Date of Award
Doctor of Philosophy (PhD)
John W. Lynn
The appearance of extracellular coats around "eggs" are associated with activation of the oocytes. This coat, termed fertilization envelope (sea urchins), chorion (fish), zona pellucida (mammals), capsule (crab) or hatching envelope (HE) (shrimp) serves as a polyspermy block (Wasserman, 1982) or microenvironment protecting the egg from bacteria or other hostile elements (Kudo and Inoue, 1989; Kudo and Teshima, 1991; Kudo, 1992; Epel, 1993). HE assembly is described for penaeoid shrimp (Lynn, et al., 1991) and is, in contrast to many systems, a fertilization independent event. However, the mechanisms of assembly appear similar to extracellular coat formation in other animal systems which utilize enzymes such a ovoperoxidase and transglutaminase in this formation. Three enzymes are postulated for shrimp HE assembly as implicated by the presence of requisite amino acids or polysaccharides in the HE composition (Pillai and Clark, 1990). Ovoperoxidase, predominate in sea urchin envelopes (Kay and Shapiro, 1985) catalyzes cross-linking of tyrosine proteins. Treatment of shrimp eggs with known peroxidase inhibitors, aminotriazole and sodium sulfite, show morphological changes as indicated in the permeability and thickness of the envelope. Investigations using diaminobenzidine or guaiacol reactions show no positive activity in HE assembly. The abundance of saccharides in isolated shrimp HEs (Pillai and Clark, 1990) and implications of chitin in copepod envelopes (Santella, 1993) indicate a role for a carbohydrate synthase. Investigations using chitinase and $\beta$-N-acetylglucosaminidase to digest HEs on spawned shrimp eggs and on isolated envelopes suggest a polysaccharide moiety. Among the chitin synthase inhibitors tested (tunicamycin, polyoxin D, nikkomycin Z), nikkomycin Z inhibited normal HE formation. Transglutaminases, predominate in fish (Oppen-Berntsen, et al., 1990) and sea urchin (Battaglia and Shapiro, 1988) egg envelopes, catalyze cross-linking of glutamine and lysine residues. Investigations with transamidase inhibitors (putrescine, cadaverine, glycine ethyl ester) indicate that while morphological structures do not appear to change, the envelope rigidity is impaired. These investigations are consistent with a multi-enzyme system responsible for the HE integrity, however, differences appear to exist in the enzyme specificity compared to other model systems. Understanding the enzyme action may lead to greater success with aquaculture programs directed toward increased fertilization and early embryonic success.
Glas, Patricia Stoops, "Elevation of the Hatching Envelope in Penaeidea Shrimp: Morphology and Assembly." (1994). LSU Historical Dissertations and Theses. 5725.