Mega-introns in the dynein gene DhDhc7(Y) on the heterochromatic Y chromosome give rise to the giant Threads loops in primary spermatocytes of Drosophila hydei
Am. Reugels et al., Mega-introns in the dynein gene DhDhc7(Y) on the heterochromatic Y chromosome give rise to the giant Threads loops in primary spermatocytes of Drosophila hydei, GENETICS, 154(2), 2000, pp. 759-769
The heterochromatic Y chromosomes of several Drosophila species harbor a sm
all number of male fertility genes (fertility) factors) with several unusua
l features. Expression of their megabase-sized loci is restricted to primar
y spermatocytes and correlates with the unfolding of species-specific lampb
rush looplike structures resulting from huge transcripts mainly derived fro
m clusters of loop-specific Y chromosomal satellites. Otherwise, there is e
vidence from genetic mapping and biochemical experiments that at least two
of these loops, Threads in Drosophila hydei and kl-5 in D. melanogaster, co
localize with the genes for the axonemal dynein beta heavy chain proteins D
hDhc7(Y) and Dhc-Yh3, respectively. Here, we make use of particular Threads
mutants with megabase-sized deletions for direct mapping of DhDhc7(Y)-spec
ific exons among the large clusters of satellite DNA within the 5.1-Mb Thre
ads transcription unit. PCR experiments with exon-specific primer pairs, in
combination with hybridization experiments with exon- and satellite-specif
ic probes on filters with large PFGE-generated DNA fragments, offer a simpl
e solution for the long lasting paradox between megabase-sized loops and pr
otein-encoding transcription units; the lampbrush loops Threads and the DhD
hc7(I? gene are one and the same transcription unit, and the giant size of
the DhDhc7(Y) gene as well as its appearance as a giant lampbrush loop are
merely the result of transcription of huge clusters of satellite DNA within
some of its 20 introns.