Polymorphisms in the Chicken Growth Differentiation Factor 9 Gene Associated with Reproductive Traits

Sex-Biased miRNAs in the Gonads of Adult Chinese Alligator (Alligator sinensis) and Their Potential Roles in Sex Maintenance

MicroRNA (miRNA) is a category of single-stranded non-coding small RNA (sRNA) that regulates gene expression by targeting mRNA. It plays a key role in the temperature-dependent sex determination of Chinese alligator (Alligator sinensis), a reptile whose sex is determined solely by the temperature during the incubation period and remains stable thereafter. However, the potential function of miRNAs in the gonads of adult Chinese alligators is still unclear. Here, we prepared and sequenced sRNA libraries of adult female and male alligator gonads, from breeding (in summer) and hibernating (in winter) animals. We obtained 130 conserved miRNAs and 683 novel miRNAs, which were assessed for sex bias in summer and winter; a total of 65 miRNAs that maintained sex bias in both seasons were identified. A regulatory network of sex-biased miRNAs and genes was constructed. Sex-biased miRNAs targeted multiple genes in the meiosis pathway of adult Chinese alligator oocytes and the antagonistic gonadal function maintenance pathway, such as MOS, MYT1, DMRT1, and GDF9. Our study emphasizes the function of miRNA in the epigenetic mechanisms of sex maintenance in crocodilians.

Endocrine and genetic factors affecting egg laying performance in chickens: a review

1. Egg-laying performance reflects the overall reproductive performance of breeding hens. The genetic traits for egg-laying performance have low or medium heritability, and, depending on the period involved, usually ranges from 0.16 to 0.64. Egg-laying in chickens is regulated by a combination of environmental, endocrine and genetic factors. 2. The main endocrine factors that regulate egg-laying are gonadotropin-releasing hormone (GnRH), prolactin (PRL), follicle-stimulating hormone (FSH) and luteinising hormone (LH). 3. In the last three decades, many studies have explored this aspect at a molecular genetic level. Recent studies identified 31 reproductive hormone-based candidate genes that were significantly associated with egg-laying performance. With the development of genome-sequencing technology, 64 new candidate genes and 108 single nucleotide polymorphisms (SNPs) related to egg-laying performance have been found using genome-wide association studies (GWAS), providing novel insights into the molecular genetic mechanisms governing egg production. At the same time, microRNAs that regulate genes responsible for egg-laying in chickens were reviewed. 4. Research on endocrinological and genetic factors affecting egg-laying performance will greatly improve the reproductive performance of chickens and promote the protection, development, and utilisation of poultry. This review summarises studies on the endocrine and genetic factors of egg-laying performance in chickens from 1972 to 2019.

Analysis of Expression and Single Nucleotide Polymorphisms of INHA Gene Associated with Reproductive Traits in Chickens

Inhibin α (INHA) is a candidate gene controlling ovulation in poultry. As the functional center of inhibin, INHA is a molecular marker associated with egg-laying performance. The objective of the current study was to analyze the expression differences of INHA in reproductive system and single nucleotide polymorphisms (SNPs) associations with reproductive traits in chickens. A total of 260 LuHua chickens (barred-feather chicken) were adopted. Twelve SNPs were detected in INHA gene. Among the exonic SNPs, three (g. 22177991A>G, g. 22178249G>C, and g. 22178414G>A) were missense mutations, resulting in the amino acid substitutions Val→Ala, Ala→Gly, and Ala→Gly, respectively. Four SNPs in the 3＇ untranslated region of INHA were predicted to either disturb or create microRNA-target interactions. Five SNPs (g. 22176870T>C, g. 22177100T>C, g. 22177149T>C, g. 22177991A>G, and g. 22178975G>A) were significantly associated with the number of eggs at 300 d of age (EN) (P < 0.05). Birds carrying GA genotype exhibited more EN than those with AA genotype (P < 0.01). In addition, quantitative real-time PCR revealed that INHA is mainly expressed in follicles on d 300 in chickens. Firstly, INHA expression increased and then decreased. The highest INHA mRNA abundance was found in the fifth largest preovulatory follicle (F5) (P < 0.01). In the prehierarchical follicles, INHA mRNA expression increased dramatically in small yellow follicles (SYF) (P < 0.01). Western blotting analysis showed that the INHA protein expression profile in the follicle was similar to its mRNA counterpart with greater expression in F5 and SYF follicles and lowest expression in F1 follicles (P < 0.05). These results suggest that INHA is a potential candidate gene improving reproductive traits in chickens.