CNS midline cells are required for establishment and differentiation of Drosophila MP2 interneurons

The Drosophila CNS develops from the ventral neuroectoderm (VNE) on both sides of the midline along the dorsoventral axis. During early neurogenesis, three homeodomain and Egfr signaling genes are required for the dorsoventral patterning of the VNE. However, the roles of CNS midline cells in patterning of the specific neural lineages are not well understood. Their roles in identity determination and differentiation of the well-established MP2 lineage were studied using several molecular markers. We showed that these cells are essential for identity determination of the MP2 lineage that originates from the VNE. The midline cells and the Egfr signaling genes were also required for the proper maintenance of MP2 and the correct formation of MP2 axonal pathways. Overexpression of sim in the midline cells activated ectopic expression of MP2 markers in the VNE. This analysis suggests that CNS midline cells and Egfr signaling genes play essential roles in the proper establishment and differentiation of the MP2 lineage.     

The Drosophila wing hearts originate from pericardial cells and are essential for wing maturation

In addition to the heart proper, insects possess wing hearts in the thorax to ensure regular hemolymph flow through the narrow wings. In Drosophila, the wing hearts consist of two bilateral muscular pumps of unknown origin. Here, we present the first developmental study on these organs and report that the wing hearts originate from eight embryonic progenitor cells arising in two pairs in parasegments 4 and 5. These progenitors represent a so far undescribed subset of the Even-skipped positive pericardial cells (EPC) and are characterized by the early loss of tinman expression in contrast to the continuously Tinman positive classical EPCs. Ectopic expression of Tinman in the wing heart progenitors omits organ formation, indicating a crucial role for Tinman during progenitor specification. The subsequent postembryonic development is a highly dynamic process, which includes proliferation and two relocation events. Adults lacking wing hearts display a severe wing phenotype and are unable to fly. The phenotype is caused by omitted clearance of the epidermal cells from the wings during maturation, which inhibits the formation of a flexible wing blade. This indicates that wing hearts are required for proper wing morphogenesis and functionality.     

A new Drosophila gene wh (wuho) with WD40 repeats is essential for spermatogenesis and has maximal expression in hub cells

Through mutagenesis by P-element transposition, we identified a series of mutants with deletions in topoisomerase 3beta gene (top3beta) and an adjacent, previously uncharacterized gene CG15897, here named wuho (wh). Whereas top3beta truncation does not affect viability or fertility, wh null mutants display male sterile and female semi-sterile phenotypes. Furthermore, wh mutants can be fully rescued by wh transgenes, but not by top3beta transgenes, suggesting that the fertility phenotypes are caused by wh deletion. The alignment of WH protein sequence with other eukaryotic putative homologues shows they are evolutionarily conserved proteins with 5 WD40 repeats in the middle portion of the protein, and a bipartite nuclear localization signal at the carboxyl terminus. Yeast homologue with 5 WD40 repeats, Trm82, is the non-catalytic subunit of a tRNA methylase. Immunostaining shows that WH has the highest expression in hub cells, a niche for germline stem cells of testis. However, WH is not required for the maintenance of hub cells or the germline stem cells. In wh mutant males, spermatogenesis is arrested at the elongating stage of the developing spermatids, resulting in an absence of mature sperms in the seminal vesicles. The decreased fertility in wh mutant females is mostly due to defects in oogenesis. There are abnormal egg chambers present in the mutant females, in which the cystocytes fail to arrest their cell division at the fourth mitotic cycle, resulting in more than 16 cells in a single egg chamber. Additionally, these abnormal cystocytes do not undergo multiple rounds of endoreplication as the nurse cells do in a normal egg chamber. Therefore, the cytological analyses demonstrate that wh has a critical function in cellular differentiation for germline cells during gametogenesis.     

Lumbo-sacral neural crest derivatives fate mapped with the aid of Wnt-1 promoter integrate but are not essential to kidney development

Neural crest (NC) cells may be involved in kidney organogenesis by providing inductive signals and contributing to cells of the renal stroma. We show here that the lumbo-sacral NC cells fate mapped with the aid of Wnt-1 promoter in the mouse migrate close to the metanephros at the initiation of organogenesis but these cells remain superficial to the condensed Pax2-expressing mesenchymal cells. NC-derived cells enter later into the kidney proper from the midline region. The NC cells contribute also to development of the extra-adrenal para-aortic bodies, Zuckerkandl's bodies and the nerve cord of the sympathetic nervous system. Splotch (Sp^2H/Sp^2H) embryos, having a NC defect in the lumbo-sacral region, develop a normal metanephros even though the kidney does not express the NC markers Sox10, Phox2b and tyrosine hydroxylase. Consistent with the histological findings, the kidneys of Sp^2H/Sp^2H embryos also express the stromal genes Foxd1, Hoxa10 and RARβ normally. Wnt-1 promoter-marked wild-type LacZ NC cells migrate intensely from the heterologous inducer tissue of the embryonic dorsal spinal cord (SPC) to the kidney mesenchyme, but tubule induction does not depend on NC migration, since the Sp^2H/Sp^2H SPC also induces tubulogenesis. The Sp^2H/Sp^2H mesenchyme also remains competent for tubulogenesis. We conclude that the NC cells fate mapped with the aid of Wnt-1 promoter migrate to the close to the metanephros and form later derivatives integrating with the kidney, but they may not be essential to the development of the stromal cells nor they may provide critical morphogenetic signals to regulate early kidney development in vivo.     

Local inhibition of Drosophila homeobox-containing neural dorsoventral patterning genes by Dpp

An important step in Drosophila neurogenesis is to establish the neural dorsoventral (DV) patterning. Here we describe how dpp loss-of- and gain-of-function mutation affects the homeobox-containing neural DV patterning genes expressed in the ventral neuroectoderm. Ventral nervous system defective (vnd), intermediate neuroblast defective (ind), muscle-specific homeobox (msh), and orthodenticle (otd) genes participate in development of the central nervous system and peripheral nervous system, and encode homeodomain proteins. otd and msh genes were ectopically expressed in dpp loss-of-function mutation, but vnd and ind were not affected. However, when dpp was ectopically expressed in the ventral neuroectoderm by rho-GAL4/UAS-dpp system, it caused the repression of vnd, and msh expressions in ventral and dorsal columns of the neuroectoderm, respectively, but not that of ind. The later expression pattern of otd was also restricted by Dpp. The expression pattern of msh, vnd and otd in dpp loss-of-function and gain-of-function mutation indicates that Dpp activity does not reach to the ventral midline and it works locally to establish the dorsal boundary of the ventral neuroectoderm.     

Cell cycle independent role of Cyclin E during neural cell fate specification in Drosophila is mediated by its regulation of Prospero function

During development, neural progenitor cells or neuroblasts generate a great intra- and inter-segmental diversity of neuronal and glial cell types in the nervous system. In thoracic segments of the embryonic central nervous system of Drosophila, the neuroblast NB6-4t undergoes an asymmetric first division to generate a neuronal and a glial sublineage, while abdominal NB6-4a divides once symmetrically to generate only 2 glial cells. We had earlier reported a critical function for the G1 cyclin, CyclinE (CycE) in regulating asymmetric cell division in NB6-4t. Here we show that (i) this function of CycE is independent of its role in cell cycle regulation and (ii) the two functions are mediated by distinct domains at the protein level. Results presented here also suggest that CycE inhibits the function of Prospero and facilitates its cortical localization, which is critical for inducing stem cell behaviour, i.e. asymmetric cell division of NB6-4t. Furthermore our data imply that CycE is required for the maintenance of stem cell identity of most other neuroblasts.     

The chitin synthase genes chs-1 and chs-2 are essential for C. elegans development and responsible for chitin deposition in the eggshell and pharynx, respectively

It is widely accepted that chitin is present in nematodes. However, its precise role in embryogenesis is unclear and it is unknown if chitin is necessary in other nematode tissues. Here, we determined the roles of chitin and the two predicted chitin synthase genes in Caenorhabditis elegans by chitin localization and gene disruption. Using a novel probe, we detected chitin in the eggshell and discovered elaborate chitin localization patterns in the pharyngeal lumen walls. Chitin deposition in these two sites is likely regulated by the activities of chs-1 (T25G3.2) and chs-2 (F48A11.1), respectively. Reducing chs-1 gene activity by RNAi led to eggs that were fragile and permeable to small molecules, and in the most severe case, absence of embryonic cell division. Complete loss of function in a chs-1 deletion resulted in embryos that lacked chitin in their eggshells and failed to divide. These results showed that eggshell chitin provides both mechanical support and chemical impermeability essential to developing embryos. Knocking down chs-2 by RNAi caused a defect in the pharynx and led to L1 larval arrest, indicating that chitin is involved in the development and function of the pharynx.