Intestine-enriched apolipoprotein b orthologs are required for stem cell progeny differentiation and regeneration in planarians.

Lipid metabolism plays an instructive role in regulating stem cell state and differentiation. However, the roles of lipid mobilization and utilization in stem cell-driven regeneration are unclear. Planarian flatworms readily restore missing tissue due to injury-induced activation of pluripotent somatic stem cells called neoblasts. Here, we identify two intestine-enriched orthologs of apolipoprotein b, apob-1 and apob-2, which mediate transport of neutral lipid stores from the intestine to target tissues including neoblasts, and are required for tissue homeostasis and regeneration. Inhibition of apob function by RNAi causes head regression and lysis in uninjured animals, and delays body axis re-establishment and regeneration of multiple organs in amputated fragments. Furthermore, apob RNAi causes expansion of the population of differentiating neoblast progeny and dysregulates expression of genes enriched in differentiating and mature cells in eight major cell type lineages. We conclude that intestine-derived lipids serve as a source of metabolites required for neoblast progeny differentiation.

Cell-type diversity and regionalized gene expression in the planarian intestine.

Proper function and repair of the digestive system are vital to most animals. Deciphering the mechanisms involved in these processes requires an atlas of gene expression and cell types. Here, we applied laser-capture microdissection (LCM) and RNA-seq to characterize the intestinal transcriptome of Schmidtea mediterranea, a planarian flatworm that can regenerate all organs, including the gut. We identified hundreds of genes with intestinal expression undetected by previous approaches. Systematic analyses revealed extensive conservation of digestive physiology and cell types with other animals, including humans. Furthermore, spatial LCM enabled us to uncover previously unappreciated regionalization of gene expression in the planarian intestine along the medio-lateral axis, especially among intestinal goblet cells. Finally, we identified two intestine-enriched transcription factors that specifically regulate regeneration (hedgehog signaling effector gli-1) or maintenance (RREB2) of goblet cells. Altogether, this work provides resources for further investigation of mechanisms involved in gastrointestinal function, repair and regeneration.

The human body has a limited ability to regenerate and repair itself after major injuries. By contrast, flatworms ­ most notably planarians such as Schmidtea mediterranea ­ have exceptional regenerative abilities and can regrow large parts of their bodies. Regrowing body parts is a complex process involving the coordinated creation of many different types of cells, and thus an important first step in understanding tissue regeneration is to develop a detailed catalog of cell types in that tissue. Laser capture microdissection, or LCM for short, is a technology used to isolate and study subregions or even individual cells from within a tissue. This approach can help to identify different cell types and to examine what makes them unique. LCM can be used to create a detailed catalog of cells, their differences and the roles they perform. Forsthoefel et al. have now used LCM to study cells from the planarian digestive system. This approach found 1,800 genes that have high activity in cells from the gut and showed many similarities between planaria and humans. LCM made it possible to study these cells in a new level of detail, revealing several hundred new genes as well as new cell types. The study showed that regeneration and survival of cells known as goblet cells particularly depended on two genes, gli-1 and RREB2. Irreversible gut damage in humans can result from surgeries and conditions such as acid reflux. Other animals are able to repair and regenerate the gut more successfully. Techniques like LCM can help researchers to understand the differences between humans and other species. In time, these insights may lead to technologies and therapies that can improve our own abilities to heal following injuries.

Arabidopsis thaliana MLO genes are expressed in discrete domains during reproductive development.

KEY MESSAGE: MLOs in Plant Reproduction. The MILDEW RESISTANCE LOCUS-O (MLO) protein family, comprised of 15 members, plays roles in diverse cell-cell communication processes such as powdery mildew susceptibility, root thigmomorphogenesis, and pollen tube reception. The NORTIA (NTA, AtMLO7) gene is expressed in the synergid cells of the female gametophyte where it functions in intercellular communication with the pollen tube. Discrepancies between previously published promoter::GUS and promoter::gene-GUS constructs expression patterns led us to explore the regulation of NTA expression. Here we found via NTApro::gNTA-GUS truncations that sequences within the NTA gene negatively regulate its expression in the stomata and carpel walls. This led to the hypothesis that other MLO family members may also have additional regulatory sequences within the gene. MLOpro::gMLO-GUS constructs were examined for each family member focusing specifically on flowers in order to determine whether other MLOs could play a role in reproductive cell-cell communication. Notably, several MLOs were expressed in the pollen, in the stigma, in the pollinated style, and in the synergids and central cell. These findings indicate that other MLOs in addition to NTA could play a role in reproduction. Previous studies on the MLO family showed that phylogenetically related MLOs had redundant functions in powdery mildew infection and root thigmomorphogenesis; however, MLO expression in reproductive tissues did not strictly follow phylogenetic relationships, indicating that MLOs from different evolutionary origins may have been recruited for function in sexual reproduction.