Worm Breeder's Gazette 7(2): 38
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.
The meiotic chromosomes of C. elegans males were reconstructed from electron micrographs of serial sections of three primary spermatocytes. Viewed from the spindle pole the chromosomes form a distinctive pattern on the metaphase I plate. The five autosomal bivalents form a ring that surrounds the centrally placed X univalent. Figure a is a computer reconstruction of the five autosomes and fig. b is a display of four of the autosomes and the X. The autosomal half-bivalents lie to either side of the equatorial plate (as shown for two autosomes in fig. c.) and the X lies on the equatorial plate. The metaphase II spindle in each lobe of a bilobed secondary spermatocyte was also reconstructed. One spindle contained six and the other five pairs of chromosomes, the X had not disjoined at anaphase I. When six chromosomes are present five chromosomes form a ring around the sixth chromosome (figs. d and e). The X cannot be distinguished from the autosomes at this time. Figure f. is a side view of the metaphase II spindle. Kinetochores could not be distinguished on these chromosomes, prepared by conventional electron microscopic techniques. Microtubules appeared to insert directly into the chromosome along the poleward face. Centrioles were present in the asters of the meiotic spindles in primary and secondary spermatocytes of both males and hermaphrodites. The overall shape of the spindles was similar to the mitotic spindles of C. elegans. In contrast, the meiotic spindles seen in oocytes have broad ends and are barrel-shaped similar to the meiotic spindles of mammalian oocytes. Centrioles are absent from the poles of barrel- shaped spindles in mammalian oocytes, and have not been seen in the barrel-shaped spindles of C. elegans. The time at which centrioles are lost in the hermaphrodite gonad has not been determined precisely. Centrioles are seen adjacent to pachytene nuclei in L4 hermaphrodites during spermatogenesis, but have not been seen in young adult hermaphrodites completing the spermatogonial divisions and beginning oogenesis, or in older adult hermaphrodites. [See Figure 1] [See Figure 2]