Indirect Effects of Ploidy Suggest X Chromosome Dose, Not the X:A Ratio, Signals Sex in Drosophila

In the textbook view, the ratio of X chromosomes to autosome sets, X:A, is the primary signal specifying sexual fate in Drosophila. An alternative idea is that X chromosome number signals sex through the direct actions of several X-encoded signal element (XSE) proteins. In this alternative, the influence of autosome dose on X chromosome counting is largely indirect. Haploids (1X;1A), which possess the male number of X chromosomes but the female X:A of 1.0, and triploid intersexes (XX;AAA), which possess a female dose of two X chromosomes and the ambiguous X:A ratio of 0.67, represent critical tests of these hypotheses. To directly address the effects of ploidy in primary sex determination, we compared the responses of the signal target, the female-specific SxlPe promoter of the switch gene Sex-lethal, in haploid, diploid, and triploid embryos. We found that haploids activate SxlPe because an extra precellular nuclear division elevates total X chromosome numbers and XSE levels beyond those in diploid males. Conversely, triploid embryos cellularize one cycle earlier than diploids, causing premature cessation of SxlPe expression. This prevents XX;AAA embryos from fully engaging the autoregulatory mechanism that maintains subsequent Sxl expression, causing them to develop as sexual mosaics. We conclude that the X:A ratio predicts sexual fate, but does not actively specify it. Instead, the instructive X chromosome signal is more appropriately seen as collective XSE dose in the early embryo. Our findings reiterate that correlations between X:A ratios and cell fates in other organisms need not implicate the value of the ratio as an active signal

Promotion of breast-feeding, health, and growth among hospital-born neonates, and among infants of a rural area of Costa Rica

capítulo de libro -- Universidad de Costa Rica. Instituto de investigaciones en Salud, 1983. Publicado en Diarrhea and Malnutrition. Interactions, Mechanisms and Interventions. L.C. Chen & N.S. Scrimshaw, editors. Plenum Press, N.Y. pp. 177-202, 1983.decline in the incidence of breast-feeding in many developing nations \--as been recorded in recent years, often in conjunction with (a) rapid changes in way of life, (b) migration from rural to urban,- centers, (c) incorporation of women into the labor force (especially in industry), and (d) increase in stress, anxiety, and violence in transitional and modern societies. The marked decline in incidence and duration of breast-feeding throughout the world is a matter of international concern. The importance of breast-feeding, particularly in developing societies, stems from its health-promoting effect, as it provides the best food known for infants, protects the child against a variety of debilitating infectious processes, and encourages attachment between mother and infant.' Furthermore, successful breast-feeding indirectly reduces the ills of bottle- feeding, especially in developing nations, as epidemiological observation in many countries has revealed that early weaning is often associated with severe infant malnutrition, neglect, child abuse, abandonment, and premature deathUniversidad de Costa Rica.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias de la Salud::Instituto de Investigaciones en Salud (INISA

Vitamin E Compared with Other Potential Risk Factor Concentrations in Patients with and without Coronary Artery Disease: A Case-Matched Study

Peer Reviewe

Daughter of Vilna: The Life in Song of Masha Roskies

Presents the life of Masha Roskies as described in an address given by her children at the National Yiddish Book Center in Amherst, Massachusetts, on April 5, 1998. Focuses on the Yiddish songs she learned as a child and young woman in Vilnius, Lithuania