טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKolotuev Irina
SubjectEvolution of Vulva Formation in Nematodes
DepartmentDepartment of Biology
Supervisor Professor Benjamin Podbilewicz


Abstract

Organogenesis is the formation of specific organs in a plant or animal involving morphogenesis and differentiation processes. The study of simple model organisms as Drosophila and C.elegans revealed in the recent years the principles of few developmental processes. Here, we have examined two different nematode species in order to understand whether cellular events during organ formation such as cell division, differentiation, migration and fate are conserved. 

In the first part of this work we characterized vulva development in a wild type strain of the nematode Pristionchus pacificus (Ppa) and compared it to what was known about vulva morphogenesis in Caenorhabditis elegans (Cel).  The major processes that are involved in organ formation, such as cell migration, ring formation, stacking of ring structures and cell fusion are conserved.  In contrast, timing of events and final ring number are different.

In the second part we studied mutations that influence proper vulva formation.  We chose a member of the nematode HOX genes cluster - mab-5.  In C. elegans, mutations in this gene show aberrant male phenotypes while the hermaphrodites are egg laying competent.  In P. pacificus mab-5 mutants, hermaphrodites are defective in egg laying, and in addition, mutants possess pseudo vulva structures posterior to the real defective vulva.  We have characterized vulva organogenesis in these animals through rearrangements of apical borders.  We have found that: 1) In Ppa-mab-5 there are 5 independent types of real and pseudo vulva defects.  2) Ring formation in Ppa is an autonomous process as it is in Cel.  3) In Ppa-mab-5 worms there are unfused cells in the most posterior part of the animal {P(11-12).p area} in 15% of the cases.  In Cel-mab-5 the same event is present in 50% of the studied cases.  4) In 4% of Cel-mab-5 animals all 5 kinds of real/pseudo vulva phenotypes observed in Ppa can be found.  Thus, we found that the main principles of vulva formation are conserved and mab-5 mutants show vulval cell transformation in both species.