The Drosophila Female-Specific Sex-Determination Gene, Sex-Lethal, Has Stage-, Tissue-, and Sex-Specific RNAs Suggesting Multiple Modes of Regulation

For proper sexual development of females, the Sex-lethal (Sxl) gene must be activated early in development and remain on during the rest of the life cycle. Conversely, in males, Sxl must remain functionally off through development. Here, we show that the Sxl transcription unit spans a DNA segment of greater than 20 kb and encodes at least 10 distinct, but overlapping, RNA species. These RNAs range in size from 4.4 to 1.7 kb and exhibit sex, stage, and tissue specificity. Six RNAs, three female specific and three male specific, are first detected by midembryogenesis and persist through the adult stage: Their expression reflects the on/off regulation of Sxl\u27s activity at the level of sex-specific alternate splicing. Four Sxl RNAs are found in adult females. Two of these RNAs are dependent on the presence of a functional germ line and may be relevant to Sxl\u27s role in adult germ-line development. All four are present in unfertilized eggs. Finally, three Sxl RNAs are found only transiently during very early embryogenesis; we suggest that the expression of these RNAs may reflect an early regulation of Sxl at the level of transcription and that these transcripts are involved in the initial selection of the Sxl activity state in response to the primary sex-determination signal, the X/A ratio

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure