PREreview of Lamp1 mediates lipid transport, but is dispensable for autophagy inDrosophila

LAMP proteins localize at the lysosomal membrane, controlling autophagy-related processes but also lipid transport and metabolism. While it is well-demonstrated the existence of a link between LAMP misfunction and human diseases, the mechanisms underlying LAMP functions are still poorly understood. To better understand the different roles of LAMP proteins, authors aimed to characterize in this work the only LAMP member identified in Drosophila, Lamp1.

Authors first developed new Lamp1 null mutant alleles, as well as an antibody against Lamp1. The validation and characterization of these molecular tools is very convincing, resulting in a valuable toolkit to explore Lamp1 in Drosophila. In this work, authors used the generated mutant alleles to assess the requirement of Lamp1 in autophagy-related processes and in lipid homeostasis. To do that, they combine genetics, confocal and electron microscopy, and biochemistry approaches. On one hand, the presented data indicates that unlike what previously reported in mammals, Lamp1 is not required, or at least is not essential, for autophagy. On the other hand, authors provide evidences supporting a role for Lamp1 in general lipid metabolism, likely including lipid transport. Therefore, the presented data suggests that the previously reported roles of LAMP proteins (autophagy and lipid metabolism) might be independent.

Given the structural and functional evolutionary conservation of LAMP proteins, this work should be of wide interest, validating Drosophila as a useful model for further studies in the field. In general, authors provide solid data. However, I found a number of minor points in the manuscript that I would recommend addressing to fully support the conclusions reached and to make the data more clear:

- Figures order does not correlate with the description order in the main text, what results confusing to follow the data. Some examples of this are: Supp. Fig. 1E-H mentioned before Supp. Fig. 1A-D, or Fig. 1D-E before Fig. 1 B-C (pages 4-5).

- Authors justify the analysis of lysotracker under starvation since “barely any Lysotracker positive structures are found under fed conditions” (page 4). However, in this work lysotracker shows a clear signal under fed conditions, where in fact the most dramatic changes between control and Lamp1 mutants are observed (quantified in Fig. 2I). Therefore, the use of starvation should be explained further, or it should be dicussed at least the unexpected clear signal observed under fed conditions.

- The current version of Figure 2 shows a clear lysotracker signal in control animals (Fig. 2A’), while in the rescue condition the signal it is barely detectable (Fig. 2D’). Given the similar signal levels showed in the quantification for both genotypes (Fig. 2I), it would be recommendable to use different images to illustrate representative examples of control and/or rescue animals.

- By the end of page 6, the description of the expression levels of Atg5 and Atg8a should refer to Fig. 4I, instead of Fig. 4E.

- In Fig. 6, to make the data easier to follow and more illustrative, it would be helpful to have first the WT panel(s), containing examples of APGLs, ALs and lysosomes, and later include the mutant panels.

- The sentence “[Research Support, N.I.H., Extramural Research Support, Non-U.S. Gov't]” appears repeatedly throughout the references list.