Increasing evidence indicates that many small secretory preproteins can undergo post-translational translocation across the membrane of the endoplasmic reticulum. Although the cellular machinery involved in post-translational translocation of small secretory preproteins has begun to be elucidated, the intrinsic signals contained within these small secretory preproteins that contribute to their efficient post-translational translocation remain unknown. Here, we analyzed the eukaryotic secretory proteome and discovered the small secretory preproteins tend to have a higher probability to harbor the positive charge in the n-region of the signal peptide (SP). Eliminating the positive charge of the n-region blocked post-translational translocation of newly synthesized preproteins and selectively impaired translocation efficiency of small secretory preproteins. The pathophysiological significance of the positive charge in the n-region of SP was underscored by recently identified preproinsulin SP mutations that impair translocation of preproinsulin and cause maturity onset diabetes of youth (MODY). Remarkably, we have found that slowing the polypeptide elongation rate of small secretory preproteins could alleviate the translocation defect caused by loss of the n-region positive charge of the signal peptide. Together, these data reveal not only a previously unrecognized role of the n-region's positive charge in ensuring efficient post-translational translocation of small secretory preproteins, but they also highlight the molecular contribution of defects in this process to the pathogenesis of genetic disorders such as MODY.

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Recently, amphioxus has served as a model for studying the origin and evolution of vertebrate immunity. However, little is known about how microRNAs (miRNAs) are involved in the immune defense in amphioxus. In this article, we present a systematic study of amphioxus miRNAs in the acute-phase response to bacterial infection; miR-92d was found to regulate the complement pathway in this basal chordate. We identified all 155 possible miRNAs present in the amphioxus Branchiostoma belcheri genome by bioinformatics analyses, including 57 newly identified miRNAs (called bbe-miRNAs), and characterized the miRNA expression pattern. Four miRNAs (bbe-miR-7, bbe-miR-4868a, bbe-miR-2065, and bbe-miR-34b) were upregulated and bbe-miR-92d was downregulated under the challenge of both Vibrio anguillarum and Staphylococcus aureus bacteria. We further predicted miRNA targets and identified mRNA targets of immune-related miRNA using the hybrid PCR method. We propose that miR-92d regulates the complement pathway through targeting C3 for controlling the acute immune response to bacterial infections. This study provides evidence for the complex immune regulation of miRNAs in the acute-phase response in basal chordates.

Ovules are female reproductive organs of angiosperms, containing sporophytic integuments and gametophytic embryo sacs. After fertilization, embryo sacs develop into embryos and endosperm whereas integuments into seed coat. Ovule development is regulated by transcription factors (TF) whose expression is often controlled by microRNAs. Mutations of Arabidopsis DICER-LIKE 1 (DCL1), a microRNA processing protein, caused defective ovule development and reduced female fertility. However, it was not clear whether other microRNA processing proteins participate in this process and how defective ovule development influenced female fertility. We report that mutations of HUA ENHANCER1 (HEN1) and HYPONASTIC LEAVES 1 (HYL1) interfered with integument growth. The sporophytic defect caused abnormal embryo sac development and inability of mutant ovules to attract pollen tubes, leading to reduced female fertility. We show that the role of HEN1 in integument growth is cell-autonomous. Although AUXIN RESPONSE FACTOR 6 (ARF6) and ARF8 were ectopically expressed in mutant ovules, consistent with the reduction of microRNA167 in hen1, introducing arf6;arf8 did not suppress ovule defects of hen1, suggesting the involvement of more microRNAs in this process. Results presented indicate that the microRNA processing machinery is critical for ovule development and seed production through multiple microRNAs and their targets.