, multipotency, and the existence of two cell populations within an epithelial stem cell niche.

In adult skin, each hair follicle contains a reservoir of stem cells (the bulge), which can be mobilized to regenerate the new follicle with each hair cycle and to reepithelialize epidermis during wound repair. Here we report new methods that permit their clonal analyses and engraftment and demonstrate the two defining features of stem cells, namely self-renewal and multipotency. We also show that, within the bulge, there are two distinct populations, one of which maintains basal lamina contact and temporally precedes the other, which is suprabasal and arises only after the start of the first postnatal hair cycle. This spatial distinction endows them with discrete transcriptional programs, but surprisingly, both populations are growth inhibited in the niche but can self-renew in vitro and make epidermis and hair when grafted. These findings suggest that the niche microenvironment imposes intrinsic "stemness" features without restricting the establishment of epithelial polarity and changes in gene expression.

3T3 Cells↗

PubMed2004

Socializing with the neighbors: stem cells and their niche.

The potential of stem cells in regenerative medicine relies upon removing them from their natural habitat, propagating them in culture, and placing them into a foreign tissue environment. To do so, it is essential to understand how stem cells interact with their microenvironment, the so-called stem cell niche, to establish and maintain their properties. In this review, we examine adult stem cell niches and their impact on stem cell biology.

Animals↗

PubMed2004

Conditional targeting of E-cadherin in skin: insights into hyperproliferative and degenerative responses.

Loss of E-cadherin has been associated with human cancers, and yet in the early mouse embryo and the lactating mammary gland, the E-cadherin null state results in tissue dysfunction and cell death. Here we targeted loss of E-cadherin in skin epithelium. The epidermal basal layer responded by elevating P-cadherin, enabling these cells to maintain adherens junctions. Suprabasal layers upregulated desmosomal cadherins, but without classical cadherins, terminal differentiation was impaired. Progressive hyperplasia developed with age, a possible consequence of proliferative maintenance in basal cells coupled with defects in terminal differentiation. In contrast, hair follicles lost integrity of the inner root sheath and hair cuticle without apparent elevation of cadherins. These findings suggest that, if no compensatory mechanisms exist, E-cadherin loss may be incompatible with epithelial tissue survival, whereas partial compensation can result in alterations in differentiation and proliferation.

Animals↗

PubMed2004

Biogenesis and function of mouse mammary epithelium depends on the presence of functional alpha-catenin.

Alpha-catenin is a structural molecule and essential to the function of epithelial adherens junctions. Its role in the morphogenesis of mammary epithelium was explored using experimental mouse genetics. Since loss of alpha-catenin in mice leads to embryonic lethality, the alpha-catenin gene was flanked by loxP sites and inactivated in mammary epithelium using the WAP-Cre and MMTV-Cre transgenes. Loss of alpha-catenin arrested alveolar epithelial expansion. These cells lacked proper polarity and markers of functional differentiation, which resulted in impaired milk protein gene expression. Without alpha-catenin, increased epithelial cell death was observed at parturition and the tissue resembled an involuted gland that is normally observed after weaning. Lastly, no tumors were detected in mammary tissue lacking alpha-catenin.

Animals↗

PubMed2004

Basal cells are a multipotent progenitor capable of renewing the bronchial epithelium.

Commitment of the pulmonary epithelium to bronchial and bronchiolar airway lineages occurs during the transition from pseudoglandular to cannalicular phases of lung development, suggesting that regional differences exist with respect to the identity of stem and progenitor cells that contribute to epithelial maintenance in adulthood. We previously defined a critical role for Clara cell secretory protein-expressing (CE) cells in renewal of bronchiolar airway epithelium following injury. Even though CE cells are also the principal progenitor for maintenance of the bronchial airway epithelium, CE cell injury is resolved through a mechanism involving recruitment of a second progenitor cell population that we now identify as a GSI-B(4) reactive, cytokeratin-14-expressing basal cell. These cells exhibit multipotent differentiation capacity as assessed by analysis of cellular phenotype within clones of LacZ-tagged cells. Clones were derived from K14-expressing cells tagged in a cell-type-specific fashion by ligand-regulable Cre recombinase-mediated genomic rearrangement of the ROSA26 recombination substrate allele. We conclude that basal cells represent an alternative multipotent progenitor cell population of bronchial airways and that progenitor cell selection is dictated by the type of airway injury.

Animals↗

PubMed2004

Alpha-catenin: at the junction of intercellular adhesion and actin dynamics.

Alpha-catenin has often been considered to be a non-regulatory intercellular adhesion protein, in contrast to beta-catenin, which has well-documented dual roles in cell-cell adhesion and signal transduction. Recently, however, alpha-catenin has been found to be important not only in connecting the E-cadherin-beta-catenin complex to the actin cytoskeleton, but also in coordinating actin dynamics and inversely correlating cell adhesion with proliferation. As the number of alpha-catenin-interacting partners increases, intriguing new connections imply even more complex regulatory functions for this protein.

Actins↗

PubMed2003

Defining the epithelial stem cell niche in skin.

Many adult regenerative cells divide infrequently but have high proliferative capacity. We developed a strategy to fluorescently label slow-cycling cells in a cell type-specific fashion. We used this method to purify the label-retaining cells (LRCs) that mark the skin stem cell (SC) niche. We found that these cells rarely divide within their niche but change properties abruptly when stimulated to exit. We determined their transcriptional profile, which, when compared to progeny and other SCs, defines the niche. Many of the >100 messenger RNAs preferentially expressed in the niche encode surface receptors and secreted proteins, enabling LRCs to signal and respond to their environment.

Animals↗

PubMed2003

Tcf3: a transcriptional regulator of axis induction in the early embryo.

The roles of Lef/Tcf proteins in determining cell fate characteristics have been described in many contexts during vertebrate embryogenesis, organ and tissue homeostasis, and cancer formation. Although much of the accumulated work on these proteins involves their ability to transactivate target genes when stimulated by beta-catenin, Lef/Tcf proteins can repress target genes in the absence of stabilized beta-catenin. By ablating Tcf3 function, we have uncovered an important requirement for a repressor function of Lef/Tcf proteins during early mouse development. Tcf3-/- embryos proceed through gastrulation to form mesoderm, but they develop expanded and often duplicated axial mesoderm structures, including nodes and notochords. These duplications are preceded by ectopic expression of Foxa2, an axial mesoderm gene involved in node specification, with a concomitant reduction in Lefty2, a marker for lateral mesoderm. By contrast, expression of a beta-catenin-dependent, Lef/Tcf reporter (TOPGal), is not ectopically activated but is faithfully maintained in the primitive streak. Taken together, these data reveal a unique requirement for Tcf3 repressor function in restricting induction of the anterior-posterior axis.

Animals↗

PubMed2003

Molecular cloning and characterization of AP-2 epsilon, a fifth member of the AP-2 family.

The mammalian AP-2 family of transcription factors consists of four members, AP-2 alpha, AP-2 beta, AP-2 gamma and AP-2 delta, which play an important role in regulating gene expression during development and differentiation of multiple organs and tissues. The defining feature of the AP-2 family is a highly conserved carboxy-terminal basic helix-turn-helix domain that is involved in dimerization and sequence-specific DNA-binding. In this report, we use bioinformatics to identify both the mouse and human AP-2 epsilon, a fifth member of the AP-2 family. The predicted mouse and human AP-2 epsilon proteins consist of 442 amino acids and show a high level of sequence similarity with other AP-2 proteins in the DNA-binding and dimerization domain and weak similarity in the N-terminal activation domain. Northern blot analysis reveals that among the adult mouse tissues examined, AP-2 epsilon is highly expressed in skin tissue. The human AP-2 epsilon gene maps to chromosome 1p42, consists of seven exons spanning 23 kb and exhibits a genomic structure similar to other AP-2 family members. Human AP-2 epsilon mRNA is expressed in human skin and keratinocytes grown in culture. Finally, we show that recombinant AP-2 epsilon can bind to AP-2 binding sequences from keratin promoters in electrophoretic mobility shift assays. Our study establishes AP-2 epsilon as a novel member of the AP-2 family, and suggests that it may play an important role in skin biology.

Amino Acid Sequence↗

PubMed2003

Mammalian formin-1 participates in adherens junctions and polymerization of linear actin cables.

During epithelial sheet formation, linear actin cables assemble at nascent adherens junctions. This process requires alpha-catenin and actin polymerization, although the underlying mechanism is poorly understood. Here, we show that formin-1 interacts with alpha-catenin, localizes to adherens junctions and nucleates unbranched actin filaments. Furthermore, disruption of the alpha-catenin-formin-1 interaction blocks assembly of radial actin cables and perturbs intercellular adhesion. A fusion protein of the beta-catenin-binding domain of alpha-catenin with the actin polymerization domains of formin-1 rescues formation of adherens junctions and associated actin cables in alpha-catenin-null keratinocytes. These findings provide new insight into how alpha-catenin orchestrates actin dynamics during intercellular junction formation.

Actin Cytoskeleton↗

PubMed2003

Defining BMP functions in the hair follicle by conditional ablation of BMP receptor IA.

Using conditional gene targeting in mice, we show that BMP receptor IA is essential for the differentiation of progenitor cells of the inner root sheath and hair shaft. Without BMPRIA activation, GATA-3 is down-regulated and its regulated control of IRS differentiation is compromised. In contrast, Lef1 is up-regulated, but its regulated control of hair differentiation is still blocked, and BMPRIA-null follicles fail to activate Lef1/beta-catenin-regulated genes, including keratin genes. Wnt-mediated transcriptional activation can be restored by transfecting BMPRIA-null keratinocytes with a constitutively activated beta-catenin. This places the block downstream from Lef1 expression but upstream from beta-catenin stabilization. Because mice lacking the BMP inhibitor Noggin fail to express Lef1, our findings support a model, whereby a sequential inhibition and then activation of BMPRIA is necessary to define a band of hair progenitor cells, which possess enough Lef1 and stabilized beta-catenin to activate the hair specific keratin genes and generate the hair shaft.

Animals↗

PubMed2003

ACF7: an essential integrator of microtubule dynamics.

ACF7 is a member of the spectraplakin family of cytoskeletal crosslinking proteins possessing actin and microtubule binding domains. Here, we show that ACF7 is an essential integrator of MT-actin dynamics. In endodermal cells, ACF7 binds along microtubules but concentrates at their distal ends and at cell borders when polarized. In ACF7's absence, microtubules still bind EB1 and CLIP170, but they no longer grow along polarized actin bundles, nor do they pause and tether to actin-rich cortical sites. The consequences are less stable, long microtubules with skewed cytoplasmic trajectories and altered dynamic instability. In response to wounding, ACF7 null cultures activate polarizing signals, but fail to maintain them and coordinate migration. Rescue of these defects requires ACF7's actin and microtubule binding domains. Thus, spectraplakins are important for controlling microtubule dynamics and reinforcing links between microtubules and polarized F-actin, so that cellular polarization and coordinated cell movements can be sustained.

Actins↗

PubMed2003

BPAG1n4 is essential for retrograde axonal transport in sensory neurons.

Disruption of the BPAG1 (bullous pemphigoid antigen 1) gene results in progressive deterioration in motor function and devastating sensory neurodegeneration in the null mice. We have previously demonstrated that BPAG1n1 and BPAG1n3 play important roles in organizing cytoskeletal networks in vivo. Here, we characterize functions of a novel BPAG1 neuronal isoform, BPAG1n4. Results obtained from yeast two-hybrid screening, blot overlay binding assays, and coimmunoprecipitations demonstrate that BPAG1n4 interacts directly with dynactin p150Glued through its unique ezrin/radixin/moesin domain. Studies using double immunofluorescent microscopy and ultrastructural analysis reveal physiological colocalization of BPAG1n4 with dynactin/dynein. Disruption of the interaction between BPAG1n4 and dynactin results in severe defects in retrograde axonal transport. We conclude that BPAG1n4 plays an essential role in retrograde axonal transport in sensory neurons. These findings might advance our understanding of pathogenesis of axonal degeneration and neuronal death.

Animals↗

PubMed2003

Differential regulation of midbrain dopaminergic neuron development by Wnt-1, Wnt-3a, and Wnt-5a.

The Wnts are a family of glycoproteins that regulate cell proliferation, fate decisions, and differentiation. In our study, we examined the contribution of Wnts to the development of ventral midbrain (VM) dopaminergic (DA) neurons. Our results show that beta-catenin is expressed in DA precursor cells and that beta-catenin signaling takes place in these cells, as assessed in TOPGAL [Tcf optimal-promoter beta-galactosidase] reporter mice. We also found that Wnt-1, -3a, and -5a expression is differentially regulated during development and that partially purified Wnts distinctively regulate VM development. Wnt-3a promoted the proliferation of precursor cells expressing the orphan nuclear receptor-related factor 1 (Nurr1) but did not increase the number of tyrosine hydroxylase-positive neurons. Instead, Wnt-1 and -5a increased the number of rat midbrain DA neurons in rat embryonic day 14.5 precursor cultures by two distinct mechanisms. Wnt-1 predominantly increased the proliferation of Nurr1+ precursors, up-regulated cyclins D1 and D3, and down-regulated p27 and p57 mRNAs. In contrast, Wnt-5a primarily increased the proportion of Nurr1+ precursors that acquired a neuronal DA phenotype and up-regulated the expression of Ptx3 and c-ret mRNA. Moreover, the soluble cysteine-rich domain of Frizzled-8 (a Wnt inhibitor) blocked endogenous Wnts and the effects of Wnt-1 and -5a on proliferation and the acquisition of a DA phenotype in precursor cultures. These findings indicate that Wnts are key regulators of proliferation and differentiation of DA precursors during VM neurogenesis and that different Wnts have specific and unique activity profiles.

Animals↗