Transcription of a satellite DNA on twoY chromosome loops ofDrosophila melanogaster

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Abstract
Primary spermatocyte nuclei ofDrosophila melanogaster exhibit three giant lampbrush-like loops formed by thekl-5, kl-3 andks-1 Y chromosome fertility factors. Detailed mapping of satellite DNA sequences along theY chromosome has recently shown that AAGAC satellite repeats are a significant component of thekl-5 andks-1 loop-forming regions. To determine whether these simple repeated sequences are transcribed on the loop structures we performed a series of DNARNA in situ hybridization experiments to fixed loop preparations using as a probe cloned AAGAC repeats. These experiments showed that the probe hybridizes with homologous transcripts specifically associated with thekl-5 andks-1 loops. These transcripts are detected at all stages of development of these two loops, do not appear to migrate to the cytoplasm and are degraded when loops disintegrate during the first meiotic prophase. Moreover, an examination of the testes revealed that the transcription of the AAGAC sequences is restricted to the loops of primary spermatocytes; the other cell types ofD. melanogaster spermatogenesis do not exhibit nuclear or cytoplasmic labeling. These experiments were confirmed by RNA blotting analysis which showed that transcription of the AAGAC sequences occurs in wild-type testes but not inX/O testes. The patterns of hybridization to the RNA blots indicated that the transcripts are highly heterogeneous in size, from large (migration at limiting mobility) to less than 1 kb. We discuss the possible function of the AAGAC satellite transcripts, in the light of the available information on theY chromosome loops ofD. melanogaster.