Isolation and characterization of two forms of a cytoskeleton

Area of Science:

• Cell biology
• Marine biology
• Biochemistry

Background:

• Sea urchin coelomocytes exhibit dynamic morphological changes.
• These cells possess complex cytoskeletal structures.

Purpose of the Study:

• To investigate the cytoskeletal basis of sea urchin coelomocyte shape transformation.
• To identify proteins involved in maintaining cytoskeletal organization.

Main Methods:

• Isolation of petaloid coelomocytes from Strongylocentrotus droebachiensis.
• Induction of morphological changes using hypotonic media.
• Analysis of Triton-insoluble cytoskeletons via electron microscopy.
• Protein identification and quantification using gel electrophoresis and densitometry.

Main Results:

• Coelomocytes transform from a petaloid (loose microfilament net) to a filopodial (paracrystalline actin bundles) form in hypotonic media.
• Actin is the primary cytoskeletal protein, with associated polypeptides of 220k, 64k, 57k, and 27k daltons.
• Filopodial cytoskeletons show a 2.5-fold increase in the 57k polypeptide relative to actin compared to petaloid forms.
• Salt treatment dissociates bundles, releasing actin and associated proteins.

Conclusions:

• The 57k polypeptide, and potentially others, likely crosslinks actin filaments to form bundles.
• These associated proteins are critical for maintaining the three-dimensional cytoskeletal structure and cell morphology.