Dr Mah Jabeen MuneeraAssistant Professor Department of AnatomyKEMU

Cell architecture; structure and functions of cytoskeletal framework

Microfilaments • Shape: double sranded helix• Diameter: 7nm • Basic protein subunit:

monomer of G-actin (globular or free actin) polymerizes to F- actin (filamentous), in presence of K & Mg.

• Formin• Polarity: _ pointed end and +

barbed end• Treadmilling• Stable- muscle cells and

microvilli • Dissociate and reassemble• Profilin & Cofilin

Toxins that bind to actin

• Prevent polymerization

• Prevent depolymerization (phalloidin found in poisosnous mushrooms)

• Disrupt the dynamic equilibrium between

F-actin and G-actin causing cell death

Cytokinesis

Microvillus

Core of actin filamentsABPs- Actin Binding

Proteins • Villin and fimbrin• Tropomyosin• Spectrin• Myosin 1 and 2

Cell cortex

Stress fibers

Intermediate filaments

• 10-12nm• Structural function• Intercellular

junctions• Nuclear lamina• Identification by

means of immunocytochemical methods

• Tissue specificity

Intercellular adhesions

Desmosomes Zonula adherens

Tissue specificityFibroblasts: Cells of

mesenchymal origin- ? IF ›50 different types divided

into 05 classes

• 1. Keratins- epithelium• 2. Vimentin-

mesenchymal cells and vascular smooth muscle

• 3. Desmin- muscle except vascular smooth muscle

• 4. Glial fibrillary acidic proteins- glial cells

• 5. Neurofilaments- neurons

Information for diagnosis and treatment of cancer

• Presence of a specific type of intermediate filament in tumors can reveal which cell originated the tumor

• Identification of intermediate filament proteins by means of immunocytochemical methods is a routine procedure

Terminal Web

• Microvilli bearing cells• Microfilaments &

intermediate filaments• Desmosomes

anchorage• ABP: spectrin & Myosin

II

Alzheimers disease• Neurofibrillary tangles: presence of structurally

abnormal but phosphorylated neurofilaments and microtubule associated proteins ??

Alexander disease• Disorder of CNS• Mutations in the coding region of GFAP gene• Altered GFAP prevents the assembly of

intermediate filaments• Accumulation of intermediate filament protein

GFAP leads to cytoplasmic inclusions in astrocytes (Rosenthal fibres)