Haemolymph lipid transport from fat body to uterine gland in pregnant females of Glossina morsitans

Molecular and Cellular Endocrinology

Michalková

et al. 2013

Tsetse flies are viviparous insects that nurture a single intrauterine progeny per gonotrophic cycle. The developing larva is nourished by the lipid-rich, milk-like secretions from a modified female accessory gland (milk gland). An essential feature of the lactation process involves lipid mobilization for incorporation into the milk. In this study, we examined roles for juvenile hormone (JH) and insulin/IGF-like (IIS) signaling pathways during tsetse pregnancy. In particular, we examined the roles for these pathways in regulating lipid homeostasis during transitions between non-lactating (dry) and lactating periods. The dry period occurs over the course of oogenesis and embryogenesis, while the lactation period spans intrauterine larvigenesis. Genes involved in the JH and IIS pathways were upregulated during dry periods, correlating with lipid accumulation between bouts of lactation. RNAi suppression of Forkhead Box Sub Group O (FOXO) expression impaired lipolysis during tsetse lactation and reduced fecundity. Similar reduction of the JH receptor Methoprene tolerant (Met), but not its paralog germ cell expressed (gce), reduced lipid accumulation during dry periods, indicating functional divergence between Met and gce during tsetse reproduction. Reduced lipid levels following Met knockdown led to impaired fecundity due to inadequate fat reserves at the initiation of milk production. Both the application of the JH analog (JHA) methoprene and injection of insulin into lactating females increased stored lipids by suppressing lipolysis and reduced transcripts of lactation-specific genes, leading to elevated rates of larval abortion. To our knowledge, this study is the first to address the molecular physiology of JH and IIS in a viviparous insect, and specifically to provide a role for JH signaling through Met in the regulation of lipid metabolism.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Juvenile hormone and insulin suppress lipolysis between periods of lactation during tsetse fly pregnancy

Baumann

Molecular and Cellular Endocrinology

Michalková

et al. 2013

“…Lipids for milk production are not generated in the milk gland, rather they are produced and stored in the fat body or are acquired directly from blood feeding (Langley et al, 1981; Tobe and Langley, 1978). The lipids from both sources are moved to the milk gland for incorporation into the milk secretion (Langley et al, 1981; Tobe and Langley, 1978). Currently, the factors responsible for lipid transport from the sites of nutrient uptake (digestive tract) or storage (fat body) through the hemolymph and to the milk gland have not been examined.…”

Section: Introductionmentioning

confidence: 99%

Lipophorin acts as a shuttle of lipids to the milk gland during tsetse fly pregnancy

Journal of Insect Physiology

Yang

Krause

et al. 2011

During pregnancy in the viviparous tsetse fly, lipid mobilization is essential for the production of milk to feed the developing intrauterine larva. Lipophorin (Lp) functions as the major lipid transport protein in insects and closely-related arthropods. In this study, we assessed the role of Lp and the lipophorin receptor (LpR) in the lipid mobilization process during tsetse reproduction. We identified single gene sequences for GmmLp and GmmLpR from the genome of Glossina morsitans morsitans, and measured spatial and temporal expression of gmmlp and gmmlpr during the female reproductive cycle. Our results show that expression of gmmlp is specific to the adult fat body and larvae. In the adult female, gmmlp expression is constitutive. However transcript levels increase in the larva as it matures within the mother’s uterus, reaching peak expression just prior to parturition. GmmLp was detected in the hemolymph of pregnant females and larvae, but not in the uterine fluid or larval gut contents ruling out the possibility of direct transfer of GmmLp from mother to offspring. Transcripts for gmmlpr were detected in the head, ovaries, midgut, milk gland/fat body, ovaries and developing larva. Levels of gmmlpr remain stable throughout the first and second gonotrophic cycles with a slight dip observed during the first gonotrophic cycle. GmmLpR was detected in multiple tissues, including the midgut, fat body, milk gland, spermatheca and head. Knockdown of gmmlp by RNA interference resulted in reduced hemolymph lipid levels, delayed oocyte development and extended larval gestation. Similar suppresion of gmmlpr did not significantly reduce hemolymph lipid levels or oogenesis duration, but did extend the duration of larval development. Thus, GmmLp and GmmLpR function as the primary shuttle for lipids originating from the midgut and fat body to the ovaries and milk gland to supply resources for developing oocytes and larval nourishment, respectively. Once in the milk gland however, lipids are apparently transferred into the developing larva not by lipophorin but by another carrier lipoprotein.

“…Twelve proteins have been identified as the major constituents of tsetse milk (10)(11)(12)(13). Lipids present in tsetse milk are generated either from metabolized blood meals or via lipolysis of stored fat body lipids (14)(15)(16)(17). During lactation, the rapid incorporation of nutrients into the milk reduces total maternal lipid content by nearly 50% and protein content by about 25% (14,18,19).…”

mentioning

confidence: 99%

“…During lactation, the rapid incorporation of nutrients into the milk reduces total maternal lipid content by nearly 50% and protein content by about 25% (14,18,19). The nutrients are transported to the milk gland as free amino acids, free fatty acids, and lipophorin-associated diacylglycerol (15,18,19). We recently showed that this process is regulated by interactions between juvenile hormone and insulin-like peptides, where high levels of both promote increased lipogenesis between bouts of lactation while low levels facilitate the increased lipid breakdown observed during milk production (20).…”

mentioning

confidence: 99%

Vitamin B ₆ Generated by Obligate Symbionts Is Critical for Maintaining Proline Homeostasis and Fecundity in Tsetse Flies

Michalková

Weiss

et al. 2014

Appl Environ Microbiol

120

121

bThe viviparous tsetse fly utilizes proline as a hemolymph-borne energy source. In tsetse, biosynthesis of proline from alanine involves the enzyme alanine-glyoxylate aminotransferase (AGAT), which requires pyridoxal phosphate (vitamin B 6 ) as a cofactor. This vitamin can be synthesized by tsetse's obligate symbiont, Wigglesworthia glossinidia. In this study, we examined the role of Wigglesworthia-produced vitamin B 6 for maintenance of proline homeostasis, specifically during the energetically expensive lactation period of the tsetse's reproductive cycle. We found that expression of agat, as well as genes involved in vitamin B 6 metabolism in both host and symbiont, increases in lactating flies. Removal of symbionts via antibiotic treatment of flies (aposymbiotic) led to hypoprolinemia, reduced levels of vitamin B 6 in lactating females, and decreased fecundity. Proline homeostasis and fecundity recovered partially when aposymbiotic tsetse were fed a diet supplemented with either yeast or Wigglesworthia extracts. RNA interference-mediated knockdown of agat in wild-type flies reduced hemolymph proline levels to that of aposymbiotic females. Aposymbiotic flies treated with agat short interfering RNA (siRNA) remained hypoprolinemic even upon dietary supplementation with microbial extracts or B vitamins. Flies infected with parasitic African trypanosomes display lower hemolymph proline levels, suggesting that the reduced fecundity observed in parasitized flies could result from parasite interference with proline homeostasis. This interference could be manifested by competition between tsetse and trypanosomes for vitamins, proline, or other factors involved in their synthesis. Collectively, these results indicate that the presence of Wigglesworthia in tsetse is critical for the maintenance of proline homeostasis through vitamin B 6 production.