Natural antisense transcription of presenilin in sea urchin reveals a possible role for natural antisense transcription in the general control of gene expression during development

One presenilin gene (PSEN) is expressed in the sea urchin embryo, in the vegetal pole of the gastrula and then mainly in cilia cells located around the digestive system of the pluteus, as we recently have reported. PSEN expression must be accurately regulated for correct execution of these two steps of development. While investigating PSEN expression changes in embryos after expansion of endoderm with LiCl or of ectoderm with Zn2+ by whole-mount in situ hybridization (WISH) and quantitative PCR (qPCR), we detected natural antisense transcription of PSEN. We then found that Endo16 and Wnt5, markers of endo-mesoderm, and of Hnf6 and Gsc, markers of ectoderm, are also sense and antisense transcribed. We discuss that general gene expression could depend on both sense and antisense transcription. This mechanism, together with the PSEN gene, should be included in gene regulatory networks (GRNs) that theorize diverse processes in this species. We suggest that it would also be relevant to investigate natural antisense transcription of PSEN in the field of Alzheimer's disease (AD) where the role of human PSEN1 and PSEN2 is well known.

Precise regulation of presenilin expression is required for sea urchin early development.

Presenilins (PSENs) are widely expressed across eukaryotes. Two PSENs are expressed in humans, where they play a crucial role in Alzheimer's disease (AD). Each PSEN can be part of the γ-secretase complex, which has multiple substrates, including Notch and amyloid-ß precursor protein (AßPP) - the source of amyloid-ß (Aß) peptides that compose the senile plaques during AD. PSENs also interact with various proteins independently of their γ-secretase activity. They can then be involved in numerous cellular functions, which makes their role in a given cell and/or organism complex to decipher. We have established the Paracentrotus lividus sea urchin embryo as a new model to study the role of PSEN. In the sea urchin embryo, the PSEN gene is present in unduplicated form and encodes a protein highly similar to human PSENs. Our results suggest that PSEN expression must be precisely tuned to control the course of the first mitotic cycles and the associated intracellular Ca2+ transients, the execution of gastrulation and, probably in association with ciliated cells, the establishment of the pluteus. We suggest that it would be relevant to study the role of PSEN within the gene regulatory network deciphered in the sea urchin.

Study of bicyclomycin biosynthesis in Streptomyces cinnamoneus by genetic and biochemical approaches.

The 2,5-Diketopiperazines (DKPs) constitute a large family of natural products with important biological activities. Bicyclomycin is a clinically-relevant DKP antibiotic that is the first and only member in a class known to target the bacterial transcription termination factor Rho. It derives from cyclo-(L-isoleucyl-L-leucyl) and has an unusual and highly oxidized bicyclic structure that is formed by an ether bridge between the hydroxylated terminal carbon atom of the isoleucine lateral chain and the alpha carbon of the leucine in the diketopiperazine ring. Here, we paired in vivo and in vitro studies to complete the characterization of the bicyclomycin biosynthetic gene cluster. The construction of in-frame deletion mutants in the biosynthetic gene cluster allowed for the accumulation and identification of biosynthetic intermediates. The identity of the intermediates, which were reproduced in vitro using purified enzymes, allowed us to characterize the pathway and corroborate previous reports. Finally, we show that the putative antibiotic transporter was dispensable for the producing strain.

Role of Mad2 expression during the early development of the sea urchin.

Mitotic arrest deficient 2 (Mad2) belongs to the spindle assembly checkpoint (SAC), a mechanism that blocks progression of the cell cycle until microtubule attachment to kinetochores is complete. It has been found to be involved in the resistance of cancer cells to "anti-mitotic" drugs such as paclitaxel. Mad2 controls meiotic progression, but its role during sea urchin development had never been investigated. Furthermore, the existence of a SAC in this species had never been proved. The present data show that a Mad2 protein, highly homologous to that of humans, is expressed in this species. Mad2 expression increases during development, becoming confined to the endomesoderm at gastrula stages. The level of Mad2 expression is enhanced in embryos that do not gastrulate after treatment with anti-mitotic drugs, lithium or inhibition of the ERK pathway. Mis-aligned and lagging chromosomes were induced after injection of an anti-Mad2 antibody or a Mad2 morpholino. Our results point to the role of a non-canonical SAC involving Mad2 in the control of mitotic divisions of the sea urchin embryo.