M. Reith et al., Lipovitellins derived from two forms of vitellogenin are differentially processed during oocyte maturation in haddock (Melanogrammus aeglefinus), J EXP ZOOL, 291(1), 2001, pp. 58-67
In the process of cloning vitellogenin (Vtg) cDNAs from haddock (Melanogram
mus aeglefinus), two related, but distinct, mRNAs were identified. Full-len
gth cDNA sequences were determined for both Vtg types (Had1 and Had2), and
the deduced amino acid sequences were found to be 54% identical to each oth
er and 48-58% identical to other teleost Vtgs. To investigate tile expressi
on of the two Vtg mRNAs, proteins from prehydrated oocytes and fertilized e
ggs were separated on SDS-polyacrylamide gels. Only a single lipovitellin I
band was detected in each sample, and the egg lipovitellin I was smaller (
97 vs. 110 kDa) than the oocyte protein, indicative of proteolytic processi
ng during oocyte hydration. Mass spectrometric (MALDI-TOFMS and tandem mass
spectrometry) analyses of tryptic fragments from the haddock oocyte and eg
g lipovitellin I revealed that the lipovitellin I from prehydrated oocytes
contained tryptic fragments that matched the sequences of both types of Vtg
, suggesting that there were two proteins in this band, while the egg lipov
itellin I contained tryptic fragments that only matched the Had1 cDNA seque
nce, indicating that the Had2 lipovitellin had been degraded during hydrati
on. Physiological data from haddock oocytes and eggs demonstrate that, as i
n other marine fish that spawn pelagic eggs, the free amino acid content in
creases during oocyte hydration and apparently contributes to hydration by
driving the osmotic uptake of water. The correlation of the disappearance o
f one lipovitellin I with the increase of free amino acids in the oocyte su
ggests that this protein is a major source of the free amino acids for oocy
te hydration. (C) 2001 Wiley-Liss, Inc.