Gαo represses insulin secretion by reducing vesicular docking in pancreatic beta-cells.
OBJECTIVE
Pertussis toxin uncoupling-based studies have shown that Gαi and Gαo can inhibit insulin secretion in pancreatic β-cells. Yet it is unclear whether Gαi and Gαo operate through identical mechanisms and how these G-protein-mediated signals inhibit insulin secretion in vivo. Our objective is to examine whether/how Gαo regulates islet development and insulin secretion in β-cells.


METHODS
Immunoassays were used to analyze the Gαo expression in mouse pancreatic cells. Gαo was specifically inactivated in pancreatic progenitor cells by pancreatic cell-specific gene deletion. Hormone expression and insulin secretion in response to different stimuli were assayed in vivo and in vitro. Electron microscope and total internal reflection fluorescence-based assays were used to evaluate how Gαo regulates insulin vesicle docking and secretion in response to glucose stimulation.


RESULTS
Islet cells differentiate properly in Gαo(-/-) mutant mice. Gαo inactivation significantly enhances insulin secretion both in vivo and in isolation. Gαo nullizygous β-cells contain an increased number of insulin granules docked on the cell plasma membrane, although the total number of vesicles per β-cell remains unchanged.


CONCLUSIONS
Gαo is not required for endocrine islet cell differentiation, but it regulates the number of insulin vesicles docked on the β-cell membrane.
Zhao
Aizhen
A
Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville,Tennessee, USA.
Ohara-Imaizumi
Mica
M
Brissova
Marcella
M
Benninger
Richard K P
RK
Xu
Yanwen
Y
Hao
Yuhan
Y
Abramowitz
Joel
J
Boulay
Guylain
G
Powers
Alvin C
AC
Piston
David
D
Jiang
Meisheng
M
Nagamatsu
Shinya
S
Birnbaumer
Lutz
L
Gu
Guoqiang
G
D000818:Animals; D002454:Cell Differentiation; D044385:GTP-Binding Protein alpha Subunits / Q000037:antagonists & inhibitors* / Q000235:genetics; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000235:genetics; D006706:Homeostasis; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D015534:Trans-Activators / Q000235:genetics
D044385:GTP-Binding Protein alpha Subunits; D018398:Homeodomain Proteins; D007328:Insulin; D015534:Trans-Activators; C084010:pancreatic and duodenal homeobox 1 protein