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.
The heterochromatic Y chromosomes of several Drosophila species harbor a small number of male fertility genes (fertility factors) with several unusual features. Expression of their megabase-sized loci is restricted to primary spermatocytes and correlates with the unfolding of species-specific lampbrush loop-like structures resulting from huge transcripts mainly derived from clusters of loop-specific Y chromosomal satellites. Otherwise, there is evidence from genetic mapping and biochemical experiments that at least two of these loops, Threads in Drosophila hydei and kl-5 in D. melanogaster, colocalize with the genes for the axonemal dynein beta heavy chain proteins DhDhc7(Y) and Dhc-Yh3, respectively. Here, we make use of particular Threads mutants with megabase-sized deletions for direct mapping of DhDhc7(Y)-specific exons among the large clusters of satellite DNA within the 5.1-Mb Threads transcription unit. PCR experiments with exon-specific primer pairs, in combination with hybridization experiments with exon- and satellite-specific probes on filters with large PFGE-generated DNA fragments, offer a simple solution for the long-lasting paradox between megabase-sized loops and protein-encoding transcription units; the lampbrush loops Threads and the DhDhc7(Y) 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.
Reugels
A M
AM
Institut für Genetik, Heinrich-Heine-Universität Düsseldorf, D-40225 Düsseldorf, Germany.
Kurek
R
R
Lammermann
U
U
Bünemann
H
H
D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D017931:DNA Primers; D004330:Drosophila / Q000235:genetics*; D004398:Dyneins / Q000235:genetics*; D005298:Fertility / Q000235:genetics; D007438:Introns; D008297:Male; D013090:Spermatocytes / Q000648:ultrastructure*; D014158:Transcription, Genetic; D014998:Y Chromosome
D017931:DNA Primers; D004398:Dyneins