Research Progress and Effects of Light on Poultry Circadian Rhythm Regulation Based on CiteSpace

Round 1

Reviewer 1 Report

The topic on light and circadian rhythm of poultry is an important one for poultry production. The authors of this review performed a literature search and analysis using CiteSpace, and the review presented the research frontier in this field. In addition, this review summarized and discussed the recent findings in regard to the mechanisms underlying theregulation of light on the circadian rhythm of poultry. The review was generally well written, butminor revisions were required as shown below:
1. Line 21: The authors may state more about "Transcription-translation negative feedback loop" so that the readers can understand it more easily.
2. Line 27-33: More information on poultry circadian rhythm may be emphasized in this paragraph.
3. Line 28-29: remove "birds, and fungi".
4. Line 29: revise "Circadian rhythm ... a 24-h cycle". It is not concise.
5. Line 38-39: References are needed for the statement on the roles of light.
6. Line 52: It is better to replace "fronts of" with "frontiers in".
7. Line 77: Please pay attention to the superscript.
8. Line 191: Please add "the relationship between" before light to make the meaning more clear to the readers.
9. Line 234: "Sensitivity ... melatonin" seems incomplete. Please double check or revise it to make it more clear.
10. Line 297: midnight
11. Line 311 and 356: Check the punctuations.
12. Section 4: I suggest that the authors add more information to introduce the possible regulatory pathways for circadian rhythm.
13. I also suggest that the authors provide more information as notes in the figure legends so that the authors can understand the figures without referring to the text.

Author Response

The topic on light and circadian rhythm of poultry is an important one for poultry production. The authors of this review performed a literature search and analysis using CiteSpace, and the review presented the research frontier in this field. In addition, this review summarized and discussed the recent findings in regard to the mechanisms underlying the regulation of light on the circadian rhythm of poultry. The review was generally well written, but minor revisions were required as shown below:

1. Line 21: The authors may state more about "Transcription-translation negative feedback loop" so that the readers can understand it more easily.

Response: Thanks for the comments and we have revised the sentences for better understanding in the abstract and section 4.

Line 21-23: Automatic regulatory feedback loop and secondary regulatory feedback loop targeted the clock genes/proteins expression play important roles in circadian rhythm regulation.

2. Line 27-33: More information on poultry circadian rhythm may be emphasized in this paragraph.

Response: We have updated the information in the introduction section.

Previous research showed that circadian rhythm plays a key role in hormone secretion, metabolism, immunity, musculoskeletal growth, and so on [3]. It was reported that light regimes can affect the frequency and duration of circadian behavior in Beijing You Chicken laying hens [4]. The disturbed circadian clock played a role in the development of feather pecking [5]. Feeding chickens by their biological rhythms reduces aggressiveness and can help to increase the efficiency of the production of poultry products [6].

Light is also a key factor affecting circadian rhythm and plays an important role in it [11]. Reasonable lighting schedule can regulate the circadian rhythm of poultry by regulating the level of melatonin and clock genes expression, whereas unreasonable lighting would disturb the circadian rhythm [12].

3. Line 28-29: remove "birds, and fungi".

Response: We have removed these words and support more information on poultry circadian rhythm.

4. Line 29: revise "Circadian rhythm ... a 24-h cycle". It is not concise.

Response: This paragraph has been rewritten for better understanding.

Circadian rhythms are endogenous autonomous oscillators of physiological activities and widely exist in humans, plants, animals, and even some bacteria, especially in poultry [1, 2]. Previous research showed that circadian rhythm plays a key role in hormone secretion, metabolism, immunity, musculoskeletal growth, and so on [3]. It was reported that light regimes can affect the frequency and duration of circadian behavior in Beijing You Chicken laying hens [4]. The disturbed circadian clock played a role in the development of feather pecking [5]. Feeding chickens by their biological rhythms reduces aggressiveness and can help to increase the efficiency of the production of poultry products [6].

5. Line 38-39: References are needed for the statement on the roles of light.

Response: Reference has been updated.

6. Line 52: It is better to replace "fronts of" with "frontiers in".

Response: These words have been replaced.

7. Line 77: Please pay attention to the superscript.

Response: The word has been revised.

8. Line 191: Please add "the relationship between" before light to make the meaning more clear to the readers.

Response: Thanks for the comments and we have added the suggested words.

9. Line 234: "Sensitivity ... melatonin" seems incomplete. Please double check or revise it to make it more clear.

Response: This sentence has been revised for better understanding.

Plasma melatonin levels begin to increase in the evening, reaching a maximum from 2:00 to 4:00 am, followed by a slow decrease with almost zero melatonin levels during the day, indicating that sensitivity to light response is a prominent feature of melatonin [46-48].

10. Line 297: midnight

Response: The word has been revised.

11. Line 311 and 356: Check the punctuations.

Response: We have checked and revised the punctuations.

12. Section 4: I suggest that the authors add more information to introduce the possible regulatory pathways for circadian rhythm.

Response: Thanks for the comments and we have updated the information.

As reported, the hypothalamic clock gene BMAL1 expression for pigeons with monochromatic light exposure was involved in the birth rate [92]. The melatonin level of 10-week-old turkeys with a significant circadian rhythm was strongly affected by light [93]. Melatonin may be associated with the expression of clock gene in chicken pancreas [94]. Light color affected the expression of cell clock regulator to regulate the expression of cAanat in eyes [95].

As shown in Figure 6, at the beginning of the circadian rhythm, the positive regulatory factor outputs cycle protein CLOCK and BMAL1 to form a heterodimer, which binds to the E-box in the promoter region of negative feedback factor period (Per) and cryptochrome (Cry) to promote their transcription [96]. The accumulation of Per and Cry can lead to the inactivation of the heterodimer to inhibit their transcriptional generation. The mRNA levels of Per and Cry decrease so that the circadian cycle begins again at dawn [97]. As the downstream gene of the Clock-Bmal1 heterodimer, when CRY is expressed in large quantities, their protein products will also form heterodimers, and then re-enter the nucleus to inhibit the formation of Clock-Bmal1 complex, as an automatic regulation feedback loop [98]. The nuclear receptor (REV-ERBα and REV-ERBβ) and orphan receptor associated with retinoic acid (RORα and RORβ) can compete for the ROR binding site on the BMAL1 promoter affecting the expression of BMAL1 [99]. Specifically, ROR activates the expression of BMAL1, while REV-ERB inhibits BMAL1, thereby inhibiting the function of the clock protein. Therefore, these genes together form a secondary regulatory feedback loop. The exploration of the relationships between clock genes and circadian rhythm was important for light regulation in poultry, which can shed light on the poultry breeding industry improving poultry health and animal welfare.

13. I also suggest that the authors provide more information as notes in the figure legends so that the authors can understand the figures without referring to the text.

Response: Thanks for the comments and we have updated the figure legends for self-explanatory.

Reviewer 2 Report

This manuscript provides some valuable information about research progress and fronts of light effect on circadian rhythm and productive performance in poultry. The paper is technically sound, and the methods are appropriate and properly conducted. However, I suggest to the authors some minor revisions. For this referee, the review is providing valuable information about the mechanisms that regulate circadian rhythm, focusing on recent advances in the role of melatonin and clock genes. The authors include some information about the relationship between melatonin and animal welfare and immunity in poultry production. If it is possible, I recommend the authors to include similar information about CLOCK genes, in order to enhance the importance of studying the relationship of the CLOCK gene network and circadian rhythm in poultry.

Author Response

This manuscript provides some valuable information about research progress and fronts of light effect on circadian rhythm and productive performance in poultry. The paper is technically sound, and the methods are appropriate and properly conducted. However, I suggest to the authors some minor revisions. For this referee, the review is providing valuable information about the mechanisms that regulate circadian rhythm, focusing on recent advances in the role of melatonin and clock genes. The authors include some information about the relationship between melatonin and animal welfare and immunity in poultry production. If it is possible, I recommend the authors to include similar information about CLOCK genes, in order to enhance the importance of studying the relationship of the CLOCK gene network and circadian rhythm in poultry.

Response: Thanks for the comments and we have updated the sentences to enhance the importance.

As reported, the hypothalamic clock gene BMAL1 expression for pigeons with monochromatic light exposure was involved in the birth rate [92]. The melatonin level of 10-week-old turkeys with a significant circadian rhythm was strongly affected by light [93]. Melatonin may be associated with the expression of clock gene in chicken pancreas [94]. Light color affected the expression of cell clock regulator to regulate the expression of cAanat in eyes [95].

As shown in Figure 6, at the beginning of the circadian rhythm, the positive regulatory factor outputs cycle protein CLOCK and BMAL1 to form a heterodimer, which binds to the E-box in the promoter region of negative feedback factor period (Per) and cryptochrome (Cry) to promote their transcription [96]. The accumulation of Per and Cry can lead to the inactivation of the heterodimer to inhibit their transcriptional generation. The mRNA levels of Per and Cry decrease so that the circadian cycle begins again at dawn [97]. As the downstream gene of the Clock-Bmal1 heterodimer, when CRY is expressed in large quantities, their protein products will also form heterodimers, and then re-enter the nucleus to inhibit the formation of Clock-Bmal1 complex, as an automatic regulation feedback loop [98]. The nuclear receptor (REV-ERBα and REV-ERBβ) and orphan receptor associated with retinoic acid (RORα and RORβ) can compete for the ROR binding site on the BMAL1 promoter affecting the expression of BMAL1 [99]. Specifically, ROR activates the expression of BMAL1, while REV-ERB inhibits BMAL1, thereby inhibiting the function of the clock protein. Therefore, these genes together form a secondary regulatory feedback loop. The exploration of the relationships between clock genes and circadian rhythm was important for light regulation in poultry, which can shed light on the poultry breeding industry improving poultry health and animal welfare.