As the fat flies: The dynamic lipid droplets of Drosophila embryos

Abstract

Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.

Temporal control of bidirectional lipid-droplet motion in Drosophila depends on the ratio of kinesin-1 and its co-factor Halo

“…We show that lipid-droplet position is tightly controlled by Halo levels. Altered droplet distribution in Drosophila embryos has so far not been linked to any organismal dysfunction, but it is intriguing that the temporal shifts in droplet transport have been conserved for at least 100 million years (reviewed in Welte, 2015). Droplet movement has been observed in many species and cell types (Welte, 2009).…”

“…Exquisite temporal regulation of run length is characteristic of bidirectional lipid-droplet motion in early Drosophila embryos (Welte, 2015). Here, microtubules are radially arranged, with plus ends towards the embryo centre and minus ends towards the periphery.…”

“…However, it is not clear how far droplets will travel that are pulled by both activated (long travel) and unactivated (short travel) motors. Multiple scenarios are conceivable -the most highly processive motor might dominate, promoting long travel; competition between activated and unactivated motors might lead to intermediate travel distances, similar to the compromise in travel characteristics observed for flagellar motors of distinct inherent velocities (Pan et al, 2006); or the short-traveling motors might dominate, if the termination of runs involve a switch (as proposed for droplets; Shubeita et al, 2008;Welte, 2015) that is triggered when the short-traveling motors end their runs. Our results are most consistent with the latter model (Fig.…”

“…Changes in droplet distribution are typically monitored by altered embryo transparency (Welte, 2015); however, it is challenging to document the dynamic changes at the transitions between phases with this qualitative method. Lipid droplets have also been quantified in sections by using electron microscopy (Welte et al, 1998) or in living embryos by using femtosecond-stimulated Raman loss (fSRL) microscopy (Dou et al, 2012).…”

Functioning of an ABC transporter, Mdr49, in Hh signaling and germ cell migration

“…Instead they depend upon exogenous sources of this lipid. All of the cholesterol in embryos is of maternal origin and is deposited in the yolk during oogenesis (reviewed by Welte, 2015). Following the cellular blastoderm stage, the yolk is incorporated into the midgut by the process of gastrulation.…”