The lateral neural plate border (NPB), the neural part of the vertebrate neural border, is composed of central nervous system (CNS) progenitors and peripheral nervous system (PNS) progenitors. In invertebrates, PNS progenitors are also juxtaposed to the lateral boundary of the CNS. Whether there are conserved molecular mechanisms determining vertebrate and invertebrate lateral neural borders remains unclear. Using single-cell-resolution gene-expression profiling and genetic analysis, we present evidence that orthologs of the NPB specification module specify the invertebrate lateral neural border, which is composed of CNS and PNS progenitors. First, like in vertebrates, the conserved neuroectoderm lateral border specifier Msx/vab-15 specifies lateral neuroblasts in Caenorhabditis elegans. Second, orthologs of the vertebrate NPB specification module (Msx/vab-15, Pax3/7/pax-3, and Zic/ref-2) are significantly enriched in worm lateral neuroblasts. In addition, like in other bilaterians, the expression domain of Msx/vab-15 is more lateral than those of Pax3/7/pax-3 and Zic/ref-2 in C. elegans. Third, we show that Msx/vab-15 regulates the development of mechanosensory neurons derived from lateral neural progenitors in multiple invertebrate species, including C. elegans, Drosophila melanogaster, and Ciona intestinalis. We also identify a novel lateral neural border specifier, ZNF703/tlp-1, which functions synergistically with Msx/vab-15 in both C. elegans and Xenopus laevis. These data suggest a common origin of the molecular mechanism specifying lateral neural borders across bilaterians.C. elegans | neural plate border | neural border | Msx/vab-15 | ZNF703/tlp-1 T he vertebrate neural border is a transient embryonic domain located between the neural plate and nonneurogenic ectoderm from late gastrulation to early neurulation. The neural border is composed of the lateral neural plate border (NPB) and preplacode ectoderm (PPE) subdomains (1, 2). The NPB and PPE give rise to the neural crest and placode, respectively, both of which undergo epithelial-to-mesenchymal transition/delamination, migrate in prototypical paths, and give rise to the peripheral nervous system (PNS) and many other cell types (3, 4). However, the NPB and PPE also have many different features (5). For example, the PPE is confined to the anterior half of embryos and does not contribute to the central nervous system (CNS), whereas the NPB is the lateral border of the whole neural plate and consists not only of progenitors for the PNS but also those for the CNS in the dorsal neural tube. The juxtaposed localization of the CNS neuroectoderm and PNS progenitors also occurs in the trunk of invertebrate embryos such as nematodes, arthropods, annelids, and urochordates (6-9), reminiscent of vertebrate NPB. In Caenorhabditis elegans, lateral neuroblasts (P, Q, and V5 cells) are located between the embryonic CNS and skin from the birth of these cells (10). In addition, worm lateral neuroblasts possess several key cellular and developmental features of vertebra...

By the end of neurogenesis in Drosophila pupal brain neuroblasts (NBs), nuclear Prospero (Pros) triggers cell cycle exit and terminates NB lifespan. Here, we reveal that in larval brain NBs, an intrinsic mechanism facilitates import and export of Pros across the nuclear envelope via a Ran‐mediated nucleocytoplasmic transport system. In rangap mutants, the export of Pros from the nucleus to cytoplasm is impaired and the nucleocytoplasmic transport of Pros becomes one‐way traffic, causing an early accumulation of Pros in the nuclei of the larval central brain NBs. This nuclear Pros retention initiates NB cell cycle exit and leads to a premature decrease of total NB numbers. Our data indicate that RanGAP plays a crucial role in this intrinsic mechanism that controls NB lifespan during neurogenesis. Our study may provide insights into understanding the lifespan of neural stem cells during neurogenesis in other organisms.

The mechanism for the basal targeting of the Miranda (Mira) complex during the asymmetric division of Drosophila neuroblasts (NBs) is yet to be fully understood. We have identified conserved Phosphotyrosyl phosphatase activator (PTPA) as a novel mediator for the basal localization of the Mira complex in larval brain NBs. In mutant Ptpa NBs, Mira remains cytoplasmic during early mitosis and its basal localization is delayed until anaphase. Detailed analyses indicate that PTPA acts independent of and before aPKC to localize Mira. Mechanistically, our data show that the phosphorylation status of the T591 residue determines the subcellular localization of Mira and that PTPA facilitates the dephosphorylation of T591. Furthermore, PTPA associates with the Protein phosphatase 4 complex to mediate localization of Mira. On the basis of these results, a two-step process for the basal localization of Mira during NB division is revealed: cortical association of Mira mediated by the PTPA-PP4 complex is followed by apical aPKC-mediated basal restriction.

Edited by Mike Shipston Atg101 is an autophagy-related gene identified in worms, flies, mice, and mammals, which encodes a protein that functions in autophagosome formation by associating with the ULK1-Atg13-Fip200 complex. In the last few years, the critical role of Atg101 in autophagy has been well-established through biochemical studies and the determination of its protein structure. However, Atg101's physiological role, both during development and in adulthood, remains less understood. Here, we describe the generation and characterization of an Atg101 lossof-function mutant in Drosophila and report on the roles of Atg101 in maintaining tissue homeostasis in both adult brains and midguts. We observed that homozygous or hemizygous Atg101 mutants were semi-lethal, with only some of them surviving into adulthood. Both developmental and starvation-induced autophagy processes were defective in the Atg101 mutant animals, and Atg101 mutant adult flies had a significantly shorter lifespan and displayed a mobility defect. Moreover, we observed the accumulation of ubiquitin-positive aggregates in Atg101 mutant brains, indicating a neuronal defect. Interestingly, Atg101 mutant adult midguts were shorter and thicker and exhibited abnormal morphology with enlarged enterocytes. Detailed analysis also revealed that the differentiation from intestinal stem cells to enterocytes was impaired in these midguts. Cell type-specific rescue experiments disclosed that Atg101 had a function in enterocytes and limited their growth. In summary, the results of our study indicate that Drosophila Atg101 is essential for tissue homeostasis in both adult brains and midguts. We propose that Atg101 may have a role in age-related processes. Autophagy (macroautophagy) is a process in which cytoplasmic materials, including organelles and macromolecules, are delivered to and degraded in the lysosome (1-4). As a major intracellular degradation system, autophagy plays important roles in development, tissue homeostasis, and aging (5-7). Defects in the autophagy pathway cause various human diseases, such as cancer and neurodegenerative diseases (8-10). Genetic studies from budding yeast have identified more than 30 Atg genes, which function at various steps during autophagy (2, 3, 11). Most of these genes are highly conserved from yeast to mammals (3, 11). Among them, the Atg1 complex acts at the initiation stage of autophagy functioning as a scaffold for the recruitment of downstream Atg 2 proteins to the preautophagosomal structure (4, 11-13). The yeast Atg1 complex consists of Atg1, Atg13, Atg17, Atg29, and Atg31, and its mammalian counterpart is composed of ULK1 (or ULK2), Atg13, FIP200 (also known as RB1CC1) and Atg101 (4, 11-13). Mammalian ULK1 and ULK2 are homologs of Atg1 (13). FIP200 is generally considered as a homolog of yeast Atg11 and Atg17 (13). Homologs of Atg29 and Atg31 are not found in higher eukaryotes (13). In contrast, Atg101 is present in most eukaryotes, with the exception of budding yeast (13). It has been proposed that the regu...