Chromogranin A (CgA) may be critical for secretory granule biogenesis in sympathoadrenal cells. We found that silencing the expression of CgA reduced the number of secretory granules in normal sympathoadrenal cells (PC12), and we therefore questioned whether a discrete domain of CgA might promote the formation of a regulated secretory pathway in variant sympathoadrenal cells (A35C) devoid of such a phenotype. The secretory granule-forming activity of a series of human CgA domains labeled with a hemagglutinin epitope, green fluorescent protein, or embryonic alkaline phosphatase was assessed in A35C cells by deconvolution and electron microscopy and by secretagoguestimulated release assays. Expression of CgA in A35C cells induced the formation of vesicular organelles throughout the cytoplasm, whereas two constitutive secretory pathway markers accumulated in the Golgi complex. The lysosome-associated membrane protein LGP110 did not co-localize with CgA, consistent with non-lysosomal targeting of the granin in A35C cells. Thus, CgA-expressing A35C cells showed electron-dense granules ϳ180 -220 nm in diameter, and secretagogue-stimulated exocytosis of CgA from A35C cells suggested that expression of the granin may be sufficient to restore a regulated secretory pathway and thereby rescue the sorting of other secretory proteins. We show that the formation of vesicular structures destined for regulated exocytosis may be mediated by a determinant located within the CgA N-terminal region (CgA-(1-115), with a necessary contribution of CgA-(40 -115)), but not the C-terminal region (CgA-(233-439)) of the protein. We propose that CgA promotes the biogenesis of secretory granules by a mechanism involving a granulogenic determinant located within CgA-(40 -115) of the mature protein.The regulated secretory pathway that exists in neurons and neuroendocrine cells is characterized by the concentration and sorting of a pool of secretory proteins into specialized intracellular organelles with a typical electron-dense appearance upon transmission electron microscopy, prompting the morphologic term dense-core granules. These granules may remain in the cell for an extended period of time after their formation, until prompted for exocytotic fusion with the plasma membrane by a secretagogue characteristic for a particular cell type.The mechanism underlying the initiation and regulation of dense-core secretory granule biogenesis is poorly understood. The formation of secretory granules is believed to be initiated at the trans-Golgi network (TGN) 2 apparatus, where aggregation and condensation of secretory proteins are typically viewed as the initial step prior to granulogenesis. Thus, formation of protein aggregates may occur in the mildly acidic environment that exists in the TGN and in the presence of millimolar concentrations of bivalent cations like Ca 2ϩ . Aggregation and condensation are the underpinning processes of two basic models of sorting of proteins within the regulated secretory pathway, viz. sorting for entry and sorting by ...