Reviewer #3 (Public Review):
Summary:
The receptor tyrosine kinase Anaplastic Lymphoma Kinase (ALK) in humans is nervous system expressed and plays an important role as an oncogene. A number of groups have been studying ALK signalling in flies to gain mechanistic insight into its various roles. In flies, ALK plays a critical role in development, particularly embryonic development and axon targeting. In addition, ALK also was also shown to regulate adult functions including sleep and memory. In this manuscript, Sukumar et al., used a suite of molecular techniques to identify downstream targets of ALK signalling. They first used targeted DamID, a technique that involves a DNA methylase to RNA polymerase II, so that GATC sites in close proximity to PolII binding sites are marked. They performed these experiments in wild type and ALK loss of function mutants (using an Alk dominant negative ALkDN), to identify Alk responsive loci. Comparing these loci with a larval single cell RNAseq dataset identified neuroendocrine cells as an important site of Alk action. They further combined these TaDa hits with data from RNA seq in Alk Loss and Gain of Function manipulations to identify a single novel target of Alk signalling - a neuropeptide precursor they named Sparkly (Spar) for its expression pattern. They generated a mutant allele of Spar, raised an antibody against Spar, and characterised its expression pattern and mutant behavioural phenotypes including defects in sleep and circadian function.
Strengths:
The molecular biology experiments using TaDa and RNAseq were elegant and very convincing. The authors identified a novel gene they named Spar. They also generated a mutant allele of Spar (using CrisprCas technology) and raised an antibody against Spar. These experiments are lovely, and the reagents will be useful to the community. The paper is also well written, and the figures are very nicely laid out making the manuscript a pleasure to read.
Weaknesses:
The manuscript has improved substantially in the revision. Yet, some concerns remain around the genetics and behavioural analysis which is incomplete and confusing. The authors generated a novel allele of Spar - Spar ΔExon1 and examined sleep and circadian phenotypes of this allele and of RNAi knockdown of Spar. The RNAi knockdown is a welcome addition. However, the authors only show one parental control the GAL4 / +, but leave out the other parental control i.e. the UAS RNAi / + e.g. in Fig. 9. It is important to show both parental controls.
Further, the sleep and circadian characterisation could be substantially improved. It is unclear how sleep was calculated - what program was used or what the criteria to define a sleep bout was. In the legend for Fig 8c, it says sleep was shown as "percentage of time flies spend sleeping measured every 5min across a 24h time span". Sleep in flies is (usually) defined as at least 5 min of inactivity. With this definition, I'm not sure how one can calculate the % time asleep in a 5 min bin! Typically people use 30min or 60min bins. The sleep numbers for controls also seem off to me e.g. in Fig. 8H and H' average sleep / day is ~100. Is this minutes of sleep? 100 min / day is far too low, is it a typo? The same applies to Figure 8, figure supplement 2. Other places e.g. Fig 8 figure supplement 1, avg sleep is around 1000 min / day. The numbers for sleep bouts are also too low to me e.g. in Fig 9 number of sleep bouts avg around 4, and in Fig. 8 figure supplement 2 they average 1 sleep bout. There are several free software packages to analyse sleep data (e.g. Sleep Mat, PMID 35998317, or SCAMP). I would recommend that the authors reanalyse their data using one of these standard packages that are used routinely in the field. That should help resolve many issues.
The circadian anticipatory activity analyses could also be improved. The standard in the field is to perform eduction analyses and quantify anticipatory activity e.g. using the method of Harrisingh et al. (PMID: 18003827). This typically computed as the ratio of activity in the 3hrs preceding light transition to activity in the 6hrs preceding light transition. The programs referenced above should help with this.
Finally, in many cases I'm not sure that the appropriate statistical tests have been used e.g. in Fig 8c, 8e, 8h t-tests have been used when are three groups in the figure. The appropriate test here would an ANOVA, followed by post-hoc comparisons.