PONE-D-20-08055

Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: what happens to the liver?

PLOS ONE

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Reviewers' comments:

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The manuscript describes a study on European eel vitellogenesis with a RNA sequencing approach, making a differential expression analysis of liver samples from yellow and silvering female eels.

In general, the experimental design and methodology seems good, the manuscript is well written, and the discussed ideas are relevant (at least considering the grade of hypothetical conclusions required for this type of results).

I included a few suggestions to be considered by the authors, and found some formal mistakes that should be corrected (especially references format!).

Introduction

L74. migration instead of migrating?

L76. 80´s or even before in some places

L87 Reference 18. For a more specific information on eel, you could use Mylonas et al., 2017 (http://dx.doi.org/10.1016/j.aquaculture.2016.04.021).

L101 (plus comments on L276 and L394). There is scarce information available on the enzymatic control of fatty acid biosynthesis in the eel. Baeza et al., 2014´s (http://dx.doi.org/10.1016/j.aquaculture.2014.03.045) and 2015´s studies (http://dx.doi.org/10.1016/j.cbpa.2014.11.022) played with the idea of a liver involved in the lipids mobilization from muscle to gonad during gonadal maturation, but also evidenced de novo synthesis of lipids in the liver (in especial palmitic acid and EPA). Can your results clarify something on the role of European eel fatty desaturases and elongases?, and maybe relating them with dietary necessities for this species?

L129, L142, L205. 20 ºC (separate number and unit)

L134. Why fish were pit-tagged?

L137. S.L.U.

L166. 150 bp

Results

L224. Maybe is better to talk of a 1.6 fold increase of HSI.

L228. Vitellogenic

L234. 57%

L249. ...in the pre-spawning samples.

L250. (VTG1 and VTG2)

L298. Aorta mention seems too specific. Vascular tissues??

Discussion

L330. ...and used for ovary development and egg yolk...

L356. Check the recent paper from Morini et al., 2020. (http://dx.doi.org/10.1017/S1751731119003355). In the European eel, up-regulation of VTG under estradiol treatment was observed in eel in vivo (Burzawa-Gérard and Dumas-Vidal, 1991) as well as in vitro by hepatocyte primary cultures (Lafont et al., 2016). Nevertheless, ovaries from E2-treated eels are not able to incorporate Vtg (Dufour et al., 1988), and CPE treatment is necessary to induce ovarian vitellogenesis (Mazzeo et al., 2014).

They found found that vtgr transcription already occurs during early PV of immature eel and is not further activated in vitellogenic oocytes. Can your (liver) data support this conclusion somehow?

L364. chemical disruptors?

L371. Morini et al. 2017 (http://dx.doi.org/10.1016/j.cbpa.2017.02.009) reported the expression of several progestin receptors in the liver of immature eels, and described the changes of the expression of these genes happening in the testes during hormonally-induced spermatogenesis. Does your data suggest differential expression of these genes in the liver induced by hormonal treatment in the females?.

References

In general, follow the journal´s format.

Full references (including volume and page numbering, doi and PMID) are required.

Write especies´s name in italics.

Avoid writing with capitals every word of the titles.

Delete “and” from the list of authors (limited to 6; rest: et al.).

Check abbreviated journal names.

L533. IUCN?

L550, 563. European

L572. It is still under review?. Add full reference or delete.

L662. Oncorhynchus

L681. Nutritional regulation of insulin-like growth factor-I mRNA expression in salmon tissues???

Reviewer #2: The experiments were well designed in the study. In my opinion, the findings based on genes included in biological processes of the study will provide new insights for vitellogenesis in the eel or reproductive studies to be considered in other fish species. However, authors should take attention some issues regarding manuscript content. Authors should make corrections by controlling the text carefully according to the journal's rules. Some mistakes, for example in line 122, the length of the fish (76 ± 136 3 cm) should be corrected. A representative figure taken from the gonadal sections (especially vitellogenic stage) pertained to week 9 should be inserted in the results with a control section (previtellogenic stage).

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Reviewer #1: Yes: Juan F. Asturiano

Reviewer #2: No

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Unravelling the changes during induced vitellogenesis in female European eel through RNA-Seq: what happens to the liver?

PONE-D-20-08055R1

Dear Dr. Bertolini,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Hubert Vaudry

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This second version reflects all the comments ans suggestions I previously did.

In my opinion, the manuscript is ready to be published.

Reviewer #2: All requested recommendations have been completed by authors. The revised manuscript can be accepted for publication.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Juan F. Asturiano

Reviewer #2: No