Characterization of a member of the CEACAM protein family as a novel marker of proton pump-rich ionocytes on the zebrafish epidermis

In humans, several members of the CEACAM receptor family have been shown to interact with intestinal pathogens in an inflammatory context. While CEACAMs have long been thought to be only present in mammals, recent studies have identified ceacam genes in other vertebrates, including teleosts. The function of these related genes remains however largely unknown. To gain insight into the function of CEACAM proteins in fish, we undertook the study of a putative member of the family, CEACAMz1, identified in Danio rerio. Sequence analysis of the ceacamz1 gene product predicted a GPI-anchored extracellular protein containing eleven immunoglobulin domains but revealed no evident orthology with human CEACAMs. Using a combination of RT-PCR analyses and in situ hybridization experiments, as well as a fluorescent reporter line, we showed that CEACAMz1 is first expressed in discrete cells on the ventral skin of zebrafish larvae and later on in the developing gills. This distribution remains constant until juvenile stage is reached, at which point CEACAMz1 is almost exclusively expressed in gills. We further observed that at late larval stages, CEACAMz1-expressing cells mostly localize on the afferent side of the branchial filaments and possibly in the inter-lamellar space. Using immunolabelling and 3D-reconstructions, we showed that CEACAMz1 is expressed in cells from the uppermost layer of skin epidermis. These cells are embedded within the keratinocytes pavement and we unambiguously identified them as proton-pump rich ionocytes (HR cells). As the expression of ceacamz1 is turned on concomitantly to that of other known markers of HR cells, we propose that ceacamz1 may serve as a novel marker of mature HR cells from the zebrafish epidermis.

Dispora speciosa, a new addition to the genus Parallela and the first coccoid member of the family Microsporaceae

The clade that currently represents the green algal family Microsporaceae is one of the few filament-forming groups of Chlorophyceae. Molecular phylogenies show this clade containing the genus Microspora and the more recently circumscribed Parallela, whose filaments are loosely arranged and often multiseriate. We initially investigated the enigmatic bog-loving Dispora speciosa as a commonly accepted member of the mucilage-forming Radiococcaceae or a putative member of crucigenoid chlorophytes (a non-monophyletic group formerly placed in Scenedesmaceae) based on its two-dimensional colony formation. However, our plastid and nuclear ribosomal phylogenies confidently placed Dispora within the genus Parallela instead, and therefore distantly related to both Radiococcaceae and crucigenoids. Upon further examination of the cell morphology and ultrastructure, we found several corresponding features between Dispora and Parallela, despite Dispora’s apparent coccoid-colonial gross morphology. Both genera have cells with a parietal plastid positioned around a large central nucleus. The loose, multiseriate filament formation in Parallela can be interpreted as similar to Dispora’s flat colony formation in its natural state. Because we only present data from one non-type species and strain of Dispora, we cannot merge the entire genus with Parallela. We do however argue that D. speciosa, of which this strain is the sole available, morphologically and ecologically faithful representative, should be transferred into Parallela, and the specimen prepared from strain ACOI 1508 be designated as type. Our study also impacts the current view on evolution of multicellular (colonial and filamentous) forms in Chlorophyceae.

The tadpole of Ameerega boehmei in southeastern Bolivia

To date, half (16 of 32) of the species of Ameerega have had their tadpoles described: A. altamazonica, A. bassleri, A. bilinguis, A. braccata, A. cainarachi, A. flavopicta, A. hahneli, A. macero, A. parvula, A. petersi, A. picta, A. rubriventris, A shihuemoy. A. silverstonei, A. smaragdina, and A. trivittata (Lescure, 1976; Silverstone, 1976; Duellman, 1978; Myers & Daly, 1979; Rodriguez & Myers, 1993; Haddad & Martins, 1994; Lötters et al., 1997; Duellman, 2005; Costa et al., 2006; Twomey & Brown, 2008; Brown & Twomey, 2009; Poelman et al., 2010; Schulze et al., 2015). Ameerega boehmei is a putative member of a clade containing Ameerega braccata, A. flavopicta, A. berohoka, A. munduruku, all of which inhabit various parts of the ‘dry diagonal’ between the Amazon and Atlantic rainforests (Prado & Gibbs, 1993). Adult frogs in this group are morphologically similar, generally dark-bodied with yellow dorsolateral stripes, orange flash marks and some also possessing bright-yellow dorsal spots. Despite considerable research on their breeding behavior, acoustics and systematics (Lötters et al., 2009; Forti et al., 2013), the tadpole of Ameerega boehmei, the southern-most and western-most distributed species in this tentative group, has not been described.

A specialized condensin complex participates in somatic nuclear maturation in Tetrahymena thermophila

Condensins are highly conserved proteins that are important for chromosome maintenance in nearly all forms of life. Although many organisms employ two forms of the condensin complex, the condensin genes in Tetrahymena have expanded even further. Here we report a form of condensin that is specifically active during sexual reproduction. This complex, condensin D, is composed of the core condensin proteins, Smc2 and Smc4, and two unique subunits, the kleisin Cph5 and Cpd2. Cpd2 is also found in somatic nuclei in vegetative cells, but is dispensable for growth and nuclear division. Immunoprecipitation experiments show that condensin D interacts with a putative member of a chromatin-remodeling complex during development. Condensin D is required for sexual reproduction and for endoreplication and genome reduction of the progeny’s somatic nuclei. Altogether, Tetrahymena possesses at least four forms of condensin to fulfill the needs of maintaining chromosomes in two different nuclei containing the somatic and germline genomes.