Figure 2. Immunolocalization and TEM analysis place SYP-3 as a structural component of the SC. (A-D) Immunolocalization of SYP-3 throughout meiotic prophase. Images in A-C are projections halfway through 3D data stacks of whole nuclei; images in D encompass entire nuclei. DAPI-stained chromosomes are in blue in A, C, and D and in white in B. a-SYP-3 is in green in A, C, and D and in white in B. a-SYP-1 is in red in A and C and in white in B. (A) Progression into transition zone is observed from left to right in this field of nuclei, as indicated by the yellow arrow. SYP-3 is observed colocalizing with SYP-1 to discrete chromosomal foci in early transition zone. (B) Progression into transition zone is observed top to bottom in this field of nuclei. SYP-3 is observed localizing extensively throughout chromosomes by mid-transition zone. High magnification images of mid-transition zone nuclei indicate that SYP-3 chromosomal localization is more extensive at this stage compared to SYP-1 (indicated by yellow arrows). The hexagonal staining pattern observed corresponding to the cellular membrane is the nonspecific background also present in the
syp-3(
ok758) null mutant (Figure 4). (C) SYP-3 colocalizes with SYP-1 continuously at the interface between paired and aligned homologs during pachytene. (D) SYP-3 localization becomes restricted to the mid-bivalents at diakinesis and progressively dissociates from chromosomes, being no longer present at late diakinesis (progression is indicated by yellow arrow). (E-G) TEM images of mid-pachytene nuclei in wild-type and
syp-3(
ok758) germlines. (E) Equatorial section of a wild-type pachytene nucleus where the large dark body slightly off-center is the nucleolus surrounded by SC stretches (indicated by yellow arrow) visible as 'zipper-like' structures flanked by electron-dense chromatin patches. (F) Higher magnification of an SC from a different wild-type nucleus. (G) In both
syp-3 mutants [exemplified here by
syp-3(
ok758)], chromatin patches are observed distributed around the nucleolus and SCs are absent. Bars in A-D, 2 um; in E and G, 500 nm; in F, 100 nm.