Effect of Steel factor and leukaemia inhibitory factor on murine primordial germ cells in culture.

Despite the importance of germ cells to the survival of species, surprisingly little is known about their embryological origin, proliferation, migration and entry into mitotic arrest or meiosis. Mutations in the murine Dominant White Spotting (W) and Steel genes, which respectively encode the c-kit tyrosine kinase receptor and the c-kit ligand (or Steel factor), impair the development of primordial germ cells (PGCs) in vivo, as well as haematopoietic stem cells and neural crest-derived melanoblasts. Here we use a monoclonal antibody against c-kit tyrosine kinase receptor and recombinant Steel factor to study the c-kit receptor-ligand system in cultured PGCs. In addition, we show that leukaemia inhibitory factor (also known as differentiation inhibitory activity), a factor secreted by STO fibroblasts, can stimulate proliferation of primordial germ cells in vitro.     

Evidence for kinks in DNA folding in the nucleosome

The nucleosome subunit of chromatin consists of DNA folded around a histone core as a 1.8-turn left-handed solenoid. The crystal structure of the nucleosome core particle revealed that it has a dyad symmetry axis and that the minor helix groove faces outwards from the protein core. Richmond et al. noticed that the path traversed by the helix has severe bends at sites approximately one and four helix turns from the dyad axis. We have developed two photochemical methods to study the structure of DNA, and in particular that wrapped around the nucleosome core. One method depends on the sensitization of singlet oxygen production by an eosin analogue. We have monitored the rate at which excited state oxygen diffuses into contact with DNA base planes, and find that it attacks the nucleosome with high specificity. We have also mapped the DNA binding of the intercalating dye methylene blue, and conclude that it binds to the same sites accessible to oxygen by diffusion. On the basis of these results we suggest that the DNA in the nucleosome is bent or kinked at two sites, 1.5 helix turns from the dyad axis.     

Partial revision of the Indo-Australian braconine wasp genus Gammabracon Quicke (Hymenoptera: Braconidae) with descriptions of new species from Indonesia (Mollucas), Malaysia,Philippines and Thailand

Ten distinctive new species of the taxonomically difficult braconine wasp genus Gammabracon Quicke, 1984 are described: G. apicoluteus sp. nov. from Malaysia (Negri); G. curticornis sp. nov. from Malaysia (Negri); G. philippinensis sp. nov. from the Philippines; G. siamensis sp. nov. from Thailand; G. striatus sp. nov. from West Malaysia; G. strandorum sp. nov. from Indonesia (Java), G. subvena sp. nov. from Malaysia (Negri and Sabah); G. townesorum sp. nov. from the Philippines; G. variipennis sp. nov. from Thailand; and G. wegeneri sp. nov. from Indonesia. Myosoma forticarinata Cameron, 1902 is transferred to Gammabracon, hence Gammabracon forticarinata comb. nov. A lectotype is designated for Gammabracon erythroura (Cameron). The status of Cratobracon strandiellus (Cameron) is discussed and a new combination proposed, Shelfordia strandiellus Cameron, 1910 comb. nov. (=Bracon strandiellus Cameron). Paucity of discrete morphological variation makes separation of most of the species with orange-red mesosoma, black metasoma and conspicuous back setae currently unrealistic and it may be that there is a single widespread and morphologically variable species.

http://zoobank.org/urn:lsid:zoobank.org:pub:56B8884E-99C8-4B53-9747-D011F552312D