Insect cuticular sclerotization: a review.

Over many years evidence has accumulated that plants and animals can regulate growth with reference to overall size rather than cell number. Thus, organs and organisms grow until they reach their characteristic size and shape and then they stop ‐ they can even compensate for experimental manipulations that change, over several fold, cell number or average cell size. If the cell size is altered, the organism responds with a change in cell number and vice versa. We look at the Drosophila wing in more detail: here, both extracellular and intracellular regulators have been identified that link cell growth, division and cell survival to final organ size. We discuss a hypothesis that the local steepness of a morphogen gradient is a measure of length in one axis, a measure that is used to determine whether there will be net growth or not. SUMMARY

http://making-of-a-fly.me/files/pdf/dev2566.pdf

Measuring dimensions: the regulation of size and shape.

The integument of decapod crustaceans consists of an outer epicuticle, an exocuticle, an endocuticle and an inner membranous layer underlain by the hypodermis. The outer three layers of the cuticle are calcified. The mineral is in the form of calcite crystals and amorphous calcium carbonate. In the epicuticle, mineral is in the form of spherulitic calcite islands surrounded by the lipid-protein matrix. In the exo- and endocuticles the calcite crystal aggregates are interspersed with chitin-protein fibers which are organized in lamellae. In some species, the organization of the mineral mirrors that of the organic fibers, but such is not the case in certain cuticular regions in the xanthid crabs. Thus, control of crystal organization is a complex phenomenon unrelated to the gross morphology of the matrix.

Since the cuticle is periodically molted to allow for growth, this necessitates a bidirectional movement of calcium into the cuticle during postmolt and out during premolt resorption of the cuticle. In two species of crabs studied to date, these movements are accomplished by active transport effected by a Ca-ATPase and Na/Ca exchange mechanism.

The epi- and exocuticular layers of the new cuticle are elaborated during premolt but do not calcify until the old cuticle is shed. This phenomenon also occurs in vitro in cuticle devoid of living tissue and implies an alteration of the nucleating sites of the cuticle in the course of the molt.

/pdf/the-structure-and-calcification-of-the-crustacean-cuticle-110ts1pea1.pdf

The Structure and Calcification of the Crustacean Cuticle

By fractionating conditioned medium (CM) from Drosophila imaginal disc cell cultures, we have identified a family of Imaginal Disc Growth Factors (IDGFs), which are the first polypeptide growth factors to be reported from invertebrates. The active fraction from CM, as well as recombinant IDGFs, cooperate with insulin to stimulate the proliferation, polarization and motility of imaginal disc cells. The IDGF family in Drosophila includes at least five members, three of which are encoded by three genes in a tight cluster. The proteins are structurally related to chitinases, but they show an amino acid substitution that is known to abrogate catalytic activity. It therefore seems likely that they have evolved from chitinases but acquired a new growth-promoting function. The IDGF genes are expressed most strongly in the embryonic yolk cells and in the fat body of the embryo and larva. The predicted molecular structure, expression patterns, and mitogenic activity of these proteins suggest that they are secreted and transported to target tissues via the hemolymph. However, the genes are also expressed in embryonic epithelia in association with invagination movements, so the proteins may have local as well as systemic functions. Similar proteins are found in mammals and may constitute a novel class of growth factors.

A new family of growth factors produced by the fat body and active on Drosophila imaginal disc cells.

The role of the haematopoietic tissue in haemocyte production and maturation in the black tiger shrimp (Penaeus monodon).

Histochemical data support the previous biochemical finding that the blood is a major site for the production of proteinaceous and diphenolic substances for tanning of the cuticle in the fiddler crab, Uca pugilator. Five types of hemocytes are described. Specifically in tanning, the hyaline cells (cystocytes) appear responsible for the production of diphenolic tanning agents whereas the granulocytes synthesize the proteins involved. Other types of hemocyte may be transitional forms involved in clotting (intermediate cells). Various histochemical reactions for each type of hemocyte and the cuticle are recorded throughout the molting cycle, and appear cyclic. The data suggest there is hormonal control of the cyclic events during the tanning process.

The roles of hemocytes in tanning during the molting cycle: a histochemical study of the fiddler crab, uca pugilator

1.	
1. Labeled N-acetyldopamine, N-acetylnoradrenalin and their beta-glucoside forms were identified by paper chromatography as metabolites of 2-14C-dopamine in the blood of the fiddler crab, Uca pugilator, undergoing ecdysis.

2.	
2. The blood appears to be the main site of synthesis of the glucoside forms.

3.	
3. The label became tightly incorporated into the cuticle at ecdysis, suggesting that the glucoside forms are involved in the tanning process.

4.	
4. The attachment of the labeled glucosides to two proteins (∼ 150,000 and >400,000 daltons) and the subsequent incorporation of these glucosides into the cuticle matrix suggests that these proteins act as carriers in the transport of tanning agents into the cuticle.

The mechanism of tanning in the fiddler crab, Uca pugilator--I. Tanning agents and protein carriers in the blood during ecdysis.

1. 1. Fluctuations in the levels of tanning agents and carrier proteins in the blood, epidermis, midgut gland, and cuticle were determined by paper chromatography after injection of 2- 14 C-dopamine into fiddler crabs at all the major periods of the molting cycle. 2. 2. During the intermolt period, when cuticle incorporation is almost nonexistent, the tanning agents are abundant in the blood, but virtually no carrier proteins are labeled. 3. 3. During proecdysis, carrier proteins become labeled, but cuticle incorporation remains negligible. 4. 4. Label is rapidly incorporated into the cuticle only early in postecdysis. A tanning hormone in the fiddler crab is postulated.

The mechanism of tanning in the fiddler crab, Uca pugilator--II. The cyclic appearance of tanning agents and attached carrier proteins in the blood during the molting cycle.

Histochemical data support the previous biochemical finding that the blood is a major site for the production of proteinaceous and diphenolic substances for tanning ofthe cuticle in the fiddler crab, Uca pugilator. Five types ofhemocytes are described. Specifically in tanning, the hyaline cells (cystocytes) appear responsible for the pro duction ofdiphenolic tanning agents whereas the granulocytes synthesize the proteins involved. Other types of hemocyte may be transitional forms involved in clotting (intermediate cells). Various histochemical reactions for each type of hemocyte and the cuticle are recorded throughout the molting cycle, and appear cyclic. The data suggest there is hormonal control of the cyclic events during the tanning process.

Linda L. Vacca

Papers

The roles of hemocytes in tanning during the molting cycle: a histochemical study of the fiddler crab, uca pugilator

The mechanism of tanning in the fiddler crab, Uca pugilator--I. Tanning agents and protein carriers in the blood during ecdysis.

The mechanism of tanning in the fiddler crab, Uca pugilator--II. The cyclic appearance of tanning agents and attached carrier proteins in the blood during the molting cycle.

Cycle: a histochemical study of the fiddler crab,