Strategic Research Evolution of Insect Metamorphosis

Evolution of Insect Metamorphosis

How does a caterpillar turn into a butterfly? This transformation has fascinated man since ancient times, and it is still an open scientific question. Our group started working on insect metamorphosis in the late 1970's from an applied point of view. Today, we focus on developmental aspects (studying the effects of the hormonal signalling pathways involved), considered under an evolutionary perspective. Our favourite work species is the cockroach Blattella germanica, which follows an ancestral metamorphosis mode and can serve, thus, as a baseline model. In recent years, due to the expansion of high throughput sequencing technologies, our group has implemented comparative transcriptomics as a new approach. Thus, acquisition and analysis of HTS data from mRNAs and small RNAs has become a current tool for studying gene regulatory networks in species with different developmental modes. We believe that this information will afford key data on the evolution of insect metamorphosis.

Main projects

  • 1.

    Key transitions in the embryogenesis of a hemimetabolan insect

    The project aims at studying the hemimetabolan embryogenesis, and the conditions that regulate every key developmental transitions using Blattella germanica as model. Among these conditions we include changes in gene expression, the modulator role of microRNAs and the role of hormones. An important part of the project aims at studying the changes in gene expression that occur in the key stages of development, within a well-defined hormonal context, which determine the transitions between stages. This is approached through comparisons of transcriptomes obtained for each key developmental stage. Transcriptome comparisons allow identifying the gene expression changes that determine the transitions between key stages. We also carry out the same analyses on the holometabolan species Drosophila melanogaster and Tribolium castaneum on the basis of publicly available data, in order to infer the corresponding evolutionary conclusions. Ultimately, the project will led to develop a robust theory on the origin and evolution of insect metamorphosis based on new data provided by the embryonic development.

  • 2.

    Regulation of tergal gland morphogenesis as minimal model of insect metamorphosis

    Metamorphosis is a complex process, and their study is especially difficult when working at organismic level. A way to make the problem tractable is working at the level of a particular organ formed de novo at metamorphosis. We propose that the tergal gland of male cockroaches could be an ideal model because: 1) is experimentally tractable, 2) is formed de novo in the last nymphal molt, so that the process is well bounded in space, 3) the genes involved in its morphogenesis are expressed in the last nymphal stage, so the process is well bounded in time. The project aims at studying how the morphogenesis of the tergal gland is regulated, and to demonstrate that this process can represent a minimal model of metamorphosis. The approach is based in the comparison of transcriptomes from tergal gland tissues in penultimate nymphal instar (when the insect is going to molt to another juvenile instar) and in the last nymphal instar (when the insect is going to molt to an adult), in order to identify those genes that are crucial for the formation of the tergal gland.

  • 3.

    Silencing the silencers. Mechanistic basis of the regulation of metamorphosis in insects

    At present, the endocrine keys that regulate insect metamorphosis are well established. 20-Hydroxiecdysone (20E) promotes molting and juvenile hormone (JH) determines the quality of the molt. However, the control of metamorphosis must have other regulatory layers. The present project aims at researching metamorphosis under the hypothesis that microRNAs play also an important role in the regulatory mechanisms. Using Blattella germanica as model, we hypothesize that microRNAs keep the nymphal genetic program during the larval life and/or regulate the shift to the adult genetic program in the last molt. We test this hypothesis by depleting the expression of dicer-1 (which generates the microRNAs) in the transition larva-larva, and in that of larva-adult. Then, we study the effects of this depletion upon the quality of the molt and on the levels of microRNAs, which are currently established by high throughput sequencing.



Bioinformatics expertise:

Group Leader:

Xavier Belles