Peptide hormones are small, processed, and secreted peptides that signal via membrane receptors and play critical roles in normal and pathological physiology. The search for novel peptide hormones has been hampered by their small size, low or restricted expression, and lack of sequence similarity. To overcome these difficulties, we developed a bioinformatics search tool based on the hidden Markov model formalism that uses several peptide hormone sequence features to estimate the likelihood that a protein contains a processed and secreted peptide of this class. Application of this tool to an alignment of mammalian proteomes ranked 90% of known peptide hormones among the top 300 proteins. An analysis of the top scoring hypothetical and poorly annotated human proteins identified two novel candidate peptide hormones. Biochemical analysis of the two candidates, which we called spexin and augurin, showed that both were localized to secretory granules in a transfected pancreatic cell line and were recovered from the cell supernatant. Spexin was expressed in the submucosal layer of the mouse esophagus and stomach, and a predicted peptide from the spexin precursor induced muscle contraction in a rat stomach explant assay. Augurin was specifically expressed in mouse endocrine tissues, including pituitary and adrenal gland, choroid plexus, and the atrio-ventricular node of the heart. Our findings demonstrate the utility of a bioinformatics approach to identify novel biologically active peptides. Peptide hormones and their receptors are important diagnostic and therapeutic targets, and our results suggest that spexin and augurin are novel peptide hormones likely to be involved in physiological homeostasis.

Cofilin/ADF proteins are a ubiquitously expressed family of F-actin depolymerizing factors found in eukaryotic cells including plants. In vitro, cofilin/ADF activity has been shown to be essential for actin driven motility, by accelerating actin filament turnover. Three actin depolymerizing factors (n-cofilin, m-cofilin, ADF) can be found in mouse and human. Here we show that in mouse the non-muscle-specific gene-n-cofilin-is essential for migration of neural crest cells as well as other cell types in the paraxial mesoderm. The main defects observed in n-cofilin mutant embryos are an impaired delamination and migration of neural crest cells, affecting the development of neural crest derived tissues. Neural crest cells lacking n-cofilin do not polarize, and F-actin bundles or fibers are not detectable. In addition, n-cofilin is required for neuronal precursor cell proliferation and scattering. These defects result in a complete lack of neural tube closure in n-cofilin mutant embryos. Although ADF is overexpressed in mutant embryos, this cannot compensate the lack of n-cofilin, suggesting that they might have a different function in embryonic development. Our data suggest that in mammalian development, regulation of the actin cytoskeleton by the F-actin depolymerizing factor n-cofilin is critical for epithelial-mesenchymal type of cell shape changes as well as cell proliferation.

Post-translational modification of tubulin serves as a powerful means for rapidly adjusting the functional diversity of microtubules. Acetylation of the e-amino group of K40 in a-tubulin is one such modification that is highly conserved in ciliated organisms. Recently, aTAT1, a Gcn5-related N-acetyltransferase, was identified as an a-tubulin acetyltransferase in Tetrahymena and C. elegans. Here we generate mice with a targeted deletion of Atat1 to determine its function in mammals. Remarkably, we observe a loss of detectable K40 a-tubulin acetylation in these mice across multiple tissues and in cellular structures such as cilia and axons where acetylation is normally enriched. Mice are viable and develop normally, however, the absence of Atat1 impacts upon sperm motility and male mouse fertility, and increases microtubule stability. Thus, aTAT1 has a conserved function as the major a-tubulin acetyltransferase in ciliated organisms and has an important role in regulating subcellular specialization of subsets of microtubules.

Many neuronal disorders such as lissencephaly, epilepsy, and schizophrenia are caused by the abnormal migration of neurons in the developing brain. The role of the actin cytoskeleton in neuronal migration disorders has in large part remained elusive. Here we show that the F-actin depolymerizing factor n-cofilin controls cell migration and cell cycle progression in the cerebral cortex. Loss of n-cofilin impairs radial migration, resulting in the lack of intermediate cortical layers. Neuronal progenitors in the ventricular zone show increased cell cycle exit and exaggerated neuronal differentiation, leading to the depletion of the neuronal progenitor pool. These results demonstrate that mutations affecting regulators of the actin cytoskeleton contribute to the pathology of cortex development.[Keywords: Cortex development; cofilins; actin cytoskeleton; neuronal migration disorders; cell cycle] Supplemental material is available at http://www.genesdev.org.

microRNAs (miRNAs) repress target transcripts through partial complementarity. By contrast, highly complementary miRNA-binding sites within viral and artificially engineered transcripts induce miRNA degradation in vitro and in cell lines. Here, we show that a genome-encoded transcript harboring a near-perfect and deeply conserved miRNA-binding site for miR-29 controls zebrafish and mouse behavior. This transcript originated in basal vertebrates as a long noncoding RNA (lncRNA) and evolved to the protein-coding gene NREP in mammals, where the miR-29-binding site is located within the 3' UTR. We show that the near-perfect miRNA site selectively triggers miR-29b destabilization through 3' trimming and restricts its spatial expression in the cerebellum. Genetic disruption of the miR-29 site within mouse Nrep results in ectopic expression of cerebellar miR-29b and impaired coordination and motor learning. Thus, we demonstrate an endogenous target-RNA-directed miRNA degradation event and its requirement for animal behavior.