The Journal of Cell Biology, Vol 71, 49-58, Copyright © 1976 by The Rockefeller University Press
Absence of rDNA amplification in the uninucleolate oocyte of the cockroach Blattella germanica (Oorthoptera: Blattidae)
MD Cave
Amplification of the genes coding for ribosomal RNA oocurs in the oocytes
of a wide variety of organisms. In oocytes of various species of crickets
(Orthoptera: Gryllidae) the amplified DNA is contained in a large
extrachromosomal DNA body. Multiple nucleoli form about the periphery of
the DNA body during the diplotene stage of meiosis I. In contrast to the
general pattern of orthopteran oocytes, oocytes of the cockroach Blattella
germanica demonstrate a single large nucleolus instead of many nucleoli. In
order to determine whether the genes coding for rRNA are amplified in the
oocytes of B. germanica, the relative amount of rDNA in oocytes was
compared with the rDNA content of spermatocytes and somatic cells. An
extrachromosomal DNA body similar to that present in crickets is not
present in B. germanica. A satellite DNA band which contains nucleotide
sequences complementary to rRNA accounts for approximately 3-5% of the
total DNA in somatic and in male and female gametogenic tissues. Female
cells contain approximately twice as much rDNA as do male cells. An XX-XO
sex-determining mechanism is operative in B. germanica. In situ
hybridization with rRNA indicates that the nucleolar organizer is located
on one end of the X chromosome and that oocytes do not contain more than
twice the amount of rDNA found in spermato cytes. The data indicate that
rDNA is not amplified in the uninucleolate oocyte of B germanica.
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