- September 2019: Lenka and Marek publish a review The juvenile hormone receptor as a target of juvenoid "insect growth regulators" in Arch. Insect Biochem. Physiol. https://doi.org/10.1002/arch.21615
- July 2019: Marek publishes invited review "Where did the pupa come from? The timing of juvenile hormone signalling supports homology between stages of hemimetabolous and holometabolous insects" in Phil. Trans. R. Soc. B 374: 20190064. https://doi.org/10.1098/rstb.2019.0064
- July 2019: Marek co-organizes the 8th International Symposium on Molecular Insect Science in Sitges, Barcelona
- January 2019: Lenka published her first paper in Marek's lab, "Exquisite ligand stereoselectivity of a Drosophila juvenile hormone receptor contrasts with its broad agonist repertoire" in J. Biol. Chem.
- October 2017: Marek awarded by the Czech Academy of Sciences for outstanding results of great scientific significance ("Discovery of juvenile hormone receptor")
- July 2017: Marek elected the Karlson Lecturer of the International Insect Hormone Workshop, Japan
Our laboratory uniquely combines several model organisms, namely the fly Drosophila melanogaster, the beetle Tribolium castaneum, and the linden bug Pyrrhocoris apterus with molecular techniques in cultured cells and in vitro. We utilize the power of reverse genetic approaches (transgenesis, mutagenesis, RNAi), in these insect models to address basic biological questions as well as insect specific issues in the context of intact, developing organisms. The biological processes of our interest include:
Hormonal and genetic regulation of insect development, metamorphosis and oogenesis.
- Molecular action of lipophilic insect hormones; juvenile hormone; nuclear hormone receptors
Insect endocrinology; developmental biology; Drosophila genetics; reverse genetics
of transcription factors in morphogenesis
Discovery of the juvenile hormone receptor
Juvenile hormone (JH) is a sesquiterpenoid of vital importance to insect development and reproduction. JH was so named for its capacity to block metamorphosis of larvae to adults: only when larvae attain an appropriate stage, a halt of JH secretion permits metamorphosis. When larvae at this stage are treated with JH or its synthetic mimics, they fail to mature. Therefore compounds with JH activity serve as efficient insecticides. The molecular action of JH had long remained an enigma because a JH receptor could not be identified. In 1986, T.G. Wilson isolated a Drosophila mutant, which he named Methoprene-tolerant (Met) based on resistance to the JH-mimicking insecticide. Met encodes a bHLH-PAS protein. This family of transcription factors includes vertebrate aryl hydrocarbon receptors (AhR) of the xenobiotic dioxin, but no receptors of known hormones.
Breakthrough data from our laboratory (Konopova & Jindra 2007 in PNAS; 2008 in Development) showed that Met is required for JH to inhibit metamorphosis in the beetle Tribolium: like depletion of JH itself, loss of Met caused precocious metamorphosis of the beetle larvae. Our following papers, published by Charles et al. (2011 in PNAS) and by Jindra et al. (2015 in PLoS Genet) have finally brought conclusive evidence for the JH receptor role of Met and of its Drosophila paralog Gce. Based on structural modeling of the JH-binding domain of Met, we prepared a set of point mutations that displace JH from the ligand-binding pocket. By testing these mutant proteins in vitro and in vivo, we determined specific amino acids contributing to the high-affinity JH binding. Using mutants unable to bind JH, we demonstrated that Met/Gce requires the ligand-binding capacity for interaction with a partner protein Taiman and, importantly, to sustain normal insect development.
Stereoselectivity of the Drosophila JH receptor Gce
Several homologs of native JH have been found in different insect and
related arthropod species. This study takes a systematic look at the
affinity of a Drosophila JH-receptor, known as germ
cell-expressed (Gce), for a set of native and synthetic JH analogs. We
characterize the potency of each ligand in terms of Gce binding, its
activity in a cell-based reporter assay and its morphogenetic effects on
fly development. Both in vitro and in vivo results
mutually confirm a remarkable stereoselectivity of Gce receptor and its
strong preference for the native ligand conformation. Proper double-bond
geometry of the natural ligand is critical for a tight receptor
binding. Interestingly, the Gce receptor can also be activated by
chemically unrelated synthetic agonists commonly used as JH-mimicking
insecticides. The molecular basis of these interactions is subject of
Juvenile hormone: mechanism of action during insect metamorphosis
Metamorphosis of holometabolous insects such as beetles or butterflies is a marked change of form between juvenile and adult stages that enables the larva to efficiently utilize food sources and the flying adult to spread the species. The entry to metamorphosis depends on the morphogenesis-promoting ecdysteroids and the antagonistically acting juvenile hormone (JH), which precludes metamorphosis until a larva attains the appropriate size and developmental stage. JH has been known to prevent metamorphosis since the work of V.B. Wigglesworth for over 70 years. However, the mechanism of JH action has remained an enigma as neither a JH receptor nor its signaling pathway are known. By using the red flour beetle Tribolium castaneum, we showed that a gene Methoprene-tolerant (Met), originally uncovered as a mutation conferring resistance to JH in the fly Drosophila, mediates the anti-metamorphic JH effect. Loss of Met function renders Tribolium insensitive to JH and, unlike in Drosophila, it also causes the beetle larvae to metamorphose precociously. We further showed that in response to JH, Met controls metamorphosis by regulating expression of the Broad-Complex and Krüppel-homolog 1 (Kr-h1) genes, which play critical roles during larva-pupa and pupa-adul metamorphic changes. Our latest studies thus for the first time demonstrate the key role of Met in the regulation of insect metamorphosis by JH and support the disputed function of Met as a receptor or transducer of the JH signal. We have recently shown that this JH signaling pathway is functionally conserved in evolutionarily distant hemimetabolous insects.