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Fig. 8.4 Germ plasm formation and RNA localization during Xenopus oogenesis. (a) Schematic
showing different stages in oogenesis in relation to the Balbiani body (Bb, tan). Oogonia show begin-
ning of mitochondria (green) clustering in relation to nuage (red) in close nuclear apposition.
Prestage I shows further development of germ plasm as germ line RNAs accumulate within Bb and
germinal granules (red circles), late stage RNAs are uniformly distributed (blue lines). Stage I
oocytes with germ plasm (red circles) at tip of mature Bb. Stages II begins expansion of Bb towards
the vegetal pole with germ plasm reaching cortical region followed by fragmented Bb containing late
pathway RNAs. Stage VI oocyte germ plasm RNAs in a small cortical region while late pathway
RNAs overlap with germ plasm but extend to a larger cortical domain. (b) Scheme of germ plasm
formation. In pre-stage I and early stage I oocytes an electron dense material called nuage (40 nm),
leaves the nucleus via nuclear pores ( 1 ). In the cytoplasm, nuage associates with specific germ plasm
components including nanos1 mRNA (red dots), Vasa protein (green dots), and the spliceosomal
protein Sm (yellow dots). Nuage aggregates coalesce into larger spherical accumulations (200–
600 nm), or nuage spheres ( 2 ) become surrounded by mitochondria, forming a large nuage/mito-
chondria complex, called mitochondria cement ( 3 ). As this complex translocates toward the Balbiani
T. Aguero et al.