Js. Clegg et al., NUCLEAR-CYTOPLASMIC TRANSLOCATIONS OF PROTEIN P26 DURING AEROBIC-ANOXIC TRANSITIONS IN EMBRYOS OF ARTEMIA-FRANCISCANA, Experimental cell research, 219(1), 1995, pp. 1-7
Embryos of the crustacean Artemia franciscana survive continuous anoxi
a for periods of years, during which their metabolism comes to a rever
sible standstill. A question of some interest concerns the maintenance
of cellular integrity in the absence of biosynthesis and an ongoing e
nergy metabolism. The present paper continues previous work on an abun
dant protein (p26) that undergoes extensive intracellular translocatio
n during aerobic-anoxic transitions, exhibits several characteristics
of stress proteins, and might be involved in metabolic regulation duri
ng aerobic-anoxic transitions. Since it has been established that intr
acellular pH (pH(i)) plays a major role in aerobic-anoxic transitions
in this system we examined the pH-dependence of nuclear-cytoplasmic tr
anslocations of p26. In unincubated and aerobic-incubated embryos (pH(
i) greater than or equal to 7.9) p26 was located in the ''soluble'' fr
action, whereas in anoxic embryos (pH about 6.3) roughly 50% was trans
located into the nucleus as shown by immunocolloidal gold electron mic
roscopy. These nuclear translocations also took place in vitro, simply
by manipulating buffer pH in a physiologically appropriate fashion. I
mmunostaining of Western blots prepared after two-dimensional electrop
horesis revealed several isoforms of native p26. The isoelectric point
of the major isoform was 7.10 +/- 0.05, a value close to the pH at wh
ich p26 translocation into the nucleus was first initiated in vitro. P
-31-NMR measurements indicated that pH(i) was maintained at acidic lev
els (about 6.3) during prolonged anoxia. We also found that pH(i) of h
ydrated (0 degrees C) but otherwise unincubated embryos was alkaline,
allowing for rapid resumption of metabolism under permissive condition
s. The significance of these pa-dependent translocations of p26 is dis
cussed. (C) 1995 Academic Press, Inc.