Stem cells in ectodermal development

Next-Generation Breast Organoids Capture Human Organogenesis with High-Resolution Live Imaging

Organoids have emerged as a powerful tool for modeling tissue growth and diseases. In this study, we introduce a groundbreaking organotypic culture technique that replicates the morphology, scale, and heterogeneity of human breast tissue, and includes a mesenchymal-like stromal component. A standout feature of this approach is the use of long-term live imaging at high temporal resolution to directly observe stem cell dynamics during organogenesis, from single cells to mature organ tissue. The system is adaptable for high throughput applications and allows for genetic manipulation of the cells. Real-time imaging of ex-vivo tissue formation reveals a non-canonical process of ductal-lobular morphogenesis and branching, and de-novo generation of a supportive stroma. Incorporating patient-derived single cells from multiple donors offers an enhanced representation of the spectrum of individual responses and the impacts of distinct exposures. While developed for breast tissue, the principles of this technology can serve as a model for the development of similar systems in other tissues, where organoids do not merely reproduce the tissue, but where their regeneration can also be observed and studied. In addition, this model provides a quantitative experimental system to study mechanisms of embryogenesis, development, and tissue organization where biomechanics plays an important role.

Overview of chromatin regulatory processes during surface ectodermal development and homeostasis

The ectoderm is the outermost of the three germ layers of the early embryo that arise during gastrulation. Once the germ layers are established, the complex interplay of cellular proliferation, differentiation, and migration results in organogenesis. The ectoderm is the progenitor of both the surface ectoderm and the neural ectoderm. Notably, the surface ectoderm develops into the epidermis and its associated appendages, nails, external exocrine glands, olfactory epithelium, and the anterior pituitary. Specification, development, and homeostasis of these organs demand a tightly orchestrated gene expression program that is often dictated by epigenetic regulation. In this review, we discuss the recent discoveries that have highlighted the importance of chromatin regulatory mechanisms mediated by transcription factors, histone and DNA modifications that aid in the development of surface ectodermal organs and maintain their homeostasis post-development.

Skin Development and Disease: A Molecular Perspective

Skin, the largest organ in the human body, is a crucial protective barrier that plays essential roles in thermoregulation, sensation, and immune defence. This complex organ undergoes intricate processes of development. Skin development initiates during the embryonic stage, orchestrated by molecular cues that control epidermal specification, commitment, stratification, terminal differentiation, and appendage growth. Key signalling pathways are integral in coordinating the development of the epidermis, hair follicles, and sweat glands. The complex interplay among these pathways is vital for the appropriate formation and functionality of the skin. Disruptions in multiple molecular pathways can give rise to a spectrum of skin diseases, from congenital skin disorders to cancers. By delving into the molecular mechanisms implicated in developmental processes, as well as in the pathogenesis of diseases, this narrative review aims to present a comprehensive understanding of these aspects. Such knowledge paves the way for developing innovative targeted therapies and personalised treatment approaches for various skin conditions.

Ontogeny of Skin Stem Cells and Molecular Underpinnings

Skin stem cells (SCs) play a pivotal role in supporting tissue homeostasis. Several types of SCs are responsible for maintaining and regenerating skin tissue. These include bulge SCs and others residing in the interfollicular epidermis, infundibulum, isthmus, sebaceous glands, and sweat glands. The emergence of skin SCs commences during embryogenesis, where multipotent SCs arise from various precursor populations. These early events set the foundation for the diverse pool of SCs that will reside in the adult skin, ready to respond to tissue repair and regeneration demands. A network of molecular cues regulates skin SC behavior, balancing quiescence, self-renewal, and differentiation. The disruption of this delicate equilibrium can lead to SC exhaustion, impaired wound healing, and pathological conditions such as skin cancer. The present review explores the intricate mechanisms governing the development, activation, and differentiation of skin SCs, shedding light on the molecular signaling pathways that drive their fate decisions and skin homeostasis. Unraveling the complexities of these molecular drivers not only enhances our fundamental knowledge of skin biology but also holds promise for developing novel strategies to modulate skin SC fate for regenerative medicine applications, ultimately benefiting patients with skin disorders and injuries.

Brain Organoids: Filling the Need for a Human Model of Neurological Disorder

Neurological disorders are among the leading causes of death worldwide, accounting for almost all onsets of dementia in the elderly, and are known to negatively affect motor ability, mental and cognitive performance, as well as overall wellbeing and happiness. Currently, most neurological disorders go untreated due to a lack of viable treatment options. The reason for this lack of options is s poor understanding of the disorders, primarily due to research models that do not translate well into the human in vivo system. Current models for researching neurological disorders, neurodevelopment, and drug interactions in the central nervous system include in vitro monolayer cell cultures, and in vivo animal models. These models have shortcomings when it comes to translating research about disorder pathology, development, and treatment to humans. Brain organoids are three-dimensional (3D) cultures of stem cell-derived neural cells that mimic the development of the in vivo human brain with high degrees of accuracy. Researchers have started developing these miniature brains to model neurodevelopment, and neuropathology. Brain organoids have been used to model a wide range of neurological disorders, including the complex and poorly understood neurodevelopmental and neurodegenerative disorders. In this review, we discuss the brain organoid technology, placing special focus on the different brain organoid models that have been developed, discussing their strengths, weaknesses, and uses in neurological disease modeling.

Functional ectodermal organ regeneration as the next generation of organ replacement therapy

In this decade, substantial progress in the fields of developmental biology and stem cell biology has ushered in a new era for three-dimensional organ regenerative therapy. The emergence of novel three-dimensional cell manipulation technologies enables the effective mimicking of embryonic organ germ formation using the fate-determined organ-inductive potential of epithelial and mesenchymal stem cells. This advance shows great potential for the regeneration of functional organs with substitution of complete original function in situ. Organoids generated from multipotent stem cells or tissue stem cells via establishment of an organ-forming field can only partially recover original organ function owing to the size limitation; they are considered ‘mini-organs’. Nevertheless, they hold great promise to realize regenerative medicine. In particular, regeneration of a functional salivary gland and an integumentary organ system by orthotopic and heterotopic implantation of organoids clearly points to the future direction of organ regeneration research. In this review, we describe multiple strategies and recent progress in regenerating functional three-dimensional organs, focusing on ectodermal organs, and discuss their potential and future directions to achieve organ replacement therapy as a next-generation regenerative medicine.

Distinct enhancer signatures in the mouse gastrula delineate progressive cell fate continuum during embryo development

Primary germ layers have the potential to form all tissues in the mature organism, and their formation during gastrulation requires precise epigenetic modulation of both proximal and distal regulatory elements. Previous studies indicated that spatial and temporal patterns of gene expression in the gastrula predispose individual regions to distinct cell fates. However, the underlying epigenetic mechanisms remain largely unexplored. Here, we profile the spatiotemporal landscape of the epigenome and transcriptome of the mouse gastrula. We reveal the asynchronous dynamics of proximal chromatin states during germ layer formation as well as unique gastrula-specific epigenomic features of regulatory elements, which have strong usage turnover dynamics and clear germ layer-specific signatures. Importantly, we also find that enhancers around organogenetic genes, which are weakly expressed at the gastrulation stage, are frequently pre-marked by histone H3 lysine 27 acetylation (H3K27ac) in the gastrula. By using the transgenic mice and genome editing system, we demonstrate that a pre-marked enhancer, which is located in the intron of a brain-specific gene 2510009E07Rik, exhibits specific enhancer activity in the ectoderm and future brain tissue, and also executes important function during mouse neural differentiation. Taken together, our study provides the comprehensive epigenetic information for embryonic patterning during mouse gastrulation, demonstrates the importance of gastrula pre-marked enhancers in regulating the correct development of the mouse embryo, and thus broadens the current understanding of mammalian embryonic development and related diseases.

De Novo PITX1 Expression Controls Bi-Stable Transcriptional Circuits to Govern Self-Renewal and Differentiation in Squamous Cell Carcinoma

Basal tumor propagating cells (TPCs) control squamous cell carcinoma (SCC) growth by self-renewing and differentiating into supra-basal SCC cells, which lack proliferative potential. While transcription factors such as SOX2 and KLF4 can drive these behaviors, their molecular roles and regulatory interactions with each other have remained elusive. Here, we show that PITX1 is specifically expressed in TPCs, where it co-localizes with SOX2 and TRP63 and determines cell fate in mouse and human SCC. Combining gene targeting with chromatin immunoprecipitation sequencing (ChIP-seq) and transcriptomic analyses reveals that PITX1 cooperates with SOX2 and TRP63 to sustain an SCC-specific transcriptional feed-forward circuit that maintains TPC-renewal, while inhibiting KLF4 expression and preventing KLF4-dependent differentiation. Conversely, KLF4 represses PITX1, SOX2, and TRP63 expression to prevent TPC expansion. This bi-stable, multi-input network reveals a molecular framework that explains self-renewal, aberrant differentiation, and SCC growth in mice and humans, providing clues for developing differentiation-inducing therapeutic strategies.

Embryonic skin development and repair

Fetal cutaneous wounds have the unique ability to completely regenerate wounded skin and heal without scarring. However, adult cutaneous wounds heal via a fibroproliferative response which results in the formation of a scar. Understanding the mechanism(s) of scarless wound healing leads to enormous clinical potential in facilitating an environment conducive to scarless healing in adult cutaneous wounds. This article reviews the embryonic development of the skin and outlines the structural and functional differences in adult and fetal wound healing phenotypes. A review of current developments made towards applying this clinical knowledge to promote scarless healing in adult wounds is addressed.

The Molecular Revolution in Cutaneous Biology: Chromosomal Territories, Higher-Order Chromatin Remodeling, and the Control of Gene Expression in Keratinocytes

Three-dimensional organization of transcription in the nucleus and mechanisms controlling the global chromatin folding, including spatial interactions between the genes, noncoding genome elements, and epigenetic and transcription machinery, are essential for establishing lineage-specific gene expression programs during cell differentiation. Spatial chromatin interactions in the nucleus involving gene promoters and distal regulatory elements are currently considered major forces that drive cell differentiation and genome evolution in general, and such interactions are substantially reorganized during many pathological conditions. During terminal differentiation of the epidermal keratinocytes, the nucleus undergoes programmed transformation from highly active status, associated with execution of the genetic program of epidermal barrier formation, to a fully inactive condition and finally becomes a part of the keratinized cells of the cornified epidermal layer. This transition is accompanied by marked remodeling of the three-dimensional nuclear organization and microanatomy, including changes in the spatial arrangement of lineage-specific genes, nuclear bodies, and heterochromatin. This mini-review highlights the important landmarks in the accumulation of our current knowledge on three-dimensional organization of the nucleus, spatial arrangement of the genes, and their distal regulatory elements, and it provides an update on the mechanisms that control higher-order chromatin remodeling in the context of epidermal keratinocyte differentiation in the skin.

Immuno- and gene expression analysis of EGFR and Nestin during mice skin development

BACKGROUND

Skin stem cell populations reside in the adult hair follicle, sebaceous gland, dermis and epidermis. However, the origin of most of the stem cell populations found in the adult epidermis is still unknown. Far more unknown is the embryonic origin of other stem cells that populate the other layers of this tissue.

OBJECTIVES

The main objectives of the present study were to identify the precise anatomical localization of stem cells in mice during skin developing; and to determine the expression levels by using immuno- and gene expression analysis.

SUBJECTS AND METHODS

In this comparative cross sectional study, six ages been chosen and divided into: embryonic days (E12.5, E14.5 and E19.5) and litter days (L7, L14 and L19). Skin were removed from the back side and processed to assess both immuno- and gene-expression of EGFR and Nestin surface antigen markers. Data of the different studied age groups was compared using the SPSS software.

RESULTS

EGFR was mainly expressed in the outer root sheath (ORS), in basal and, to a lesser extent, in suprabasal keratinocytes and tend to lie where the dermis comes closest to the skin surface, while Nestin expressed throughout the dermis in the early embryo, but it is subsequently restricted to the follicular connective tissue sheaths later in development and to hair follicles after birth. Immunoexpression analysis showed a strong EGFR expression in all group ages except E12.5 which recorded as moderate, while Nestin showed strong expression level for all embryonic stages, while in the litters it was moderate. The qRT-PCR results were consistent with those of the immunohistochemical study. The Pearson correlation analyze present a correlation between the cases of study with age (p≤0.01), which indicated to the effect of age to mice development.

CONCLUSION

EGFR and Nestin showed to have vital role during mice development, and considered to be suitable markers for the study of skin stem cells.

Cbx4 maintains the epithelial lineage identity and cell proliferation in the developing stratified epithelium

During development, multipotent progenitor cells establish lineage-specific programmers of gene activation and silencing underlying their differentiation into specialized cell types. We show that the Polycomb component Cbx4 serves as a critical determinant that maintains the epithelial identity in the developing epidermis by repressing nonepidermal gene expression programs. Cbx4 ablation in mice results in a marked decrease of the epidermal thickness and keratinocyte (KC) proliferation associated with activation of numerous neuronal genes and genes encoding cyclin-dependent kinase inhibitors (p16/p19 and p57). Furthermore, the chromodomain- and SUMO E3 ligase-dependent Cbx4 activities differentially regulate proliferation, differentiation, and expression of nonepidermal genes in KCs. Finally, Cbx4 expression in KCs is directly regulated by p63 transcription factor, whereas Cbx4 overexpression is capable of partially rescuing the effects of p63 ablation on epidermal development. These data demonstrate that Cbx4 plays a crucial role in the p63-regulated program of epidermal differentiation, maintaining the epithelial identity and proliferative activity in KCs via repression of the selected nonepidermal lineage and cell cycle inhibitor genes.

Embryonic Origin of Postnatal Neural Stem Cells

Adult neural stem/progenitor (B1) cells within the walls of the lateral ventricles generate different types of neurons for the olfactory bulb (OB). The location of B1 cells determines the types of OB neurons they generate. Here we show that the majority of mouse B1 cell precursors are produced between embryonic days (E) 13.5 and 15.5 and remain largely quiescent until they become reactivated postnatally. Using a retroviral library carrying over 100,000 genetic tags, we found that B1 cells share a common progenitor with embryonic cells of the cortex, striatum, and septum, but this lineage relationship is lost before E15.5. The regional specification of B1 cells is evident as early as E11.5 and is spatially linked to the production of neurons that populate different areas of the forebrain. This study reveals an early embryonic regional specification of postnatal neural stem cells and the lineage relationship between them and embryonic progenitor cells.

Knocking out Smad3 favors allogeneic mouse fetal skin development in adult wounds

Fetal skin development represents a process of the interaction between skin progenitor cells and their unique extracellular matrix niche, which is also important for the mechanism study of skin progenitor cell differentiation and fetal scarless wound healing. Thus, a change in the niche environment, such as altered expression levels of growth factors or cytokines, may also change the outcome of fetal skin development. This study tested the hypothesis that deletion of mouse Smad3 creates a favorable environment for fetal skin development in adult wounds. Fetal skin of green fluorescent protein mouse (C57BL/B6) of gestational day 16.5 was respectively transplanted to the wound beds of wild-type (WT), heterozygous (HT), and homologous (KO) Smad3 deletion mice (C57BL/B6 × 129SV). The results showed that green fluorescent protein fetal mouse skin after its transplantation developed much better into hair follicle containing skin in KO or HT wound beds than in WT wound beds with significant differences in the number of follicles per mm(2) among the three groups at 1, 2, and 3 weeks posttransplantation (p < 0.05). In addition, less fibrosis was observed in KO wounds than in HT and WT wounds with significant difference in the wound bed thickness among the three groups at 3 weeks posttransplantation (p < 0.05). Interestingly, there was a delayed graft rejection in the KO group when compared with the HT and WT groups. In conclusion, deletion of Smad3 in a wound bed creates a better environment for skin progenitor cell differentiation and fetal skin development. Translation of such a concept to the creation of a wound environment that is favorable for adult stem cell differentiation and skin appendage formation may become an important strategy for the regeneration of wounded skin.

Concepts of Dhatu Siddhanta (theory of tissues formation and differentiation) and Rasayana; probable predecessor of stem cell therapy

To maintain health and to cure diseases through Rasayana (rejuvenation) therapy along with main treatment is the unique approach of Ayurveda. The basic constituent unit of a living being is always a functional cell. Question arises from where it is generated? How it attains its final specific differentiation form? As age progresses, various changes occur at every cell level and cell undergoes to adaptation accordingly. Microenvironment for cell nourishment diminishes with age or as disease condition persists. In this context, Acharyas had contributed and documented various facts and theories through their insight wisdom. Hidden secretes in the basic principles of any medical system are needed to be explained in terms of contemporary knowledge. Contemporary research areas should be opened to include various explanations of different fields of ancient thoughts to support these new doctrines, if any. This review may be helpful to open the door of future research area in the field of reverse scientific approach of Ayurveda in the context of Dhatu Siddhanta (theory of tissues formation and differentiation) and theory of stem cell.

Skin, fascias, and scars: symptoms and systemic connections

Every element or cell in the human body produces substances that communicate and respond in an autocrine or paracrine mode, consequently affecting organs and structures that are seemingly far from each other. The same also applies to the skin. In fact, when the integrity of the skin has been altered, or when its healing process is disturbed, it becomes a source of symptoms that are not merely cutaneous. The skin is an organ, and similar to any other structure, it has different functions in addition to connections with the central and peripheral nervous system. This article examines pathological responses produced by scars, analyzing definitions and differences. At the same time, it considers the subcutaneous fascias, as this connective structure is altered when there is a discontinuous cutaneous surface. The consequence is an ample symptomatology, which is not limited to the body area where the scar is located, such as a postural or trigeminal disorder.