The homeobox gene Six3 regulates forebrain development. Here we show that Six3 is also crucial for lens formation. Conditional deletion of mouse Six3 in the presumptive lens ectoderm (PLE) disrupted lens formation. In the most severe cases, lens induction and specification were defective, and the lens placode and lens were absent. In Six3-mutant embryos, Pax6 was downregulated, and Sox2 was absent in the lens preplacodal ectoderm. Using ChIP, electrophoretic mobility shift assay, and luciferase reporter assays, we determined that Six3 activates Pax6 and Sox2 expression. Misexpression of mouse Six3 into chick embryos promoted the ectopic expansion of the ectodermal Pax6 expression domain. Our results position Six3 at the top of the regulatory pathway leading to lens formation. We conclude that Six3 directly activates Pax6 and probably also Sox2 in the PLE and regulates cell autonomously the earliest stages of mammalian lens induction.

Crucial components of the vertebrate eye, ear and nose develop from discrete patches of surface epithelium, called placodes, which fold into spheroids and undergo complex morphogenesis. Little is known about how the changes in cell and tissue shapes are coordinated with the acquisition of cell fates. Here we explore whether these processes are regulated by common transcriptional mechanisms in the developing ear. After specification, inner ear precursors elongate to form the placode, which invaginates and is transformed into the complex structure of the adult ear. We show that the transcription factor Pax2 plays a key role in coordinating otic fate and placode morphogenesis, but appears to regulate each process independently. In the absence of Pax2, otic progenitors not only lose otic marker expression, but also fail to elongate due to the loss of apically localised N-cadherin and N-CAM. In the absence of either N-cadherin or N-CAM otic cells lose apical cell–cell contact and their epithelial shape. While misexpression of Pax2 leads to ectopic activation of both adhesion molecules, it is not sufficient to confer otic identity. These observations suggest that Pax2 controls cell shape independently from cell identity and thus acts as coordinator for these processes.

Spectraplakins are large multifunctional cytoskeletal interacting molecules implicated in various processes, including gastrulation, wound healing, skin blistering and neuronal degeneration. It has been speculated that the various functional domains and regions found in Spectraplakins are used in context-specific manners, a model which would provide a crucial explanation for the multifunctional nature of Spectraplakins. Here we tested this possibility by studying domain requirements of the Drosophila Spectraplakin Short stop (Shot) in three different cellular contexts in vivo: (1) neuronal growth, which requires dynamic actin-microtubule interaction; (2) formation and maintenance of tendon cells, which depends on highly stabilised arrays of actin filaments and microtubules, and (3) compartmentalisation in neurons, which is likely to involve cortical F-actin networks. Using these cellular contexts for rescue experiments with Shot deletion constructs in shot mutant background, a number of differential domain requirements were uncovered. First, binding of Shot to F-actin through the first Calponin domain is essential in neuronal contexts but dispensable in tendon cells. This finding is supported by our analyses of shot(kakP2) mutant embryos, which produce only endogenous isoforms lacking the first Calponin domain. Thus, our data demonstrate a functional relevance for these isoforms in vivo. Second, we provide the first functional role for the Plakin domain of Shot, which has a strong requirement for compartmentalisation in neurons and axonal growth, demonstrating that Plakin domains of long Spectraplakin isoforms are of functional relevance. Like the Calponin domain, also the Plakin domain is dispensable in tendon cells, and the currently assumed role of Shot as a linker of microtubules to the tendon cell surface may have to be reconsidered. Third, we demonstrate a function of Shot as an actin-microtubule linker in dendritic growth, thus shedding new light into principal growth mechanisms of this neurite type. Taken together, our data clearly support the view that Spectraplakins function in tissue-specific modes in vivo, and even domains believed to be crucial for Spectraplakin function can be dispensable in specific contexts.

Hundsdoerfer, AK., Mende, MB., Kitching, IJ. & Cordellier, M. (2011). Taxonomy, phylogeography and climate relations of the Western Palaearctic spurge hawkmoth (Lepidoptera, Sphingidae, Macroglossinae). —Zoologica Scripta, 40, 403–417. The primary aim of this study was to analyse mitochondrial genetic variability within the Hyles euphorbiae lineage in the Western Palaearctic, where observations of morphology have indicated much greater differentiation than is implied by the current taxonomy. The scope of the study is broadened further by including an analysis of the possible influences of climatic factors on lineage distributions. Mitochondrial sequences from three genes totalling an unambiguous alignment of 2284 bp were obtained for 356 individuals of the H. euphorbiae complex (HEC) s.s. Genetic admixture, network and climatic factor analyses were used to analyse the data. Unexpected mitochondrial variability was uncovered within the distribution range of H. euphorbiae in southern Europe, with two additional distinct clusters being found, both with rather patchy occurrences. The results of the genetic analysis presented here confirm a distinct H. cretica on Crete and the Dodecanese Islands and a distinct H. robertsi in Iran that hybridises with H. euphorbiae. Comparison of the molecular data with larval morphology shows only limited correlation of genetic clusters with pattern elements. The genetic network of the HEC s.s. shows strong incongruence with traditional taxonomy. Ecological niche modelling based on climate data revealed that the three best‐sampled clusters (H. tithymali, the well‐known H. euphorbiae lineage from Europe, and the previously unknown mitochondrial H. euphorbiae lineage that occurs mainly in Italy) could all occur in southern Italy and on the Mediterranean Islands. Biotic interactions appear to explain the observed ranges better than abiotic factors alone.