Highlights of January 2005 issue of Biology of Reproduction

01/03/05

The January 2005 issue of Biology of Reproduction marks the start of the co-editorship of Drs. John Eppig and Mary Ann Handel. The new editors-in-chief, along with members of their board of associate editors, will provide highlights of some of the prominent papers in each issue of the journal. Following are the January highlights of groundbreaking papers dealing with genetic modification of germline stem cells and offering new insights into the "2-cell block" of embryo development in vitro.

"Genetic selection of mouse male germline stem cells in vitro: Offspring from single stem cells." Mito Kanatsu-Shinohara, Shinya Toyokuni, and Takashi Shinohara.

Since the classic work of Brinster and colleagues demonstrating that spermatogonial stem cells could be transplanted within seminiferous tubules, where they proliferate and undergo sperm development, it has been hoped that the system could be adapted for germline modifications. This, however, entails a number of challenging technical steps such as the propagation of cultures of spermatogonial stem cells, introduction of genetic modifications, and selection of the modified stem cells. Mito Kanatsu-Shinohara and colleagues met the first challenge with a cocktail of growth factors, published previously in Biology of Reproduction (Kanatsu-Shinohara M, Ogonuki N, Inoue K, Miki H, Ogura A, Toyokuni S, Shinohara T. Long-term proliferation in culture and germline transmission of mouse male germline stem cells. Biol Reprod 2003; 69: 612-616.); they refer to the spermatogonial stem cells established in this way as germline stem cells (GS). In the January 2005 issue of Biology of Reproduction, this group reports another very significant step forward. They transfected the GS cells with a construct designed to express both enhanced green fluorescent protein (EGFP) and neo to allow drug selection of modified cells. The colonies derived from single modified and selected GS cells were expanded and then injected into seminiferous tubules of germ cell-free mutant mice. After mating, these mice produced offspring that not only expressed the introduced EGFP construct but also passed it on to their offspring and subsequent generations. This groundbreaking work sets the stage for further germline modifications that will be important for a wide range of experimental analyses. Further, this work will have profound implications if the technologies can be applied to the clinic. (The full text of this paper is available from Biology of Reproduction--Papers in Press at www.biolreprod.org/cgi/rapidpdf/biolreprod.104.035659v1.pdf)

"Similar effects of osmolarity, glucose, and phosphate on cleavage past the 2-Cell stage in mouse embryos from outbred and F1 hybrid females." Timin Hadi, Mary-Anne Hammer, Carolyn Algire, Tiffany Richards, and Jay M. Baltz.

For many years it has been a puzzle why embryos from most random-bred and inbred female mice exhibit a block at the 2-cell stage in classical embryo culture media. Because embryos of many F1 hybrids develop beyond this stage, it has been thought that the phenotype is dependent on the genotype of the female giving rise to the egg - there are "blocking" and "non-blocking" types of females. In the January 2005 issue of Biology of Reproduction, Hadi, Hammer, Algire, Richards, and Baltz revisit this issue. The recent development of media in which even blocking embryos develop to the blastocyst stage allowed them to address specific properties implicated in the 2-cell block and to test the hypothesis that the 2-cell block is not restricted to particular genotypes, but that instead there is varying susceptibility. They show that both blocked and non-blocked embryos are indeed susceptible to culture effects, with differences in the threshold of susceptibility. Increase in osmolarity or glucose/phosphate levels can cause 2-cell arrest of both blocking and non-blocking embryos, and the blocking effect of osmolarity is rescued by glycine. These results not only clear up long-standing confusion about the etiology of the 2-cell block but also highlight the important effects of culture conditions on experimental design. (The full text of this paper is available from Biology of Reproduction--Papers in Press at www.biolreprod.org/cgi/rapidpdf/biolreprod.104.033324v1.pdf).

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