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Yolk Degradation in Tick Eggs: III. Developmentally Regulated Acidification of the Yolk Spheres
Author(s) -
Fagotto Françis
Publication year - 1991
Publication title -
development, growth and differentiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.864
H-Index - 66
eISSN - 1440-169X
pISSN - 0012-1592
DOI - 10.1111/j.1440-169x.1991.00057.x
Subject(s) - yolk , hatching , cathepsin , embryogenesis , biology , biochemistry , chemistry , microbiology and biotechnology , enzyme , embryo , food science , ecology
Yolk spheres in tick eggs contain a latent procathepsin L, which is activated in vivo , in parallel with yolk degradation, and in vitro by acid treatment (Fagotto, F., Arch. Insect Biochem. Physiol., 1990b in press). Mature cathepsin L hydrolyzes vitellin at acidic pH (Fagotto, F., Arch. Insect Biochem. Physiol., 1990a in press). Here, yolk spheres' pH has been estimated using acridine orange. In the early development, all yolk spheres are neutral, then an increasing number acidify, until hatching, where general acidification seems to occur. This fits well with vitellin utilized slowly during embryogenesis, more intensely at hatching (Chinzei, Y. and I. Yano, Experientia 41 , 948, 1985), and can be related to sequential degradation of individual spheres observed during embryonic development, then extensive yolk liquefaction in the larva. Different yolk spheres populations have been separaded on Percoll density gradients. In freshly laid eggs, yolk spheres are dense, neutral, undegrated and contain exclusively the precursor of cathepsin L. In later stages, yolk spheres are progressively recovered in lower density fractions, displaying acidic interior and cytological signs of degradation. They cosediment with mature cathepsin L. It is concluded that acidification initiates yolk degradation through procathepsin L activation.