Curvature-Driven Migration of Colloids on Tense Lipid Bilayers

Inspired by proteins that generate membrane curvature, sense the underlying membrane geometry, and migrate driven by curvature gradients, we explore the question: Can colloids, adhered to lipid bilayers, also sense and respond to membrane geometry? We report the migration of Janus microparticles adhered to giant unilamellar vesicles elongated to present spatially varying curvatures. In our experiments, colloids migrate only when the membranes are tense, suggesting that they migrate to minimize membrane area. By determining the energy dissipated along a trajectory, the energy field is inferred to depend on the local deviatoric curvature, like curvature driven capillary migration on interfaces between immiscible fluids. In this latter system, energy gradients are larger, so colloids move deterministically, whereas the paths traced by colloids on vesicles have significant fluctuations. By addressing the role of Brownian motion, we show that the observed migration is analogous to curvature driven capillary migration, with membrane tension playing the role of interfacial tension. Since this motion is mediated by membrane shape, it can be turned on and off by dynamically deforming the vesicle. While particle-particle interactions on lipid membranes have been considered in many contributions, we report here an exciting and previously unexplored modality to actively direct the migration of colloids to desired locations on lipid bilayers.

On the magnetic properties of iron nanostructures fabricated via focused electron beam induced deposition and autocatalytic growth processes

We employ Electron beam induced deposition (EBID) in combination with autocatalytic growth (AG) processes to fabricate magnetic nanostructures with controllable shapes and thicknesses. Following this route, different Fe deposits were prepared on silicon nitride membranes under ultra-high vacuum conditions and studied by scanning electron microscopy (SEM) and scanning transmission x-ray microspectroscopy (STXM). The originally deposited Fe nanostructures are composed of pure iron, especially when fabricated via autocatalytic growth processes. Quantitative near-edge x-ray absorption fine structure (NEXAFS) spectroscopy was employed to derive information on the thickness dependent composition. X-ray magnetic circular dichroism (XMCD) in STXM was used to derive the magnetic properties of the EBID prepared structures. STXM and XMCD analysis evinces the existence of a thin iron oxide layer at the deposit-vacuum interface, which is formed during exposure to ambient conditions. We were able to extract magnetic hysteresis loops for individual deposits from XMCD micrographs with varying external magnetic field. Within the investigated thickness range (2-16 nm), the magnetic coercivity, as evaluated from the width of the hysteresis loops, increases with deposit thickness and reaches a maximum value of ∼160 Oe at around 10 nm. In summary, we present a viable technique to fabricate ferromagnetic nanostructures in a controllable way and gain detailed insight into their chemical and magnetic properties.

miR-34a targets the inhibin beta B gene, promoting granulosa cell apoptosis in the porcine ovary

During ovarian follicular growth and development, only a few follicles actually ovulate. Recently, it was found that follicular atresia is triggered by granulosa cell apoptosis, but the molecular mechanism of follicular atresia was not understood. Using flow cytometry, we found that miR-34a promotes granulosa cell apoptosis in pig ovarian follicles. In addition, inhibin beta B was found to be a miR-34a target gene, based on luciferase reporter assays, quantitative RT-PCR and Western blotting. Taken together, our data indicate that miR-34a plays an important role in granulosa cell apoptosis by targeting the INHBB gene in the porcine ovary.

Immunogenicity of L(d+) transgenic mouse hearts

BACKGROUND

C57BL/6 mice transfected with the L(d) gene coupled to the alpha-myosin heavy chain promoter result in transgenic mice with L(d) antigen expressed only on cardiac tissue. These transgenic animals allow the examination of immune reactivity against cardiac L(d) by "self" or by adoptively transferred L(d) specific 2C cells, and the response of nontransgenic C57BL/6 mice to the transplanted L(d+) heart.

METHODS

Naïve cardiac L(d+) transgenic mice were examined for evidence of L(d) "autoimmunity." Forty million fresh 2C cells or 2C cells sensitized in vitro for 7 days against Balb/c (L(d+)) + interleukin-2 were also given intravenously to L(d+) transgenic mice. At 5 and 12 days after injection, heart-infiltrating lymphocytes were analyzed by fluorescence-activated cell sorter. The L(d+) transgenic hearts were also transplanted to syngeneic L(d-) nontransgenic C57BL/6 to evaluate the heart's immunogenicity.

RESULTS

Naïve L(d+) transgenic mice did not exhibit any evidence of lymphocytic infiltration on histologic examination. Adoptive transfer of either fresh or in vitro sensitized 2C cells was also unable to reject the native L(d+) heart in transgenic mice (100% of the mice survived long term [more than 60 days]). Sensitization of the L(d+) transgenic mice with a Balb/c skin graft and interleukin-2 pump infusion (7 days) beginning 1 day before 2C cell injection also did not promote rejection of the native L(d+) heart. However, fluorescence-activated cell sorter analysis did reveal that a significantly greater number of in vitro sensitized 2C cells homed to the L(d+), but not L(d-), heart after both 5 and 12 days (P <.01, P <.001). In contrast, C57BL/6 mice rejected the L(d+) (C57BL/6 background) transgenic heart in a mean survival time of 17 +/- 9.7 days (P <.01), whereas a syngeneic C57BL/6 heart transplant was accepted indefinitely. Lymphocytic infiltration consistent with rejection was present in all animals receiving an Ld+ transgenic heart transplant, whereas no infiltrate was present in those receiving a syngeneic C57BL/6 heart transplant.

CONCLUSIONS

Although the class I L(d) transgene is not recognized in its native host, its immunogenicity is shown by the homing of anti-L(d) 2C cells to the heart in situ and rejection of L(d+) heart grafts when transplanted into syngeneic C57BL/6 mice.

Intrathymic alloantigen-mediated, tolerant, completely major histocompatibility complex-mismatched mouse hearts are specifically rejected by adoptively transferred anti-class I L(d+)-specific 2C cells

BACKGROUND

Tolerance to cardiac allografts can be induced in mice and rats by the injection of donor alloantigen into the thymus in combination with a CD4 T-cell-depleting antibody. CD8(+) cells in these animals are hyporesponsive to graft-specific alloantigens. Most of the CD8(+) T cells in the transgenic 2C mouse express a T-cell receptor specific for the class I major histocompatibility complex L(d+) locus. This study was designed to determine whether the adoptive transfer of these 2C T cells could precipitate rejection of a tolerant, completely major histocompatibility complex-mismatched L(d+) or L(d-) heart.

METHODS

C57BL/6 mice (L(d-)) were given 10 x 10(6) cells of BALB/c (L(d+)) or dm2 (BALB/c background lacking L(d) [L(d-)]) splenocytes intrathymically and GK1. 5 (10 mg/kg) intraperitoneally. Twenty-one days later, BALB/c or dm2 hearts were transplanted. On the day of transplantation or after long-term allograft acceptance, recipients received naive 2C cells or 2C cells sensitized by in vitro mixed lymphocyte culture with BALB/c (L(d+)).

RESULTS

Mean survival time of BALB/c cardiac allografts in untreated C57BL/6 mice was 7.3 days, although 73% of the mice that were pretreated with BALB/c splenocytes IT plus GK1.5 accepted the donor antigen-specific heart allografts indefinitely. All recipients that were pretreated with the intrathymic plus GK1.5 and that were injected with naive 2C cells at the time of heart transplantation experienced rejection of the BALB/c (L(d+)), but not the dm2 (L(d-)) hearts. In contrast, naive 2C cells could not reject tolerant (>30 days acceptance) BALB/c (L(d+)) hearts. 2C cells sensitized in vitro against L(d) were able to reject established BALB/c hearts but could not reject the L(d-) dm2 hearts.

CONCLUSIONS

L(d)-specific 2C T-cell receptor transgenic T cells that are adoptively transferred to recipients will precipitate the rejection of accepted hearts that express class I L(d+) in mice rendered tolerant by an intrathymic injection of alloantigen plus anti-CD4 monoclonal antibodies.

Evidence for clonal deletion and clonal anergy after intrathymic antigen injection in a transplantation model

Intrathymic (IT) antigen injection has been shown to induce antigen-specific systemic tolerance in the rodent. To delineate the mechanisms responsible for the induction of tolerance, we used the 2C line of T cell receptor transgenic mice. The majority of T cells in 2C mice express an antigen receptor specific for the major histocompatibility complex class I alloantigen Ld and can be identified with the clonotypic monoclonal antibody 1B2. IT injection of lymphoid cells expressing Ld was found to induce a significant prolongation in BALB/c skin allograft survival. The allograft prolongation was associated with a marked reduction in the number of developing 1B2+ thymocytes (clonal deletion), which occurred primarily at the CD4+ CD8+ stage of thymocyte development, as well as a reduction in the number of mature CD8+ 1B2+ 2C T cells in peripheral lymphoid tissue. In addition, CD8+ 1B2+ 2C T cells that survive deletion have decreased CD8 expression levels and a significantly reduced in vitro proliferative response to specific alloantigen (clonal anergy). Exogenous recombinant interleukin 2 restores the capacity of 2C T cells to respond in vitro to alloantigen. Experiments involving separation of cells by fluorescence-activated cell sorter indicate that there is a precise correlation between the reduction in CD8 expression and anergy induction. Collectively, these data indicate that IT antigen injection can induce antigen-specific systemic tolerance by both clonal deletion and clonal anergy.

Regulated expression of a cell division control-related protein kinase during development

Protein kinases are important signaling molecules that are known constituents of cellular pathways critical for normal cellular growth and development. We have recently identified a new protein kinase, p58, which contains a large domain that is highly homologous to the cell division control p34cdc2 protein kinase. This new cell division control-related protein kinase was originally identified as a component of semipurified galactosyltransferase; thus, it has been denoted galactosyltransferase-associated protein kinase. In vitro, this protein kinase has been shown to phosphorylate a number of substrates, including histone H1, casein, and galactosyltransferase. In vivo, we have found that this protein kinase affects galactosyltransferase enzyme activity and that it is apparently involved in some aspect of normal cell cycle regulation. In this report, we find that the p58 gene is evolutionarily well conserved and expressed ubiquitously, but to varying extents, in adult tissues. In developmentally staged embryos, p58 expression was elevated early in embryogenesis and then decreased dramatically. In the murine submandibular gland, p58 expression was elevated between day 14 and day 16 post coitus. Expression in the submandibular gland appeared to parallel the proliferation and differentiation of specific cell types as judged by in situ hybridization. These studies indicate that the p58 protein kinase may have a critical function during normal embryonic development and that this protein kinase continues to be expressed in differentiated adult tissues.