Pluripotency of spermatogonial stem cells from adult mouse testis

Embryonic germ cells as well as germline stem cells from neonatal mouse testis are pluripotent and have differentiation potential similar to embryonic stem cells, suggesting that the germline lineage may retain the ability to generate pluripotent cells. However, until now there has been no evidence for the pluripotency and plasticity of adult spermatogonial stem cells (SSCs), which are responsible for maintaining spermatogenesis throughout life in the male. Here we show the isolation of SSCs from adult mouse testis using genetic selection, with a success rate of 27%. These isolated SSCs respond to culture conditions and acquire embryonic stem cell properties. We name these cells multipotent adult germline stem cells (maGSCs). They are able to spontaneously differentiate into derivatives of the three embryonic germ layers in vitro and generate teratomas in immunodeficient mice. When injected into an early blastocyst, SSCs contribute to the development of various organs and show germline transmission. Thus, the capacity to form multipotent cells persists in adult mouse testis. Establishment of human maGSCs from testicular biopsies may allow individual cell-based therapy without the ethical and immunological problems associated with human embryonic stem cells. Furthermore, these cells may provide new opportunities to study genetic diseases in various cell lineages.     

The voltage-sensitive sodium channel is a bell-shaped molecule with several cavities

Voltage-sensitive membrane channels, the sodium channel, the potassium channel and the calcium channel operate together to amplify, transmit and generate electric pulses in higher forms of life. Sodium and calcium channels are involved in cell excitation, neuronal transmission, muscle contraction and many functions that relate directly to human diseases. Sodium channels--glycosylated proteins with a relative molecular mass of about 300,000 (ref. 5)--are responsible for signal transduction and amplification, and are chief targets of anaesthetic drugs and neurotoxins. Here we present the three-dimensional structure of the voltage-sensitive sodium channel from the eel Electrophorus electricus. The 19 A structure was determined by helium-cooled cryo-electron microscopy and single-particle image analysis of the solubilized sodium channel. The channel has a bell-shaped outer surface of 135 A in height and 100 A in side length at the square-shaped bottom, and a spherical top with a diameter of 65 A. Several inner cavities are connected to four small holes and eight orifices close to the extracellular and cytoplasmic membrane surfaces. Homologous voltage-sensitive calcium and tetrameric potassium channels, which regulate secretory processes and the membrane potential, may possess a related structure.     

Interocular rivalry revealed in the human cortical blind-spot representation

To understand conscious vision, scientists must elucidate how the brain selects specific visual signals for awareness. When different monocular patterns are presented to the two eyes, they rival for conscious expression such that only one monocular image is perceived at a time. Controversy surrounds whether this binocular rivalry reflects neural competition among pattern representations or monocular channels. Here we show that rivalry arises from interocular competition, using functional magnetic resonance imaging of activity in a monocular region of primary visual cortex corresponding to the blind spot. This cortical region greatly prefers stimulation of the ipsilateral eye to that of the blind-spot eye. Subjects reported their dominant percept while viewing rivalrous orthogonal gratings in the visual location corresponding to the blind spot and its surround. As predicted by interocular rivalry, the monocular blind-spot representation was activated when the ipsilateral grating became perceptually dominant and suppressed when the blind-spot grating became dominant. These responses were as large as those observed during actual alternations between the gratings, indicating that rivalry may be fully resolved in monocular visual cortex. Our findings provide the first physiological evidence, to our knowledge, that interocular competition mediates binocular rivalry, and indicate that V1 may be important in the selection and expression of conscious visual information.     

Reappearance of HCG-receptors in immature rat ovary after HCG-treatment is not due to receptor synthesis

Summary In 24-day-old rats the reappearance of ovarian HCG-receptors after the injection of 200 IU HCG is independent of protein synthesis. The reutilization of occupied receptors in immature female rats is due to dissociation of the receptor-hormone complex.This work was supported in part by the Deutsche Forschungsgemeinschaft (SFB 46). Purified HCG was a gift of Schering AG, Berlin West. We thank Mrs Margarete Lindig and Mrs Rita Rudolph for assistance and Mr A. Schlegel for radioimmunological determinations.