The underlying mechanisms of vertebrate seasonal reproduction

Abstract

Animals make use of changes in photoperiod to adapt their physiology to the forthcoming breeding season. Comparative studies have contributed to our understanding of the mechanisms of seasonal reproduction in vertebrates. Birds are excellent models for studying these phenomena because of their rapid and dramatic responses to changes in photoperiod. Deep brain photoreceptors in birds perceive and transmit light information to the pars tuberalis (PT) in the pituitary gland, where the thyroid-stimulating hormone (TSH) is produced. This PT-TSH locally increases the level of the bioactive thyroid hormone T3 via the induction of type 2 deiodinase production in the mediobasal hypothalamus, and an increased T3 level, in turn, controls seasonal gonadotropin-releasing hormone secretion. In mammals, the eyes are the only photoreceptive structure, and nocturnal melatonin secretion encodes day-length information and regulates the PT-TSH signaling cascade. In Salmonidae, the saccus vasculosus plays a pivotal role as a photoperiodic sensor. Together, these studies have uncovered the universality and diversity of fundamental traits in vertebrates.

Ontogeny of OPN4, OPN5, GnRH and GnIH mRNA Expression in the Posthatch Male and Female Pekin Duck (Anas platyrhynchos domesticus) Suggests OPN4 May Have Additional Functions beyond Reproduction

“…Upon stimulation, the MBH produces the type 2 deiodinase (DIO2) that converts thyoxine (T4) to triiodothyronine (T3). Conversely, during short day lengths, the MBH produces a thyroid hormone (TH)-deactivating enzyme from the DIO3 gene, which converts T4 and T3 into inactive reverse triiodothyronine, an inactive form of thyroid hormone [ 13 ]. Thyroid hormone is critical for many physiological changes associated with post-hatch development and maturation of the central nervous system (CNS).…”

Maternal GABAergic and GnRH/corazonin pathway modulates egg diapause phenotype of the silkwormBombyx mori

“…The proportions of diapause eggs oviposited from wt (wt) and KO mutant (−) female moths of 25DD were measured as well as that of moths injected with plant alkaloid PTX, Crz, and DH at 50 μg, 1 nmol, and 100 pmol per pupa, respectively. The significant differences vs. wt reproductive activity (42,43). For seasonal breeders, activation of the HPG axis, including control of GnRH secretion, results in a considerable change in gonadal size, particularly in birds, in which it increases more than a 100-fold during the breeding season in response to seasonal changes, such as in photoperiod (42,43).…”

“…Reproduction in vertebrates is primarily regulated by the hypothalamic–pituitary–gonadal (HPG) axis. GnRH released from the hypothalamus induces the secretion of gonadotropins from the pituitary, which activates gonadal function and triggers reproductive activity ( 42 , 43 ). For seasonal breeders, activation of the HPG axis, including control of GnRH secretion, results in a considerable change in gonadal size, particularly in birds, in which it increases more than a 100-fold during the breeding season in response to seasonal changes, such as in photoperiod ( 42 , 43 ).…”

“…GnRH released from the hypothalamus induces the secretion of gonadotropins from the pituitary, which activates gonadal function and triggers reproductive activity ( 42 , 43 ). For seasonal breeders, activation of the HPG axis, including control of GnRH secretion, results in a considerable change in gonadal size, particularly in birds, in which it increases more than a 100-fold during the breeding season in response to seasonal changes, such as in photoperiod ( 42 , 43 ). Not only Crz structurally belongs to the GnRH superfamily, but SG/CC is also functionally comparable to the vertebrate pituitary gland ( 44 ).…”

Photoperiod induced the pituitary differential regulation of lncRNAs and mRNAs related to reproduction in sheep

“…Animals can schedule reproduction events to maximize adaptation to the changing environment and the survival of offspring. Most animals, including birds, mammals and even in the human, have a highly accurate mechanism for photoperiod measurement and show dramatic changes in seasonal response to small changes in photoperiod ( Nakayama & Yoshimura, 2017 ; Guh, Tamai & Yoshimura, 2019 ). In sheep, the efficiency of reproduction is significantly related to the frequency of estrus ( Li et al, 2019a ).…”