Recent research（２）
Analysis of DNase II-like acid DNase (DLAD) knockout mice
Eye lens is known to degrade their own nuclei to keep the transparency. However, DNase II is not expressed in lens cells. Which DNase is responsible for degrading DNA in eye lens? We found that DLAD, homolog of DNase II, was expressed specificall in eye lens.
Analysis of DLAD knockout mice
The DLAD -/- mice develop cataracts of the nucleus lentis, and their response to light on electroretinograms is severely reduced. These results indicate that DLAD is responsible for the degradation of nuclear DNA during lens cell differentiation, and that DNA is left undigested in the lens, it caused cataracts of the nucleus lentis, blocking the light path.
The mechanisms of eliminations of the apoptotic cells by macrophages
Macrophages engulf apoptotic cells, depending on "eat me" signals exposed on the surface of apoptotic cells. To identify "eat me" signals , we screened the hamster monoclonal antibody library against mouse thioglycollate-induced peritoneal macrophages .
1) MFG-E8
We found that milk fat globule-EGF-factor 8 (MFG-E8) secreted from thioglycollate-induced peritoneal macrophages specifically bound to apoptotic cells by recognizing phosphatidylserine. The NIH3T3 cell transformants that expressed a high level of alpha(v)beta(3) integrin were found to engulf apoptotic cells when MFG-E8 was added.
2) Analysis of MFG-E8 knockout mice
Tingible body macrophages in the germinal centers of the spleen and lymph nodes strongly express MFG-E8. Many apoptotic lymphocytes were found on the MFG-E8-deficient tingible body macrophages, but they were not efficiently engulfed. The MFG-E8-deficient mice developed splenomegaly, with the formation of numerous germinal centers, and suffered from glomerulonephritis as a result of autoantibody production. These data demonstrate that MFG-E8 has a critical role in removing apoptotic B cells in the germinal centers and that its failure can lead to autoimmune diseases.
3) TIM4
Macrophages such as resident peritoneal macrophages can engulf apoptotic cells efficiently without expressing MFG-E8. We screened again by the same method as MFG-E8 to identify another "eat me" signal and found that TIM4 bound to apoptotic cells by recognizing phosphatidylserine as same as MFG-E8.
