Immunoglobulin secretion is modulated by a competition between use of a weak promoter proximal poly(A) site and a non-consensus splice site in the last secretory-specific exon of the heavy chain pre-mRNA. RNA polymerase II transcription elongation factor ELL2, induced in plasma cells, enhanced both polyadenylation and exon skipping with the Igh gene and reporter constructs. Lowering ELL2 expression by hnRNP F transfection or siRNA reduced secretory-specific forms of IgH mRNA. ELL2 and polyadenylation factor CstF-64 co-tracked with RNA polymerase II across the Igh mu and gamma gene segments; association of both factors was blocked by ELL2 siRNA. Thus loading of ELL2 and CstF-64 on RNAP-II was linked, causative for enhanced proximal poly(A) site use and necessary for IgH mRNA processing.

A great challenge in development biology is to understand how interacting networks of regulatory genes can direct the often highly complex patterning of cells in a 3D embryo. Here, we detail the gene regulatory network that describes the distribution of ciliary band-associated neurons in the bipinnaria larva of the sea star. This larva, typically for the ancestral deuterostome dipleurula larval type that it represents, forms two loops of ciliary bands that extend across much of the anterior-posterior and dorsal-ventral ectoderm. We show that the sea star first likely uses maternally inherited factors and the Wnt and Delta pathways to distinguish neurogenic ectoderm from endomesoderm. The broad neurogenic potential of the ectoderm persists throughout much of gastrulation. Nodal, bone morphogenetic protein 2/4 (Bmp2/4), and Six3-dependent pathways then sculpt a complex ciliary band territory that is defined by the expression of the forkhead transcription factor, foxg. Foxg is needed to define two molecularly distinct ectodermal domains, and for the formation of differentiated neurons along the edge of these two territories. Thus, significantly, Bmp2/4 signaling in sea stars does not distinguish differentiated neurons from nonneuronal ectoderm as it does in many other animals, but instead contributes to the patterning of an ectodermal territory, which then, in turn, provides cues to permit the final steps of neuronal differentiation. The modularity between specification and patterning likely reflects the evolutionary history of this gene regulatory network, in which an ancient module for specification of a broad neurogenic potential ectoderm was subsequently overlaid with a module for patterning.echinoderm | neural patterning | evolution

The tumor suppressor Adenomatous polyposis coli (APC) negatively regulates Wnt signaling through its activity in the destruction complex. APC binds directly to the main effector of the pathway, b-catenin (bcat, Drosophila Armadillo), and helps to target it for degradation. In vitro studies demonstrated that a nonphosphorylated 20-amino-acid repeat (20R) of APC binds to bcat through the N-terminal extended region of a 20R. When phosphorylated, the phospho-region of an APC 20R also binds bcat and the affinity is significantly increased. These distinct APC-bcat interactions suggest different models for the sequential steps of destruction complex activity. However, the in vivo role of 20R phosphorylation and extended region interactions has not been rigorously tested. Here we investigated the functional role of these molecular interactions by making targeted mutations in Drosophila melanogaster APC2 that disrupt phosphorylation and extended region interactions and deletion mutants missing the Armadillo binding repeats. We tested the ability of these mutants to regulate Wnt signaling in APC2 null and in APC2 APC1 double-null embryos. Overall, our in vivo data support the role of phosphorylation and extended region interactions in APC2's destruction complex function, but suggest that the extended region plays a more significant functional role. Furthermore, we show that the Drosophila 20Rs with homology to the vertebrate APC repeats that have the highest affinity for bcat are functionally dispensable, contrary to biochemical predictions. Finally, for some mutants, destruction complex function was dependent on APC1, suggesting that APC2 and APC1 may act cooperatively in the destruction complex.