The Notch pathway is an essential regulator of cell proliferation and differentiation during development. Its involvement in insect oogenesis has been examined in insect species with meroistic ovaries, and it is known to play a fundamental role in cell fate decisions and the induction of the mitosis-to-endocycle switch in follicular cells (FCs). This work reports the functions of the main components of the Notch pathway (Notch and its ligands Delta and Serrate) during oogenesis in Blattella germanica, a phylogenetically basal species with panoistic ovary. As is revealed by RNAi-based analyses, Notch and Delta were found to contribute towards maintaining the FCs in an immature, non-apoptotic state. This ancestral function of Notch appears in opposition to the induction of transition from mitosis to endocycle that Notch exerts in Drosophila melanogaster, a change in the Notch function that might be in agreement with the evolution of the insect ovary types. Notch was also shown to play an active role in inducing ovarian follicle elongation via the regulation of the cytoskeleton. In addition, Delta and Notch interactions were seen to determine the differentiation of the posterior population of FCs. Serrate levels were found to be Notch-dependent and are involved in the control of the FC programme, although they would appear to play no crucial role in panoistic ovary oogenesis.

This work was supported by the Ministry of Science and Innovation, Spain (grant no. BFU2011-22404), by the Catalan Regional Government (grant no. 2014 SGR 619), and by CONICYT + PAI Concurso Nacional Apoyo al Retorno de Investigadores desde el Extranjero, Convocatoria 2013 + 821320046. P.I. is the recipient of a postdoctoral research grant (BECAS CHILE from CONICYT. N.E. is the recipient of a JAE pre-doctoral research grant from the Consejo Superior de Investigaciones Científicas (CSIC)