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hormonally regulated. That a proper balance between cell death and survival-promoting proteins is critical to achieve Transgenic mice expressing high levels of the BclxL or this physiological apoptotic wave at an early stage of Bcl2 proteins in the male germinal cells show a highly testicular germinal cell differentiation is substantiated by abnormal adult spermatogenesis accompanied by the finding of a comparable syndrome in mice defective sterility. This appears to result from the prevention of in the bax gene (Knudson et al., 1995). This early an early and massive wave of apoptosis in the testis, apoptotic wave of germ cells during establishment of which occurs among germinal cells during the first spermatogenesis may be required to maintain a proper round of spermatogenesis. In contrast, sporadic cell number ratio between maturing germ cells and Sertoli apoptosis among spermatogonia, which occurs in nor-cells. An intricate relationship involving a constant modumal adult testis, is not prevented in adult transgenic lation of activity and exchange of differentiation signals mice. The physiological early apoptotic wave in the indeed exists between these two cell types (reviewed in testis is coincident, in timing and localization, with a Jegou, 1993) from the first stage of spermatogenesis, and temporary high expression of the apoptosis-promoting its perturbation may extend to the life-long process of protein Bax, which disappears at sexual maturity. mature spermatogenesis. The critical role played by the intracellular balance, probably hormonally controlled, of the BclxL and Bax proteins (Bcl2 is apparently not expressed in normal Results mouse testis) in this early apoptotic wave is shown byMale transgenic mice expressing Bcl2 or the occurrence of a comparable testicular syndrome in overexpressing BclxL in their germinal cells are mice defective in the bax gene. The apoptotic wave sterile and display marked alterations in the late appears necessary for normal mature spermatogenesis stages of spermatogenesis to develop, probably because it maintains a critical cellMice bearing a human bcl2 or a human bclx transgene number ratio between some germinal cell stages and placed under the control of the promoter of the murine Sertoli cells, whose normal functions and differentihousekeeping phosphoglycerate kinase-1 (pgk-1) gene ation involve an elaborate network of communication.were generated. One male and four female founders Keywords: apoptosis/germinal cells/spermatogenesis/ bearing a bcl2 transgene were obtained. The male (T41) transgenic was sterile and one of the females (T56) showed a lack of vaginal opening at sexual maturity. The ovaries of this founder female were, however, functional, since, when grafted onto ovariectomized normal female mice, they

Embryonic stem (ES) cells are fully pluripotent in that they can differentiate into all cell types, including gametes. We have derived 35 ES cell lines via nuclear transfer (ntES cell lines) from adult mouse somatic cells of inbred, hybrid, and mutant strains. ntES cells contributed to an extensive variety of cell types, including dopaminergic and serotonergic neurons in vitro and germ cells in vivo. Cloning by transfer of ntES cell nuclei could result in normal development of fertile adults. These studies demonstrate the full pluripotency of ntES cells.

Mammals rely heavily on olfaction to interact adequately with each other and with their environment. They make use of seven-transmembrane G-protein-coupled receptors to identify odorants and pheromones. These receptors are present on dendrites of olfactory sensory neurons located in the main olfactory or vomeronasal sensory epithelia, and pertain to the odorant, trace amine-associated receptor and vomeronasal type 1 (ref. 4) or 2 (refs 5-7) receptor superfamilies. Whether these four sensor classes represent the complete olfactory molecular repertoire used by mammals to make sense of the outside world is unknown. Here we report the expression of formyl peptide receptor-related genes by vomeronasal sensory neurons, in multiple mammalian species. Similar to the four known olfactory receptor gene classes, these genes encode seven-transmembrane proteins, and are characterized by monogenic transcription and a punctate expression pattern in the sensory neuroepithelium. In vitro expression of mouse formyl peptide receptor-like 1, 3, 4, 6 and 7 provides sensitivity to disease/inflammation-related ligands. Establishing an in situ approach that combines whole-mount vomeronasal preparations with dendritic calcium imaging in the intact neuroepithelium, we show neuronal responses to the same molecules, which therefore represent a new class of vomeronasal agonists. Taken together, these results suggest that formyl peptide receptor-like proteins have an olfactory function associated with the identification of pathogens, or of pathogenic states.

The vomeronasal system mediates pheromonal effects in mammals. We have employed gene targeting technology to introduce mutations in a putative pheromone receptor gene, VR2, in the germline of mice. By generating alleles differentially tagged with the histological markers taulacZ and tauGFP, we show that VR2 is monoallelically expressed in a given neuron. Axons of VR2-expressing neurons converge onto numerous glomeruli in the accessory olfactory bulb. The pattern of axonal projections is complex and variable. This wiring diagram is substantially different from that of the main olfactory system. The projection pattern is disrupted by deleting the coding region of VR2, but an unrelated seven-transmembrane protein, the odorant receptor M71, can partially substitute for VR2.