![]() ![]() Two groups of genes are involved in the localization of the RNAs and thereby initiate the formation of the segmented regions along the antero– posterior axis: the anterior system is necessary for the formation of head and thoracic structures, whereas the posterior system is responsible for abdomen formation and for assembly of the germ plasm. T he antero–posterior axis of the Drosophila embryo is determined by the localization of maternal mRNAs in the egg. We propose that the sponge bodies are structures that, by assembly and transport of included molecules or associated structures, are involved in localization of mRNAs in Drosophila oocytes. Microtubules and microfilaments are not present in sponge bodies, although transport of the sponge bodies through the cells is implied by their presence in cytoplasmic bridges. Sponge bodies surround nuage, a possible polar granule precursor. However, neither the intensity of this staining nor the accumulation of Exuperantia in the sponge bodies is dependent on the amount of bicoid mRNA present in the ovaries. RNA staining indicates that sponge bodies contain RNA. We suggest that the sponge bodies are homologous to the mitochondrial cloud in Xenopus oocytes, a granulo-fibrillar structure that contains RNAs involved in patterning of the embryo.Įxuperantia protein, the earliest factor known to be required for the localization of bicoid mRNA to the anterior pole of the Drosophila oocyte, is highly enriched in the sponge bodies but not an essential structural component of these. ![]() The sponge bodies are not identical to the Golgi complexes. ![]() It lacks a surrounding membrane and is frequently associated with mitochondria. This structure, which we have termed “sponge body,” consists of ER-like cisternae, embedded in an amorphous electron-dense mass. Here we describe a subcellular structure in nurse cells and oocytes which may function as an intracellular compartment for assembly and transport of maternal products involved in RNA localization. Localization of maternally provided RNAs during oogenesis is required for formation of the antero–posterior axis of the Drosophila embryo. ![]()
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