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Topic Review
Stem Cell Therapy for Infertility
Stem cells are a subtype of cells that remain in undifferentiated form in embryos and in adult tissues and can self-renew and differentiate as and when required. Stem cells in differentiated organs contribute to the restoration of function through organ damage repair. According to their origin, stem cells are classified as embryonic stem cells (ESC), adult stem cells (includes mesenchymal stem cells MSC), induced pluripotent stem cells (iPSC), spermatogonial stem cells (SSCs), and ovarian stem cells. Stem Cells can be applicable for several disorders including infertility both in male and female.
  • 779
  • 22 Jul 2021
Topic Review
Development of SARS-CoV-2 Variants
A novel coronavirus (SARS-CoV-2) emerged towards the end of 2019 that caused a severe respiratory disease in humans called COVID-19. It led to a pandemic with a high rate of morbidity and mortality that is ongoing and threatening humankind. Most of the mutations occurring in SARS-CoV-2 are synonymous or deleterious, but a few of them produce improved viral functions. The first known mutation associated with higher transmissibility, D614G, was detected in early 2020. Since then, the virus has evolved; new mutations have occurred, and many variants have been described. Depending on the genes affected and the location of the mutations, they could provide altered infectivity, transmissibility, or immune escape. To date, mutations that cause variations in the SARS-CoV-2 spike protein have been among the most studied because of the protein’s role in the initial virus–cell contact and because it is the most variable region in the virus genome. Some concerning mutations associated with an impact on viral fitness have been described in the Spike protein, such as D614G, N501Y, E484K, K417N/T, L452R, and P681R, among others. To understand the impact of the infectivity and antigenicity of the virus, the mutation landscape of SARS-CoV-2 has been under constant global scrutiny. The virus variants are defined according to their origin, their genetic profile (some characteristic mutations prevalent in the lineage), and the severity of the disease they produce, which determines the level of concern. If they increase fitness, new variants can outcompete others in the population. The Alpha variant was more transmissible than previous versions and quickly spread globally. The Beta and Gamma variants accumulated mutations that partially escape the immune defenses and affect the effectiveness of vaccines. Nowadays, the Delta variant, identified around March 2021, has spread and displaced the other variants, becoming the most concerning of all lineages that have emerged. The Delta variant has a particular genetic profile, bearing unique mutations, such as T478K in the spike protein and M203R in the nucleocapsid. This entry summarizes the current knowledge of the different mutations that have appeared in SARS-CoV-2, mainly on the spike protein. It analyzes their impact on the protein function and, subsequently, on the level of concern of different variants and their importance in the ongoing pandemic. 
  • 765
  • 28 Dec 2021
Topic Review
Alveologenesis
Alveologenesis is the final stage of lung maturation, when an alveolar region is divided into smaller units called alveoli via the process known as secondary septation. Each of the formed septa serves as a new gas exchange surface, and all together, they dramatically increase the respiratory surface area. Alveologenesis is divided into 2 phases: classical and continued. During the classical alveologenesis, the secondary septa are formed and the number of alveoli increases. During the continued alveologenesis, the maturation and thinning of the septa occur and the size of alveoli increases. The disruption of alveologenesis leads to the simplification of the alveoli, as seen in preterm infants diagnosed with bronchopulmonary dysplasia (BPD), a widespread pulmonary disease that is often connected with lifelong respiratory failure.
  • 735
  • 23 Nov 2021
Topic Review
Endocytosis and Signaling Regulation
Cellular trafficking through the endosomal–lysosomal system is essential for the transport of cargo proteins, receptors and lipids from the plasma membrane inside the cells and across membranous organelles. By acting as sorting stations, vesicle compartments direct the fate of their content for degradation, recycling to the membrane or transport to the trans-Golgi network. To effectively communicate with their neighbors, cells need to regulate their compartmentation and guide their signaling machineries to cortical membranes underlying these contact sites. Endosomal trafficking is indispensable for the polarized distribution of fate determinants, adaptors and junctional proteins. Conversely, endocytic machineries cooperate with polarity and scaffolding components to internalize receptors and target them to discrete membrane domains. Depending on the cell and tissue context, receptor endocytosis can terminate signaling responses but can also activate them within endosomes that act as signaling platforms. Therefore, cell homeostasis and responses to environmental cues rely on the dynamic cooperation of endosomal–lysosomal machineries with polarity and signaling cues. 
  • 711
  • 07 May 2022
Topic Review
The “3Ds” of Growing Kidney Organoids
A kidney organoid is a three-dimensional (3D) cellular aggregate grown from stem cells in vitro that undergoes self-organization, recapitulating aspects of normal renal development to produce nephron structures that resemble the native kidney organ. These miniature kidney-like structures can also be derived from primary patient cells and thus provide simplified context to observe how mutations in kidney-disease-associated genes affect organogenesis and physiological function.
  • 708
  • 17 Feb 2023
Topic Review
Air Pollution Affects Placental DNA Methylation
The Developmental Origins of Health and Disease (DOHaD) concept postulates that in utero exposures influence fetal programming and health in later life. Throughout pregnancy, the placenta plays a central role in fetal programming; it regulates the in utero environment and acts as a gatekeeper for nutrient and waste exchange between the mother and the fetus. Maternal exposure to air pollution, including heavy metals, can reach the placenta, where they alter DNA methylation patterns, leading to changes in placental function and fetal reprogramming. In this entry, we explore the current knowledge on placental DNA methylation changes associated with prenatal air pollution (including heavy metals) exposure and highlight its effects on fetal development and disease susceptibility.
  • 682
  • 15 Nov 2021
Topic Review
Stage-Crisis View
The stage-crisis view is a theory of adult development that was established by Daniel Levinson. Although largely influenced by the work of Erik Erikson, Levinson sought to create a broader theory that would encompass all aspects of adult development as opposed to just the psychosocial. This theory is characterized by both definitive eras as well as transition phases, whose purpose is to facilitate a smooth transition out of one era and into the next. According to his theory, various developmental tasks must be mastered as one progresses through each era; pre-adulthood, early adulthood, middle adulthood, and late adulthood. Crises are also experienced throughout the lifecycle and occur when one become burdened by either internal or external factors, such as during the midlife crisis that occurs during the midlife transition from early adulthood to middle adulthood. Levinson researched both men and women, and found that they typically go through the same cycles, though he suggested that women's cycles were more closely tied to the domestic sphere, or their family life. Due to the use of biased research methods however, the extent to which his results can be generalized remains controversial. Although not widely accepted, his theories entail many implications for both behavioral and cultural psychology.
  • 673
  • 11 Oct 2022
Topic Review
Chromatoid Bodies in the Regulation of Spermatogenesis
The CB is a membrane-less perinuclear organelle present in male germ cells which serve as storehouse for mRNAs transported by RNA binding and transport proteins like GRTH/DDX25. It also serves as a processing center of mRNAs awaiting translation during later stages of spermatogenesis. These CBs are involved in diverse pathways like RNA transport, decay, surveillance and regulate the stability of mRNAs to secure the correct timing of protein expression at different stages of spermiogenesis.
  • 666
  • 11 Mar 2022
Topic Review
Ubiquitination of ETS Transcription Factors
Genome expansion, whole genome and gene duplication events during metazoan evolution produced an extensive family of ETS genes whose members express transcription factors with a conserved winged helix-turn-helix DNA-binding domain. Key determinants of the cellular repertoire of ETS proteins are their stability and turnover, controlled largely by the actions of selective E3 ubiquitin ligases and deubiquitinases. Here we discuss the known relationships between ETS proteins and enzymes that determine their ubiquitin status, their integration with other developmental signal transduction pathways and how suppression of ETS protein ubiquitination contributes to the malignant cell phenotype in multiple cancers.
  • 663
  • 21 Jul 2021
Topic Review
Spleen Reparative Regeneration
The spleen is the largest lymphoid unpaired parenchymal organ of the abdominal cavity found in all vertebrates. Spleen is able to regenerate, though not necessarily to the initial volume. The recovery lasts one month and preserves the architecture, albeit with an increase in the relative volume of lymphoid follicles. The renovated tissues, however, exhibit skewed functional profiles; notably, the decreased production of antibodies and the low cytotoxic activity of T cells, consistent with the decline of T-dependent zones and prolonged reduction in T cell numbers. Autotransplantations of splenic material are of particular clinical interest, as the procedure can possibly mitigate the development of post-splenectomy syndrome. Under these conditions, regeneration lasts 1-2 months, depending on the species. The transplants effectively destroy senescent erythrocytes, assist in microbial clearance, and produce antibodies, thus averting sepsis and bacterial pneumonia. Meanwhile, cellular sources of splenic recovery in such models remain obscure, as well as the time required for T and B cell number re-constitution.
  • 658
  • 21 Jun 2022
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