| Summary: | 碩士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 103 === Epithelial cells are linked by cell-cell junctions that hold the tissue together, and function as a protective barrier. In the nematode Caenorhabditis elegans, epidermal seam cells are arranged in longitudinal rows on the left and right sides of the body and are embedded in the cylindrical hyp7 syncytium. Seam cells and hyp7 are connected by adhesion junctions along their apical borders. These cell junctions are essential for cell polarity, adhesion and innate immunity. In the 4th larval (L4) stage, seam cells become terminally differentiated and are fused to make one syncytium of 16 cells on each side. Using AJM-1::GFP and HMR-1::GFP fusion proteins that mark the apical adhesion junction, I observed two almost parallel lines that run along the seam syncytium boundary on each side of the body in the wild-type adult animals. However, in mutants defective in blmp-1, which encodes a zinc finger transcription factor similar to mammalian transcriptional repressor BLIMP-1(B lymphocyte-induced maturation protein 1), the apical epithelial junctions showed a bubble-like arrangement in seam cells in adult. By performing the time-course analysis of the AJM-1::GFP pattern in hypodermis, I found that, in the blmp-1 mutant, seam cell fusion and the adhesion junction arrangement is normal in L4, but the border between seam cell and hyp7 became irregular and the opposite sides of the border started became attached at multiple points during the L4/adult molt. The epidermal basolateral region marker LET-413::GFP showed no detectable abnormality in the basal region of the seam syncytium. In addition, inactivation of blmp-1 by RNA interference in either seam or hyp7 resulted in bubble-like apical epithelial junctions, showing that blmp-1 is essential in both seam and hyp7 to maintain the normal apical surface of the seam syncitium. Since BLMP-1 can function as a transcriptional repressor, this seam cell apical surface defect may be caused by abnormally high expression of some target genes. Using candidate genes approach and a function test, I found that bus-8 RNAi significantly reduced the percentage of blmp-1 mutants with the abnormal apical seam cell shape. BUS-8 is predicted as a mannosyltransferases involved in protein glycosylation, such as bus-2, bus-4, bus-12, partially rescued the apical seam cell shape defect of the blmp-1 mutant. On the basis of these data, I proposed that loss of blmp-1 caused the abnormality of apical seam cell shape due to abnormal protein glycosylation by BUS-8, in particular, and BUS-2, BUS-4 and BUS-12, in part, in seam and/ or hyp7 cells and that proper glycosylation of extracellular proteins or membrane proteins is important for the maintenance of the apical epithelial cell shape.
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