Ecdysteroids makisterones

Dietary sterols of sunflower seeds were incorporated essentially unchanged into the tissues and, when injected, neither radiolabeled campesterol nor sitosterol was metabolized to cholesterol. Apparently, there was some selective uptake of dietary cholesterol, indicated by an enrichment of cholesterol in the insect sterols compared to the cholesterol concentration in the seed sterols. A C28 ecdysteroid, makisterone A (Figure 1), was identified as the major ecdysteroid of milkweed bug eggs (18) and, subsequently, makisterone A was identified as the major ec steroid in hemolymph of last stage milkweed bug nymphs and two other phytophagous species of the Pentatomomorpha group of Hemiptera (19). Makisterone A was... 

It is significant that, although the C27 ecdysteroids ecdysone and 20-hydroxyecdysone are the most commonly found molting hormones in insects, the C28 ecdysteroid, makisterone A, is the major molting hormone of many insects that are unable to dealkylate. In addition, the C29 ecdysteroid, makisterone C, has been identified as a major embryonic molting hormone of a hemipteran that lacks dealkylation capabilities. The ability to synthesize makisterone A is present even in certain insects that ordinarily have adequate cholesterol in their diets as shown for the hemipteran, P. maculiventris, and the higher Diptera. So this appears to be a well-conserved biochemical mechanism. 

The steroids known to play major regulatory roles in insect development and metamorphosis all fall into the class of polyhydroxylated ketosteroids called ecdysones (19-22). With the exception of Makisterone A (a C2 ecdysteroid identified from the milkweed bug Oncopeltus fasciatus) the known insect ecdysteroids constitute a group of eight or nine steroids that differ from one another... 

Ecdysteroids All ecdysteroids used in this work were a kind gift of Prof. Dr. Jan Koolmann, University of Marburg. They were ecdysone, 20-hydroxyecdysone, makisterone and muristerone for the growth experiments, as well as radiolabeled ponasterone A for the binding assay. Preparation of stock solutions, sterilization and addition to media was exactly the same as for brassinosteroids. 

Figure 5 Effect of 4 different ecdysteroids on the fresh weight increase of LA6 calli. E Ecdysone OH-E B-Hydroxy-ecdysone MA Makisterone MU Muristerone. Concentration range 10 8 to 10-6 M. Age of cultures 3 weeks. CV < 10%...

It has become increasingly evident that considerable variability in steroid utilization and metabolism exists among phytophagous species of insects. In recent years, we have discovered several phytophagous species that are unable to convert C28 or C29 phytosterols to cholesterol. This Includes one species that dealkylates the C-24 substituent of the side chain but produces mostly saturated sterols and several species that totally lack the ability to dealkylate the sterol side chain. Certain members of this latter group are of particular interest because they have adapted to utilizing a Cos sterol as an ecdysteroid precursor and makisterone A (C28) has been identified as the major ecdysteroid of certain developmental stages of these species. 

In fact, H-24-methylenecholesterol has been traced unchanged through two generations of bees (28). Thus, there is a very unusual mechanism that enables the workerTee to selectively transfer certain dietary sterols or sterols cycled from their endogenous pools to the brood food to maintain a constant supply of certain sterols for the brood food. The utilization of neutral sterols by the honey bee and the inability to produce cholesterol from the dealkylation of 24-alkyl C20 and C29 phytosterols is reflected in the recent isolation of makisterone A as the major ecdysteroid at peak titer in the honey bee pupa (29). 

Figure 7.15 Some ecdysteroid examples. Makisterone A is used by some insects, including Apis mellifera arui Drosophila melanogaster, and by crabs and is a phytoecdysteroid in Podocarpus trees arui the wild flower Lychnis flos-cuculi (ragged robin). Ecdysone 22-palmitate is an example of a storage product found in insect ovaries arui eggs. Ajugasterone C is an example of a phytoecdysteroidfrom the Labiatae, Compositae and Verbenaceae, but also identified in an Anthozoa (corals and sea anemones)...

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