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Gap Junctions: Connections between cells which allow passage of small molecules and electric current. Gap junctions were first described anatomically as regions of close apposition between cells with a narrow (1-2 nm) gap between cell membranes. The variety in the properties of gap junctions is reflected in the number of Connexins, the family of proteins which form the junctions.

Gap Junctions

JoVE 10986

Multicellular organisms employ a variety of ways for cells to communicate with each other. Gap junctions are specialized proteins that form pores between neighboring cells in animals, connecting the cytoplasm between the two, and allowing for the exchange of molecules and ions. They are found in a wide range of invertebrate and vertebrate species, mediate numerous functions including cell differentiation and development, and are associated with numerous human diseases, including cardiac and skin disorders. Vertebrate gap junctions are composed of transmembrane proteins called connexins (CX), and six connexins form a hemichannel called a connexon. Humans have at least 21 different forms of connexins that are expressed in almost all cell types. A connexon hemichannel is said to be homomeric when all six connexins are the same, and heteromeric when composed of different types. Most cells express more than one type of connexin. These can form functional connexon hemichannels or a full gap junction channel by pairing up with a counterpart on an adjacent cell. The gap junctions are considered homotypic when each connexon is the same, and heterotypic when they differ. Clusters called gap junction plaques often form where the channels are continually recycled and degraded at the center of the plaques and replaced at the periphery. Gap junctions allow th

 Core: Biology

Contact-dependent Signaling

JoVE 10715

Contact-dependent signaling uses specialized cytoplasmic channels between cells that allow the flow of small molecules between them. In animal cells, these channels are called gap junctions. In plants, they are known as plasmodesmata.

Gap junctions form when two hemichannels, or connexons, join; one connexon from one cell coupling to a connexon of an adjacent cell. Each cell’s connexon is formed from six proteins creating a circular channel. There are over 20 different types of these proteins, or connexins, so there is substantial variation in how they come together as connexons and as gap junctions. Connexins have four transmembrane subunits with both their N- and C-terminus endings located intracellularly. The C-terminus has multiple phosphorylation sites so it can be activated by numerous different kinases- further adding to gap junction variety. Depending on the activating kinase, and the C-terminal amino acid residues of connexins that are phosphorylated, gap junctions can be partially or fully opened. This selectively allows small molecules to flow from one cell into another. A gap junction may also exclude by electrochemical charge. The selectivity of gap junctions allows a single cell to coordinate a complex multicellular response. However, some toxic molecules, matching the size and electrochemical preference of the gap junction, can also p

 Core: Biology

Cleavage and Blastulation

JoVE 10908

After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage is a mitotic cell division that does not result in growth. With each round of successive cell division, daughter cells get increasingly smaller.

At the beginning of embryogenesis, maternal mRNAs control development. However, by the eight-cell stage of cleavage, embryonic genes become activated in a process called zygotic genome activation (ZGA). As a result, maternal mRNAs get degraded, and ZGA causes a transition from maternal to zygotic genetic control of developing an embryo. Although maternal mRNAs get degraded, previously translated proteins may remain in the embryo through later stages of development. Cleavage patterns vary between organisms depending on the presence and distribution of egg yolk amongst other factors. For example, mammals have a holoblastic rotational cleavage pattern. They are holoblastic because they have sparse, but evenly distributed yolk and therefore end up with a cleavage furrow that extends through the entire embryo as opposed to being meroblastic where the cleavage furrow does not extend through the yolk-dense portion of the cytoplasm. At the onset of cleavage, rotational cleavage begins when the zygote first divides to form two smaller daughter cells called blas

 Core: Biology

The Synapse

JoVE 10997

Neurons communicate with one another by passing on their electrical signals to other neurons. A synapse is the location where two neurons meet to exchange signals. At the synapse, the neuron that sends the signal is called the presynaptic cell, while the neuron that receives the message is called the postsynaptic cell. Note that most neurons can be both presynaptic and postsynaptic, as they both transmit and receive information. An electrical synapse is one type of synapse in which the pre- and postsynaptic cells are physically coupled by proteins called gap junctions. This allows electrical signals to be directly transmitted to the postsynaptic cell. One feature of these synapses is that they can transmit electrical signals extremely quickly—sometimes at a fraction of a millisecond—and do not require any energy input. This is often useful in circuits that are part of escape behaviors, such as that found in the crayfish that couples the sensation of a predator with the activation of the motor response. In contrast, transmission at chemical synapses is a stepwise process. When an action potential reaches the end of the axonal terminal, voltage-gated calcium channels open and allows calcium ions to enter. These ions trigger fusion of neurotransmitter-containing vesicles with the cellular membrane, releasing neurotransmitters into the small space

 Core: Biology

What is Cell Signaling?

JoVE 10985

Despite the protective membrane that separates a cell from the environment, cells need the ability to detect and respond to environmental changes. Additionally, cells often need to communicate with one another. Unicellular and multicellular organisms use a variety of cell signaling mechanisms to communicate to respond to the environment.

Cells respond to many types of information, often through receptor proteins positioned on the membrane. For example, skin cells respond to and transmit touch information, while photoreceptors in the retina can detect light. Most cells, however, have evolved to respond to chemical signals, including hormones, neurotransmitters, and many other types of signaling molecules. Cells can even coordinate different responses elicited by the same signaling molecule. Typically, cell signaling involves three steps: (1) reception of the signal, (2) signal transduction, and (3) a response. In most signal reception, a membrane-impermeable molecule, or ligand, causes a change in a membrane receptor; however, some signaling molecules, such as hormones, can traverse the membrane to reach their internal receptors. The membrane receptor can then send this signal to intracellular messengers, which transduces the message into a cellular response. This intracellular response may include a change transcription, translation, protein activation,

 Core: Biology

Simultaneous Electrical and Mechanical Stimulation to Enhance Cells' Cardiomyogenic Potential

1Insuficiencia Cardiaca y Regeneración Cardiaca (ICREC) Research Program, Health Science Research Institute Germans Trias i Pujol, 2Amsterdam Universitair Medisch Centrum (UMC), Vrije Universiteit Amsterdam, Pulmonology and Physiology, Amsterdam Cardiovascular Sciences, 3Electronic and Biomedical Instrumentation Group, Departament d'Enginyeria Electrònica, Universitat Politècnica de Catalunya, 4Cardiology Service, Germans Trias i Pujol University Hospital, 5Department of Medicine, Universitat Autònoma de Barcelona, 6Centro de Investigación Biomédica en Red (CIBER) Cardiovascular, Instituto de Salud Carlos III

JoVE 58934


Application of Retinoic Acid to Obtain Osteocytes Cultures from Primary Mouse Osteoblasts

1Renal Research Laboratory, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, 2Department of Nephrology, Dialysis and Renal Transplant, Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico, 3Renal Physiopathology Laboratory, Department of Medical, Surgical and Health Sciences, University of Trieste

JoVE 51465

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