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2015 ; 116
(5
): 778-86
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ORC4 surrounds extruded chromatin in female meiosis
#MMPMID25502171
Nguyen H
; Ortega MA
; Ko M
; Marh J
; Ward WS
J Cell Biochem
2015[May]; 116
(5
): 778-86
PMID25502171
show ga
Six proteins, ORC1-6, make up the origin recognition complex (ORC) that initiates
licensing of DNA replication origins. We have previously reported that subunit
ORC2 is localized between the separating maternal chromosomes at anaphase II just
after fertilization and is present in zygotic pronuclei at G1. Here, we found
that ORC1, 3, and 5 all localize between the chromosomes at anaphase II, but
could not be detected in zygotic G1. ORC6 localized to the periphery of the
nucleoli at all zygotic stages. We identified an unexpected potential role for
ORC4 in polar body formation. We found that in both female meiotic divisions,
ORC4 surrounds the set of chromosomes, as a sphere-like structure, that will
eventually be discarded in the polar bodies, but not the chromosomes that
segregate into the oocyte. None of the other five ORC proteins are involved in
this structure. In Zygotic G1, ORC4 surrounds the nuclei of the polar bodies, but
was not detectable in the pronuclei. When the zygote entered mitosis ORC4 was
only detected in the polar body. However, ORC4 appeared on both sets of
separating chromosomes at telophase. At this point, the ORC4 that was in the
polar body also migrated into the nuclei, suggesting that ORC4 or an associated
protein is modified during the first embryonic cell cycle to allow it to bind
DNA. Our results suggest that ORC4 may help identify the chromosomes that are
destined to be expelled in the polar body, and may play a role in polar body
extrusion. ORC4 surrounds the chromatin that will be extruded in the polar body
in both female meiotic divisions, then makes a transition from the cytoplasm to
the chromosomes at zygotic anaphase, suggesting multiple roles for this
replication licensing protein.
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