Molecular insights into the mechanisms underlying doubly uniparental inheritance (DUI) of mitochondrial DNA and sex determination in marine mussels (Mytilus spp.)

• Autores: Sofía Blanco González
• Directores de la Tesis: Ángel Pérez Diz (dir. tes.)
• Lectura: En la Universidade de Vigo ( España ) en 2025
• Idioma: inglés
• Programa de doctorado: Programa de Doctorado en Ciencias Marinas, Tecnología y Gestión por la Universidad de A Coruña; la Universidad de Santiago de Compostela; la Universidad de Vigo; Universidade de Aveiro(Portugal); Universidade de Porto(Portugal); Universidade de Trás-os-Montes e Alto Douro(Portugal) y Universidade do Minho (Portugal)
• Materias:
  • Ciencias de la tierra y del espacio
    • Oceanografía
      • Zoología marina
• Enlaces
  • Tesis en acceso abierto en: Investigo
• Resumen

  • Marine mussels of the Mytilus edulis complex represent a genus comprising three related species: Mytilus edulis, M. galloprovincialis, and M. trossulus. These organisms are of significant ecological importance and constitute a valuable economic resource in global aquaculture. Moreover, they serve as model organisms for research in reproductive and developmental biology, particularly among bivalves of aquacultural relevance. However, their study remains challenging due to the complex architecture of their genome and the still limited understanding of biological processes such as sex determination and mitochondrial inheritance. One of their distinctive features is their mitochondrial inheritance system, known as doubly uniparental inheritance (DUI), in which both maternal and paternal mitochondrial genomes are transmitted to the next generation. This mechanism is non-causally associated with sex determination. In embryos destined to develop as females, sperm mitochondria get dispersed and degraded at later developmental stages. In male-biased embryos, they aggregate within the blastomere that will give rise to the germ line. Moreover, females have been observed that produce offspring with skewed sex ratios regardless of the male involved in fertilisation. However, the prevalence of such females remains unknown. This phenomenon suggests a maternal control over both DUI and sex determination, likely mediated by factors present within the egg. Nonetheless, the molecular mechanisms underlying these processes remain largely unexplored. This doctoral thesis explores both mechanisms across five chapters using experimental approaches ranging from in vitro crosses and electrophoretic mobility assays to high-throughput techniques. In Chapter 1, sex-biased lines of eggs, embryos, and M. galloprovincialis adults were successfully isolated in laboratory conditions for the first time. This work, which covered several Galician populations and in which more than 300 females and 10,000 embryos were analysed, allowed females to be classified according to the sex ratio of their offspring, the estimation of their prevalence, and the isolation of sex-biased eggs that serve as a basis for subsequent studies. Chapter 2 addresses the challenges associated with the cryopreservation of mussel eggs, a bottleneck in the production of mussel seed in hatcheries and, consequently, in the long-term maintenance of sex-biased lines. Using a multidisciplinary approach that combined functional assays, proteomics, and electron microscopy, it provides the first molecular insights into the limited success obtained in marine invertebrate eggs. Eggs derived from sex-biased females were used as core for investigating the molecular mechanisms underlying DUI and sex determination in the final chapters. Chapter 3 employed fertilised sex-biased eggs to test the DUI model proposing an active role for paternal mtDNA in its aggregation and inheritance. This was achieved through electrophoretic mobility assays and proteomics to detect a specific interaction between the paternal genome and an egg-specific protein in male-biased lines. In Chapter 4, the proteome evolution in sex-biased eggs, before and after fertilisation and up to a larval stage, was firstly characterised for the first time. Additionally, novel targets potentially involved in DUI and sex determination were proposed. Finally, Chapter 5 adopted a similar approach at the transcriptomic level, using RNA-Seq to identify differentially abundant RNAs in sex-biased eggs lines, both pre- and post-fertilisation. This study not only enabled the characterisation of how candidate factors change before and after fertilisation, but also allowed for the assessment of the concordance between transcriptomic and proteomic results. The results obtained were discussed in the context of the current genetic models, contributing to their refinement and to a deeper understanding of both DUI and sex determination in marine mussels.