Stage-specific control of stem cell niche architecture in the Drosophila testis by the posterior Hox gene Abd-B

A fundamental question in biology is how complex structures are maintained after their initial specification. We address this question by reviewing the role of the Hox gene Abd-B in Drosophila testis organogenesis, which proceeds through embryonic, larval and pupal stages to reach maturation in adult stages. The data presented in this review highlight a cell- and stage-specific function of Abd-B, since the mechanisms regulating stem cell niche positioning and architecture at different stages seem to be different despite the employment of similar factors. In addition to its described role in the male embryonic gonads, sustained activity of Abd-B in the pre-meiotic germline spermatocytes during larval stages is required to maintain the architecture of the stem cell niche by regulating βPS-integrin localization in the neighboring somatic cyst cells. Loss of Abd-B is associated with cell non-autonomous effects within the niche, leading to a dramatic reduction of pre-meiotic cell populations in adult testes. Identification of Abd-B target genes revealed that Abd-B mediates its effects by controlling the activity of the sevenless ligand Boss via its direct targets Src42A and Sec63. During adult stages, when testis morphogenesis is completed with the addition of the acto-myosin sheath originating from the genital disc, stem cell niche positioning and integrity are regulated by Abd-B activity in the acto-myosin sheath whereas integrin acts in an Abd-B independent way. It seems that the occurrence of new cell types and cell interactions in the course of testis organogenesis made it necessary to adapt the system to the new cellular conditions by reusing the same players for testis stem cell niche positioning in an alternative manner. © 2015 Papagiannouli, Lohmann. Published by Elsevier B.V. on behalf of the Research Network of Computational and Structural Biotechnology

Stage-specific control of niche positioning and integrity in the Drosophila testis

A fundamental question is how complex structures are maintained after their initial specification. Stem cells reside in a specialized microenvironment, called niche, which provides essential signals controlling stem cell behavior. We addressed this question by studying the Drosophila male stem cell niche, called the hub. Once specified, the hub cells need to maintain their position and architectural integrity through embryonic, larval and pupal stages of testis organogenesis and during adult life. The Hox gene Abd-. B, in addition to its described role in male embryonic gonads, maintains the architecture and positioning of the larval hub from the germline by affecting integrin localization in the neighboring somatic cyst cells. We find that the AbdB-Boss/Sev cascade affects integrin independent of Talin, while genetic interactions depict integrin as the central downstream player in this system. Focal adhesion and integrin-adaptor proteins within the somatic stem cells and cyst cells, such as Paxillin, Pinch and Vav, also contribute to proper hub integrity and positioning. During adult stages, hub positioning is controlled by Abd-B activity in the outer acto-myosin sheath, while Abd-B expression in adult spermatocytes exerts no effect on hub positioning and integrin localization. Our data point at a cell- and stage-specific function of Abd-B and suggest that the occurrence of new cell types and cell interactions in the course of testis organogenesis made it necessary to adapt the whole system by reusing the same players for male stem cell niche positioning and integrity in an alternative manner. © 2015

Dynein light chain 1 functions in somatic cyst cells regulate spermatogonial divisions in Drosophila

Stem cell progeny often undergo transit amplifying divisions before differentiation. In Drosophila, a spermatogonial precursor divides four times within an enclosure formed by two somatic-origin cyst cells, before differentiating into spermatocytes. Although germline and cyst cell-intrinsic factors are known to regulate these divisions, the mechanistic details are unclear. Here, we show that loss of dynein-light-chain-1 (DDLC1/LC8) in the cyst cells eliminates bag-of-marbles (bam) expression in spermatogonia, causing gonial cell hyperplasia in Drosophila testis. The phenotype is dominantly enhanced by Dhc64C (cytoplasmic Dynein) and didum (Myosin V) loss-of-function alleles. Loss of DDLC1 or Myosin V in the cyst cells also affects their differentiation. Furthermore, cyst cell-specific loss of ddlc1 disrupts Armadillo, DE-cadherin and Integrin-βPS localizations in the cyst. Together, these results suggest that Dynein and Myosin V activities, and independent DDLC1 functions in the cyst cells organize the somatic microenvironment that regulates spermatogonial proliferation and differentiation

The internal structure of embryonic gonads and testis development in Drosophila melanogaster requires scrib, lgl and dlg activity in the soma

Interest in the mechanism leading to the formation of the germline and its differentiation during Drosophila development, initiated even as soon as the first ever cloned tumour suppressor gene in Drosophila, the lethal (2) giant larvae (lgl), had been identified. Further work has shown that the lgl, as well as discs large-1 (dlg) and scribble (scrib) tumor suppressor genes code for scaffolding proteins associated with either the cytoskeletal matrix or the septate junctions that act in common pathways in various tissues. This study analysed the role of Dlg, Scrib and Lgl in the embryonic gonads and testis of Drosophila melanogaster. Loss of scrib, dlg and lgl had no effect on gonad formation, but Dlg and Scrib in the gonadal mesoderm acted critically in the somatic wrapping of the pole cells and the internal structure of the Drosophila embryonic gonads. Dlg also affected the incorporation of the male-specific Sox100B positive mesodermal cells into the male embryonic gonads, yet Sox100B expression in dlg testis remained unaffected. Analysis at later stages revealed that scrib and lgl expression in the somatic lineage of the Drosophila testis, similar to what was previously shown for dlg, was indispensable for testis development and homeostasis, as depletion of these genes resulted in extensive testes defects. The data presented here emphasize the somatic requirement of Scrib, Dlg and Lgl in embryonic gonads, as well as in the Drosophila testis that underlines the importance of the somatic lineage in the establishment and maintenance of testis formation throughout successive developmental stage

An old player on a new task

Gamete development requires a coordinated soma-germ line interaction that ensures renewal and differentiation of germline and somatic stem cells. The physical contact between the germline and somatic cell populations is crucial because it allows the exchange of diffusible signals among them. The tumor suppressor gene discs large (dlg) encodes a septate junction protein with functions in epithelial cell polarity, asymmetric neuroblast division and formation of neuromuscular junctions. Our recent work reveals a new role of dlg in the Drosophila testis, as mutations in dlg lead to testis defects and cell death. Dlg is required throughout spermatogenesis in the somatic lineage and its localization changes from a uniform distribution along the plasma membrane of somatic cells in the testis apex, to a restricted localization on the distally located somatic cell in growing cysts. The extensive defects in dlg testis underline the importance of the somatic cells in the establishment and maintenance of the male stem cell niche and somatic cell differentiation. Here, we discuss our latest findings on the role of dlg in the Drosophila testis, supporting the view that junction proteins are dynamic structures, which can provide guiding cues to recruit scaffold proteins or other signaling molecules

Chapter Five - The HOX-Apoptosis Regulatory Interplay in Development and Disease

Apoptosis is a cellular suicide program, which is on the one hand used to remove superfluous cells thereby promoting tissue or organ morphogenesis. On the other hand, the programmed killing of cells is also critical when potentially harmful cells emerge in a developing or adult organism thereby endangering survival. Due to its critical role apoptosis is tightly controlled, however so far, its regulation on the transcriptional level is less studied and understood. Hox genes, a highly conserved gene family encoding homeodomain transcription factors, have crucial roles in development. One of their prominent functions is to shape animal body plans by eliciting different developmental programs along the anterior-posterior axis. To this end, Hox proteins transcriptionally regulate numerous processes in a coordinated manner, including cell-type specification, differentiation, motility, proliferation as well as apoptosis. In this review, we will focus on how Hox proteins control organismal morphology and function by regulating the apoptotic machinery. We will first focus on well-established paradigms of Hox-apoptosis interactions and summarize how Hox transcription factors control morphological outputs and differentially shape tissues along the anterior-posterior axis by fine-tuning apoptosis in a healthy organism. We will then discuss the consequences when this interaction is disturbed and will conclude with some ideas and concepts emerging from these studies. © 2015 Elsevier Inc

Fullerene-porphyrin [N] pseudorotaxanes: Self-assembly, photophysics and third-order NLO response

By means of different spectroscopic techniques, we investigate a novel series of porphyrin derivatives (H2TPP), connected to dibenzo-24-crown-8 (DB24C8) moieties, which undergo self-assembly with different methano[60]fullerene units bearing dibenzylammonium (DBA) cations. The formation of both [2] and [3]pseudorotaxanes was proved by means of NMR, UV-Vis-NIR absorption and emission spectroscopies. With the support of molecular modelling studies, spectroscopic investigations showed the presence of a secondary interaction between the porphyrin and the C60 chromophores leading to the formation of different types of "face-to-face" assemblies. Remarkably, investigations of the non-linear optical response of these supramolecular systems showed that individual porphyrin and fullerene derivatives exhibit significantly lower second hyperpolarizability values when compared to their pseudorotaxanes functionalised counterparts. This proves that this class of supramolecular materials possesses relevant NLO response, which strongly depends on the structural arrangement of the chromophores in solution

The cis-regulatory code of Hox function in Drosophila

Spatiotemporal control of gene expression is orchestrated by the combinatorial interplay of transcription factor (TF) complexes with cis-regulatory DNA elements. However, it remains mostly unclear how TFs, many of which are active in several cell types, acquire cell-type specific functions. An ideal model to study the mechanisms underlying TF tissue-specificity are the Homeobox (Hox) TFs, which despite their broad expression, activate or repress transcriptional programs in a highly context dependent manner. To address how a widely expressed transcriptional regulator is able to modulate downstream gene activity with high cellular specificity, we have quantitatively identified binding regions for the Hox TF Deformed (Dfd) in the Drosophila genome. By analyzing Dfd bound cis-regulatory modules (CRMs), we show that architectural features like motif-pair associations and motif distance preferences are essential for cell-type specific expression of associated target genes. CRM features indeed determine specificity, since they alone accurately predict target gene function and expression patterns. We also find that Dfd and Ultrabithorax (Ubx), another Hox TF specifying different morphological traits, interact exclusively with non-overlapping genomic regions in vivo, regardless of their similar DNA binding preferences. Despite their comparable basic design principles, Dfd and Ubx CRMs show distinct motif compositions and motif-pair associations, explaining the high functional specificity of the two Hox proteins. Our results uncover the regulatory code of Hox CRMs and elucidate the mechanisms underlying functional specificity of TFs in vivo

Temporal metrology for advanced ultrashort XUV sources

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Impure infrared vortex driven high harmonic generation

International audienceWe demonstrate that high harmonic generation when driven by vortex driver contaminated with various orbital angular momentum (OAM) modes, the upconverted EUV harmonic deviates from perturbative conversion law to exhibit a spectrum of OAM orders