The appearance of surface H-2 antigens on fetal and postnatal murine hepatocytes in vivo and in vitro: A comparative study of MHC control

We have collected data on the kinetics of in vivo development of H-2^b antigens in fetal and postnatal hepatocytes from days 15–89 postcoitum (pc) in C57BL/10 mice using a sensitive immunoferritin labeling method combined with electron microscopy. We compared these data with data on the kinetic development of H-2^b antigens on fetal hepatocytes cultured from days 15, 16, and 17 pc onwards. Using the same techniques, we also compared the surface concentrations of H-2 antigens on the hepatocytes of pregnant and age-matched male and virgin female mice at day 110 pc. We found that the surface concentration of H-2 antigens on fetal and postnatal hepatocytes increased with time but that the birth event was associated with an increase in H-2 antigen expression from 60–80 ferritin grains per meter (F/m) to 190 F/m followed by a decrease to 115 F/m within 72 h of birth. The concentration of antigens on postnatal hepatocytes increased gradually and reached a maximum of 640 F/m on day 41 pc. By day 89 pc, however, this level had decreased 433 F/m, which was not significantly different from that found in day 110 pc males and virgin females. In contrast to previous findings, we found that hepatocytes cultured from days 15, 16, and 17 pc exhibited a large increase in H-2 surface antigen concentration within 48 h from 60–80 F/m to 1500–2200 F/m. After day 2, the H-2 concentration decreased and by days 14–17 in culture it was not significantly different from day 110 pc male and virgin female levels (485 F/m). Lastly, we found that the H-2 concentration on hepatocytes from pregnant mice was increased significantly (725 F/m) compared with the concentration of hepatocytes from day 110 pc males or virgin females. We postulate that the control of cell-surface major histocompatibility complex antigen concentration is achieved by a combination of intra and extracellular mechanisms and we discuss how this might be of benefit to the animal in vivo.     

Oviposition mechanisms in the whitefly parasitoids Encarsia transvena and Eretmocerus mundus

The ovipositors of two whitefly parasitoids, Encarsia transvena and Eretmocerus mundus were examined using scanning and transmission electron microscopy. That of Encarsia is straight, has an apparently hard and sharply pointed upper valve, and appears well-suited to penetrating a hard substrate. That of Eretmocerus is curved, thick-walled, but has a blunt and apparently flexible tip. These features correlate well with what is known of the mode of oviposition and host feeding in the two taxa, with Encarsia and Eretmocerus ovipositing internally and externally respectively.     

A light-inducible organelle-targeting system for dynamically activating and inactivating signaling in budding yeast

Protein localization plays a central role in cell biology. Although powerful tools exist to assay the spatial and temporal dynamics of proteins in living cells, our ability to control these dynamics has been much more limited. We previously used the phytochrome B– phytochrome-interacting factor light-gated dimerization system to recruit proteins to the plasma membrane, enabling us to control the activation of intracellular signals in mammalian cells. Here we extend this approach to achieve rapid, reversible, and titratable control of protein localization for eight different organelles/positions in budding yeast. By tagging genes at the endogenous locus, we can recruit proteins to or away from their normal sites of action. This system provides a general strategy for dynamically activating or inactivating proteins of interest by controlling their localization and therefore their availability to binding partners and substrates, as we demonstrate for galactose signaling. More importantly, the temporal and spatial precision of the system make it possible to identify when and where a given protein''s activity is necessary for function, as we demonstrate for the mitotic cyclin Clb2 in nuclear fission and spindle stabilization. Our light-inducible organelle-targeting system represents a powerful approach for achieving a better understanding of complex biological systems.     

The giant cells produced by Telenomus remus (Hymenoptera: Scelionidae)

The parasitic larva of Telenomus remus is surrounded by giant cells throughout its first instar. These cells arise in the embryonic serosa of the parasite and grow in size, starting with a radius of 5nm and ending with 27nm. Young cells are round and mononuclear, whereas older ones are often polynuclear and have varied, irregular contours. Most cells are profusely vacuolated, the vacuoles being especially large in some of the older cells. Only a few of the giant cells are devoured by the first instar parasite larva, but all disappear at the end of this stage. No giant cells seem to be produced by supernumerary larvae. Once the parasite egg hatches, the host tissue disintegrates almost instantaneously.