PATTERNS OF LOCALIZATION AND CYTOSKELETAL ASSOCIATION OF 2 VEGETALLY LOCALIZED RNAS, VG1 AND XCAT-2

In Xenopus, localization of a rare class of mRNAs during oogenesis is believed to initiate pattern formation in the early embryo. We have de termined the pattern of RNA localization for one of these RNAs, Xcat-2 , which encodes a putative RNA-binding protein related to Drasophila n anos (Mosquera, L., Forristall, C., Zhou, Y. and King, M. L. (1993) De velopment 117, 377-386). Xcat-2 is exclusively localized to the mitoch ondrial cloud in stage I oocytes, moves with this body into the vegeta l cortex during stage II and, later, partitions into islands consisten t with it being a component of the germ plasm. As previously shown, Vg 1 is not localized to the vegetal cortex until stage IV and distribute s to all vegetal blastomeres during development. We found a direct cor relation between the localized condition of these RNAs and their recov ery in a detergent-insoluble fraction. We present evidence suggesting that differential RNA binding to a cytoskeletal component(s) in the ve getal cortex determines the pattern of inheritance for that RNA in the embryo.