Temporal and spatial expression of amyloid β precursor protein（APP）in Xenopus Laevis

Abstract:

Objective：Amyloid β protein（Aβ） is the central component of neuritic plaques，and also the main neuropathological marker of Alzheimer’s Disease（AD）. Aβ is derived from the amyloid β precursor protein（APP，amyloid beta precursor protein；XB-GENE-479158；NCBI：Xl.8671），the main pathogenic genes of this disease，and the temporal and partial expression patterns of APP in the embryonic period of Xeponus Laevis（X.laevis） has not been clear yet. This study was designed to examine the temporal and spatial expression pattern of APP in the embryonic period of X.laevis and its possible functions. Methods：The normal embryonic tissues from frogs（at embryonic stages 2 to 4） were collected，and the expression of APP in different stages of embryonic development was detected by the whole-mount in situ hybridization and RT-PCR. The promoter activity was measured by the dual-reporter assays，and the Western blot analysis was used to determine the protein expression. Results：Our data revealed that the APP gene mainly had two types of mRNA variants：shorter 693-694aa and longer 750-751aa protein products，and the main difference was the alternative splicing of exon 7. All the APP transcripts were maternally ex－pressed，and the shorter variant expressed predominantly，with a steadily increased expression level during the development，while the longer variant expressed weakly，but maintained a constant level during the whole embryonic stage. Results of the whole-mount in situ hybridization showed that the APP mainly expressed in hatching and cement gland at neural plate stage，and after the closure of neural tube，the transcript level of APP elevated，presenting high expression in somatic mesoderm，pronephros and dorsal neural tube. At late tail-bud stage，the APP expressed in lens，telencephalon，epiphysis，diencephalon and dorsal otic vesicle. At tadpole stage，the APP highly expressed in the digestive system，including pancreas，stomach and duodenum. Conclusion：The speci－ficity in the distribution of temporal and partial expression of APP，a maternally expressed gene，indicates the important role it plays in embryonic development，thus providing a new path to study the role of key pathogenic genes of AD in early embryogenesis.