A FUNCTION OF MESSENGER RNA AS A CYTOPLASMIC FACTOR 工S INVOLVED
工N POLE CELL FORMATION OF DROSOPH工LA EMBRYOS

Masukichi Okada and Satoru Kobayashi
工nstitute of Bio1ogica1 Sciences，University of Tsukuba，Sakura‑mura，Ibaraki，305 Japan

Cytop1丑 smic factors h呂 ve b告邑 n postu1丑 ted to perform import丑nt ro1es inpo1e ce11 formation and d巴七日 rmination of th日 po1巴 C日 11s to differentiate 工nto
germ cells in Drosophi1~ embryogenesis.

One of the factors active in po1日ce11 formation has b号 色 n found precipi七品 ting with 丑

postmitochondria1

subce11u1ar fraction prepared from homogenate of who1e 巴 mbryos.

Th自 factor

10st its activity when the subcellu1ar fraction was digested with RNase.
To find the molecul邑 species responsible for po1e cell forrnation，RNA wasextract巴d from the postmitochondrial subcellular fraction frorn homogenat巴 ofwhole embryos and 品 ssayed for its pole cell inducing activity.

For assaying

the activity，RNA was injected into the posterior pole of c1eavage embryosthat had been sterilized with radiation of ultra violet light (u.
v.
) with th日
wavelen守七 h of 280 nm 呂七 a dose of 200 J/m2，昌 nd the r邑 cipient embryos wereallowed to develop up to blastoderm stage and examined for presence or absenceof pole cells. Crude RNA fraction showed pole cell inducing activity・ RNA
was divided into 七背 o fractions，one 時 ith and the oth色 E 官 ithout polyadenylatesequences (poly(A)+ ，and poly(A)‑ RNA fraction).
retained apparent pole cell inducing activity.

Only poly(A)+ RNA fraction

The activity of a poly(A)+ RNA

fraction was depending on stages of 控 mbryos from which RNA w品 S 邑 xtracted.

Ahigh activity was retained in RNA fraction extracted from embryos at 20 min
after egg laying (min AEL)，but not in one from 150 min‑AEL embryos. A cDNA
恥工ibrary w昌 s prepared from a poly(A)争 RおA fraction extr
丑cted from 20‑min‑AEL

embryos，and screen日d for cDNA clon自由 that hybr工dize with RNA s巴 quenc日 s speci

21

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fically present in 20‑min‑AEL embryos with a competitiv母 colony hybridization
method. Hundred colonies have been selected and being under further screening
for the sequences responsible for pole cell formation.
Treatment of cleavage with cycloh母 ximide at the posterior pole pr芭 V告 nted
the embryos from pole cell formation without affecting somatic cells. Thissuggests that translation from messages is required in the posterior polecytoplasm for accomplishment of pole cell formation.
Morphology of pol日 cells formed in u.v.‑irradiated embryos injected withpoly(A)+ RNA was described.

These pole cells showed similar featur倍 s tonormal pole cells as far as structures TE滋 呂 nd SE滋 E告 V邑 aling were concerned.
In addition，the RNA‑induced pole cells were normal also for their behavior，migration to penetrate gonads.

These pole cells were different from normal

ones only in their developmental f昌 te: for th邑 present it h丑 s not been shownthat the RNA induced pole cells are able to differentiate into germ cells.
叩References
S. and M. Okada (1982)
Togashi，工n: "The Ultrastructures and Func‑.，King，R.C. and Moroho日 hi，tioning of 工nsect Cells"，(Akai，HS. eds).

41‑44，Soc. Insect Cells，Tokyo.

R. and M. Okada(1982) Proc. Natl. Acad. Sci. USA，79:6946 6950.
Ueda，S. and M. Ok昌 da (1983) Develop. Gro百 th and Differ. 25:133‑141.
Togashi，. Togashi (1空85) 工nt. J. Invertebrate Reproduct. andOkada，M. and S
Develop. 8:207‑217.

Proc.Arthropoa.Embryol.Soc.Jpn.，
l型85