Gf. Dunglison et al., STIMULATION OF ENDOCYTOSIS IN MOUSE BLASTOCYSTS BY INSULIN - A QUANTITATIVE MORPHOLOGICAL ANALYSIS, Journal of Reproduction and Fertility, 105(1), 1995, pp. 115-123
The effects of insulin on the endotytic activity of mouse blastocysts
in vitro were investigated using confocal laser scanning microscopy, q
uantitative image analysis and electron microscopy. Confocal studies s
howed that fluorescein isothiocyanate-labelled markers, dextran (fluid
phase) and albumin (combined membrane and fluid phase), were endocyto
sed by blastocysts and localized within vesicles (about 2.5 mu m in di
ameter) in the outer trophectoderm cells. No labelling was detected in
the inner cell mass cells or the blastocoel cavity. Treatment with 17
0 nmol insulin l(-1) stimulated the endocytosis of fluorescently label
led dextran in freshly collected blastocysts, increasing mean vesicle
diameter per embryo by 15% (P < 0.05) after incubation with insulin fo
r 2.5 h and mean vesicle number per embryo by 56% (P < 0.01) after 6 h
. Both effects were also evident in blastocysts that had been cultured
from the late eight-cell stage. Blastocysts incubated for 6 h with in
sulin displayed increased convolutions in the trophectoderm apical mem
brane compared with controls, indicating increased membrane activity a
nd suggesting macropinosome formation. Collectively, these results sug
gest that insulin enhances endocytosis in the trophectoderm by stimula
ting uptake at the apical membrane into larger and more numerous endoc
ytic vesicles and with some evidence of vesicle fusion. This mechanism
may provide a metabolic basis for the stimulation by insulin of biosy
nthesis, proliferation and morphological development in early embryos.