טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentPolsky Avital
SubjectMolecular Principles of a Developmental Tradeoff in
Embryogenesis
DepartmentDepartment of Biology
Supervisor Professor Itai Yanai
Full Thesis textFull thesis text - English Version


Abstract

All organisms implement a life history strategy, which includes determining how fast to grow, when to reproduce, and when to die.  The rate at which an embryo completes development is a part of that strategy and is highly variable across even closely related species.  The model organism Caenorhabditis elegans is a quick-developer going from a single-cell embryo to a larva in just thirteen hours.  Conversely, the nematode Acrobeloides nanus takes four times longer to achieve the same.  Evidence that this difference follows from the nutrients initially deposited by the mother comes from studies showing that C. elegans - but not A. nanus - is able to undergo seven cell cleavages in the absence of zygotic transcription. It remains a mystery, however, how such a developmental strategy is encoded at the molecular level.  To address this question we took a comparative transcriptomics approach by determining for the first time the A. nanus transcriptome and examining its dynamics through embryogenesis by constructing a high-resolution developmental time-course.  We found that C. elegans contains in its maternal deposit transcripts of genes enriched for basic cellular processes and energy production, whereas the A. nanus maternal deposit is enriched for transcripts necessary for the production of translational machinery.  We propose that this difference in maternal deposit underpins a developmental trade-off between developmental speed and longevity: an organism that provides its offspring with transcripts to promote cellular processes (i.e., cytokinesis) and energy production will develop faster overall at the expense of a shorter lifespan because of this large expenditure. In contrast, the organism that provides its offspring with transcripts to manufacture cellular components (e.g., ribosomes) will produce slower embryos but benefit itself with a longer lifespan.  Our results demonstrate that by comparing high-resolution developmental transcriptomic time-courses of distantly related species, it is possible to elucidate some of the molecular determinants of life history strategies.  Furthermore, this dataset will be useful in understanding how organisms with a similar final morphology build themselves by alternative molecular pathways.  It will be interesting to see if this kind of principle is applicable to other phyla.