Abstract
In Xenopus, localization of a rare class of mRNAs during oogenesis is believed to initiate pattern formation in the early embryo. We have determined the pattern of RNA localization for one of these RNAs, Xcat-2, which encodes a putative RNA-binding protein related to Drosophila nanos (Mosquera, L., Forristall, C., Zhou, Y. and King, M. L. (1993) Development 117, 377-386). Xcat-2 is exclusively localized to the mitochondrial cloud in stage I oocytes, moves with this body into the vegetal cortex during stage II and, later, partitions into islands consistent with it being a component of the germ plasm. As previously shown, Vg1 is not localized to the vegetal cortex until stage IV and distributes to all vegetal blastomeres during development. We found a direct correlation between the localized condition of these RNAs and their recovery in a detergent-insoluble fraction. We present evidence suggesting that differential RNA binding to a cytoskeletal component(s) in the vegetal cortex determines the pattern of inheritance for that RNA in the embryo.
Highlights
Localized RNAs represent a rare class of RNAs in germ cells that are involved in establishing regional cell fates
We have shown that three RNAs found in the vegetal cortex of stage VI oocytes, Vg1, Xcat-2 and Xcat3, are 20- to 60-fold enriched in a detergent-insoluble fraction (DIF) (Pondel and King, 1988; Mosquera et al, 1993; Elinson et al, 1993)
We have shown that Xcat-2 and Vg1 RNAs are both concentrated in the vegetal cortex of fully grown stage VI oocytes (Elinson et al, 1993)
Summary
Localized RNAs represent a rare class of RNAs in germ cells that are involved in establishing regional cell fates. The vegetally localized RNAs are of particular interest, as this region is known to have important developmental functions in Xenopus, including the specification of mesoderm, the dorsal-ventral axis, and the primordial germ cells (see Slack, 1991). We reported that by sequence homology, Xcat-2 appears to belong to the same family of RNA-binding proteins as nanos (Mosquera et al, 1993). Nanos binds to and suppresses the translation of the RNA for the transcription factor hunchback in Drosophila, allowing the specification of the abdominal region and the proper environment for germ cell development (Wang and Lehmann, 1991). The activities of these proteins correlate well with the functions of the vegetal region of the oocyte
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