In many animal groups, factors required for germline formation are localized in germ plasm, a region of the egg cytoplasm. In Drosophila embryos, germ plasm is located in the posterior pole region and is inherited in pole cells, the germline progenitors. Transplantation experiments have demonstrated that germ plasm contains factors that can form germline, and germ plasm also directs abdomen formation. Genetic analysis has shown that a common mechanism directs the localization of the abdomen and germline-forming factors to the posterior pole. The critical factor for abdomen formation is the nanos (nos) protein (nanos). Here we show that nos is also essential for germline formation in Drosophila; pole cells lacking nanos activity fail to migrate into the gonads, and so do not become functional germ cells. In such pole cells, gene expression, which normally initiates within the gonad, begins prematurely during pole-cell migration. Premature activation of genes in germline precursors may mean that these cells fail to develop normally. A function for nos protein in Drosophila germline formation is compatible with observations of its association with germ plasm in other animals.

Continuous, coherent subterahertz radiation arises when a dc voltage is applied across a stack of the many intrinsic Josephson junctions in a Bi2Sr2CaCu2O(8+δ) single crystal. The active junctions produce an equal number of I-V characteristic branches. Each branch radiates at a slightly tunable frequency obeying the Josephson relation. The overall output is broadly tunable and nearly independent of heating effects and internal cavity frequencies. Amplification by a surrounding external cavity to allow for the development of a useful high-power source is proposed.

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Strong, monochromatic, coherent and continuous terahertz (THz) radiation was generated from the intrinsic Josephson junctions in a cylindrical stand-alone mesa sandwich structure fabricated from a single crystal of the high-temperature superconductor Bi2Sr2CaCu2O8+δ. By varying the base temperature and the dc bias current-voltage characteristic (IVC) points, the emission frequency is tunable from 0.5 to a record high 2.4 THz observed on two inner IVC branch points. Strong emission power peaks were observed at 1.0 THz and 1.6 THz. This device is hence an excellent candidate to fill the “THz gap” between ∼1.4 and 2.0 THz.