Michal Gadot

Role of the brain in juvenile hormone synthesis and Oöcyte development: effects of dietary protein in the cockroach Blattella germanica (L.)

Abstract We demonstrate links between the protein content of diets, food intake, the resultant body mass, juvenile hormone synthesis by the corpora allata, and oocyte maturation in Blattella germanica. Oocyte development and oviposition were suppressed in starved females as well as in females fed deficient artificial diets (low- or high-protein contents). On all diets, as well as in starved females, oocyte growth was significantly potentiated by hydroprene, indicating that the suppressed oocyte growth on deficient diets was largely due to juvenile hormone deficiency. Also, under all dietary treatments, including in starved females, transection of the nervi corporis cardiaci (NCC)-I and II significantly potentiated juvenile hormone biosynthesis, oocyte development and oviposition compared with the respective sham-operated females. These results clearly show that intact nerves are a major route of allatostatic signals from the brain which in turn are regulated by food quality. However, a partial suppression of juvenile hormone synthesis and smaller oocytes in females with denervated corpora allata that were fed protein-deficient diets (starved, 0%, 5%) or high-protein diets (78%) compared with females that were fed normal diets (25%, dog and rat foods) highlights the importance of humoral signals in allata activity. Oocyte size and juvenile hormone biosynthetic rates were also significantly lower in adult females that were fed a 7.5%-protein diet as nymphs compared with females fed a 25%-protein diet. Denervation of the corpora allata resulted in potentiation of their activity, but to significantly lower rates in females that were raised on the low-protein diet as nymphs, further supporting the importance of the nutritional milieu in corpus allatum activation. Both food intake and body mass varied directly with the protein content of the diet, confounding the conclusion that corpus allatum activity was affected by signals related to the dietary protein content. To dissociate food consumption and body mass from corpora allata activity and oocyte growth, 2% trypsin synthesis inhibitor was added to a 7.5%-protein diet. Neither body mass nor total food consumption were changed relative to control females, but oocytes were significantly small on this diet. Together with data showing that oocyte maturation can be induced with hydroprene in protein-deprived or even in starved females, these data argue that signals associated with the protein content of the diet partially lift brain inhibition of the corpora allata.

Farnesoic acid-stimulated rates of juvenile hormone biosynthesis during the gonotrophic cycle in Blattella germanica

Juvenile hormone III biosynthesis in vitro by the corpora allata of adult female Blattella germanica is precisely correlated with the gonotrophic cycle. Farnesoic acid-stimulated rates of juvenile hormone synthesis are always higher than the corresponding basal rates, and follow the same pattern of cyclic changes during oocyte maturation. Both basal and farnesoic acid-stimulated rates decline to undetectable levels while the female carries an ootheca and oocyte development is inhibited (‘pregnancy’). This suggests that, in this species, the main control mechanism of the corpora allata operates through structural/developmental processes, affecting the maximal biochemical capacity of the glands. Morphometric data relating gland volume and the main events during oocyte development and ‘pregnancy’ support this conclusion. We speculate that the type of corpora allata control which is predominant in different insects might be functionally related to their ovipositional behavior.

Cyclic juvenile hormone biosynthesis in the cockroach, Blattella germanica: Effects of ovariectomy and corpus allatum denervation

The corpora allata (CA) of ovariectomized adult Blattella germanica females exhibited delayed but high rates of juvenile hormone biosynthesis in vitro. Using the onset of sexual receptivity as a probe of the degree of CA activation in females, we demonstrated at least one cycle of CA activity in the experimentally synchronized ovariectomized females. Following their activation, the CA exhibited a partial and transient decline in activity, but in contrast to the CA of intact females, this decline was not accompanied by a regression in CA volume. CA of intact and ovariectomized females that were denervated from the brain were activated, but the subsequent decline in CA activity at the end of the cycle was prevented in ovariectomized females. The presence of an egg-case suppressed the reactivation of the inactive CA in intact females but not in CA-denervated females. We conclude that activation of the CA in B. germanica is not dependent upon either the presence of the ovary or intact nervous connections between the CA and the brain. The brain exerts a partial inhibition on CA activity through intact nerves which is relieved (by disinhibition) in the presence of a young ovary but is enhanced and sustained in the presence of the egg-case. Inhibition of the CA also occurs independently of nervous connections with the brain through factors that originate in the mature ovary and affect both CA activity and morphology.

Morphometric analysis of corpus allatum cells in adult females of three cockroach species

The number of cells and their sizes in the corpus allatum (CA) of adult female Blattella germanica, Supella longipalpa and Diploptera punctata were determined during oocyte maturation. Cell number and size were directly measured in cell suspensions following enzymatic dissociation of freshly excised CA. Cell numbers were verified by total cell counts in whole-mount CA monolayers and by hemocytometric sampling. In all three species, cell number did not change during the period of CA activation, averaging ca. 2000 cells per gland in B. germanica, 3500 cells per gland in S. longipalpa and 11,000 cells per gland in D. punctata. Cell diameter increased significantly in all three species during this period from a mean value of 8.9 microns to 11.7 microns in B. germanica, from 9.2 microns to 14.6 microns in S. longipalpa and from 10.0 microns to 15.6 microns in D. punctata. During a 4 h incubation period, dissociated CA cells incorporated L-[methyl-3H]-methionine into juvenile hormone-III at rates comparable to intact glands. These data suggest that CA activation in the first ovarian cycle of these species is associated mainly with an increase in cell size with minor changes in cell number.

Developmental regulation of juvenile hormone synthesis: ovarian synchronization of volumetric changes of corpus allatum cells in cockroaches

The corpus allatum (CA) cells of adult Blattella germanica females undergo cyclic volumetric changes in relation to juvenile hormone (JH) synthesis. In intact females the size of CA cells changes synchronously during the gonotrophic cycle, resulting in cyclic JH synthesis. In ovariectomized females volumetric changes among CA cells become asynchronous, resulting in highly variable but high rates of JH synthesis. Injection of the steroid hormone 20-hydroxyecdysone into ovariectomized females with active CA resulted in a transient decline followed by an increase in both CA volume and JH biosynthesis. This response was due to a change in the size distribution of CA cells and not in the total number of CA cells. In ovariectomized females, CA cells can be re-synchronized into a uniform population of small inactive cells with injection of 20-hydroxyecdysone and implantation of an artificial egg-case, mimicking the successive events of ovulation, oviposition and pregnancy.

Biochemistry and regulation of pheromone production in Blattella germanica (L.) (Dictyoptera, Blattellidae)

Abstract Females of the German cockroach, Blattella germanica , produce a contact sex pheromone consisting of the methyl ketones 3,11-dimethyl-2-heptacosanone, 3,11-dimethyl-2-nonacosanone, 29-hydroxy- and 29-oxo-3,11-dimethyl-2-nonacosanone. We review evidence in support of the hypothesis that in adult females the hydrocarbon 3,11-dimethylnonacosane is oxidized to the corresponding methyl ketone pheromone. Recent studies on the precursors and directionality of synthesis of the methyl-branched alkane indicate that it is formed by the insertion of methylmalonyl units derived from propionate, isoleucine, valine, methionine and succinate early in chain elongation. The hydrocarbon is then hydroxylated and oxidized at the 2-position to form the methyl ketone pheromone. The in vivo synthesis of pheromone and its accumulation on the cuticle are correlated to the synthesis of juvenile hormone (JH) by the corpora allata (CA) in vitro and to oocyte development, suggesting common regulation by JH of pheromone production as well as other reproductive events. The patterns of pheromone and hydrocarbon production in starved, allatectomized and head-ligated females, as well as in females rescued with hormone-replacement therapy, suggest two mechanisms of regulation of pheromone production: a JH-induced conversion of hydrocarbon to pheromone is related to the CA cycle and to oocyte development, while a JH-independent mechanism, which is probably related to feeding, supplies precursors for hydrocarbon biosynthesis.

Sexual differentiation of nymphal corpora allata and the effects of ovariectomy on adult gland morphometrics inBlattella germanica

Changes in the number of corpus allatum (CA) cells were investigated in nymphs and in intact and ovariectomized adult femaleBlattella germanica. The CA of intact adult females exhibit cyclic changes in volume in relation to juvenile hormone (JH) synthesis, while the CA of ovariectomized females become significantly hypertrophied as a result of a gradual and continuous increase in volume that is independent of JH biosynthesis. In both intact and ovariectomized females changes in JH synthesis and CA volume are not related to total cell number which remains relatively constant. However, adult females have twice as many CA cells as do adult males as a result of a female-specific increase in total cell number late in the last nymphal instar.

Juvenile hormone regulation of the left colleterial gland in intact and ovariectomized Blattella germanica (L.) (Dictyoptera: Blattellidae)

Abstract The left colleterial glands of intact and ovariectomized females were shown to accumulate protein in response to juvenile hormone III. Their distal tubule diameter was highly correlated with their protein content. While intact females excreted the oothecal proteins to produce an egg case, ovariectomized females retained these proteins without apparent loss from the gland. In overiectomized females the colleterial gland therefore became larger and contained more protein than in intact females. The size and protein content of the left colleterial gland of ovariectomized females were arrested after the insects were allatectomized, and both were induced by injections of synthetic juvenile hormone III. Thus, the left colleterial gland can be used as a cumulative record of circulating juvenile hormone within an individual ovariectomized female, much as the basal oocytes are used in intact females, and it can be used to distinguish betwen females that had increased juvenile hormone synthesis and those that had not.

Changes in Number and Size of Corpus Allatum Cells of Blattella germanica during Oocyte Maturation

The corpus allatum (CA) of the female German cockroach shows cyclic changes in both size and juvenile hormone III (JH III) biosynthesis during the gonotrophic cycle (Gadot et al., 1989). The increase in CA volume during oocyte maturation has been considered mainly due to increases in both cell number and cell size (Cassier, 1979; Tobe and Stay, 1985). To date, the number of nuclei in the CA has been estimated from sections of fixed thickness in fixed organs (Scharrer and von Harnack, 1958; Szibbo and Tobe, 1981; Tobe et al., 1984). Since nuclear size and shape vary with different developmental stages of the CA during the gonotrophic cycle in Diploptera punctata (Johnson et al., 1985) and other insects (Cassier, 1979), nuclear counts from sections may under- or over-estimate the total number of cells. The size of CA cells is usually presented as the nucleocytoplasmic ratio in fixed glands (Engelmann, 1957). We report on changes in number and size of CA cells of Blattella germanica during oocyte maturation by direct measurements of enzymatically dissociated cells.

Patterns of Corpora Allata Activity in Ovariectomized Blattella germanica

The corpora allata (CA) of adult female cockroaches, including Blattella germanica (Gadot et al., 1989a,b), synthesize juvenile hormone-III (JH-III) in a precisely regulated cycle which corresponds to the ovarian cycle. The brain, the ovary and the ootheca have been implicated as the main sources of regulatory factors which modulate the activity of the CA (Tobe and Stay, 1985). In Nauphoeta cinerea and Diploptera punctata, the maturing ovary activates the CA at the beginning of the first ovarian cycle, while the mature ovary (just before ovulation) has an inhibitory effect on JH-III synthesis (Lanzrein et al., 1981; Rankin, 1989). Herein we examine the role of the ovary in modulating CA activity in B. germanica.