Mj. Dobson et al., SYNAPTONEMAL COMPLEX PROTEINS - OCCURRENCE, EPITOPE MAPPING AND CHROMOSOME DISJUNCTION, Journal of Cell Science, 107, 1994, pp. 2749-2760
We have used polyclonal antibodies against fusion proteins produced fr
om cDNA fragments of a meiotic chromosome core protein, Cor1, and a pr
otein present only in the synapsed portions of the cores, Syn1, to det
ect the occurrence and the locations of these proteins in rodent meiot
ic prophase chromosomes. The 234 amino acid Cor1 protein is present in
early unpaired cores, in the lateral domains of the synaptonemal comp
lex and in the chromosome cores when they separate at diplotene, A nov
el observation showed the presence of Cor1 axial to the metaphase I ch
romosomes and substantial amounts of Cor1 in association with pairs of
sister centromeres. The centromere-associated Cor1 protein becomes di
ssociated from the centromeres at anaphase II and it is not found in m
itotic metaphase centromeres. The extended presence of Cor1 suggests t
hat it may have a role in chromosome disjunction by fastening chiasmat
a at metaphase I and by joining sister kinetochores, which ensures co-
segregation at anaphase I. Two-colour immunofluorescence of Cor1 and S
yn1 demonstrates that synapsis between homologous cores is initiated a
t few sites but advances rapidly relative to the establishment of new
initiation sites. If the rapid advance of synapsis deters additional i
nitiation sites between pairs of homologues, it may provide a mechanis
m for positive recombination interference. Immunogold epitope mapping
of antibodies to four Syn1 fusion proteins places the amino terminus o
f Syn1 towards the centre of the synaptonemal complex while the carbox
yl terminus extends well into the lateral domain of the synaptonemal c
omplex. The Syn1 fusion proteins have a non-specific DNA binding capac
ity. Immunogold labelling of Cor1 antigens indicates that the lateral
domain of the synaptonemal complex is about twice as wide as the appar
ent width of lateral elements when stained with electron-dense metal i
ons. Electron microscopy of shadow-cast surface-spread SCs confirms th
e greater width of the lateral domain. The implication of these dimens
ions is that the proteins that comprise the synaptic domain overlap,vi
th the protein constituents of the lateral domains of the synaptonemal
complex more than was apparent from earlier observations. This arrang
ement suggests that direct interactions might be expected between some
of the synaptonemal complex proteins.