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VITELLOGENINS OF THE COCKROACH FAT BODY: STRUCTURE, BIOSYNTHESIS, SECRETION AND A POSSIBLE ROLE FOR FAT BODY CYTOSOLIC JUVENILE HORMONE BINDING PROTEINS IN VITELLOGENESIS
Abstract
Cockroach fat body vitellogenesis has been employed as a model for studies concerning the juvenile hormone (JH) induction and biosynthetic processing of insect vitellogenins (VGs). Fat body of Blaberus discoidalis was shown to synthesize and secrete two discrete VGs in response to JH. Oocyte-bound vitellins (VTs) corresponding to each VG were purified by salt fractionation and gel filtration. The native VTs were of similar size (17S, 8.8 nm radii, 680K Mr), yet (i) separated in NaBr density gradients, (ii) possessed unique peptide substructures (6 and 8 peptides of 36K to 192K Mr), and (iii) were immunologically unrelated. Using antiserum to purified VT, precursor VGs for each VT were demonstrated to be synthesized and secreted by fat body cultured in vitro. In fat body cytosol, JH binding components potentially mediating JH induction of VG were indicated by a developmental concomitancy in the onset of vitellogenesis, and the expression of a saturable, specific, high-affinity JH-III binding protein (Kd (TURN) 10-9M, 5.5nm radius, 7.5S, 180K Mr). Prior to equilibrium analyses, JH-degradative, low Mr fat body esterases were separated from JH binding activity on Biogel A-1.5. The JH analogue ZR-515 competed for saturable JH-III sites (Kd (TURN) 2 x 10-6) while farnesal did not, indicating that both the epoxy and terminal ester functions of JH were required for efficient binding. Additionally, maximum likelihood nonlinear regression analysis of equilibrium data, JH-III dissociation kinetics, and DEAE-Cellulose fractionation of JH binding activity resolved a second JH binder (Kd (TURN) 10-8 M) constitutively expressed by fat body. In Blattella germanica, efficient in vivo radiolabeling of VG allowed an examination of the role of glycosylation in its biosynthetic processing and secretion from fat body. The antibiotic tunicamycin inhibited VG glycosylation and the subsequent cleavage of a pro-VG peptide into the 160K and 100K peptides of controls. Glycosylation was also required for the efficient secretion of VG from fat body. Mapping of VG and VT peptides helped to define the normal sequence of VG processing during its secretion and ovarian storage.
Subject Area
Biology|Entomology
Recommended Citation
WOJCHOWSKI, DON MICHAEL, "VITELLOGENINS OF THE COCKROACH FAT BODY: STRUCTURE, BIOSYNTHESIS, SECRETION AND A POSSIBLE ROLE FOR FAT BODY CYTOSOLIC JUVENILE HORMONE BINDING PROTEINS IN VITELLOGENESIS" (1984). Doctoral Dissertations Available from Proquest. AAI8410346.
https://scholarworks.umass.edu/dissertations/AAI8410346