Spillover in the direct-type PSI-PSII megacomplex isolated from Arabidopsis thaliana is regulated by pH.

Various megacomplexes in which Photosystem I and Photosystem II are physically bound (PSI-PSII m.c.) have been found in many organisms.

Formation of a Stable PSI-PSII Megacomplex in Rice That Conducts Energy Spillover.

In green plants, photosystem I (PSI) and photosystem II (PSII) bind to their respective light-harvesting complexes (LHCI and LHCII) to form the PSI-LHCI supercomplex and the PSII-LHCII supercomplex, respectively. These supercomplexes further form megacomplexes, like PSI-PSII and PSII-PSII in Arabidopsis (Arabidopsis thaliana) and spinach to modulate their light-harvesting properties, but not in the green alga Chlamydomonas reinhardtii. Here, we fractionated and characterized the stable rice PSI-PSII megacomplex.

The photosystem I supercomplex from a primordial green alga harbors three light-harvesting complex trimers.

As a ubiquitous picophytoplankton in the ocean and an early-branching green alga, is a model prasinophyte species for studying the functional evolution of the light-harvesting systems in photosynthesis. Here, we report the structure and function of the photosystem I (PSI) supercomplex in low light conditions, where it expands its photon-absorbing capacity by assembling with the light-harvesting complexes I (LHCI) and a prasinophyte-specific light-harvesting complex (Lhcp). The architecture of the supercomplex exhibits hybrid features of the plant-type and the green algal-type PSI supercomplexes, consisting of a PSI core, an Lhca1-Lhca4-Lhca2-Lhca3 belt attached on one side and an Lhca5-Lhca6 heterodimer associated on the other side between PsaG and PsaH.

Competition for Mitogens Regulates Spermatogenic Stem Cell Homeostasis in an Open Niche.

In many tissues, homeostasis is maintained by physical contact between stem cells and an anatomically defined niche. However, how stem cell homeostasis is achieved in environments where cells are motile and dispersed among their progeny remains unknown. Using murine spermatogenesis as a model, we find that spermatogenic stem cell density is tightly regulated by the supply of fibroblast growth factors (FGFs) from lymphatic endothelial cells.

SHISA6 Confers Resistance to Differentiation-Promoting Wnt/β-Catenin Signaling in Mouse Spermatogenic Stem Cells.

In the seminiferous tubules of mouse testes, a population of glial cell line-derived neurotrophic factor family receptor alpha 1 (GFRα1)-positive spermatogonia harbors the stem cell functionality and supports continual spermatogenesis, likely independent of asymmetric division or definitive niche control. Here, we show that activation of Wnt/β-catenin signaling promotes spermatogonial differentiation and reduces the GFRα1 cell pool. We further discovered that SHISA6 is a cell-autonomous Wnt inhibitor that is expressed in a restricted subset of GFRα1 cells and confers resistance to the Wnt/β-catenin signaling.

Different populations of Wnt-containing vesicles are individually released from polarized epithelial cells.

Accumulating evidence suggests that exosomes are heterogeneous in molecular composition and physical properties. Here we examined whether epithelial cells secrete a heterogeneous population of exosomes, and if that is the case, whether epithelial cell polarity affects release of different populations of exosomes, especially that of those carrying Wnt. Sucrose-density ultracentrifugation and molecular marker analysis revealed that different populations of exosomes or exosome-like vesicles were released from MDCK cells depending on the cell polarity.

Hierarchical differentiation competence in response to retinoic acid ensures stem cell maintenance during mouse spermatogenesis.

Stem cells ensure tissue homeostasis through the production of differentiating and self-renewing progeny. In some tissues, this is achieved by the function of a definitive stem cell niche. However, the mechanisms that operate in mouse spermatogenesis are unknown because undifferentiated spermatogonia (Aundiff) are motile and intermingle with differentiating cells in an 'open' niche environment of seminiferous tubules.

Molecular characterization of embryonic gonads by gene expression profiling in Drosophila melanogaster.

In many animal species, germ-line progenitors associate with gonadal somatic cells to form the embryonic gonads (EGs) that later develop into functional organ producing gametes. To explore the genetic regulation of the germ-line development, we initiated a comprehensive identification and functional analysis of the genes expressed within the EGs. First, we generated a cDNA library from gonads purified from Drosophila embryos by FACS.

Isolation of germline cells from Drosophila embryos by flow cytometry.

Primordial germ cells (PGC) are the earliest identifiable germ cells in the embryo. To understand the molecular basis of germline development, isolation of pure PGC is required. We report here the use of fluorescence-activated cell sorting (FACS) to isolate pure populations of Drosophila pole cells, which are the presumptive primordial germ cells in flies.