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Summary: IJEVELOPMENTAL BIOLOGY 109,436-451 (1985)
Expression of CX-and ,8-Tubulin Genes during
Development of Sea Urchin Embryos
DESPINA ALEXANDRAKI' AND JOAN V. RUDERMAN'
Department of Anatomy, Harvard Medical School, 25 Shattuck Street, Boston, Massachusetts
Received June 29, 1984; accepted in revised form November 26, 1984
Mature unfertilized eggs of the sea urchin Lytechinus pictus contain multiple cu-tubulin mRNAs, which range in
size from 1.75 to 4.8 kb, and two /3-tubulin mRNAs, 1.8 and 2.25 kb. These mRNAs were found at similar levels
throughout the early cleavage stages. RNA gel blot hybridizations showed that prominent quantitative and qualitative
changes in tubulin mRNAs occurred between the early blastula and hatched blastula stages. The overall amounts of
o(- and fl-tubulin mRNAs increased two- to fivefold between blastula and pluteus. These increases were due mainly
to a rise in a 1.75-kb o( RNA and a new 2.0-kb 0 RNA. Other, minor changes also occurred during subsequent
development. All size classes of (Y- and P-tubulin RNAs in early and late embryos contained poly(A)+ translatable
sequences. As reported earlier, some of each of the cy RNAs, but neither of the @ RNAs, are translated in the egg
and a small portion of each of the stored o and p RNAs is recruited onto polysomes within 30 min of fertilization.
In the work described here, subsequent development up to the morula stage was accompanied by a gradual
recruitment of tubulin mRNAs into polysomes. By the early blastula stage, most of the maternal tubulin sequences
were associated with polysomes. In contrast to the gradual recruitment of maternal sequences throughout cleavage,
the tubulin mRNAs which appeared at the blastula stage showed no delay in entering polysomes. The exact fraction
of each mRNA that was translationally active at later stages varied somewhat among the individual mRNAs. From
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