Anti-Isl1 polyclonal antibody

The LIM-homeodomain transcription factor Tailup (Tup) is a component of the complex cardiac transcriptional network governing specification and differentiation of cardiac cells in Drosophila. LIM-domain containing factors are known to interact with the adaptor molecule Chip/Ldb1 to form higher order protein complexes to regulate gene expression thereby determining a cell's developmental fate. However, with respect to Drosophila heart development, it has not been investigated yet, whether Chip and tup interact to regulate the generation of different cardiac cell types. Here we show that Chip is required for normal heart development and that it interacts with tup in this context. Particularly the number of Odd skipped-expressing pericardial cells depends on balanced amounts of Chip and Tup. Data from luciferase assays using Hand-and even-skipped reporter constructs in Drosophila S2 cells indicate that Chip and Tup act as a tetrameric complex on the regulatory regions of Hand and even-skipped (eve). Finally we have identified and verified five Tup binding sites in the eve mesodermal enhancer, which adds Tup as novel factor to directly regulate eve expression. Taken together this study provides novel findings regarding cardiac gene expression regulation in Drosophila.

LIM-homeodomain (HD) transcription factors form a multimeric complex and assign neuronal subtype identities, as demonstrated by the hexameric ISL1-LHX3 complex which gives rise to somatic motor (SM) neurons. However, the roles of combinatorial LIM code in motor neuron diversification and their subsequent differentiation is much less well understood. In the present study, we demonstrate that the ISL1 controls postmitotic cranial branchiomotor (BM) neurons including the positioning of the cell bodies and peripheral axon pathfinding. Unlike SM neurons, which transform into interneurons, BM neurons are normal in number and in marker expression in Isl1 mutant mice. Nevertheless, the movement of trigeminal and facial BM somata is stalled, and their peripheral axons are fewer or misrouted, with ectopic branches. Among genes whose expression level changes in previous ChIP-seq and microarray analyses in Isl1-deficient cell lines, we found that Slit2 transcript was almost absent from BM neurons of Isl1 mutants. Both ISL1-LHX3 and ISL1-LHX4 bound to the Slit2 enhancer and drove endogenous Slit2 expression in SM and BM neurons. Our findings suggest that combinations of ISL1 and LHX factors establish cell-type specificity and functional diversity in terms of motor neuron identities and/or axon development.