Guni Kadmon

Expression of cell adhesion molecules in the olfactory system of the adult mouse: Presence of the embryonic form of N-CAM

The expression of the neural cell adhesion molecules N-CAM and L1 was investigated in the olfactory system of the mouse using immunocytochemical and immunochemical techniques. In the olfactory epithelium, globose basal cells and olfactory neurons were stained by the polyclonal N-CAM antibody reacting with all three components of N-CAM (N-CAM total) in their adult and embryonic states. Dark basal cells and supporting cells were not found positive for N-CAM total. The embryonic form of N-CAM (E-N-CAM) was only observed on the majority of globose basal cells, the precursor cells of olfactory neurons, and some neuronal elements, probably immature neurons, since they were localized adjacent to the basal cell layer. Differentiated neurons in the olfactory epithelium did not express E-N-CAM. In contrast to N-CAM total, the 180-kDa component of N-CAM (N-CAM180) and E-N-CAM, L1 was not detectable on cell bodies in the olfactory epithelium. L1 and N-CAM180 were strongly expressed on axons leaving the olfactory epithelium. Olfactory axons were also labeled by antibodies to N-CAM180 and L1 in the lamina propria and the nerve fiber and glomerular layers of the olfactory bulb, but only some axons showed a positive immunoreaction for E-N-CAM. Ensheathing cells in the olfactory nerve were observed to bear some labeling for N-CAM total, L1, and N-CAM180, but not E-N-CAM. In the olfactory bulb, L1 was not present on glial cells. In contrast, N-CAM180 was detectable on some glia and N-CAM total on virtually all glia. Glia in the nerve fiber layer were labeled by E-N-CAM antibody only at the external glial limiting membrane. In the glomerular layer, E-N-CAM expression was particularly pronounced at contacts between olfactory axons and target cells. The presence of E-N-CAM in the adult olfactory epithelium and bulb was confirmed by Western blot analysis. The continued presence of E-N-CAM in adulthood on neuronal precursor cells, a subpopulation of olfactory axons, glial cells at the glia limitans, and contacts between olfactory axons and their target cells indicates the retention of embryonic features in the mammalian olfactory system, which may underlie its remarkable regenerative capacity.

Expression of L1 and N-CAM cell adhesion molecules during development of the mouse olfactory system

The expression of the neural adhesion molecules L1 and N-CAM has been studied in the embryonic and early postnatal olfactory system of the mouse in order to gain insight into the function of these molecules during development of a neural structure which retains neuronal turnover capacities throughout adulthood. N-CAM was slightly expressed and L1 was not significantly expressed in the olfactory placode on Embryonic Day 9, the earliest stage tested. Rather, N-CAM was strongly expressed in the mesenchyme underlying the olfactory placode. In the developing nasal pit, L1 and N-CAM were detectable in the developing olfactory epithelium, but not in regions developing into the respiratory epithelium. At early developmental stages, expression of the so-called embryonic form of N-CAM (E-N-CAM) coincides with the expression of N-CAM, whereas at later developmental stages and in the adult it is restricted to a smaller number of sensory cell bodies and axons, suggesting that the less adhesive embryonic form is characteristic of morphogenetically dynamic neuronal structures. Moreover, E-N-CAM is highly expressed at contact sites between olfactory axons and their target cells in the glomeruli of the olfactory bulb. L1 and N-CAM 180, the component of N-CAM that accumulates at cell contacts by interaction with the cytoskeleton are detectable as early as the first axons extend toward the primordial olfactory bulb. L1 remains prominent throughout development on axonal processes, both at contacts with other axons and with ensheathing cells. Contrary to N-CAM 180 which remains detectable on differentiating sensory neuronal cell bodies, L1 is only transiently expressed on these and is no longer detectable on primary olfactory neuronal cell bodies in the adult. Furthermore, whereas throughout development L1 has a molecular form similar to that seen in other parts of the developing and adult central nervous systems, N-CAM and, in particular, N-CAM 180 retain their highly sialylated form at least partially throughout all ages studied. These observations suggest that E-N-CAM and N-CAM 180 are characteristic of developmentally active structures and L1 may not only be involved in neurite outgrowth, but also in stabilization of contacts among fasciculating axons and between axons and ensheathing cells, as it has previously been found in the developing peripheral nervous system.

RETENTION OF J1/TENASCIN AND THE POLYSIALYLATED FORM OF THE NEURAL CELL ADHESION MOLECULE (N-CAM) IN THE ADULT OLFACTORY BULB

SummaryTo gain insight into the cellular and molecular mechanisms underlying neurogenesis in adult mouse olfactory bulb, several adhesion molecules expressed by glial cells and neurons were investigated. In the germinal zone of the olfactory bulb, the subependymal layer of the rostral region of the lateral ventricles, two adhesion molecules are detectable that are characteristic of early morphogenetic events: J1/tenascin and the polysialylated form, the so-called embryonic form, of N-CAM. The polysialylated form of N-CAM is expressed by most cells in the subependymal layer, and by some astrocytes and neurons in the granular layer adjacent to the subependymal layer. This suggests that bipotential precursor cells retain expression of the embryonic form during their migration from the subependymal layer and during the first stages of differentiation into neurons and glia.Expression of the polysialylated form of N-CAM is also retained in monolayer cultures of six-day-old olfactory bulbs, 55 days after seedingin vitro. J1/tenascin was detectable in the subependymal layer using two monoclonal antibodies. The immunostaining pattern was different between the two antibodies and more restricted to the subependymal layer than when staining with polyclonal J1 antibodies was performed, indicating that J1/tenascin exists in distinct isoforms.Finally, our observations suggest that, in the adult olfactory bulb, L1 is not only a neuron-neuron adhesion molecule, but it may also be involved in neuron-glia interactions, since it is found at contact sites between these two cell types. L1, therefore, may be a neuron-glia adhesion molecule in some parts of the CNS, while it is not in others.

Evidence for Cis Interaction and Cooperative Signalling by the Heat‐stable Antigen Nectadrin (murine CD24) and the Cell Adhesion Molecule L1 in Neurons

L1 is a transmembranal hornophilic cell adhesion molecule of the immunoglobulin superfamily expressed by neural and lymphoid cells. The heat‐stable antigen (HSA, murine CD24) nectadrin is a highly and heterogeneously glycosylated glycophosphatidylinositol‐linked differentiation antigen of haematopoietic and neural cells. L1 and nectadrin have been shown to mediate cell adhesion and intracellular Ca2+ signals in neurons and B lymphoblasts, respectively. Here we show that nectadrin is co‐expressed with L1 in murine cerebellar granule cell neurons and neuroblastoma N2A cells. Purified nectadrin bound to L1 with an apparent binding ratio of five nectadrin molecules to one L1 molecule at saturation. Binding between nectadrin and purified N‐CAM was not observed. In co‐capping experiments nectadrin co‐redistributed with L1 and N‐CAM. Since in these cells N‐CAM and L1 cohere by cis binding nectadrin appears to join the L1‐N‐CAM complex through binding to L1. Antibodies to each L1 and nectadrin evoked small increases in the intracellular Ca2+ concentration. However, when both antibodies were added together or in tandem to the cells, a strong intracellular Ca2+ signal was measured that was at least 6‐ and 10‐fold stronger than the signal separately induced by L1 and nectadrin antibodies respectively. Such a cooperative effect was not observed in B lymphoblasts, using the same antibodies, or in neurons, using a combination of L1 and Thy‐1 antibodies. Both the weak Ca2+ signal mediated by L1 alone and the enhanced signal jointly triggered by antibodies to L1 and nectadrin were inhibited by phorbol 12‐myristate 13‐acetate and were not significantly affected by Ni2+ and Cd2+ cations, suggesting that they are related to one another and involve recruitment of intracellular Ca2+. Nectadrin therefore appears to join a functional complex of neuronal adhesion molecules and to potentiate the signal transduction pathway of L1, possibly in response to neuron‐neuron contact formation.

L1 makes immunological progress by expanding its relations.

The cell-adhesion molecule L1 was originally described in the nervous system. It has recently been detected in CD4+ T lymphocytes, peripheral B lymphocytes, and granulocytes in the human immune system and in similar leucocyte types in the murine immune system. L mediates neural recognition by Ca+2, Mg+2-independent homophilic binding. In the human and murine immune systems, L1 binds to the “classical” vitronectin receptor, αVβ3, and fibronectin receptor, α5β1, respectively, and abstains from homophilic binding. Homophilic L1 binding probably involves antiparallel alignment of several interactive domains. Integrin binding is mediated by a short segment of immunoglobulinlike domain 6, which includes two RGD repeats in rodent L1 and one RGD motif in human L1. L1 is modulated in activated leucocytes in vitro in parallel to L-selectin, and diverse cell types release intact L in vivo and in vitro. Released L1 can bind to laminin and adheres to the extracellular matrix of sciatic nerve, M21 melanoma, and possibly spleen and other tissues. It can support integrin-dependent cell migration and preliminary data implicate it in tumor development and transnodal lymphocyte migration.

Predictive value of the school-leaving grade and prognosis of different admission groups for academic performance and continuity in the medical course - a longitudinal study.

Background: The school-leaving GPA and the time since completion of secondary education are the major criteria for admission to German medical schools. However, the predictive value of the school-leaving grade and the admission delay have not been thoroughly examined since the amendment of the Medical Licensing Regulations and the introduction of reformed curricula in 2002. Detailed information on the prognosis of the different admission groups is also missing. Aim: To examine the predictive values of the school-leaving grade and the age at enrolment for academic performance and continuity throughout the reformed medical course. Methods: The study includes the central admission groups “GPA-best” and “delayed admission” as well as the primary and secondary local admission groups of three consecutive cohorts. The relationship between the criteria academic performance and continuity and the predictors school-leaving GPA, enrolment age, and admission group affiliation were examined up to the beginning of the final clerkship year. Results: The academic performance and the prolongation of the pre-clinical part of undergraduate training were significantly related to the school-leaving GPA. Conversely, the dropout rate was related to age at enrolment. The students of the GPA-best group and the primary local admission group performed best and had the lowest dropout rates. The students of the delayed admission group and secondary local admission group performed significantly worse. More than 20% of these students dropped out within the pre-clinical course, half of them due to poor academic performance. However, the academic performance of all of the admission groups was highly variable and only about 35% of the students of each group reached the final clerkship year within the regular time. Discussion: The school-leaving grade and age appear to have different prognostic implications for academic performance and continuity. Both factors have consequences for the delayed admission group. The academic prognosis of the secondary local admission group is as problematic as that of the delayed admission group. Additional admission instruments would be necessary, in order to recognise potentially able applicants independently of their school-leaving grade and to avoid the secondary admission procedure.