Cellular Communication in Multicellular OrganismsIn Plants and Animals

What is communication?

Main aspects involved

Signal – in general acoustic or vibrational signals olfactory or chemical signals visual signals

Signaller

Signal receiver

Honesty of Signals

Deceptive signals

How does a cell communicate?

It uses a Cellphone

HA HAA HA

How does a cell communicate

Cells communicate by generating, transmitting and receiving chemical signals.

Cell communication processes share common features that reflect a shared evolutionary history In single-celled organisms, signal transduction pathways

influence how the cell responds to its environment. In multicellular organisms, signal transduction pathways

coordinate the activities within individual cells that support the function of the organism as a whole.

http://www.mpi-dortmund.mpg.de/departments/dep1/signaltransduktion/image3.gif

Why do Unicellullar organisms need to communicate?

Why do cells in multicellular organisms need to communicate?

Why cells need to communicate?

Here are a few reasons: Coordinate activities in multicellular organisms Hormone actions Cell recognition To find mates (yeast cells) Turn pathways on/off apoptosis

Cell – Cell Communication

It’s a prerequisite for differentiation and development in multicellular organisms.

Allows cells to respond to both their internal and external environments

It has to be tightly regulated to ensure precision.

The basic chemical processes by which cells communicate are shared across evolutionary lines of descent Bacteria Multicellular organisms

Outside the body

Ex. Pheromone

s

Ex. Quorum sensing

Inside the body

Short Distance

Long Distance

Modes of cell signaling

1. Direct cell-cell

2. Indirect: Secreted molecules.

A. Endocrine signaling..

B. Paracrine signaling. C. Autocrine signaling.

Types of Chemical Signaling Chemical signaling between cells is one of

the most important ways that activities of

tissues and organs are coordinated.

The nervous system is the other major

coordinating system in animals, but even

here chemical signaling is used between

adjacent neurons

History In 1879 – Eduard Tangl – first to unravel how plant cells communicate

Referred those as ‘ cytoplasmic bridges ’

In 1901- Eduard Strasburger named these cytoplasmic bridges “plasmodesmata”

Descriptions of symplasmic connections b/w animal cells – published 40 years ago - gap junctions

During last decade – so called tunneling nanotubes (TNT) – identified in variety of cell types.

Signalling in plants

Plant cells surrounded by a cell wall together with the turgor pressure provides a structural stability

Two different signaling pathways evolved in plants

One pathway includes the fusion of small molecules – peptides and phytohormones through the matrix of CW and PM receptors

Second involves a mechanism, whereby, during cytokinesis dividing cells remain connected through the formation of plasmodesmata.

Structure of Plasmodesmata

These were thought to be nonselective pores that passively allow diffusion of macromolecules between neighboring cells.

There are several different plasmodesmal morphotypes:- It shares diameter of about 20-50 nm and are lined by continuous PM Desmotubule(DT) – central axial structure having a diameter of about 15

nm It has been suggested to be involved in the regulation of permeability

providing stability to whole structure The major path for symplasmic transport through plasmodesmata is the

cytoplasmic sleeve between the PM and DT

Desmotubule formation

Tunneling nanotube

Gap junction

Molecules within the cytoplasmic sleeve reduce the space in plasmodesmata and thereby limit symplasmic transport of small micro channels – 2.5-4 nm

Adiitional proteins or callose deposition can block the cell wall. Example:- β-1,3-glucanase in A.thaliana

These structural features determine the size of molecules that can diffuse through plasmodesmata and is referred as Size exclusion limit.

Primary and Secondary plasmodesmata

Ex. Plant cells communicate directly through openings called plasmodesmata.

SIGNALLING IN ANIMALS

In animals, gap junctions were identified several decades ago as symplasmic connections between cells.

In 2004, identified other cellular bridges, the so-called TNTs.

Two novel forms of TNT channels- epithelial bridges I and II

Epithelial bridges represent the longest direct tubular connections between cells – up to 1mm

Structure of Gap Junctions

Narrow channels with a pore size of 2 to 3 nm

Protein building blocks of gap junctions in vertebrates are connexins which are transmembrane proteins

Connexins are assembled in the cytoplasm and transported to the plasma membrane.

Proteomic approaches have revealed a large number of connexin-binding proteins that are collectively referred to as the “gap junction proteome”

Posttranslational modifiers like kinases, phosphatases, and ubiquitin have been reported to bind to and/or modify connexins

Contd…..

Connexins, the protein building blocks of gap junctions in vertebrates, have extremely short half-lives of about only 2 h

20 isoforms of connexins are known, of which the most prominent is connexin 43 (Cx43).

Cx43 is the major gap junction protein in the heart, mutations in the corresponding gene might be responsible for complex heart malformations.

History

In 2004, for the first time, Hans-Hermann Gerdes as a researcher at EMBL Germany reported a novel cell-to-cell communication channels that called tunneling nanotubes

Discovered these structures in rat pheochromocytoma PC12 cells and rat kidney NRK cells

TNTs also called as intercellular nanotubes (ICNs)

Tunneling nanotubes

TNTs are thin protrusions of the plasma membrane

A diameter of 50 to 200 nm

Gap junctions and TNTs enable the exchange of cytoplasmic factors through direct contact between the cytoplasm itself of connected cells

Together with gap junctions, they might facilitate the electrical synchronization of distant cells.

Formation of TNTs

De Novo between cells – actin involved

One cell forms actin-driven protrusions directed to the neighboring cell

which is remodeled into a straight and thin structure

TNTs are formed when attached cells depart from each other. Ex:- T cells

Implication in Disease

TNTs may be involved in the spread of pathogenic viruses and prions Nanotubes provide a hitherto unknown route for HIV-1 transmission

between T cells in a receptor-mediated manner. HIV-1-infected human T cells were recently found to be interconnected

by TNTs HIV-1 negative factor (Nef) protein is thought to be responsible for its

induction The Nef protein can block the generation of effective neutralizing

antibodies against HIV-1 by antibody-producing plasma cell progeny of B cells in AIDS patients

Contd….

HIV is able to utilize the communication system of TNTs to spread intercellularly

Creutzfeldt–Jacob disease, the pathogenic prions PrPSc enter the body with contaminated food and can spread from the intestinal entry site to the central nervous system by intercellular transfer from the lymphoid system to the peripheral nervous system.

Cx mutant associated

Cx gene knockout (KO) strategies in mice were first applied to Cx43 by Reaume et al[10] in 1995.

Mutant mice embryos lacking Cx43 die at birth as a result of a failure in pulmonary gas exchange caused by a swelling and blockage of the right ventricular outflow tract from the heart, indicating that Cx43 plays an essential role in heart development

References Cell-to-cell communication in plants, animals, and fungi : a comparative

review Sandra Bloemendal & Ulrich Kück Tunneling nanotubes : Emerging view of their molecular components and

formation mechanisms Shunsuke Kimura, KojiHasec, Hiroshi Ohno Connexin mutant embryonic stem cells and human diseases Kiyomasa

Nishii, Yosaburo Shibata, Yasushi Kobayashi Emerging physiological and pathological implications of tunneling

nanotubes formation between cells Sajjad Sisakhtnezhad∗, Leila Khosravi Signalling and Reception Leena Lindstro ¨m,University of Jyva¨skyla¨,

Jyva¨skyla¨, Finland Janne S Kotiaho,University of Jyva¨skyla¨, Jyva¨skyla¨, Finland

Molecular Bioloy of The Cell- Bruce Alberts – 5th Edition Genes Benjamin - by Lewin Prentice, Hall

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