Esdeveniments | 31 May 2024 | Friday talks

Oocytes for "A Fistful of Ribosomes": "The Small, the Non-Coding, and the Ugly" during gametogenesis in fish



Chelon labrosus mullets from polluted transitional waters in the Southern Biscay Bay show high prevalence of intersex condition, producing previtellogenic perinucleolar oocytes in male testes. A morphological characteristic of such oocytes in teleosts is the presence of many nucleoli, indicative of rRNA production and ribosomal subunit assembly. Oocytes are unique cells in metazoans as they accumulate molecules to be used by a different individual: the embryo. Protein synthesis being one of the energetically most demanding processes in a cell, oocytes do part of the job for the embryo by accumulating and contributing the necessary ribosomes. The RNA profiles in ovaries (Ov), testes (T) and intersex testes (IT) of mullets from Gernika estuary show that 5S rRNA and tRNAs, both specifically produced by RNA polymerase-III, are powerful markers of the presence of oocytes, and thus can be used as proxy to identify intersex condition. Analysis of these non-coding RNAs through a simple electrophoresis of total RNA and their quantification relative to the presence of 45S rRNA maturation-products (generating 5S rRNA/18S rRNA and tRNA/5,8S rRNA indexes), can be used to rank IT gonads according to the severity of the condition. In the same way, these indexes can be used to identify molecularly, and without bias, the developmental stage of the ovaries in any teleost species along its reproductive cycle. This could have important applications in the monitoring of fecundity in important commercial fisheries. Fish genomes have multiple copies of tRNA genes in their genomes (with over 15000 genes in D. rerio) coding for the 61 codon-specific aminoacyl-tRNAs, and the complement of genes (isoaceptors and isodecoders) transcribed in the oocyte could modulate the population of mRNAs that are going to be preferentially translated in the embryo. This could thus define the quality of the eggs. Similarly, other non-coding RNAs necessary for rRNA, tRNA and mRNA post-transcriptional modification and cleavage in the nucleoli and in spliceosomes show multiple paralogous genes in fish genomes. The characterisation of non-coding RNAs in Ov, Te and IT of C. labrosus via a miRNA-Seq approach allowed annotation of 278 miRNAs, over  95 different small nucleolar RNAs, 10 small nuclear (spliceosome) RNAs and hundreds of tRNAs showing differential transcriptional profiles that cluster IT closer to Ov than to Te. The high levels of tRNAs, and specific rRNAs, snoRNAs and snRNAs pinpoint their upregulation as a consequence of male mullet feminisation under xenoestrogen-exposure and flag ribogenesis-control as a crucial process during oocyte differentiation and maturation. Molecular tools based on these marker non-coding RNAs are proposed as useful to study feminization in xenoestrogens exposed fish, but also for the analysis of oogenesis and possibly oocyte quality.


Brief biography

Full Professor in Cell Biology in the University of the Basque Country and researcher in the Plentzia Marine Station within the consolidated research group in “Cell Biology & Environmental Toxicology-One health” of the Basque Government. Responsible for the incorporation of the Plentzia Marine Station to the European Research Infrastructure EMBRC-ERIC (, European Marine Biology Resource Center) and Director of its Spanish node. He has coordinated the official Masters degree in “Environmental Contamination & Toxicology” (2012-2020). Together with other 12 European Universities he has participated in student and staff exchange programs within the "Environmental Sciences and Education". He has carried out research stays at Universities of Wales (1992-1993), Amsterdam (1994) and Heidelberg (Germany, 1995-1996), Fisheries Research Service (Scotland, 2001) and Catholic Univ. of Leuven (Belgium, 2002), with over three years research experience abroad. He has supervised 17 Master theses and 8 International PhD theses + 2 ongoing.  Research activity focuses on 2 main interrelated research lines: Cell & Molecular Biology of fish sex differentiation and Applications of Cell Biology in Toxicology (toxicognenomics, pollution molecular & cellular biomarkers, endocrine disruption). He has published 9 book chapters, 71 papers in international peer-reviewed journals and 9 in national ones (h index=28). He obtained the 2nd and 3rd CAF-Elhuyar prizes to the best manuscripts in Science-didactics in Basque (2006 and 2007). Over 85 invited conferences and seminars in Universities and different institutions with extensive outreach activity nationally (exhibitions, radio, TV…). 70 research projects. He is, or has been, main researcher of different provincial, regional, national and European research projects being main researcher in projects on xenoestrogenicity and fish sex differentiation.