Three-dimensional organisation of RNA-processing machinery in avian growing oocyte nucleus

Abstract

Chromosome architecture and assorted nuclear compartments play an essential role in RNA transcription and processing. Growing vertebrate oocytes represent an advantageous model to study the principles of nuclear structure and function. In this article, the data on three-dimensional (3D) organisation of intact and non-deformed oocyte nuclei (germinal vesicles) in four species of birds (domestic chicken, Japanese quail, rock pigeon and chaffinch) obtained by confocal laser scanning microscopy are presented. The nucleus of the growing avian oocyte has an unusual structure of RNA processing machinery. Germinal vesicles from any of the avian species studied, with the exception of the rock pigeon, are characterized by absence of extrachromosomal RNA-enriched nuclear bodies including Cajal bodies, histone locus bodies and interchromatin granule clusters. The absence of Cajal bodies and histone locus bodies in chicken oocytes correlated with the inactivation of nucleolus organizer and clustered histone genes. Splicing factors such as SR-protein SC35 accumulated in chromosome-associated domains that were classified as complex loops (terminal giant and lumpy loops). Formation of such depot in avian oocyte nuclei is supposed to be nucleated by transcripts of non-coding tandem repeats. The results obtained strongly support a model of RNA-mediated nuclear domains formation.

The Chromosomes of Birds during Meiosis

“…In the chicken, clustered histone genes are inactive at the lampbrush stage [Krasikova et al, 2012], and transcription of ribosomal RNA in the germinal vesicle is repressed, so nucleoli are absent in avian diplotene-stage oocytes [Gaginskaya, 1972]. Moreover, no protein-coding sequences were found to be transcribed from the gene-rich microchromosomes.…”

“…It has been proposed that the noncoding RNA product of satellite repeat transcription can hybridize to form long dsRNA molecules. These duplex-forming RNAs sequestered within the oocyte might provide a pool for the production of siRNAs, required for functional regulation during early stages of embryogenesis [Krasikova et al, 2012;reviewed in Gaginskaya et al, 2009].…”

Transcription of highly repetitive tandemly organized DNA in amphibians and birds: A historical overview and modern concepts

“…52 It should be noted that the PO41 RNAs were detected on the lampbrush chromosomes inside intact 3D-preserved nuclei (germinal vesicles) manually isolated from the chicken and Japanese quail oocytes, complementing cytological observations obtained by spreading technique. 53 Arrays of the conserved PO41 repeat lie adjacent to the other 41 bp repeat families: the species-specific CNM (chicken nuclear-membrane-associated sequence) and the BglII-(BglIIdigested) repeats which localize on the chicken and Japanese quail chromosomes correspondingly. 52 CNM repeat is transcribed from both strands forming loop-specific pattern of Gand C-rich transcripts.…”

Expression profiles of long and short RNA s in the cytoplasm and nuclei of growing chicken (Gallus gallus domesticus) oocytes

“…Ядра (зародышевые пузырьки) отделяли от остального содер-жимого ооцита и его оболочек микрохирургическим путем с помощью вольфрамовых игл в среде «5:1 + фосфаты» (83,0 mМ KCl, 17,0 mM NaCl, 6,5 mM Na 2 HPO 4 , 3,5 mM KH 2 PO 4 , 1 mM MgCl 2 ) при наблюдении под стереомик-роскопом (Krasikova et al, 2012). Наиболее оптимальными для изолирования ядер оказались белые неиерархические фолликулы.…”

“…Эти данные находятся в соот-ветствии с высказанными ранее предположениями о роли фолликулярного эпителия в снабжении ооцита курицы различными видами РНК (Gaginskaia, Chin, 1980) и све-дениями о наличии в фолликулярных клетках в яичниках птиц одного или нескольких ядрышек (Gilbert et al, 1983;Krasikova et al, 2012).…”