© Springer International Publishing Switzerland 2017 173
F. Pelegri et al. (eds.), Vertebrate Development, Advances in Experimental
Medicine and Biology 953, DOI 10.1007/978-3-319-46095-6_5
Chapter 5
Localization in Oogenesis of Maternal
Regulators of Embryonic Development
Matias Escobar-Aguirre, Yaniv M. Elkouby, and Mary C. Mullins
Abstract Cell polarity generates intracellular asymmetries and functional region-
alization in tissues and morphogenetic processes. Cell polarity in development
often relies on mechanisms of RNA localization to specific subcellular domains to
define the identity of future developing tissues. The totipotent egg of most animals
illustrates in a grand way the importance of cell polarity and RNA localization in
regulating multiple crucial developmental events. The polarization of the egg arises
during its development in oogenesis. RNAs localize asymmetrically in the early
oocyte defining its animal-vegetal (AV) axis, which upon further elaboration in
mid- and late-oogenesis stages produces a mature egg with specific localized factors
along its AV axis. These localized factors will define the future anterior-posterior
(AP) and dorsal-ventral (DV) axes of the embryo. Furthermore, AV polarity con-
fines germ cell determinants to the vegetal pole, from where they redistribute to the
cleavage furrows of the 2- and 4-cell stage embryo, ultimately specifying the pri-
mordial germ cells (PGCs). The sperm entry region during fertilization is also
defined by the AV axis. In frogs and fish, sperm enters through the animal pole,
similar to the mouse where it enters predominantly in the animal half. Thus, AV
polarity establishment and RNA localization are involved in all the major events of
early embryonic development. In this chapter, we will review the RNA localization
mechanisms in vertebrate oocytes that are key to embryonic patterning, referring to
some of the groundbreaking studies in frog oocytes and incorporating the current
genetic evidence from the zebrafish.
Keywords Balbiani body • Bucky ball • Oocyte polarity • Germplasm • RNA localiza-
tion • Oogenesis • Fertilization • Cytoskeleton • Axis formation • Animal- vegetal axis
M. Escobar-Aguirre • Y.M. Elkouby • M.C. Mullins (*)
Department of Cell and Developmental Biology, University of Pennsylvania Perelman School
of Medicine, 1152 BRBII/III, 421 Curie Boulevard, Philadelphia, PA 19104-6058, USA
e-mail: [email protected]