Distribution of splicing proteins and putative coiled bodies during pollen development and androgenesis in Brassica...

Small nuclear ribonucleoprotein particles (snRNPs) are subunits of splicing complexes, which show a transcription-dependent localization pattern. We have analyzed the labelling pattern of snRNPs during pollen development and microspore and pollen embryogenesis in Brassica napus with an antibody which recognizes protein D of U1, U2, U4, U5, and U6 snRNPs. It was found that nuclei were labelled almost uniformly for snRNPs in microspores and young bicellular pollen. In the generative nuclei of late-bicellular pollen and in the vegetative nuclei and sperm nuclei of mature pollen no snRNPs could be detected. The snRNP-positive nuclei contained mostly one or two brightly labelled nuclear bodies, most likely coiled bodies, often closely related to the nucleolus. These nuclear bodies increased in size from 0.5 micron in nuclei of young microspores up to 2 microns in nuclei of late microspores and the vegetative nucleus of early-bicellular pollen. Also their number increased during these developmental stages. After induction of embryogenesis the size of the coiled bodies decreased to about 0.5 micron and in several occasions the coiled body was found free in the nucleoplasm, away from the nucleolus. The results support the idea that the size and number of coiled bodies coincide with changes in general nuclear activity. They also indicate that, in nuclei of Brassica napus, at least assembly and disassembly of coiled bodies takes place in the nucleoplasm, whereas mature coiled bodies are located adjacent to the nucleolus.