Opposing effects of Notch-signaling in maintaining the proliferative state of follicle cells in the telotrophic ovary of the beetle Tribolium

Introduction: establishment of distinct follicle cell fates at the early stages of drosophila oogenesis is crucial for achieving proper morphology of individual egg chambers. in drosophila oogenesis,notch-signaling controls proliferation and differentiation of follicular cells,which eventually results in the polarization of the anterior-posterior axis of the oocyte. here we analyzed the functions of tribolium notch-signaling factors during telotrophic oogenesis,which differs fundamentally from the polytrophic ovary of drosophila.results: we found notch-signaling to be required for maintaining the mitotic cycle of somatic follicle cells. upon delta rnai,follicle cells enter endocycle prematurely,which affects egg-chamber formation and patterning. interestingly,our results indicate that delta rnai phenotypes are not solely due to the premature termination of cell proliferation. therefore,we monitored the terminal/stalk cell precursor lineage by molecular markers. we observed that upon delta rnai terminal and stalk cell populations were absent,suggesting that notch-signaling is also required for the specification of follicle cell populations,including terminal and stalk precursor cells.conclusions: we demonstrate that with respect to mitotic cycle/endocycle switch notch-signaling in tribolium and drosophila has opposing effects. while in drosophila a delta-signal brings about the follicle cells to leave mitosis,notch-signaling in triboliumis necessary to retain telotrophic egg-chambers in an immature state. in most instances,notch-signaling is involved in maintaining undifferentiated (or preventing specialized) cell fates. hence,the role of notch in tribolium may reflectthe ancestral function of notch-signaling in insect oogenesis.the functions of notch-signaling in patterning the follicle cell epithelium suggest that tribolium oogenesis may - analogous to drosophila - involve the stepwise determination of different follicle cell populations. moreover,our results imply that notch-signaling may contribute at least to some aspects of oocyte polarization and ap axis also in telotrophic oogenesis. © 2012 bäumer et al.; licensee biomed central ltd.