Investigation of tissue-specific expression and functions of MLF1-IP during development and in the immune system

Myeloid leukemia factor 1-interacting protein (MLF1-IP) has been found to exert functions in mitosis, although studies have been conducted only in cell lines up to now. To understand its roles during ontogeny and immunity, we analyzed its mRNA expression pattern by in situ hybridization and generated MLF1-IP gene knockout (KO) mice. MLF1-IP was expressed at elevated levels in most rudimentary tissues during the mid-gestation stage, between embryonic day 9.5 (e9.5) and e15.5. It declined afterwards in these tissues, but was very high in the testes and ovaries in adulthood. At post-natal day 10 (p10), the retina and cerebellum still expressed moderate MLF1-IP levels, although these tissues do not contain fast-proliferating cells at this stage. MLF1-IP expression in lymphoid organs, such as the thymus, lymph nodes, spleen and bone marrow, was high between e15.5 and p10, and decreased in adulthood. MLF1-IP KO embryos failed to develop beyond e6.5. On the other hand, MLF1-IP^+/− mice were alive and fertile, with no obvious anomalies. Lymphoid organ size, weight, cellularity and cell sub-populations in MLF1-IP^+/− mice were in the normal range. The functions of MLF1-IP^+/− T cells and naïve CD4 cells, in terms of TCR-stimulated proliferation and Th1, Th17 and Treg cell differentiation in vitro, were comparable to those of wild type T cells. Our study demonstrates that MLF1-IP performs unique functions during mouse embryonic development, particularly around e6.5, when there was degeneration of epiblasts. However, the cells could proliferate dozens of rounds without MLF1-IP. MLF1-IP expression at about 50% of its normal level is sufficient to sustain mice life and the development of their immune system without apparent abnormalities. Our results also raise an intriguing question that MLF1-IP might have additional functions unrelated to cell proliferation.

Impaired synaptic plasticity and cAMP response element-binding protein activation in Ca2+/calmodulin-dependent protein kinase type IV/Gr-deficient mice

The Ca(2+)/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is a key effector of neuronal Ca(2+) signaling; its function was analyzed by targeted gene disruption in mice. CaMKIV/Gr-deficient mice exhibited impaired neuronal cAMP-responsive element binding protein (CREB) phosphorylation and Ca(2+)/CREB-dependent gene expression. They were also deficient in two forms of synaptic plasticity: long-term potentiation (LTP) in hippocampal CA1 neurons and a late phase of long-term depression in cerebellar Purkinje neurons. However, despite impaired LTP and CREB activation, CaMKIV/Gr-deficient mice exhibited no obvious deficits in spatial learning and memory. These results support an important role for CaMKIV/Gr in Ca(2+)-regulated neuronal gene transcription and synaptic plasticity and suggest that the contribution of other signaling pathways may spare spatial memory of CaMKIV/Gr-deficient mice.

Characterization of a 23-kDa protein associated with CD40

CD40 is a 45-kDa glycoprotein member of the tumor necrosis factor receptor (TNFR) family expressed on B cells, thymic epithelial cells, dendritic cells, and some carcinoma cells. The unique capacity of CD40 to trigger immunoglobulin isotype switching is dependent on the activation of protein-tyrosine kinases, yet CD40 possesses no kinase domain and no known consensus sequences for binding to protein-tyrosine kinases. Recently, an intracellular protein (CD40bp/LAP-1/CRAF-1) which belongs to the family of TNFR-associated proteins was reported to associate with CD40. We describe a 23-kDa cell surface protein (p23) which is specifically associated with CD40 on B cells and on urinary bladder transitional carcinoma cells. Protein microsequencing revealed that p23 shows no homology to any known protein. A rabbit antibody raised against a peptide derived from p23 recognized a 23-kDa protein in CD40 immunoprecipitates. In contrast to CD40bp/LAP-1/CRAF-1, p23 was not associated with TNFR p80 (CD120b). These findings suggest that p23 is a novel member of the CD40 receptor complex.

Opioid peptides in pituitary gland, brain regions and peripheral tissues of spontaneously hypertensive and Wistar-Kyoto normotensive rats

The concentrations of beta-endorphin (beta-END), dynorphin (DYN) and methionine-enkephalin (MEK) in pituitary, brain regions, heart, kidney and adrenal of 8 week old male spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) normotensive rats were determined by radioimmunoassay and compared. The brain regions examined were hypothalamus, striatum, pons + medulla, midbrain and cortex. The concentration of beta-END in pituitary of SHR rats was 49% higher than those of WKY rats. The concentration of beta-END in the striatum of SHR rats was 71% lower as compared to WKY rats. The concentration of beta-END in the heart, adrenals and kidney of SHR rats was significantly lower (92, 48 and 57%, respectively), than those of WKY rat tissues. The concentration of DYN in pituitary, striatum and heart were lower by 38, 55 and 46%, respectively, in SHR compared to WKY rats, but in hypothalamus it was greater (33%) than in WKY rats. The concentration of DYN in other brain areas and in kidney and adrenal did not differ. The tissues of SHR and WKY rats which showed significant difference in the concentration of MEK were pituitary, pons + medulla, cerebral cortex and adrenals. The concentration of MEK was greater in SHR rats with pons + medulla, cortex and adrenals showing 33, 40, 268% higher levels, respectively, over the WKY rat tissues. However, the concentration of MEK in pituitary of SHR rats was 40% lower than that of WKY rats. These studies suggest that the endogenous opioid peptides of both central and peripheral tissues may be important in the regulation of blood pressure in SHR rats.