PCR test to identify expression of ovarian 5S rRNA vs somatic 5S rRNA in teleost tissues.
Supervisors: Oihane Diaz de Cerio, Ibon Cancio (UPV/EHU)
Aquatic environment is considered a sink for pollutants such as xenoestrogens. These compounds disrupt the endocrine system of marine vertebrates in some cases resulting in feminization in fish populations. Teleosts as the largest group of vertebrates, can provide insights into the presence of xenoestrogens in the ocean. Mature female teleosts go through oogenesis for the development of mature eggs implicating different molecular and cellular mechanism that require differential gene transcription that prepare the egg for spawning, fertilization and successful embryo development. Protein synthesis is essential for cell growth during embryogenesis, so ribosomes need to be provided maternally through oocyte accumulation of ribosomal intermediates. 5S rRNA, the smallest of the ribosomal RNA molecules is essential for the assembly of functional ribosomes and it is one the most abundant RNAs in teleost oocytes, both in ovaries and in intersex testes. 5S rRNA coding genes are thus highly expressed during oogenesis, making 5S rDNA a good molecular biomarker of the presence of oocytes in a tissue. Two functional families of 5S rDNA genes have been described in fish genomes, one for specific transcription in oocytes and the other for expression in somatic cells and testis. Therefore, the present study aims i) to determine in silico the possible presence, 5S rDNA genes haplotypes in Tunnus albacares, Ictalurus punctatus and Mugil cephalus genomes together with their structure putative binding transcription factors and deduced 2D structures, and ii) to analyze the transcription pattern of ribosomes binding protein in different tissues of thicklip grey mullet through qPCR analysis. Two main haplotypes were identified in the three teleost species where the differing nucleotide sites were preset in regions for the possible binding of 17 transcription factors some of them involved in gonadal transcription regulation. Tissue-specific transcription profile of the translation factors (eif5a, hapb4, eef2) linked to ribosomal dormancy showed highest transcription levels in gonads and eggs. Transcription was highest in ovaries intersex testis showing transcription levels between normal testes and ovaries. In conclusion, basic knowledge has been obtained explaining how oocytes can accumulate high amount of ribosomal intermediates mediating protein transcription when necessary during embryo development and how this can be employed to study the effects of exposure to xenoestrogens in the field. Key words: teleost oocytes, sex differentiation, xenoestrogenicity, 5S rDNA, 5S rRNA, maternal factors, gametogenesis, translation factors, ribosomal dormancy.