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Keywords:

  • EM algorithm;
  • multimodality;
  • stereology;
  • unit granule;
  • Wicksell corpuscle problem

ABSTRACT

The size distribution of vesicles exocytosed from secretory cells displays quantal nature, vesicle volume is periodic multi-modal, suggesting that these heterogeneous vesicles are aggregate sums of a variable number of homogeneous basic granules. Whether heterogeneity is a lumping-together artifact of the measurement or an inherent intra-cell feature of the vesicles is an unresolved question. Recent empirical evidence will be provided for the quantal nature of intra-cell vesicle volume, supporting the controversial paradigm of homotypic fusion: basic cytoplasmic granules fuse with each other to create heterogeneously sized vesicles. An EM-algorithm-based method is presented for the conversion of multi-modal to quantal data that provides as by-product estimates of means and variances of basic granule packaging. Microsc. Res. Tech. 77:1–10, 2014. © 2013 Wiley Periodicals, Inc.