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1. Fine structure of the retrocerebral organ in the rotifer Trichocerca similis (Monogononta)

   https://doi.org/10.1111/ivb.12396  

   Hochberg, Rick ; Araújo, Thiago Q. ; Walsh, Elizabeth J. ; Mohl, Jonathon E. ; Wallace, Robert L. ( March 2023 , Invertebrate Biology)

   The retrocerebral organ (RCO) is a complex glandular system that is widely distributed across species of phylum Rotifera (sensu stricto). This system is hypothesized to secrete mucus that aids in benthic locomotion, adhesion, and/or reproduction. Unfortunately, the ultrastructure of the RCO is mostly unknown, having only been partially examined in one species. We used transmission electron microscopy and confocal laser scanning microscopy to describe the RCO in the planktonic freshwater rotiferTrichocerca similis. Results reveal the RCO to be a singular syncytial organ composed of a posterior glandular region, an expansive reservoir, and an anterior duct. The glandular portion has an active synthetic cytoplasm with paired nuclei, abundant rER, ribosomes, Golgi, and mitochondria. Electron‐dense secretion granules accumulate at the anterior end of the gland and undergo homotypic fusion to create larger, more electron‐lucent granules with numerous mesh‐like contents that gradually fuse into tubular secretions that accumulate in the reservoir. Ultrastructure of these secretions suggests they may be hydrated glycoproteins. Cross‐striated longitudinal muscles form a partial sleeve around the reservoir and may function to squeeze the secretions through the single cytoplasmic duct that penetrates the cerebral ganglion. A review of the RCOs from other rotifers suggests that further ultrastructural analyses are required before attempting to discern their functions and homologies.

    

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2. Cellular distribution of secretory pathway markers in the haploid synergid cells of Arabidopsis thaliana

   https://doi.org/10.1111/tpj.13848  

   Jones, Daniel S. ; Liu, Xunliang ; Willoughby, Andrew C. ; Smith, Benjamin E. ; Palanivelu, Ravishankar ; Kessler, Sharon A. ( March 2018 , The Plant Journal)

   In flowering plants, cell–cell communication plays a key role in reproductive success, as both pollination and fertilization require pathways that regulate interactions between many different cell types. Some of the most critical of these interactions are those between the pollen tube (PT) and the embryo sac, which ensure the delivery of sperm cells required for double fertilization. Synergid cells function to attract thePTthrough secretion of small peptides and inPTreception via membrane‐bound proteins associated with the endomembrane system and the cell surface. While many synergid‐expressed components regulatingPTattraction and reception have been identified, few tools exist to study the localization of membrane‐bound proteins and the components of the endomembrane system in this cell type. In this study, we describe the localization and distribution of seven fluorescent markers that labelled components of the secretory pathway in synergid cells ofArabidopsis thaliana. These markers were used in co‐localization experiments to investigate the subcellular distribution of the twoPTreception componentsLORELEI, aGPI‐anchored surface protein, andNORTIA, aMILDEW RESISTANCE LOCUSO protein, both found within the endomembrane system of the synergid cell. These secretory markers are useful tools for both reproductive and cell biologists, enabling the analysis of membrane‐associated trafficking within a haploid cell actively involved in polar transport.

    

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3. Tuning of shortening speed in coleoid cephalopod muscle: no evidence for tissue‐specific muscle myosin heavy chain isoforms

   https://doi.org/10.1111/ivb.12111  

   Shaffer, Justin F. ; Kier, William M. ( January 2016 , Invertebrate Biology)

   The contractile protein myosinIIis ubiquitous in muscle. It is widely accepted that animals express tissue‐specific myosin isoforms that differ in amino acid sequence andATPase activity in order to tune muscle contractile velocities. Recent studies, however, suggested that the squidDoryteuthis pealeiimight be an exception; members of this species do not express muscle‐specific myosin isoforms, but instead alter sarcomeric ultrastructure to adjust contractile velocities. We investigated whether this alternative mechanism of tuning muscle contractile velocity is found in other coleoid cephalopods. We analyzed myosin heavy chain transcript sequences and expression profiles from muscular tissues of a cuttlefish,Sepia officinalis, and an octopus,Octopus bimaculoides, to determine if these cephalopods express tissue‐specific myosin heavy chain isoforms. We identified transcripts of four and six different myosin heavy chain isoforms inS. officinalisandO. bimaculoidesmuscular tissues, respectively. Transcripts of all isoforms were expressed in all muscular tissues studied, and thusS. officinalisandO. bimaculoidesdo not appear to express tissue‐specific muscle myosin isoforms. We also examined the sarcomeric ultrastructure in the transverse muscle fibers of the arms ofO. bimaculoidesand the arms and tentacles ofS. officinalisusing transmission electron microscopy and found that the fast contracting fibers of the prey capture tentacles ofS. officinalishave shorter thick filaments than those found in the slower transverse muscle fibers of the arms of both species. It thus appears that coleoid cephalopods, including the cuttlefish and octopus, may use ultrastructural modifications rather than tissue‐specific myosin isoforms to adjust contractile velocities.

    

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4. Morphological diversity and phylogeny of the diatom genus Entomoneis (Bacillariophyta) in marine plankton: six new species from the Adriatic Sea

   https://doi.org/10.1111/jpy.12622  

   Mejdandžić, Maja ; Bosak, Sunčica ; Nakov, Teofil ; Ruck, Elizabeth ; Orlić, Sandi ; Gligora Udovič, Marija ; Peharec Štefanić, Petra ; Špoljarić, Igor ; Mršić, Gordan ; Ljubešić, Zrinka ; et al ( March 2018 , Journal of Phycology)

   The diatom genusEntomoneisis known from the benthos and plankton of marine, brackish, and freshwaters.Entomoneisincludes diatoms with a bilobate keel elevated above the valve surface, a sigmoid canal raphe, and numerous girdle bands. Owing mostly to the scarcity of molecular data for a diverse set of species, the phylogeny ofEntomoneishas not been investigated in depth. The few previous studies that includedEntomoneiswere focused on broader questions and the available data were from a small number of either unidentifiedEntomoneisor well‐known species (e.g.,E. paludosa). Since the first description of new species combining both molecular and morphological characters (E. tenera), we have continued to cultivate and investigateEntomoneisin the plankton of the Adriatic Sea. Combined multigene phylogeny (SSU rDNAsequences,rbcL, andpsbC genes) and morphological observations (LM,SEMandTEM) revealed six newEntomoneisspecies supported by phylogenetic and morphological data:E. pusilla,E. gracilis,E. vilicicii,E. infula,E. adriatica,andE. umbratica. The most important morphological features for species delineation were cell shape, the degree and mode of torsion, valve apices, the appearance and structure of the transition between keel and valve body, the ultrastructure and the shape of the girdle bands, and the arrangement and density of perforations along the valve and valvocopulae. Our results highlight the underappreciated diversity ofEntomoneisand call for a more in‐depth morphological and molecular investigation of this genus especially in planktonic habitats.

    

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5. Purification and characterization of Arabidopsis thaliana oligosaccharyltransferase complexes from the native host: a protein super‐expression system for structural studies

   https://doi.org/10.1111/tpj.13847  

   Jeong, In Sil ; Lee, Sangmin ; Bonkhofer, Florian ; Tolley, Jordan ; Fukudome, Akihito ; Nagashima, Yukihiro ; May, Kimberly ; Rips, Stephan ; Lee, Sang Y. ; Gallois, Patrick ; et al ( March 2018 , The Plant Journal)

   The oligosaccharyltransferase (OT) complex catalyzesN‐glycosylation of nascent secretory polypeptides in the lumen of the endoplasmic reticulum. Despite their importance, little is known about the structure and function of plantOTcomplexes, mainly due to lack of efficient recombinant protein production systems suitable for studies on large plant protein complexes. Here, we purified ArabidopsisOTcomplexes using the tandem affinity‐taggedOTsubunitSTAUROSPORINE AND TEMPERATURE SENSITIVE3a (STT3a) expressed by an Arabidopsis protein super‐expression platform. Mass‐spectrometry analysis of the purified complexes identified three essentialOTsubunits,OLIGOSACCHARYLTRANSFERASE1 (OST1),HAPLESS6 (HAP6),DEFECTIVE GLYCOSYLATION1 (DGL1), and a number of ribosomal subunits. Transmission‐electron microscopy showed thatSTT3a becomes incorporated intoOT–ribosome super‐complexes formedin vivo, demonstrating that this expression/purification platform is suitable for analysis of large protein complexes. Pairwisein plantainteraction analyses of individualOTsubunits demonstrated that all subunits identified in animalOTcomplexes are conserved in Arabidopsis and physically interact withSTT3a. Genetic analysis of newly establishedOTsubunit mutants forOST1andDEFENDER AGAINST APOTOTIC DEATH(DAD) family genes revealed thatOST1 andDAD1/2 subunits are essential for the plant life cycle. However, mutations in these individual isoforms produced much milder growth/underglycosylation phenotypes than previously reported for mutations inDGL1,OST3/6andSTT3a.

    

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