Geschlechtsbestimmung und Geschlechtsdifferenzierung

Sex determination in mammals proceeds like a cascade from the level of the sex chromosomes to the gonads, to the genital ducts, and finally to the expression of the male or female phenotype. At the level of the genital ducts male sex organs are induced by testosterone. Its action depends on an intact cytoplasmic androgen receptor protein. The testicular feminization mutation (Tfm) leads to loss of hormone binding capacity. Individuals with testes but female external phenotype develop. In the mouse the interaction of androgen insensitiveTfm cells with normal cells can be studied in mosaic individuals composed of both cell types, and in organ culture by recombination ofTfm and normal tissues. The experiments show that under the action of testosterone the normal cells express male differentiated cellular functions, whereas theTfm cells differentiate in female direction. In respect to proliferation and expression of male or female organ structures, however, both cell types communicate via local factors. Thus, instead of irregular malformations intersex organs develop.     

Participation for understanding: an interactive method

INTRODUCTION: There are many available models that help evaluate the effectiveness of safety and health measures, but many are complex and require input from many departments within an organization. There is a need to develop a more user-friendly model. METHOD: A participative model was developed that involves face-to-face interviewers with workers, maintenance department, purchasing department and health and safety experts. They were asked about costs, efforts, benefits, and effects of gauging the effects of prevention efforts. RESULTS: Cost effectiveness analyses are essential in all cases and can include whatever the end-user requires, whether it is a small or lasting improvement. Having management participate helps validate the data. CONCLUSIONS: Organizations who collaborate with someone with at least some skill in cost-benefit evaluations will find that they will be able to establish policies and procedures from the data. The end result is a calculation that is understood by all involved.     

Snake fangs from the Lower Miocene of Germany: evolutionary stability of perfect weapons

There is a general consensus that most of today’s nonvenomous snakes are descendants of venomous snakes that lost their venomous capabilities secondarily. This implies that the evolutionary history of venomous snakes and their venom apparatus should be older than the current evidence from the fossil record. We compared some of the oldest-known fossil snake fangs from the Lower Miocene of Germany with those of modern viperids and elapids and found their morphology to be indistinguishable from the modern forms. The primary function of recent elapid and viperid snake fangs is to facilitate the extremely rapid, stab-like application of highly toxic venoms. Our findings therefore indicate that the other components of the venom-delivery system of Early Miocene vipers and elapids were also highly developed, and that these snakes used their venom in the same way as their modern relatives. Thus, the fossil record supports the view that snakes used their venoms to rapidly subdue prey long before the mid-Tertiary onset of the global environmental changes that seem to have supported the successful radiation of venomous snakes.     

Sedimenttoxizit?t — ein inhaltlicher Schwerpunkt beim SETAC Europe 16th Annual Meeting World Forum Convention Center in Den Haag, Niederlangden, 7–11 Mai 2006

Tagungsankündigungen

Sedimenttoxizit?t — ein inhaltlicher Schwerpunkt beim SETAC Europe 16th Annual Meeting World Forum Convention Center in Den Haag, Niederlangden, 7–11 Mai 2006