Reproductive strategy of a small endemic cyprinid, the Yarqon bleak (Acanthobrama telavivensis), in a mediterranean-type stream

A mediterranean-type climate exists in five widely separated regions; the Mediterranean basin, parts of western North America, parts of western and southern Australia, southwestern South Africa and parts of central Chile. Streams in these regions feature seasonal disturbances of contrasting hydrology with high predictability of the timing of flooding and drying but low constancy. We would expect fish living in these streams to avoid scouring flow and breed after cessation of the flood period. The aim of the present study was to examine the adaptation of the Yarqon bleak, Acanthobrama telavivensis, an endemic cyprinid in the coastal streams of Israel, to mediterranean-type stream (mediterranean—written with a small m, is used in connection with climate or ecological region and is distinguished from Mediterranean that is used in a geographical context, referring to the Mediterranean basin.) conditions. For that we studied its reproductive strategy (age at maturity and life span, gonad activity, oocyte maturation, spawning activity and habitats, appearance of juveniles), in a major costal stream (Yarqon). Our findings show that the Yarqon bleak exhibits life history traits attuned with a mediterranean-climate hydrologic regime. It breeds in late winter and early spring, a window of opportunity between flash floods and habitat desiccation. Being a multiple spawner allows the fish to compensate for the potential loss of part of its reproductive output due to scouring flows of late floods. The ability of the Yarqon bleak to spawn on different substrate-types enables it to take advantage of different stream conditions that pertain in different years. The fish attains pre-adult size (ca. 33–42 mm) within the first year, prior to drying out of most stream reaches, and matures by the beginning of the second year (males >41; females >42 mm). The cost of these tactics is a short life span (4–5 age groups). The reproductive strategy of the Yarqon bleak falls into the category of in-channel breeding but, unlike the case suggested by a low flow recruitment model, the fish breed during the period of flood cessation, a transitional time between high and low flows, rather than at the time of low flow. Breeding at this time of the year in mediterranean-type streams puts early stages somewhat at risk of being washed away by late floods, but gains them a longer period of growth under favorable conditions. We suggest an additional positive tradeoff that should be investigated: the reduced competition with age 0 of other fish that breed later in the season. This suggested model of recruitment during the period of flood cessation seems appropriate for fish in streams with seasonal contrasting flows of high predictability but low constancy.     

Conjugation to Nedd8 instigates ubiquitylation and down-regulation of activated receptor tyrosine kinases

When appended to the epidermal growth factor receptor (EGFR), ubiquitin serves as a sorting signal for lysosomal degradation. Here we demonstrate that the ubiquitin ligase of EGFR, namely c-Cbl, also mediates receptor modification with the ubiquitin-like molecule Nedd8. EGF stimulates receptor neddylation, which enhances subsequent ubiquitylation, as well as sorting of EGFR for degradation. Multiple lysine residues, located within the tyrosine kinase domain of EGFR, serve as attachment sites for Nedd8. A set of clathrin coat-associated binders of ubiquitin also bind Nedd8, but they undergo ubiquitylation, not neddylation. We discuss the emerging versatility of the concerted action of ubiquitylation and neddylation in the process that desensitizes growth factor-activated receptor tyrosine kinases.     

A molecular dynamics study of the effect of Ca2+ removal on calmodulin structure

Calmodulin is a small (148 residues), ubiquitous, highly-conserved Ca(2+) binding protein serving as a modulator of many calcium-dependent processes. In this study, we followed, by means of molecular dynamics, the structural stability of the protein when one of its four bound Ca(2+) ions is removed, and compared it to a simulation of the fully Ca(2+) bound protein. We found that the removal of a single Ca(2+) ion from the N-lobe of the protein, which has a lower affinity for the ion, is sufficient to initiate a considerable structural rearrangement. Although the overall structure of the fully 4 Ca(2+) bound protein remained intact in the extended conformation, the Ca(2+)-removed protein changed its conformation into a compact state. The observation that the 3 Ca(2+) loaded protein assumes a compacted solution state is in accord with experimental observation that the NSCP protein, which binds only three Ca(2+) ions, is natively in a compact state. Examination of the folding dynamics reveals a cooperation between the C-lobe, N-lobe, and the interdomain helix that enable the conformation change. The forces driving this conformational change are discussed.     

Reduced fertility of female mice lacking CD81

In somatic cells, the tetraspanins CD81 and CD9 associate with each other, with additional tetraspanins and with non-tetraspanin molecules to form proteolipidic complexes. Here we show that CD81 is expressed on the surface of oocytes where it associates with tetraspanin-enriched membrane structures. A major CD9 and CD81 partner, CD9P-1, is also expressed by oocytes. Deletion of CD81 gene in mice results in a 40% reduction of female fertility. In vitro insemination indicated that this infertility is due to a deficiency of oocytes to fuse with sperm. While the fertility of CD9-/- mice is severely but not completely impaired, double knock-out CD9-/- CD81-/- mice were completely infertile indicating that CD9 and CD81 play complementary roles in sperm-egg fusion. Finally, a fraction of CD9 was transferred from CD81-/- oocytes to sperm present in the perivitelline space indicating that the defect of fusion of CD81-/- oocytes does not result from an impaired initial gamete interaction.     

Dissociation of the complex between CD151 and laminin-binding integrins permits migration of epithelial cells

Laminin-binding integrins form a complex with CD151, a member of the tetraspanin family suggested to be involved in the regulation of cell migration. In the epidermis, CD151 is localized with alpha3beta1 and alpha6beta4 integrins at cell-cell and cell-matrix contacts, respectively, characteristic structures of non-migrating cells. Taking advantage of a monoclonal antibody against CD151, TS151r, which epitope overlaps with the tetraspanin integrin-binding site, we have investigated the role of CD151 in epithelial cell migration. Under standard culture conditions, the migratory capacity of epithelial HaCaT cells on laminins is low, apparently due to endogenous laminin 5. However, challenging HaCaT cells with TS151r allows a re-arrangement of the actin cytoskeleton, dismantling of cell-cell and beta4 integrin-mediated cell-matrix contacts and cell migration. In vivo, free CD151 is absent in resting epithelial cells of interfollicular epidermis, and all CD151 is bound to integrins in intercellular and cell-matrix contacts. By contrast, free CD151 is present at intercellular contacts in the epithelial sheet lining the deeper region of anagen hair follicles, which is considered to contain migrating cells. Together, these results strongly suggest that dissociation of the CD151-integrin complex permits remodeling of epithelial cell interactions with the extracellular matrix and cell migration.     

The P1812A and P25T BRCA1 and the 5164del4 BRCA2 mutations: occurrence in high-risk non-Ashkenazi Jews

Founder mutations in the BRCA1 and BRCA2 genes have been discovered in the Ashkenazic Jewish population, but a founder mutation(s) has not been discovered among non-Ashkenazi Jews (NAJ). Two BRCA1 mutations (P1812A, P25T), and a BRCA2 mutation (5164del4) have been detected in NAJ high-risk families. We studied the prevalence of these three mutations in 270 high-risk NAJ families, including 85 from Iraq/Iran, 67 from North Africa, 27 from Yemen, 50 from the Balkan region, and 41 with mixed ancestry. The three mutations were detected only in individuals related to the original families. We conclude that the P1812A and P25T BRCA1 and 5164del4 BRCA2 mutations are not likely to be founder mutations in NAJ high-risk families. We also assessed the pathogenicity of the BRCA1 P1812A mutation in vitro using reporter gene assays in yeast and mammalian cells. We found that the BRCA1 P1812A variant activity assays yielded a slightly reduced reporter gene activity. Thus, there is some uncertainty as to the pathogenicity of BRCA1 P1812A.     

TspanC8 tetraspanins regulate ADAM10/Kuzbanian trafficking and promote Notch activation in flies and mammals

The metalloprotease ADAM10/Kuzbanian catalyzes the ligand-dependent ectodomain shedding of Notch receptors and activates Notch. Here, we show that the human tetraspanins of the evolutionary conserved TspanC8 subfamily (Tspan5, Tspan10, Tspan14, Tspan15, Tspan17, and Tspan33) directly interact with ADAM10, regulate its exit from the endoplasmic reticulum, and that four of them regulate ADAM10 surface expression levels. In an independent RNAi screen in Drosophila, two TspanC8 genes were identified as Notch regulators. Functional analysis of the three Drosophila TspanC8 genes (Tsp3A, Tsp86D, and Tsp26D) indicated that these genes act redundantly to promote Notch signaling. During oogenesis, TspanC8 genes were up-regulated in border cells and regulated Kuzbanian distribution, Notch activity, and cell migration. Furthermore, the human TspanC8 tetraspanins Tspan5 and Tspan14 positively regulated ligand-induced ADAM10-dependent Notch1 signaling. We conclude that TspanC8 tetraspanins have a conserved function in the regulation of ADAM10 trafficking and activity, thereby positively regulating Notch receptor activation.     

Glucocorticoid alternative effects on proliferating and differentiated mammary epithelium are associated to opposite regulation of cell-cycle inhibitor expression

Glucocorticoids influence post-natal mammary gland development by sequentially controlling cell proliferation, differentiation, and apoptosis. In the mammary gland, it has been demonstrated that glucocorticoid treatment inhibits epithelial apoptosis in post-lactating glands. In this study, our first goal was to identify new glucocorticoid target genes that could be involved in generating this effect. Expression profiling, by microarray analysis, revealed that expression of several cell-cycle control genes was altered by dexamethasone (DEX) treatment after lactation. Importantly, it was determined that not only the exogenous synthetic hormone, but also the endogenous glucocorticoids regulated the expression of these genes. Particularly, we found that the expression of cell cycle inhibitors p21CIP1, p18INK4c, and Atm was differentially regulated by glucocorticoids through the successive stages of mammary gland development. In undifferentiated cells, DEX treatment induced their expression and reduced cell proliferation, while in differentiated cells this hormone repressed expression of those cell cycle inhibitors and promoted survival. Therefore, differentiation status determined the effect of glucocorticoids on mammary cell fate. Particularly, we have determined that p21CIP1 inhibition would mediate the activity of these hormones in differentiated mammary cells because over-expression of this protein blocked DEX-induced apoptosis protection. Together, our data suggest that the multiple roles played by glucocorticoids in mammary gland development and function might be at least partially due to the alternative roles that these hormones play on the expression of cell cycle regulators.