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by claude@2026-07, 2026-07-06
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The study investigated how rainbow trout transition between two consecutive reproductive cycles, focusing on communication between eggs, the ovary, and the central nervous system, by using egg removal versus egg retention as a switch and longitudinally measuring circulating microRNAs in blood plasma and ovarian fluid. Egg removal caused a dramatic downregulation of a single brain-predominant microRNA, miR-139-5p, in blood plasma, whereas distinct circulating miRNA profiles were observed when eggs were retained; dynamic changes also included brain/pituitary-enriched miR-135c and postovulatory ovary–predominant miR-457a, along with a drop in ovarian-fluid miR-202-5p. The authors identified possible miR-139-5p functional targets in trout and related iteroparous species, noting differences compared with semelparous salmonids. This paper does not explicitly discuss endometriosis or adenomyosis; it was included in the corpus via a keyword match in the upstream search index.
Abstract
Mechanisms regulating the transition between two consecutive reproductive cycles are complex and remain poorly understood, mostly because they involve a dialog between the ovary and the central nervous system that is difficult to disentangle. In rainbow trout ( Oncorhynchus mykiss ), an iteroparous species spawning every year, removal of the eggs from the body cavity was used as a switch to trigger the onset of the next reproductive cycle. Changes in circulating miRNAs (c-miRNAs) levels in blood plasma and ovarian fluid were then monitored over time. Upon removal of the eggs from the body cavity we observed the dramatic down regulation of the blood plasma levels of a single c-miRNA (miR-139-5p) that is predominantly expressed in the brain. In contrast, very distinct c-miRNAs profiles were observed in blood plasma when eggs are retained in the body cavity. Among plasma c-miRNAs showing dynamic changes with egg retention, miR-135c is strongly expressed in the brain and pituitary, while miR-457a is predominant in the postovulatory ovary. In addition, egg retention in the body cavity triggers a dramatic drop in ovarian fluid levels of miR-202-5p, a miRNA known to regulate egg production in fish. Our observations reveal that the transition between two successive reproductive cycles involves a crosstalk between the eggs and the central system and that a single miRNA, miR-139, predominantly expressed in the brain, is associated with the onset of the next reproductive cycle. We identified possible miR-139-5p functional targets in rainbow trout and other iteroparous species that have been lost in semelparous salmonids. Our results offer new research perspectives to better understand the mechanisms triggering the next reproductive cycle in iteroparous fish species, including post-transcriptional regulations by miR-139 in the brain.
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Abstract
Mechanisms regulating the transition between two consecutive reproductive cycles are complex and remain poorly understood, mostly because they involve a dialog between the ovary and the central nervous system that is difficult to disentangle. In rainbow trout (Oncorhynchus mykiss), an iteroparous species spawning every year, removal of the eggs from the body cavity was used as a switch to trigger the onset of the next reproductive cycle. Changes in circulating miRNAs (c-miRNAs) levels in blood plasma and ovarian fluid were then monitored over time. Upon removal of the eggs from the body cavity we observed the dramatic down regulation of the blood plasma levels of a single c-miRNA (miR-139-5p) that is predominantly expressed in the brain. In contrast, very distinct c-miRNAs profiles were observed in blood plasma when eggs are retained in the body cavity. Among plasma c-miRNAs showing dynamic changes with egg retention, miR-135c is strongly expressed in the brain and pituitary, while miR-457a is predominant in the postovulatory ovary. In addition, egg retention in the body cavity triggers a dramatic drop in ovarian fluid levels of miR-202-5p, a miRNA known to regulate egg production in fish. Our observations reveal that the transition between two successive reproductive cycles involves a crosstalk between the eggs and the central system and that a single miRNA, miR-139, predominantly expressed in the brain, is associated with the onset of the next reproductive cycle. We identified possible miR-139-5p functional targets in rainbow trout and other iteroparous species that have been lost in semelparous salmonids. Our results offer new research perspectives to better understand the mechanisms triggering the next reproductive cycle in iteroparous fish species, including post-transcriptional regulations by miR-139 in the brain.
Competing Interest Statement
The authors have declared no competing interest.
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