77. Physiology | Cytoskeleton and Complex Cell Behavior II

Spectrin defects weaken the RBC membrane →

hereditary spherocytosis. Spectrin–actin lattice maintains RBC biconcave shape; deficiency → hereditary spherocytosis with splenomegaly & hemolytic anemia.

WASp activates the

Arp2/3 complex. A WAS gene mutation cripples actin branching in hematopoietic cells → thrombocytopenia, eczema, and recurrent infections (Wiskott‑Aldrich syndrome).

Defective microtubule dynein arms

Causes primary ciliary dyskinesia (Kartagener)

Mutated dystrophin gene

X‑linked muscular dystrophy—progressive proximal muscle weakness

Homozygous mutation of the CFTR gene

Cystic fibrosis—recurrent pulmonary infections with elevated sweat chloride.

Dystrophin

Links cortical actin to the sarcolemma; an X‑linked loss produces Duchenne muscular dystrophy marked by progressive weakness and pseudohypertrophy.

Tropomyosin

Regulates actin–myosin interaction; mutations would cause contractile defects

Keratin

Intermediate filament in epithelium

Myosin

Motor protein

Troponin I

Cardiac‑specific troponin I (and T) rise within hours and remain elevated; highly specific for myocardial injury