The fatty acyl-CoA reductase Waterproof mediates airway clearance in Drosophila

Abstract

The transition from a liquid to a gas filled tubular network is the prerequisite for normal function of vertebrate lungs and invertebrate tracheal systems. However, the mechanisms underlying the process of gas filling remain obscure. Here we show that waterproof, encoding a fatty acyl-CoA reductase (FAR), is essential for the gas filling of the tracheal tubes during Drosophila embryogenesis, and does not affect branch network formation or key tracheal maturation processes. However, electron microscopic analysis reveals that in waterproof mutant embryos the formation of the outermost tracheal cuticle sublayer, the envelope, is disrupted and the hydrophobic tracheal coating is damaged. Genetic and gain-of-function experiments indicate a non-cell-autonomous waterproof function for the beginning of the tracheal gas filling process. Interestingly, Waterproof reduces very long chain fatty acids of 24 and 26 carbon atoms to fatty alcohols. Thus, we propose that Waterproof plays a key role in tracheal gas filling by providing very long chain fatty alcohols that serve as potential substrates for wax ester synthesis or related hydrophobic substances that ultimately coat the inner lining of the trachea. The hydrophobicity in turn reduces the tensile strength of the liquid inside the trachea, leading to the formation of a gas bubble, the focal point for subsequent gas filling. Waterproof represents the first enzyme described to date that is necessary for tracheal gas filling without affecting branch morphology. Considering its conservation throughout evolution, Waterproof orthologues may play a similar role in the vertebrate lung.

Synthesis of oleyl oleate wax esters in Arabidopsis thaliana and Camelina sativa seed oil

“…As long‐chained wax esters harbouring one double bond on either side of the ester bond may be best suited for lubrication purposes, we aimed to identify an enzyme combination that exhibited the (i) best specificity for the preferential formation of oleyl oleate and (ii) highest overall wax ester accumulation in seed oils. Therefore, we tested seven different combinations of FARs and WSs from different organisms selected by their published substrate specificity: mCherry: Mm FAR1/EYFP: Mm WS, Oleo3:mCherry: Mm FAR1∆c/EYFP: Mm WS, Oleo3:mCherry: Mm FAR1∆c/Oleo3:EYFP: Mm WS (Heilmann et al ., ), Oleo3:mCherry: Mm FAR1∆c/ Sc WS (Lardizabal et al ., ), Sc FAR/ Sc WS (Metz et al ., ), Dm FAR/ Sc WS [ Dm FAR from Drosophila (Jaspers et al ., )] and Ma FAR/ Sc WS (Iven et al ., ) (Figure ). We screened the seed oil of fifty heterozygous Arabidopsis T2 lines each for wax ester production applying thin layer chromatography as described recently (Iven et al ., ).…”

Functional analysis of Aarf domain‐containing kinase 1 in Drosophila melanogaster

“…31,32 In addition, lipid phosphate phosphatases encoded by the Drosophila Wunen family are required for normal tracheal development during embryogenesis. The fatty acyl-CoA reductase encoded by the waterproof locus is required for gas filling of the trachea at the molts, and lipoprotein-mediated lipid uptake is necessary for the proper structure of the tracheal lumen.…”

Biotechnological potential of insect fatty acid-modifying enzymes

“…The majority of information is available for one insect group -the moths [18]. FA-modifying enzymes from other insect orders, such as beetles (Coleoptera) [26], flies (Diptera) [27][28][29], crickets (Orthoptera) [30,31] and bees (Hymenoptera) [32][33][34], are substantially less well explored and usually connected to primary FA metabolism rather than pheromone biosynthesis. Two enzyme groups that are encoded by large multigene families in insects -the membrane fatty acyl desaturases (mFADs) [35,36] and the fatty acyl reductases (FARs) [37] -have attracted the most research attention.…”

“…The fatty alcohols are precursors of waxes that serve as surface-protective compounds in plant pollen [96], preventing excessive water loss in insects [29], and are secreted as skin-, eye-, or featherprotective compounds in mammals and birds [97,98]. The fatty alcohols are also components of ether lipids, which are abundant in the cell membranes of cardiac, nervous and lymphoid tissues [99].…”

“…FARs from insects other than moths are virtually unexplored. A FAR presumably involved in biosynthesis of fatty alcohol precursors of waxes has been identified in Drosophila [29], and honeybee (Apis mellifera) FAR capable of reducing hydroxylated fatty acyl precursors and saturated C16-C22 fatty acyls has been characterized [34]. FARs from pheromone-producing glands in the butterfly Bicyclus anynana reduce C14 and C16 fatty acyls [86].…”