An Ancient Mutation in the TPH1 Gene is Consistent with the Changes in Mammalian Reproductive Rhythm

The Reserve/Maximum Capacity of Melatonin's Synthetic Function for the Potential Dimorphism of Melatonin Production and Its Biological Significance in Mammals

In this article, we attempt to classify a potential dimorphism of melatonin production. Thus, a new concept of "reserve or maximum capacity of melatonin synthetic function" is introduced to explain the subtle dimorphism of melatonin production in mammals. Considering ASMT/ASMTL genes in the pseudoautosomal region of sex chromosomes with high prevalence of mutation in males, as well as the sex bias of the mitochondria in which melatonin is synthesized, we hypothesize the existence of a dimorphism in melatonin production to favor females, which are assumed to possess a higher reserve capacity for melatonin synthesis than males. Under physiological conditions, this subtle dimorphism is masked by the fact that cells or tissues only need baseline melatonin production, which can be accomplished without exploiting the full potential of melatonin's synthetic capacity. This capacity is believed to exceed the already remarkable nocturnal increase as observed within the circadian cycle. However, during aging or under stressful conditions, the reserve capacity of melatonin's synthetic function is required to be activated to produce sufficiently high levels of melatonin for protective purposes. Females seem to possess a higher reserve/maximum capacity for producing more melatonin than males. Thus, this dimorphism of melatonin production becomes manifest and detectable under these conditions. The biological significance of the reserve/maximum capacity of melatonin's synthetic function is to improve the recovery rate of organisms from injury, to increase resistance to pathogen infection, and even to enhance their chances of survival by maximizing melatonin production under stressful conditions. The higher reserve/maximum capacity of melatonin synthesis in females may also contribute to the dimorphism in longevity, favoring females in mammals.

Transcriptome Analysis of Neuroendocrine Regulation of Ovine Hypothalamus-Pituitary-Ovary Axis during Ovine Anestrus and the Breeding Season

Most sheep are seasonal estrus, and they breed in autumn when the days get shorter. Seasonal estrus is an important factor that affects the productivity and fertility of sheep. The key point to solve this problem is to explore the regulation mechanism of estrus in sheep. Therefore, in this study, transcriptomic sequencing technology was used to identify differentially expressed mRNAs in the hypothalamus, pituitary and ovary of Small Tail Han sheep (year-round estrus) and tan sheep (seasonal estrus) among luteal, proestrus and estrus stages. There were 256,923,304,156 mRNAs being identified in the hypothalamus, pituitary and ovary, respectively. Functional analysis showed that the photosensor, leucine and isoleucine biosynthesis pathways were enriched significantly. It is speculated that photoperiod may initiate estrus by stimulating the corresponding pathways in hypothalamus. ODC1, PRLH, CRYBB2, SMAD5, OPN1SW, TPH1 are believed to be key genes involved in the estrogen process. In conclusion, this study expanded the database of indigenous sheep breeds, and also provided new candidate genes for future genetic and molecular studies on the seasonal estrus trait in sheep.

Contribution of the mutation T865G in TPH1 gene to the genetic potentiality of housed Mongolian sheep to year-round breeding

Seasonal breeding is widespread in sheep and significantly affects the development of the housed sheep industry. To improve and balance the reproduction performance of sheep, year-round breeding has the goal of modern sheep farming. The tryptophan hydroxylase (TPH), which initiates and regulates biosynthesis of melatonin, is an important player in the formation of mammalian year-round breeding. However, little is known about its role in regulation of sheep seasonal breeding. In this study, a missense mutation, T865G in TPH1 gene was detected in 328 individuals of six Mongolian sheep groups. It was positively selected among Mongolian sheep. This mutation may appear between 13,683 and 350,973 years ago and only exist in Hu sheep now. In Hu sheep, the frequency of allele T was 89.66%, and that of allele G was 10.34%. The TPH1 protein structure and property analysis suggested that this mutation from T to G affect the three-dimensional structure and reduce the hydropathicity of catalytic core. When the allele is T, the protein activity is twice that of the allele G, and their difference was significant (p < .05). In conclusion, T865G is an ancient mutation of TPH1 gene and affects the function of TPH protein, which may contribute to the genetic potentiality of Mongolian sheep to year-round breeding.

The role of melatonin and Tryptophan-5-hydroxylase-1 in different abiotic stressors in Apis cerana cerana

Tryptophan-5-hydroxylase-1 (T5H-1) is the rate-limiting enzyme in the biosynthesis of serotonin, which is involved in the biosynthesis of melatonin (Mel). Mel, a biological hormone, plays crucial roles in stressors tolerance, such as cold, hot, Ultraviolet (UV) and pesticide tolerance. However, the direct correlation between T5H-1 and Mel and the underlying mechanism in organisms remains elusive. Mel-mediated cold tolerance was studied extensively in plants and somewhat in insects, including bees. The present study isolated the Mel synthesis gene T5H-1 from Apis cerana cerana for the first time. qRT-PCR analysis indicated that AccT5H-1 played vital roles during some adverse conditions, including 4 °C, 8 °C, 10 °C, 45 °C, UV, cyhalothrin, abamectin, paraquat and bifenthrin exposure. Knockdown of AccT5H-1 using RNA interference (RNAi) technology upregulated most antioxidant genes. Additionally, an enzyme activity assay revealed higher contents of Malondialdehyde (MDA) and Hydrogen peroxide (H₂O₂), lower content of Vitamin C (VC), and higher activities of Glutathione S-transferase (GST), Superoxide dismutase (SOD), Catalase (CAT) and Peroxidase (POD) in the AccT5H-1 silenced group than the control group. These results suggest that AccT5H-1 is involved in the response to different oxidative stressors in A. cerana cerana. The survival rate of A. cerana cerana exposed to low temperature treatment revealed that the optimal concentration of Mel in the diet was 10 µg/mL. We also found that the antioxidant enzyme (GST, SOD, POD and CAT) concentrations at 10 µg/mL Mel increased to different degrees, and the content of oxidizing substances (MDA and H₂O₂) decreased, the content of VC increased, and the content of substances that promote cold resistance (glycerol and glycogen) increased. Mel increased the resistance of A. cerana cerana exposed to low temperatures. The expression of AccT5H-1 decreased after the feeding of exogenous Mel to bees. These results provide a reference for other insect studies on Mel and T5H-1.