Sphingomyelinase Activity in Mother's Milk Is Essential for Juvenile Development: A Case from Lactating Tsetse Flies1

Abstract

Sphingosine is a structural component of sphingolipids. The metabolism of phosphoethanolamine ceramide (sphingomyelin) by sphingomyelinase (SMase), followed by the breakdown of ceramide by ceramidase (CDase) yields sphingosine. Female tsetse fly is viviparous and generates a single progeny within her uterus during each gonotrophic cycle. The mother provides her offspring with nutrients required for development solely via intrauterine lactation. Quantitative PCR showed that acid smase1 (asmase1) increases in mother's milk gland during lactation. aSMase1 was detected in the milk gland and larval gut, indicating this protein is generated during lactation and consumed by the larva. The higher levels of SMase activity in larval gut contents indicate that this enzyme is activated by the low gut pH. In addition, cdase is expressed at high levels in the larval gut. Breakdown of the resulting ceramide is likely accomplished by the larval gut-secreted CDase, which allows absorption of sphingosine. We used the tsetse system to understand the critical role(s) of SMase and CDase during pregnancy and lactation and their downstream effects on adult progeny fitness. Reduction of asmase1 by short interfering RNA negatively impacted pregnancy and progeny performance, resulting in a 4-5-day extension in pregnancy, 10%-15% reduction in pupal mass, lower pupal hatch rates, impaired heat tolerance, reduced symbiont levels, and reduced fecundity of adult progeny. This study suggests that the SMase activity associated with tsetse lactation and larval digestion is similar in function to that of mammalian lactation and represents a critical process for juvenile development, with important effects on the health of progeny during their adulthood.

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

“…For determination of the knockdown phenotypes, flies were injected either 1–2d after adult emergence with siRNAs targeting genes expressed early in pregnancy ( Met , gce and JHAMT ) or 7–9d after adult emergence to target genes expressed late in pregnancy ( bmm and FOXO ). Previous studies have shown that siRNA injection into the mother has no discernible effect on larval transcript levels (Attardo et al, 2012; Benoit et al, 2012). Three to five days after siRNA injection, expression levels of target and downstream genes were determined by qPCR (as described) and normalized to tub after removal of the larva.…”

“…Female flies were mated 3d after emergence and stored in groups of 15 flies. Female flies were collected for analysis according to developmental markers based on the progeny developmental state which were established to analyze pregnancy according to previous studies (Attardo et al, 2006; Benoit et al, 2012). …”

“…During the four to six day larvigenesis period, the milk gland secretes 20–30 mg of milk, which consists of various carbohydrates, lipids, and proteins (Cmelik et al, 1969). The protein constituents of the milk include a lipocalin (milk gland protein, MGP1; Attard et al, 2006), several novel, tsetse-specific proteins called milk gland proteins (MGP2 and MGP3, Yang et al, 2010; Transferrin, Guz et al 2007; Acid sphingomyelinase 1, aSMase1, Benoit et al 2012) and Peptidoglycan Recognition Protein-LB (Wang et al, 2012). The lipids present in the milk originate directly from the digestion products of the blood meal and from lipolysis of stored lipids in the fat body (Attardo et al, 2012; Langley et al, 1981; Pimley et al, 1981; 1982).…”

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

“…During each lactation cycle, the milk gland secretes up to 25 mg of milk that consists primarily of lipids and proteins (9). 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).…”

First Characterization of Sphingomyeline Phosphodiesterase Expression in the Bumblebee, Bombus lantschouensis

“…Furthermore, based on microarray analysis, it was found that SMPD expression levels decreased with the sugar regulation (Zinke et al, 2002). Interestingly, it was suggested that the silence of SMPD gene by siRNA has strong influence on pregnancy and progeny development in Glossina morsitans morsitans Westwood (Diptera: Glossinidade) (Benoit et al, 2012). However, the function of SMPD in bees hasn't been explored.…”