Worm Breeder's Gazette 8(1): 33

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

2-NM Filaments in Worm Sperm

T. Roberts

At the May, 1983 Worm Meetings, I described 2-nm filaments found in 
the pseudopods of crawling sperm.  Recently, much better images of 
these filaments have been obtained by fixing intact crawling cells on 
nickel grids, positive staining with uranyl acetate, and critical-
point drying.  Sperm flatten their pseudopods when they crawl (
thickness ~1-2  m) so that the edges of the pseudopod of whole cells 
can be studied in a conventional electron microscope operated at 100 
These intact cells contain an impressive array of 2-nm filaments 
surrounded by the amorphous, granular pseudopod cytoplasm.  The 
filaments are relatively short ( 100 nm) and are most oriented nearly 
parallel to the long axis of the cell.  I often find several filaments 
of about the same length lying parallel to one another but have not 
seen any interconnections between them.  Many of the filaments at the 
very edge of the pseudopod abut the cytoplasmic face of the plasma 
membrane.  One sidelight of this work has been the continued, 
consistent failure to find filamentous actin.  Sperm clearly lack F-
actin and, therefore, must use a different mechanism to crawl.
The polypeptide that makes up the 2-nm filaments has not yet been 
identified.  Major sperm protein, described by Mike Klass, remains the 
leading candidate based on its abundance, its localization in the 
pseudopod, and its colocalization (by immunofluorescence) with 
filamentous structures in fibrous bodies of spermatocytes (Ward and 
Klass, 1982, Dev.  Biol.  92: 203-208).  I have been trying to 
immunolabel the 2-nm filaments with an antibody to MSP (we have both a 
polyclonal rabbit anti-MSP, obtained from Sam Ward, and a new 
monoclonal anti-MSP generated in our lab).  This approach has been 
hindered by my inability to remove the granular cytoplasm surrounding 
the filaments without extracting the filaments as well.  Recently, I 
have found that 10-30 min fixation in formaldehyde followed by 
extraction in Triton X-100 lyses the plasma membrane and removes much 
of the pseudopod cytoplasm.  The pseudopod remnant consists of a 
honeycomb-like arrangement of cytoplasm which contains numerous 2-nm 
filaments.  These filaments may be sufficiently freed of surrounding 
cytoplasm to label them convincingly with ferritin- or gold-conjugated