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

Abstract

The occurrence and synthesis of soluble proteins from certain larval tissues of O. 8tygia have been examined by acrylamide.gel electrophoresis and autoradiography at the feeding (days 4-6), wandering (days 7-10), and quiescent (day 11) stages of third-instar development. The protein species investigated are distributed as follows: fat body, 22; plasma, 21; body wall, 18; salivary gland cells, 16; salivary secretion, 18.The predominant soluble proteins of fat body, body wall, and salivary gland cells are in each case synthesized in situ. All ma.jor plasma proteins are synthesized in the fat body and are electrophoretically comparable with those released by the fat body in vitro. Most of the proteins of the salivary secretion are synthesized by the gland cells: the main secretory species are not derived directly from the haemolymph. A minimum of 40,25, and 45% respectively of the soluble species detectable in extracts of fat body, body wall, and salivary gland cells are specific to these tissues.Individual protein species fall into three contrasting groups according to whether their synthesis occurs: (1) in the feeding stage only; (2) in post-feeding stages only; (3) throughout third instar.In each tissue an abrupt and coordinated reduction in protein synthesis takes place at the end of the feeding stage. Unidentified, presumably humoral, regulatory agents appear likely to be responsible. The synthesis of certain specific proteins is differentially affected by these controlling influences.

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

“…The bulk ofthe increase in fat body protein which occurs between days 7 and 11 oflarval development is due to an increase in the proteins of bands FI5-19, and, at the quiescent stage, to bands F4-1O also (Kinnear, Martin, and Thomson 1971). The fat body protein spectrum of third-ins tar larvae is qualitatively similar (Kinnear, Martin, and Thomson 1971) during the period from day 4 to day 11, which includes both feeding and wandering stages.…”

“…2(b)] revealed that radioactivity was present in fat body bands F15-19. These are electrophoretically comparable with plasma proteins H15-19, except that the fat body contains no band corresponding to the slower of the two overlapping components of H15 (Kinnear, Martin, and Thomson 1971). There was no apparent radioactivity at the positions of bands H4, 11, 20, or 21.…”

“…1(b)J. The bulk of the radioactivity received by recipient larvae was located in those plasma bands designated H15-19 and, to a much lesser extent, in bands H4, lO, 11, 20, and 21 (for details of band numbers see Kinnear, Martin, and Thomson 1971). …”

“…Electrophoresis was carried out at 4°C on horizontal 5% acrylamide gel using a discontinuous Tris-citrate/borate buffer system at pH 8·7/pH 8·2 (Kinnear, Martin, and Thomson 1971). Proteins were stained with amido black and the gels were subsequently dried and autoradiographed against X-ray film.…”

“…(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.…”