Cilia and flagella are highly conserved organelles in eukaryotic cells that drive cell movement and act as cell antennae that receive and transmit signals. In addition to receiving and transducing ...external signals that activate signal cascades, cilia also secrete ciliary ectosomes that send signals to recipient cells, and thereby mediate cell-cell communication. Abnormal ciliary function leads to various ciliopathies, and the precise transport and localization of ciliary membrane proteins are essential for cilium function. This review summarizes current knowledge about the transport processes of ciliary membrane proteins after their synthesis at the endoplasmic reticulum: modification and sorting in the Golgi apparatus, transport through vesicles to the ciliary base, entrance into cilia through the diffusion barrier, and turnover by ectosome secretion. The molecular mechanisms and regulation involved in each step are also discussed. Transport of ciliary membrane proteins is a complex, precise cellular process coordinated among multiple organelles. By systematically analyzing the existing research, we identify topics that should be further investigated to promote progress in this field of research.
Cilia are microtubule-based organelles and perform motile, sensing and signaling functions. The assembly and maintenance of cilia depend on intraflagellar transport (IFT). Besides ciliary ...localization, most IFT proteins accumulate at basal bodies. However, little is known about the molecular mechanism of basal body targeting of IFT proteins. We first identified the possible basal body-targeting sequence in IFT46 by expressing IFT46 truncation constructs in an
mutant. The C-terminal sequence between residues 246-321, termed BBTS3, was sufficient to target YFP to basal bodies in the
strain. Interestingly, BBTS3 is also responsible for the ciliary targeting of IFT46. BBTS3::YFP moves bidirectionally in flagella and interacts with other IFT complex B (IFT-B) proteins. Using IFT and motor mutants, we show that the basal body localization of IFT46 depends on IFT52, but not on IFT81, IFT88, IFT122, FLA10 or DHC1b. IFT52 interacts with IFT46 through residues L285 and L286 of IFT46 and recruits it to basal bodies. Ectopic expression of the C-terminal domain of IFT52 in the nucleus resulted in accumulation of IFT46 in nuclei. These data suggest that IFT52 and IFT46 can preassemble as a complex in the cytoplasm, which is then targeted to basal bodies.
Cold environments, such as glaciers and alpine regions, constitute unique habitats for organisms living on Earth. In these harsh ecosystems, snow algae survive, florish, and even become primary ...producers for microbial communities. How the snow algae maintain physiological activity during violent ambient temperature changes remains unsolved. To explore the cold adaptation mechanisms of the unicellular snow alga
, we compared its physiological responses to a model organism from the same genus,
. When both cell types were exposed to a shift from 22°C to 4°C,
exhibited an apparent advantage in cold tolerance over
, as
had both a higher growth rate and photosynthetic efficiency. To determine the cold tolerance mechanisms of
, RNA sequencing was used to compare transcriptomes of both species after 1 h of cold treatment, mimicking temperature fluctuations in the polar region. Differential expression analysis showed that
had fewer transcriptomic changes and was more stable during rapid temperature decrease relative to
, especially for the expression of photosynthesis related genes. Additionally, we found that transcription in
was precisely regulated by the cold response network, consisting of at least 12 transcription factors and 3 RNA-binding proteins. Moreover, genes participating in nitrogen metabolism, the pentose phosphate pathway, and polysaccharide biosynthesis were upregulated, indicating that increasing resource assimilation and remodeling of metabolisms were critical for cold adaptation in
. Furthermore, we identified horizontally transferred genes differentially expressed in
, which are critical for cold adaptation in other psychrophiles. Our results reveal that
adapts rapid temperature decrease by efficiently regulating transcription of specific genes to optimize resource assimilation and metabolic pathways, providing critical insights into how snow algae survive and propagate in cold environments.
Hermansky-Pudlak syndrome (HPS) is a human autosomal recessive disorder that is characterized by oculocutaneous albinism and a deficiency of the platelet storage pool resulting from defective ...biogenesis of lysosome-related organelles (LROs). To date, 10 HPS genes have been identified, three of which belong to the octamer complex BLOC-1 (biogenesis of lysosome-related organelles complex 1). One subunit of the BLOC-1 complex, BLOS1, also participates in the BLOC-1-related complex (BORC). Due to lethality at the early embryo stage in BLOS1 knockout mice, the function of BLOS1 in the above two complexes and whether it has a novel function are unclear. Here, we generated three zebrafish mutant lines with a BLOC-1 deficiency, in which melanin and silver pigment formation was attenuated as a result of mutation of
,
, and
, suggesting that they function in the same complex. In addition, mutations of
and
caused an accumulation of clusters of lysosomal vesicles at the posterior part of the tectum, representing a BORC-specific function in zebrafish. Moreover,
is highly expressed in the swimbladder during postembryonic stages and is required for positively regulating the expression of the genes, which is known to govern surfactant production and lung development in mammals. Our study identified BLOS1 as a crucial regulator of the surfactant system. Thus, the zebrafish swimbladder might be an easy system to screen and study genetic modifiers that control surfactant production and homeostasis.
Snow in Antarctica is a vast terrestrial ecosystem and plays a key role that has likely been underestimated. Algae are the key primary producers on the coloured snow surface, and they support a ...microbial community that includes bacteria, fungi and/or invertebrates. We analysed microbial communities that co-exist in green and red snow samples from the Fildes Peninsula by Illumina sequencing, Antarctica, as well as the influence of snow physicochemical properties. We detected several species of green algae from Chlorophyta and Ochrophyta as well as fungi and cercozoans. The three red snow samples (RS1, RS2 and RS3) were represented by mixed eukaryotic microalgae from
Sanguina
,
Chloromonas
and Trebouxiophyceae. The green snow sample GS5 exhibited lake-to-snow colonisation composed of Trebouxiophyceae, Ulvophyceae and Chrysophyta representatives. The red snow RS4, predominantly by
Chlainomonas
sp. from slush layers, which presented a different microbial community from the other red snow samples, was sampled close to green snow sample GS5 near Lake Changhu. The environmental parameters were involved into descriptive differences among these coloured snow samples. The two snow algae
Chlainomonas
and
Sanguina
were firstly reported from Antarctica, which indicates distinguished snow algae colonisation that is closely connected with the melting snow at the lake ice-cover. Meanwhile, consistent with previous bacterial community profiles, Proteobacteria and Bacteroidetes were mostly represented in all the coloured snow samples
. Polaromonas
(Betaproteobacteria) was the most abundant genus, and its presence was reportedly essential for the sustained growth of snow algae.
Flavobacterium
from Bacteroidetes was the most frequently detected genera in GS5, but the Sphingobacteriia with only a few reads were an interestingly minority in GS5. The snow-algae-associated bacteria were closely related to psychrophilic strains or sequences from low-temperature environments. Many possible factors influence on the coloured snow microbial communities would require attentions, to help understand their occurrence mechanisms, their biogeographic distributions in polar regions.
Coordinated beating is crucial for the function of multiple cilia. However, the molecular mechanism is poorly understood. Here, we characterize a conserved ciliary protein CYB5D1 with a heme-binding ...domain and a cordon-bleu ubiquitin-like domain. Mutation or knockdown of
in zebrafish impaired coordinated ciliary beating in the otic vesicle and olfactory epithelium. Similarly, the two flagella of an insertional mutant of the CYB5D1 ortholog in
(
) showed an uncoordinated pattern due to a defect in the
-flagellum. Biochemical analyses revealed that CrCYB5D1 is a radial spoke stalk protein that binds heme only under oxidizing conditions. Lack of CrCYB5D1 resulted in a reductive shift in flagellar redox state and slowing down of the phototactic response. Treatment of
with oxidants restored coordinated flagellar beating. Taken together, these data suggest that CrCYB5D1 may integrate environmental and intraciliary signals and regulate the redox state of cilia, which is crucial for the coordinated beating of multiple cilia.
Intraflagellar transport (IFT) was initially identified as a transport machine with multiple protein subunits, and it is essential for the assembly, disassembly, and maintenance of cilium/flagellum, ...which serves as the nexus of extracellular-to-intracellular signal integration. To date, in addition to its well-established and indispensable roles in ciliated cells, most IFT subunits have presented more general functions of vesicular trafficking in the non-ciliated cells. Thus, this review aims to summarize the recent progress on the vesicular trafficking functions of the IFT subunits and to highlight the issues that may arise in future research.
The disassembly of cilia and flagella is linked to the cell cycle and environmental cues. We have found that ubiquitination of flageliar proteins is an integral part of flageliar disassembly. Free ...ubiquitin and the ubiquitin-conjugating enzyme CrUbc13 are detected in flagella, and several proteins are ubiquitinated in isolated flagella when exogenous ubiquitin and adenosine triphosphatase are added, suggesting that the ubiquitin conjugation system operates in flagella. Levels of ubiquitinated flageliar proteins increase during flageliar résorption, especially in intraflagellar transport (lFF) mutants, suggesting that disassembly products are labeled with ubiquitin and transported to the cell body by lFT. Substrates of the ubiquitin conjugation system include α-tubulin (but not ß-tubulin), a dynein subunit (lC2), two signaling proteins involved in the mating process, cyclic guanosine monophosphate-dependent kinase, and the cation channel polycystic kidney disease 2. Ubiquitination of flageliar proteins is enhanced early in mating, suggesting that ubiquitination also plays an active role in regulating signaling pathways in flagella.
Calcium (Ca(2+)) and redox signalling play important roles in acclimation processes from archaea to eukaryotic organisms. Herein we characterized a unique protein from Chlamydomonas reinhardtii that ...has the competence to integrate Ca(2+)- and redox-related signalling. This protein, designated as calredoxin (CRX), combines four Ca(2+)-binding EF-hands and a thioredoxin (TRX) domain. A crystal structure of CRX, at 1.6 Å resolution, revealed an unusual calmodulin-fold of the Ca(2+)-binding EF-hands, which is functionally linked via an inter-domain communication path with the enzymatically active TRX domain. CRX is chloroplast-localized and interacted with a chloroplast 2-Cys peroxiredoxin (PRX1). Ca(2+)-binding to CRX is critical for its TRX activity and for efficient binding and reduction of PRX1. Thereby, CRX represents a new class of Ca(2+)-dependent 'sensor-responder' proteins. Genetically engineered Chlamydomonas strains with strongly diminished amounts of CRX revealed altered photosynthetic electron transfer and were affected in oxidative stress response underpinning a function of CRX in stress acclimation.
DMC1 is a recombinase that is essential for meiotic synapsis. Experiments in extensive species of eukaryotes have indicated the independent role of DMC1 in repairing double strand breaks (DSBs) ...produced during meiosis I. Mutation of dmc1 in mice and human often leads to obstacles in spermatogenesis and male sterility. Here, we report on the disruption of dmc1 in male medaka (Oryzias latipes). Synapsis was disturbed in the mutant medaka testis nuclei, as observed in mice and other organisms. Unexpectedly, the mutant medaka could produce a few sperm and, although most of these had multiple tail or multiple head malformations, some of them could swim, and few of them even had insemination ability. Our transcriptome analysis showed that there was not a remarkable change in the expression of most of the genes involved in the pathways associated with the meiotic DNA repair and flagella assembly. Our results provided an indication of the accessory mechanisms that might be involved in the repair of DSBs during meiosis. In a species besides humans, we provided evidence that disorders in meiosis recombination might lead to the malformation of sperm.
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