Identifying Universal Fish Biomarker Genes in Response to PCB126 Exposure by Comparative Transcriptomic Analyses

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper is a laborious work that exposed adult fish of two major laboratory fish species, zebrafish and medaka, to PCB126, a major coplanar PCB, and comprehensively examined changes of gene expression in the liver using RNA-seq. First, the authors should elaborate on AhR agonists, including PCB126, in the Introduction. The same changes in the resulting four fish species were obtained in the induction of CYP1A and CYP1C, which has been reported in many cases. Authors should add useful discuss in detail the genes that were induced by PCB126, other than CYPs.

 

General comments:

1)     Isn't it “Results and Discussion”, not “Results”?　Currently, I can’t find a Discussion section.

2)     The only genes with altered expression levels common to the four fish species studied were CYP1A and CYP1C. However, a number of reports on these have already been published. On the other hand, if these were altered, it would indicate that they may have been exposed to AhR agonists, but nobody knows if it was TCDD, other coplanar PCBs, or other aromatic hydrocarbons. The author should explain this somewhere.

3)     The value of this paper is that the comprehensive gene expression changes caused by PCB126 were compared between zebrafish and medaka. However, only CYP1A and CYP1C were genes that were commonly changes in four fish species including guppy and tilapia. The authors should add a meaningful discussion on genes with significantly altered expression other than CYP1A and CYP1C.

 

Specific comments:

1) The first paragraph of Introduction: It is concerning that while the study focuses on PCBs, the introduction extensively discusses Minamata disease, which is caused by methylmercury.

2) A paragraph from L72: The explanation for why PCB 126 was chosen among the water contaminants seems weak. For example, it is necessary to clarify that PCB 126 is a typical coplanar PCB. In addition, the authors should add an explanation of AhR agonists, including PCB126.

3) 2.1. Fish maintenance: How did Authors obtain zebrafish and medaka? Did Authors buy them from some supplier? Which temperatures did the authors use for maintenance and experiments? Which kind of solution did Authors use?

4) 2.2. Acute PCB126 treatment: Which kind of 5L tank did Authors use for exposure to PCB126? Glass or some plastic tank? PCB126 can be readily adsorbed to plastics like polyethylene microplastics.

5) Results part in L324-358: At what temperature did the guppies and tilapia grow and were exposed to PCB 126?　 Can water temperature influence gene expression?

Author Response

Please see the attachment,

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The study entitled: Identifying universal fish biomarker genes in response to PCB126 exposure by comparative transcriptomic analyses reports a promising strategy to identify common biomarker genes to be used for fish analyses. The authors employed zebrafish and medaka to expose PCB126 to obtain transcriptomic liver data from RNA-seq and to develop universal PCR primers, potentially suitable for all species of fish, have designed primer degenerate tests in in the two model species as well as in tilapia and another species without available genomic sequence, guppy. In conclusion, they believe that a diagnostic PCR matrix can be developed to predict water contamination from any species of wild fish sampled in different water bodies.

The manuscript contains important data but needs to be revised, following some suggestions.

Abstract:

Line 15: Add medaka;

Line 23: what species of fish? Teleostei or….?

Line 26: what species of fish?

In the Abstract and the Introduction it was not specified in which sample the study was carried out

The introduction should, in my opinion, be reviewed as it is not clear in which anatomical district the study was carried out. In addition, see line 74, the authors add information that should be included in the materials and methods.

In addition, the information from line 85 to line 95 should be inserted at the beginning of the discussion/conclusion paragraph.

 

Materials and Methods

Materials and methods should be rewritten for a better understanding of the manuscript. n particular, would it be useful to have more information on the following points.

 

1. Was the experiment conducted in Facility?

2. How long did the experiment last?

3. How many control animals were used per species used?

4. Were same-sex animals used for each species?

5. Better explain the timing of PCB126 administration

6. Was the water to which PCB126 was added stagnant?

7. Has each species of fish used been housed in tank?

8. Specify the age of each species of fish used.

 

Line 164: The authors report: More batches of zebra fish, medaka, tilapia and guppy.. explain them better. If other fish have been added, this shall be reported in material and methods.

Results

From line 288 to line 296 is unclear. Can authors rewrite these sentences?

Line 330: “exposed independent batches of all four teleost species” Is it possible to explain better this sentence?

Line 351: which table?

 Conclusion

Authors should review that paragraph taking into account the suggestions reported so far

Author Response

pls see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

No comments.

Reviewer 2 Report

Comments and Suggestions for Authors

Authors answered questions making sentences clearer