Invagination

Caveolae are invaginations of the plasma membrane. They contain the protein caveolin and are rich in certain phospholipids. Similar to coated pits, they bud off internally forming endocytic vesicles. Caveolae play an important role in the internalization of certain cell surface receptors. 

T-tubule is a transverse invagination of the plasma membrane, which occurs at the specified sites characteristic to animal species and organs, i.e. at the Z-line in cardiac ventricle muscle and non-mammalian vertebrate skeletal muscle and at the A-I junction in mammalian skeletal muscle. It is absent in all avian cardiac cells, all cardiac conduction cells, many mammalian atrial cells and most smooth muscle cells. T-tubule serves as an inward conduit for the action potential. 

The mitochondrion has an outer and an inner membrane (Figure 1). The outer membrane contains pores formed from a protein, porin, which allow exchange of molecules with molecular weights up to about 2,000 between the cytosol and the intermembrane space. The inner membrane is extensively invaginated to increase its surface area. It has a different lipid composition from the outer membrane and is rich in the acidic phospholipid cardiolipin (diphosphatidyl-glycerol) which is only found in animal cells in mitochondria. Cardiolipin confers good electrical insulating properties on the inner membrane which is impermeable... 

Figure 41 -15. Two types of endocytosis. An endocytotic vesicle (V) forms as a result of invagination of a portion of the plasma membrane. Fluid-phase endocytosis (A) is random and nondirected. Receptor-mediated endocytosis (B) is selective and occurs in coated pits (CP) lined with the protein clathrin (the fuzzy material). Targeting is provided by receptors (black symbols) specific for a variety of molecules. This results in the formation of a coated vesicle (CV).

Herman T, Horvitz HR Three proteins involved in Caenorhabditis elegans vulval invagination are similar to components of a gly-cosylation pathway. Proc Natl Acad Sci U S A 1999 96 974. 

The differentiation of cells occurs concomitantly to modifications of wall components. The nature of the pectins of the walls changes under the action of enzymes, among which esterases, secreted between the apical meristematic cells and the more basal differentiated cells. The apposition of new layers of pectins with different compositions at the inner surface of the walls is another mechanism by which the cells adapt their immediate environment. Using the 2F4 antibody, we have observed, in plant suspensions as well as in tissues, a third mechanism involved in wall modification. Numerous invaginations of the... 

There are several major classes of Ca channels (1) receptor-operated Ca channels in plasma membranes (2) ligand-gated Ca " channels in intracellular membranes and (3) voltage-dependent Ca channels that are usually found in plasma membranes or the invaginations of the plasma membrane that are known as transverse tubule membranes. Receptor-dependent or receptor-operated Ca channels (ROCCs) are primarily opened in response to activation of their associated receptors and, by definition, exhibit a certain amount of selectivity for Ca " over other cations. Several potentially different types of ROCCs have been characterized including ATP-sensitive channels in smooth muscle [1], mitogen and IP3-sensitive... 

The chemosensory stem cells give rise to several types of neuronal and non-neuronal cell lines under the influence of multiple organisers. From a ventro-lateral infolding, the olfactory pit is produced and this invagination soon becomes separated into two areas which will produce the main and accessory olfactory neurones [Figs. 4.2(a)-(d)]. 

Fig. 4.2 Differentiation from olfactory placode of main and VN primordia (a) to (b), embryonic stages in reptiles (Squamates and Crocodylia). (a), Early invagination of placode (a ), late separation of primordia for AOS/MOS and (b), agenesis of presumptive VN(JO) cells in crocodile (NPT, nasal pit) (from Parsons, 1970).

Fig. 4.2 (c) to (d), Early and late embryonic stages in mammals, invagination and separation of AOS from MOS (from Farbmann, 1992). 

This process occurs in the mitochondria, organelles present in the cells of all multicellular organisms (see Figs 6.8 and 6.26). Mitochondria have two membranes. The invaginations of the internal membrane into the inner space of the organelle (matrix space) are termed crests (from the Latin, cristae). 

III. Endocytosis Invagination of the plasma membrane forming an internalized membrane vesicle. 

Textbooks on neuroscience often describe the location and function of hundreds of individual brain regions (see references above). However, for current purposes these will be kept to a minimum (Figure 2.1). Anatomically, the brain can be subdivided into the forebrain containing the telencephalon and diencephalon, the midbrain or mesencephalon and the hindbrain (metencephalon and myelencephalon). The telencephalon includes the left and right cerebral hemispheres encompassed by the cerebral cortex (neocortex). Cortex is a translation of the word bark and is so-called because its surface, made up of numerous sulci (grooves or invaginations) and gyri (raised areas), is on the outer surface of the brain like the bark of a tree. Each hemisphere is divided into four lobes, named from the front (rostral) to back (caudal) of the brain frontal, temporal, parietal and occipital. 

Figure 14.10 Overview of cellular entry of (non-viral) gene delivery systems, with subsequent plasmid relocation to the nucleus. The delivery systems (e.g. lipoplexes and polyplexes) initially enter the cell via endocytosis (the invagination of a small section of plasma membrane to form small membrane-bound vesicles termed endosomes). Endosomes subsequently fuse with golgi-derived vesicles, forming lysosomes. Golgi-derived hydrolytic lysosomal enzymes then degrade the lysosomal contents. A proportion of the plasmid DNA must escape lysosomal destruction via entry into the cytoplasm. Some plasmids subsequently enter the nucleus. Refer to text for further details...

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