All cells need to interpret their environment. Efficient processing of signals from the extracellular milieu is achieved through dynamic signal-transduction systems. The components of this system that come into contact first with external signals are cell-surface receptors. RTKs (Receptor Tyrosine Kinases) comprise one large group of receptors that respond to polypeptide growth factors and have intrinsic tyrosine kinase activity. On ligand binding, receptor signaling is activated. The activation of RTKs initiates signal transduction and receptor endocytosis. Most activated RTKs are efficiently cleared from the cell surface by endocytosis and sorted to Lysosomes for degradation. In contrast, inactive RTKs are constitutively internalized and recycled back to the cell[..]

Phagocytosis is an important process for nutrition in unicellular organisms, while in multicellular organisms it is found in specialized cells called phagocytes. Phagocytosis consists in recognition and ingestion of particles larger than 0.5 𝜇m into a plasma membrane derived vesicle, known as phagosome. Phagocytes can ingest microbial pathogens, but importantly also apoptotic cells. In this way, they contribute to the clearance of billions of cells that are turned over every day. Thus phagocytosis becomes essential not only for microbial elimination, but also for tissue homeostasis. Professional phagocytes include monocytes, macrophages, neutrophils, dendritic cells, osteoclasts, and eosinophils. It can be divided into four main steps: (i) recognition of the[..]

Vitiligo is an acquired autoimmune skin disorder characterized by the destruction of skin melanocytes, resulting in the development of white patches. This disease can be psychologically devastating for the patients. It affects all races and occurs in 0.3–1.0% of the world population, and in 50% of cases the condition begins before the age of 20 years. More women than men are referred with Vitiligo, although the incidence of the disorder is not believed to be sex-linked.  Several hypotheses have been proposed regarding the cause of the disease, major among them include stress and autoimmunity (Ref.1). The autoimmune theory is still the leading hypothesis, with several strong reasons supporting it. One of the major reasons is strong association of vitiligo[..]

Plants respond to insect attack, defense against herbivory, and wound-healing by activating jasmonate family of signaling molecules. Jasmonic Acid (JAs) are plant hormones that regulate several physiological processes like defense responses to a variety of biotic and abiotic stresses, growth, development, fertility, and senescence. JAs can also inhibit growth by suppressing mitosis in apical meristems as well as inhibit photosynthesis and energy-generating processes. In Arabidopsis, JA mediated defense response against both herbivore and necrotrophic pathogen attack occurs via interaction of both JA and ethylene (ET)-signaling pathways in a synergistic interaction. This leads to the activation of pathogen-related defense genes like PR5 (pathogenesis-related[..]

Apoptosis (also called programmed cell death) is a cellular death program that is inherent to all mammalian cells and plays an important role in the regulation of various physiological and pathological conditions. It serves to eliminate any unnecessary or unwanted cells and is a highly regulated process. There are a wide variety of conditions that will result in the apoptotic pathway becoming activated including DNA damage or uncontrolled proliferation. The apoptotic pathway is activated by both intracellular and extracellular signals. The central apoptotic machinery can be divided into two major signaling pathways, comprising the death receptor (extrinsic) and the mitochondrial (intrinsic) pathway. Both pathways eventually fuel into a common effector phase that is[..]

Cell Polarity is an essential characteristic of virtually every cell type. The budding yeast S. cerevisiae (Saccharomyces cerevisiae) has been critical for elucidation of proteins and mechanisms that underlie Cell Polarity development. Polarized Growth is mediated by a series of steps involving cortical landmarks, Rho GTPases and a polarized Actin cytoskeleton. Actin cortical patches are essential for normal Endocytosis and secretion is targeted to the bud or mating projection, allowing selective growth in that area. Patches are associated with invaginations of the plasma membrane and occur in polarized clusters at regions of cell growth in budding cells. One of the crucial Rho type GTPases is CDC42 (Cell Division Control Protein-42) which facilitates decisive event[..]

Actin cortical patches are one of the major cytoskeletal structures in yeast and are essential for normal Endocytosis, Cell Growth and Morphology. Actin cortical patches are associated with invaginations of the plasma membrane and occur in polarized clusters at regions of cell growth in budding cells (Ref.1). Patch Assembly probably begins with the association of assembly factors recruited to the plasma membrane by CDC42 (Cell Division Control Protein-42) and its associated proteins and is then followed by nucleation of Actin filaments and Actin-dependent association of proteins regulating filament assembly and stability. Prior to bud emergence in S. cerevisiae (Saccharomyces cerevisiae), cells polarize the Actin cytoskeleton toward the future bud site and assemble a[..]

The S. cerevisiae (Saccharomyces cerevisiae) CDC42 (Cell Division Control Protein-42), a member of the Rho/Rac subfamily of Ras-Like GTPases (GTP-Binding Proteins) and Ras superfamily of low molecular-weight GTPases, is essential for the control of cell polarity during the yeast cell cycle. CDC42 occurs in both soluble and particulate pools, and neither its abundance nor its distribution varied through the cell cycle. In S. cerevisiae, CDC42 is localized to the bud site early in the cell cycle and this localization is critical for the selection of the proper site for Bud Emergence and for Polarized Cell Growth. It plays an important role in multiple Actin-dependent morphogenetic events such as Bud Emergence, Mating-Projection Formation and Pseudohyphal Growth. CDC42[..]

Ovarian sex steroid production is essential for Follicular growth and subsequent Ovulation in Xenopus laevis. In the Xenopus ovary, Oocytes are arrested in an immature form in the Cell Cycle at Prophase-I boundary of the first meiotic cycle, and grow to their maximal size. Prophase-I arrest is terminated by specific signals, often Steroid Hormones, that cause release from Cell Cycle arrest and induce progression  of the Meiotic Cell Cycles to an arrest point during the second Meiotic division, often at Metaphase-II. This process, referred to as “Oocyte Maturation” transforms the immature Oocyte into a fertilizable egg. Two Steroid Hormones: Progesterone and Androgens are the primary mediators of Xenopus oocyte maturation. These hormones are synthesized[..]

Oocyte maturation is the final process of oogenesis where the fully grown ooocytes undergo meiosis to become fertilizable. Oocyte maturation begins with the breakdown of the oocyte nucleus, the germinal vesicle (GV), which occurs by the rapid condensation of the chromosomes to the metaphase state which then move towards the animal pole and divide into two haploid sets and enter the meiosis II. Oocyte maturation in vertebrates is a complex process that requires several morphological, biochemical and ultra structural signaling events and may lead to decreased fertility if any of the programs is disrupted.  Hormones like Progesterone can induce oocyte maturation in Xenopus laevis (X.laevis) (Ref.1 and 2). In Xenopus laevis, immature oocytes are physiologically[..]

Melanocytes are melanin-producing cells found in skin, hair follicles, eyes, inner ear, bones, heart and brain of humans. Melanocytes are generally important for their role in Skin pigmentation, and their ability to produce and distribute Melanin is well known. Melanocytes are responsible for the endogenous synthesis of melanin pigments. Melanin is produced in Melanosomes, specialized organelles that are translocated from the center of the Melanocyte cytoplasm to the tip of its Dendrites. The Dendrites are then involved in the transfer of the Melanosomes to the Keratinocytes.Two main types of melanin pigment are synthesized in human, pheomelanin and eumelanin, and their combination leads to skin colour. Pheomelanin and eumelanin derive from a single precursor, the[..]

The processing of visual information begins in the retina with the detection of light by photoreceptor cells. In humans, two types of photoreceptors in the retina mediate the light response: the rods which mediate vision in dim light and the cones which mediate bright light and color vision. Humans have one rod and three cones for long, medium- and short-waves. Rhodopsin is the photosensitive pigment of the rod photoreceptor cell that initiates the visual signaling cascade and is comprised of a protein part (opsin) and the 11-cis form of vitamin A aldehyde (11-cis retinal) covalently bound to the opsin via a Schiff base linkage. Light converts the 11-cis bond to all-trans changing the inverse agonist to an agonist to enable the opsin to activate its G protein[..]