Source of a new crop of oocytes inTilapia mossambica

Summary 1. In the teleostTilapia mossambica (Peters), new crops of oocytes arise from nests of cells of the germinal epithelium as well as from the epithelial strands ramifying into the ovocoel.2. There is no evidence to indicate that degenerating follicle cells form a source for a new crop of oocytes.3. After one spawning is over, the follicular layer of the mature unspawned ova alone undergo atresia.4. Neither immature oocytes nor oocytes in the growth stages undergo degeneration.5. The occurrence of immature, maturing, and fully ripe ova in the ovary at a particular time account for asynchronism inTilapia mossambica.

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Origine des poussées ovocytaires chezTilapia mossambica

Extrait L'ovaire deTilapia mossambica a été étudié dans le but de préciser l'origine des poussées ovocytaires. Après la ponte l'ovaire n'est pas vide pour autant, et il y subsiste des ovocytes à tous les stades du développement. Les replis de l'épithélium germinatif et les tractus épithéliaux ramifiés contiennent des flots de cellules qui produisent des ovogonies primaires, lesquelles se transforment en ovocytes et en cellules folliculaires. Il ne semble pas qu'une nouvelle poussée ovocytaire puisse se faire à partir des résidus des follicules des ovocytes atrétiques. Seuls les ovules mûrs non évacués par la ponte subissent une atrésie et se résorbent; les ovocytes immatures ou en voie de croissance ne dégénèrent pas. L'asynchronisme deT. mossambica se traduit par la présence simultanée, dans l'ovaire, d'ovocytes à tous les stades de croissance et de maturation.

     

Nuclear disintegration of target cells by killer B lymphocytes from tumor-bearing mice

Normal murine B lymphocytes are not known to be effectors of the Fc receptor-mediated, antibody-dependent cellular cytotoxicity (ADCC). In contrast, we report here that highly purified splenic B cells from mammary tumor-bearing mice develop the potential of lysing antibody-coated target cells. These lymphocytes are characterized by being G-10 nonadherent, nylon wool adherent, sIg+, FcR+, Thy 1.2-, asialo GM1-, and the immunoglobulin heavy-chain genes of both chromosomes are rearranged. The lytic reaction is characterized by a noninterdigitating binding and by the appearance of endocytotic vesicles in the target cells. Nuclear disintegration occurs 18 h after initial effector-target cell conjugate formation. At such time, only minor cytoplasmic membrane alterations are evident. The emergence of killer B cells in tumor-bearing hosts indicates that all lymphoreticular cell types bearing Fc receptors are capable of mediating ADCC.     

The nucleotide sequence of the right-hand terminal SmaI-K fragment of adenovirus type 2 DNA

The primary structure of the SmaI-K fragment of adenovirus type 2 (Ad2) DNA has been determined. This region includes one of the origins of DNA replication (Winnacker, 1978; Sussenbach and Kuijk, 1978). A leader sequence for an early mRNA in region 4 (Berk and Sharp, 1977; 1978) has also been mapped in this region. The comparison of the primary structure of this region in Ad2 DNA with the corresponding region in Ad5 DNA shows a remarkable homology which may be significant in view of the fact that Ad2 and Ad5 DNAs can interchangeably function in the in vitro replication system of Challberg and Kelly (1979).