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Chromosome organization during male meiosis in Bombyx mori
Abstract:
Chromatin organization during male meiosis in Bombyx mori has been investigated utilizing the Miller spreading procedure. During meiotic prophase, the linear 200-300 A chromatin fibers evident at interphase are folded into tandem arrays of approximately 7,000 loops per haploid genome. Adjacent loops visualized during early prophase are separated by 0.15-0.2 nm of nucleosomal DNA. Meiotic metaphase chromosomes display numerous loops which project radially from the central region of the chromosome suggesting that the loop conformation of prophase is maintained throughout meiosis. Spread preparations of spermatogenic stages through pachytene allow the visualization of actively transcribed ribosomal DNA. Throughout this period, these transcription units appear to be organized into loops in such a way that one active transcription unit exists on a single loop. Furthermore, there are various levels of transcription on different ribosomal loops, although the number of loops displaying active transcription remains constant throughout this period.
Insights
Chromatin fibers in Bombyx mori male meiosis form approximately 7,000 loops per genome. These loops, containing nucleosomal DNA, are maintained throughout meiosis, with active ribosomal DNA transcription occurring on single loops.
Area of Science:
- Cell Biology
- Genetics
- Molecular Biology
Background:
- Chromatin organization is crucial for genome function, particularly during meiosis.
- Understanding chromatin structure in male meiosis provides insights into reproductive processes.
Purpose of the Study:
- To investigate the organization of chromatin during male meiosis in Bombyx mori.
- To visualize and characterize chromatin loops and ribosomal DNA transcription during meiotic stages.
Main Methods:
- Utilized the Miller spreading procedure for chromatin visualization.
- Examined spermatogenic stages from prophase through pachytene.
Main Results:
- Interphase chromatin fibers (200-300 Å) fold into ~7,000 loops per haploid genome during meiotic prophase.
- Loops are separated by 0.15-0.2 nm of nucleosomal DNA and maintain their conformation through metaphase.
- Actively transcribed ribosomal DNA units are organized into single loops, with varying transcription levels across different ribosomal loops.
Conclusions:
- Chromatin in Bombyx mori male meiosis is organized into a loop structure maintained throughout the process.
- Ribosomal DNA transcription occurs on a per-loop basis during specific meiotic stages.