Molecular Reproduction & Development 78:3–8 (2011)
Polar Bodies—More a Lack of Understanding Than a
Lack of Respect
SAMUEL SCHMERLER1AND GARY M. WESSEL2*
1Department of Ecology and Evolutionary Biology, Brown University, Providence,
2Department of Molecular and Cellular Biology, Brown University, Providence,
Polar bodies are as diverse as the organisms that produce them. Although in many
animals these cells often die following meiotic maturation of the oocyte, in other
highlight some of this diversity and summarize the evolutionary basis for their utility.
Mol. Reprod. Dev. 78: 3–8, 2011. ? 2010 Wiley-Liss, Inc.
Received 8 October 2010; Accepted 17 November 2010
* Corresponding author:
185 Meeting Street, Box G-SFH
Providence, RI 02912.
Grant sponsor: Supported by NIH,
number: RO1 HD28152.
A polar body is the byproduct of an oocyte meiotic
division. It is the small cell that normally apoptoses, and in
textbook figures, it usually just disappears. This portrayal,
though, does not do the cell justice.
Polar bodies typically form by asymmetric cytokinesis:
cytosol and organelles are shunted into the secondary
oocyte during meiosis I, and then into the egg in meiosis
II (Fig. 1A). This leaves the ovum’s sister and aunt (or
cousins, if the first polar body also undergoes meiosis II)
with relatively little cytoplasm, so in most organisms, these
polar bodies simply degenerate. The polar body of human
oocytes, for example, apoptoses in 17–24hr following its
formation, and the resulting fragments remain entrapped
within the zona pellucida (Longo, 1997). Polar bodies were
first reported in 1824 by Carus in gastropods, but their role
was not clarified until the work of Butschli in 1875, Giard in
1902). These structures were often confused with egg
fragments or expelled yolk masses, but were eventually
referred to as directional bodies (or Richtungskorper), a
The common names ‘‘polocytes’’ and ‘‘polar bodies’’ derive
from their polar position in the eggs (e.g. Fig. 1B).
Some may not consider the polar body to meet the
standards ofa cell, but indeedit does. Human polar bodies,
for example, have a nucleus, ribosomes, Golgi, mitochon-
dria and cortical granules (Zamboni, 1970), although the
Abbreviations: DNA, deoxyribonucleic acid; FISH, fluorescence in situ
hybridization; PGD, preimplantation genetic diagnoses.
products and their descendent
cell lineages pertains to some of
evolution’s most vexing
questions . . .
? 2010 WILEY-LISS, INC.
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Mol Reprod Dev 78:3–8 (2011)
Molecular Reproduction & Development
SCHMERLER AND WESSEL