Developmental Changes in Tile Late Laitv a of Calliphora Stygia II. Protein Synthesis

Abstract

SummaryThe pattern of incorporation of [3H]leucine into proteins of fat body, plasma, body wall, and salivary gland has been studied in third-instar larvae of O. stygia. The rate of incorporation is higher in these tissues at day 5 of development than at days 7 and 11 (quiescent stage).The amount of acid-precipitable protein in the fat body increases little between days 5 and 7 in spite of the high synthetic rate early in the instar, whereas from day 7 to 11 there is almost a threefold increase. Simultaneously, the protein content of the plasma increases fourfold from day 5 to 7, and decreases by approximately one-third from day 7 to 11. The total protein of the body wall tissues remains constant from day 5 on, whilst that of the salivary gland cells shows a slow and steady increase during the instar.Changes in the relative specific activities of fat body and plasma proteins with age suggest two major alterations in the biosynthetic functions of fat body: (1) the cessation, between days 5 and 7, of the phase of intense protein synthesis associated with rising levels of plasma protein; (2) the initiation, at the quiescent stage, of a new phase of synthesis involving protein retention in the fat body. In addition, the reduced level of plasma protein between days 7 and 11 apparently reflects uptake by the fat body at this time. Protein synthesis in the tissues of the body wall decreases after day 5, and there is no evidence of any subsequent major change in protein biosynthesis in this tissue. Salivary gland cells appear to show a transition from rapid protein synthesis and quick release of protein at day 5, to slower synthesis with increased protein storage at the quiescent stage.

Developmental Changes in the Late Larva of Calliphora Stygia Iii. The Occurrence and Synthesis of Specific Tissue Proteins

“…In C. stygia, this finding is confirmed both in vivo (Martin, Kinnear, and Thomson 1969) and in vitro by the present results. The delayed appearance oflabelled protein in plasma relative to fat body is consistent with this relationship.…”

“…INTRODUCTION The synthesis of proteins in certain tissues of an Australian blowfly, Oalliphora stygia (Fabr.) Schiner, is discontinuous during the late larval period (Martin, Kinnear, and Thomson 1969). The sequential changes in gross protein synthesis observed in the fat body and salivary gland are paralleled by alterations in the dispersion of the polytene chromosomes (Thomson 1969) and by changes in the number and type of nuclear inclusions (Thomson and Gunson 1970).…”

Developmental Changes in the Late Larva of Calliphora Stygia Iv. Uptake of Plasma Protein by the Fat Body

“…IV. DISCUSSION After the commencement of the wandering phase of larval development at day 7, the fat body of C. stygia shows a major, progressive increase in protein content up to the prepupal stage (Table 2, and see also Table 1 in Martin, Kinnear, and Thomson 1969). Concurrently, synthetic activity in the fat body is greatly reduced, especially from day 7 to day 10.…”

“…(1) a period of very active protein synthesis in the fat body, with rapid concurrent release into the haemolymph; (2) abrupt cessation of the synthesis by the fat body of many protein species, including those constituting some 70% of the total haemolymph protein (Kinnear, Martin, and Thomson 1971); (3) uptake of specific proteins from the haemolymph into fat body cells, measured directly in the present work and correlated with decreasing haemolymph protein concentrations and increasing protein content of the fat body late in larval life ; (4) a phase of increased protein synthesis, with retention of the nascent protein, close to puparium formation (Martin, Kinnear, and Thomson 1969). The haemolymph thus serves as a temporary storage organ for protein until the predominant function of the fat body changes from synthesis to storage.…”

“…The total fat body protein at day 7 is approximately 1· 0 mgjlarva (Martin, Kinnear, and Thomson 1969). If it is assumed that uptake of plasma proteins commences at day 7 and continues steadily (see Fig.…”