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The
process of spermiogenesis .
In the left panel a round spermatid begins to extend long
thin projections all around its periphery. Soon the projections
become fewer, longer, and congregated at one pole of the cell
(second panel). Next, the projections begin to fuse and balloon
out into a pseudopod (third panel). At right is a fully mature
spermatozoon , with knobby projections called filopodia extending
from its pseudopod. The cell body (right half of cell) is
pockmarked with pores from the fusion of membranous organelles
to the plasma membrane. |
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Spermiogenesis in action This video shows spermatids undergoing spermiogenesis on a microscope slide in response to a chemical that was added to them. The clock shows elapsed time in minutes:seconds. Note how rapidly the entire transformation proceeds. The spermatid at the upper left fails to activate. |
In
C. elegans, spermiogenesis is the final maturation of sperm,
when the cell builds its pseudopod, acquires the ability to crawl,
and becomes capable of fertilizing an oocyte. For a hermaphrodite's
own sperm, spermiogenesis begins when the spermatids (the immature
undifferentiated cells) arrive in the spermatheca, the chamber in
the reproductive tract where fertilization will take place. Spermiogenesis
of male spermatids is triggered upon mating. Spermiogenesis is a very
rapid process; it only takes about 5 minutes to complete. During spermiogenesis,
a set of dramatic cellular rearrangements take place, including plasma
membrane flow at the site of the newly forming pseudopod, fusion of
mysterious organelles, called membranous organelles, to the plasma
membrane of the cell body, and the formation of a dynamic cytoskeleton
in the pseudopod from the polymerization of a unique protein called
the major sperm protein (msp, pictured at left). 
Remarkably, all of these changes are accomplished
without any new gene expression or protein synthesis, since spermatids
lack transcription and translation machinery. Our lab has learned
how to artificially stimulate C. elegans spermatids to undergo
spermiogenesis on a microscope slide by adding various chemicals,
so we can directly observe all the processes accompanying spermiogenesis.
We also have a collection of mutants defective in various aspects
of spermiogenesis. Thus, we see spermiogenesis as an interesting and
useful paradigm for learning about cellular differentiation. Some
of the questions about spermiogenesis that we are trying to answer
are:
What triggers spermiogenesis?
How is the MSP cytoskeleton built and regulated?
How does the sperm cell crawl?
What directs the sperm cell toward the oocyte?
http://www.mcb.arizona.edu/wardlab/spermio.html
All Contents Copyright © 2000. All rights reserved.
Last Modified: September 29, 1998
Paul Muhlrad pmuhlrad@u.arizona.edu