The Journal of Cell Biology, Vol 96, 1258-1265, Copyright © 1983 by The Rockefeller University Press
Firm structural associations between migratory pigment granules and microtubules in crayfish retinula cells
E Frixione
The morphology of associations between mobile pigment granules and
microtubules of the crayfish retinula cells was examined with transmission
electron microscopy. Many pigment granules were found associated with
microtubules through linkages of fuzzy appearance in thin sections. The
linkages were revealed as discrete strands of variable shape in
rotary-shadowed replicas of freeze-fractured and deep- etched specimens.
The only feature of constant morphology among these connections consisted
of 2-4-nm filaments projecting laterally from the microtubules. The
firmness of the pigment granule-microtubule associations was judged by
their ability to hold up during cell disruption procedures of increasing
disaggregation effects in a low- Ca++ stabilization buffer. The results of
these tests were inspected with scanning electron microscopy and with
transmission electron microscopy of negatively stained preparations.
Numerous pigment granules remained associated with a stable microtubule
framework after the plasma membrane had been stripped away. Moreover,
granule- microtubule attachments survived breakdown of this framework into
free fascicles of microtubules. The pigment granules were associated with
the free microtubules either individually or as clusters entangled in a
fibrous material interwoven with 10-nm filaments. These findings attest
that many pigment granules are bound to microtubules through linkages that
constitute effective attachments. Further, it is demonstrated that a highly
cohesive substance associates the pigment granules with one another. These
conclusions are discussed in terms of a pigment transport mechanism in
which a network of interconnected granules would establish firm transient
interactions with a supporting skeleton of microtubules.
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