Molecular keys in structural evolution of insect ovaries

The present work aims at establishing the first bases for studying the insect oocyte polarity in a phylogenetically basal species, the cockroach Blattella germanica. Our approach was to choose some genes that have been described as key in the establishment of oocyte polarity in Drosophila melanogaster. Among them we studied, Capicua, a HMG box transcription factor repressor in B. germanica, which is required for the establishment of dorsal-ventral patterning of eggshell and embryo. The epidermal growth factor receptor (EGFR) that is also essential for the polarity establishment in the oocyte. We study the function of Notch pathway and how the components of this pathway participate in the proper development of the oocyte. Otherwise, trying to study the relationships between Capicua and EGFR, we assess the function of Pipe in B. germanica ovary, and embryo.El presente trabajo quiere asentar las bases para estudiar la polaridad en el oocito en una especie filogenéticamente basal como la cucaracha Blattella germanica. Para ello, y basándonos en la información disponible sobre genes implicados en el establecimiento de la polaridad en Drosophila melanogaster, escogimos algunos genes clave. Hemos estudiado el factor de transcripción Capicua, que en B. germanica actúa como represor de la transcripción, y es imprescindible para la formación del eje dorso-ventral del huevo y del embrión. EGFR (epidermal growth factor receptor) que participa también en el establecimiento de la polaridad en el folículo ovárico. Estudiamos la función de la vía Notch, y como los componentes de esta vía afectan el correcto desarrollo del oocito. Además, tratando de establecer una relación entre Capicua y EGFR estudiamos la función de Pipe en el ovario y el embrión de B. germanica

The notch pathway regulates both the proliferation and differentiation of follicular cells in the panoistic ovary of Blattella germanica

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