LEE,R.F., R.F.*; ANDO, S.; WALKER, A.: Synthesis of a High Density Lipoprotein (LpI) by Blue Crab Embryos

Lipids in hemolymph of blue crabs(Callinectes sapidus), and other crustaceans, are associated with a high density lipoprotein (LpI: density: 1.12-1.21 g/ml). LpI is composed of phospholipid (45%), cholesterol (2%), triacylglycerol (3%0 and one peptide (49%; 112,000 daltons). LpI functions as a carrier of lipid from the hepatopancreas to peripheral tissues, such as muscle, and also serves as a beta-1,3-glucan binding protein which plays a role in crustacean immune recognition {Hall et al., Biochim. Biphys. Res. Commun. 216, 939-946 (1995)]. In the present study the concentrations of LpI in different embryo developmental stages (stages 1-9 are enclosed in an egg sac followed by hatching into zoea stage) were determined by a competitive ELISA procedure using a monoclonal antibody against the LpI peptide.There was a steady increase in the LpI concentrations from stage 5 (2.3 ng LpI/embryo) to stage 9 (19.6 ng LpI/embryo. LpI was absent from embryo stages 1-4. Stage 5 was characterized by a distinct embryonic region and approximately 50% of the yolk is still present. Fixed sections of the various embryonic stages were probed with the anti-LpI antibody. No immunoreactivity was observed in developing oocytes or in early embryonic stages. Immunoreactivity in stage 7 embryos was associated with cuboidal cells, which are assumed to become the hepatopancreas. These cuboidal cells were adjacent to lipovitellin (yolk) stores. LpI is not transferred from the female to the yolk of the developing oocytes but is synthesized during later stages of embryogenesis. LpI may play an important role in the embryo immune system.