Genetic identification of source and likely vector of a widespread marine invader

The identification of native sources and vectors of introduced species informs their ecological and evolutionary history and may guide policies that seek to prevent future introductions. Population genetics provides a powerful set of tools to identify origins and vectors. However, these tools can mislead when the native range is poorly sampled or few molecular markers are used. Here, we traced the introduction of the Asian seaweed Gracilaria vermiculophylla (Rhodophyta) into estuaries in coastal western North America, the eastern United States, Europe, and northwestern Africa by genotyping more than 2,500 thalli from 37 native and 53 non‐native sites at mitochondrial cox1 and 10 nuclear microsatellite loci. Overall, greater than 90% of introduced thalli had a genetic signature similar to thalli sampled from the coastline of northeastern Japan, strongly indicating this region served as the principal source of the invasion. Notably, northeastern Japan exported the vast majority of the oyster Crassostrea gigas during the 20th century. The preponderance of evidence suggests G. vermiculophylla may have been inadvertently introduced with C. gigas shipments and that northeastern Japan is a common source region for estuarine invaders. Each invaded coastline reflected a complex mix of direct introductions from Japan and secondary introductions from other invaded coastlines. The spread of G. vermiculophylla along each coastline was likely facilitated by aquaculture, fishing, and boating activities. Our ability to document a source region was enabled by a robust sampling of locations and loci that previous studies lacked and strong phylogeographic structure along native coastlines.     

Repair of DNA containing O6-alkylguanine.

O6-Alkylguanines, important DNA adducts formed by alkylating agents, can lead to mutations and to cell death unless repaired. The major pathway of repair involves the transfer of the alkyl group from the DNA to a cysteine acceptor site in the protein O6-alkylguanine-DNA alkyltransferase. The alkyltransferase brings about this transfer without need for cofactors and the DNA is restored completely by the action of a single protein, but the cysteine acceptor site is not regenerated and the number of O6-alkylguanines that can be repaired is equal to the number of active alkyltransferase molecules. The alkylated form of the protein is unstable in mammalian cells and is degraded rapidly. Cloning of the cDNAs for the alkyltransferase proteins from bacteria, yeast, and mammals indicates a significant similarity, particularly in the region surrounding the cysteine acceptor site. There is a major difference in the regulation of the alkyltransferase between mammalian cells and certain bacteria, where it is induced as part of the adaptive response to alkylating agents. Regulation of the content of alkyltransferase in mammalian cells differs with species and cell type and, in some cases, the level of the protein is increased by exposure to alkylating agents or X rays. A significant fraction of human tumor cell lines do not express the alkyltransferase gene and, thus, are much more sensitive to mutagenesis and killing by alkylating agents. The frequency of primary tumor cells that lack alkyltransferase protein is not yet clear. However, it is known that the level of alkyltransferase in tumors is a significant factor in resistance to both methylating agents and bifunctional chloroethylating agents. Inactivation of the alkyltransferase, which can be brought about by pretreatment with an alkylating agent or by exposure to O6-benzylguanine (a powerful nontoxic inhibitor), sensitizes tumor cells to these chemotherapeutic alkylating agents and may prove a useful therapeutic strategy.     

High resolution ultrasound-guided microinjection for interventional studies of early embryonic and placental development in vivo in mice

Background  

In utero microinjection has proven valuable for exploring the developmental consequences of altering gene expression, and for studying cell lineage or migration during the latter half of embryonic mouse development (from embryonic day 9.5 of gestation (E9.5)). In the current study, we use ultrasound guidance to accurately target microinjections in the conceptus at E6.5–E7.5, which is prior to cardiovascular or placental dependence. This method may be useful for determining the developmental effects of targeted genetic or cellular interventions at critical stages of placentation, gastrulation, axis formation, and neural tube closure.     

Mature domestic cat oocyte does not express a cortical granule-free domain.

A premature release of cortical granules (CG), found in the cortex of unfertilized oocytes, and the resulting formation of a CG-free domain (CGFD) over the metaphase II spindle are associated with nuclear maturation in the hamster and mouse. The objectives of our study were to characterize and compare the distribution of CG in immature, in vitro-matured, and in vivo-matured domestic cat oocytes while determining if a CGFD is formed that may be useful as a marker for stage and normalcy of oocyte maturation. Immature, intrafollicular oocytes were collected from ovaries obtained from local veterinary clinics, and a portion of these oocytes were matured in vitro. In vivo-matured, metaphase II oocytes were flushed from the oviducts of gonadotropin-treated, ovariohysterectomized cats. CG were visualized by Lens culinaris agglutinin-biotin/Texas red-strepavidin fluorescence, routine transmission electron microscopy, and Lens culinaris agglutinin-biotin/gold-labeled strepavidin transmission electron microscopy. No CGFD was detected in any domestic cat oocyte. Immature, in vitro-matured, and in vivo-matured oocytes had similar, uniform distributions of CG throughout the entire cortical region as measured by fluorescence microscopy. In vivo-matured oocytes were further examined by transmission electron microscopy, which confirmed the lack of a CGFD. All oocytes contained CG having a mean diameter of 0.28 +/- 0.03 micron/granule and a mean density of 51.5 +/- 13.0 CG/100 microns of plasma membrane.(ABSTRACT TRUNCATED AT 250 WORDS)