טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentMichal Levin
SubjectComparative Transcriptomics of Nematode Development
DepartmentDepartment of Biology
Supervisor Professor Yanai Itai
Full Thesis textFull thesis text - English Version


Abstract

A fundamental question in developmental biology relates to the connection between developmental stages as they appear morphologically and their underlying molecular activity. Using species-specific custom-made microarrays we queried gene expression levels of all genes across ten different stages of embryonic development of five nematode species belonging to the Caenorhabditis Genus. These species are very diverse at the genomic level and show different developmental rates. Nevertheless, their developmental process is almost identical in terms of division steps, cell movements and major morphogenesis and tissue differentiation progression.  

Global analysis of the developmental time-course data demonstrates that development of five Caenorhabditis species proceeds through multiple distinct stages - or ‘milestones’ - in which the transcriptome is resistant to differences in species-specific developmental timings. By comparing the complete protein-coding transcriptomes of individually timed embryos across ten morphological markers, we found three developmental milestones, including one we identify as the nematode phylotypic stage. Between such milestones, embryos follow transitory states characterized by an acceleration of transcriptional activity. By comparing the nematode developmental transcriptome with that of the chordate X. tropicalis and the Arthropod D. melanogaster we report on the macro evolution of a milestone by heterochrony or change in timing. This module-centric view of development will allow for a more complete understanding of how the functional organization of the embryo has influenced the evolution of animal morphology and diversity.