The evolutionary origin of the centrosome–centriole system is unknown. It is composed of paired centrioles embedded within a pericentriolar matrix, the composition of which is poorly understood. The centrosome is the major microtubule organizing center (MTOC) of animal cells and many protists. These observations provoke the question of whether cnRNAs and the nucleolinus serve as cytological progenitors of the centrosome and may support a symbiogenetic model for its evolution. After oocyte activation and germinal vesicle breakdown, cnRNA65 persists as a cytoplasmic patch within which γ-tubulin-stained centrosomes can be seen. At this stage, the in situ signal resembles the nucleolinus, a poorly understood organelle proposed to play a role in spindle formation. Its expression, therefore, precedes the appearance of γ-tubulin-containing centrosomes. In situ localization of cnRNA65, a molecule with an RNA polymerase domain, showed it is present in the intact oocyte nucleus (germinal vesicle). A subset of cnRNAs contain functional domains that are highly conserved across distant taxa, such as nucleotide polymerase motifs. Thus, we resolve the debate over the existence of centrosome-associated RNA (cnRNA). Here, from a library of RNAs extracted from isolated surf clam ( Spisula solidissima) centrosomes, we describe a group of centrosome-associated transcripts representing a structurally unique intron-poor collection of nuclear genes skewed toward nucleic acid metabolism. To date, most reports of centrosome-associated nucleic acids have used generalized reagents such as RNases and nucleic acid dyes. Nucleic acids endogenous to the MTOC would support evolutionary origin by symbiogenesis. Centrioles, like mitochondria and chloroplasts, duplicate independently of the nucleus and constitute a heritable system independent of chromosomal DNA. The evolutionary origin of centriole/kinetosomes, centrosomes, and other microtubule organizing centers (MTOCs), whether by direct filiation or symbiogenesis, has been controversial for >50 years.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |