Guiling Cao

Litter size is a critical determinant of reproductive efficiency and economic productivity in livestock breeding. Inhibin, a glycoprotein hormone of the transforming growth factor-β (TGF-β) superfamily, plays a pivotal role in regulating follicle-stimulating hormone (FSH) secretion through negative feedback within the hypothalamic–pituitary–gonadal axis. By modulating FSH levels, inhibin influences follicular recruitment, maturation, and ovulation rate—key processes that determine litter size. This review provides a comprehensive analysis of inhibin isoforms (inhibin A and inhibin B), their antagonistic relationship with activin signaling, and their species-specific roles in reproductive regulation. Genetic studies in small ruminants and non-ruminants indicate that polymorphisms in inhibin-related genes, particularly INHA, may contribute to variation in prolificacy-related traits; however, the strength and consistency of these associations differ among species and populations. This review further integrates findings from functional validation studies, particularly in mouse models, demonstrating that partial reduction of inhibin bioactivity can enhance FSH secretion, promote follicular recruitment, and increase ovulation rate and litter size, whereas excessive disruption of inhibin signaling may impair reproductive efficiency. Importantly, the biological effects of inhibin modulation depend on the degree of pathway alteration and the balance between follicular recruitment and prenatal survival. Although inhibin represents an important endocrine regulator of reproductive performance, current genomic evidence suggests that litter-size variation is controlled by multiple interacting pathways, and the contribution of inhibin-related genes requires further functional validation. Future integration of genomic, endocrine, and functional approaches will be essential to clarify the role of inhibin pathways and determine their potential application in sustainable livestock breeding strategies.

Lin28a and Lin28b serve as crucial regulators in gametogenesis. However, it remains unclear whether the two genes are expressed in goat ovarian tissues. In the present study, we examined the distribution of Lin28a proteins in the ovarian tissues of juvenile and pubertal Jining Grey (JG) goats. Additionally, we investigated the mutations in Lin28a and Lin28b and their association with litter size in JG goats. Lin28a proteins were predominantly expressed in the oocytes and granulosa cells of the follicles at different stages of development. Lin28a was also expressed in the corpus luteum, and its expression level declined as the corpus luteum formed and degenerated into the corpus albicans. A mutation (12298T>C) was identified in intron 2 of Lin28a, and there was no significant difference (P>0.05) in terms of the kidding number among the three genotypes of JG goats. For Lin28b, a mutation (718A>T) in exon 4 was found, presenting three genotypes. The frequency of genotypes AA, AT, and TT was 0.466, 0.504, and 0.03, respectively. The A allele was the dominant allele in JG goats, with an allele frequency of 0.718. At this locus, JG female goats with genotypes TT and AT had 0.83 (PPP>0.05) was observed in terms of litter size between the TT and AT genotypes. The present study preliminarily indicated an association between the T allele at the 718 locus in Lin28b and a larger litter size in JG goats. Moreover, Lin28a was widely expressed in follicles. These results suggest a potential DNA marker for improving the kidding number in goats and hold significance for goat breeding.

The transforming growth factor-beta (TGF-β) superfamily plays a crucial role in regulating female reproductive traits, particularly litter size, in small ruminants, such as sheep and goats. This review comprehensively examines the molecular mechanisms through which TGF-β superfamily members—including bone morphogenetic proteins (BMPs), growth differentiation factor 9 (GDF9), inhibin (INHA and INHB), and associated signaling genes—influence ovarian follicular development, ovulation rate, and ultimately, litter size. We synthesize recent findings on polymorphisms in key genes, such as BMPR1B, BMP15, GDF9, inhibins and SMADs family genes, across diverse sheep and goat breeds worldwide. The manuscript highlights how specific mutations in these genes create an intricate signaling network that modulates granulosa cell proliferation, follicular sensitivity to FSH, and the prevention of dominant follicle selection. These molecular interactions result in increased ovulation rates and larger litter sizes in prolific breeds. The gene dosage effects observed in heterozygous versus homozygous mutation carriers further illuminate the complex nature of these reproductive regulations. This improved the understanding of the genetic basis for prolificacy provides valuable insights for marker-assisted selection strategies aimed at enhancing reproductive efficiency in small ruminant breeding programs, with significant implications for improving livestock productivity and economic outcomes.

Tail fat is important for fat-tailed or fat-rumped sheep to survive in harsh environments. However, the molecular mechanism underlying tail fat deposition in sheep remains unclear. In this study, we comprehensively characterized the transcriptome, untargeted lipidome, and targeted metabolome profiles of the tail adipose tissues from Large-tailed Han sheep (long fat-tailed sheep) and Hu sheep (short fat-tailed sheep). We identified 183 differentially expressed genes (DEGs), 55 differential lipids (DLs) and 17 differential metabolites (DMs) in the adipose tissues of the tails from Large-tailed Han and Hu sheep. Among the 183 DEGs selected (Q values ≤ 0.05 and│Log2(FC)│≥ 0.5), 18 DEGs, such as UCP3, ELOVL7 and GDF10, were directly associated with lipid metabolism identified via Gene Ontology (GO) analysis. Some genes, such as PPP3R1A, ADRA1, and DSLC46A2, were reportedly associated with lipid metabolism. A fold change ≥ 1.2 or ≤ 0.83 and a P-value < 0.05 were set as the default threshold to select the DLs and DMs. Among the 55 DLs, 36 DLs were phosphatidylcholines and 9 DLs were phosphatidylethanolamines. The top six DLs with the greatest differences in content were LPE (20:4) (up), PC (42:10) (up), PC (42:8) (up), PC (16:1/16:1) (down), PC (29:0) (down), and PC (32:2) (down). DMs related to the tricarboxylic acid cycle, such as D-glucose, cis-aconitic acid and citric acid were abundant in the tail fat of Large-tailed Han sheep. The DEGs, DLs and DMs were enriched mainly in the ferroptosis, the extracellular matrix (ECM)-receptor interaction, cGMP-PKG, calcium signaling and pathways related to cardiomyopathy and the tricarboxylic acid cycle. This study obtained profiles of the transcriptome, lipidome and metabolome of the tail fat tissues of sheep with long and short fat tails. The findings suggested that ELOVL7, UCP3 and ferroptosis, ECM-receptor interaction pathways contributed to the difference in fat deposition, and phosphatidylcholines biosynthesis and tricarboxylic acid cycle may affect lipid metabolism in sheep tails. The results enhance our understanding of the differences in fat deposition in sheep tail.

Lin28b and let-7 miRNA regulate mammalian pubertal initiation and Gonadotropin-releasing hormone (GnRH) production. However, it remains unclear which signaling pathways Lin28b regulates to modulate GnRH production. In this study, the mRNA expression levels of Lin28b and let-7 in the pubertal and juvenile goat hypothalamus and pituitary gland were detected, and Lin28b expression in the pubertal hypothalamus decreased significantly compared with that in juvenile tissues. It was predicted that Lin28b might inhibit GnRH1 expression, which was verified in the GnRH-producing cell model GT1-7 cells. Lin28b inhibited GnRH1 expression and promoted Kiss1/Gpr54 signaling. The pyruvate content and the expression of Hif1a and Hk2, which were related to glycolysis, were also promoted by Lin28b overexpression. Additionally, 77 differentially expressed miRNAs (DEMIs) in Lin28b-overexpressed GT1-7 cells were identified. Bioinformatics analysis and mRNA expression of the target genes of DEMIs revealed that the MAPK and PI3K-AKT-mTOR signaling pathways were key pathways that involved the regulatory effect of Lin28b on GnRH. In GT1-7 cells, GnRH1 expression was suppressed by blocking mTOR signaling with rapamycin, which was rescued by Lin28b overexpression. These results indicate that Lin28b-let-7 regulates GnRH1 expression through several pathways, including the Kiss1/Gpr54, MAPK, and mTOR signaling pathways, which are all related to glucose metabolism and provide new insights into the molecular mechanism of the regulatory role of Lin28b on GnRH production.

Background: Many recent studies have shown that miRNAs play important roles in the regulation of animal reproduction, including seasonal reproduction. The pineal gland is a crucial hub in the regulation of seasonal reproduction. However, little is known about the expression characteristics of pineal miRNAs in different reproductive seasons (anestrus and breeding season). Therefore, the expression profiles and regulatory roles of ovine pineal miRNAs were investigated during different reproductive stages using Solexa sequencing technology and dual luciferase reporter assays.Results: A total of 427 miRNAs were identified in the sheep pineal gland. Significant differences in miRNA expression were demonstrated between anestrus and the breeding season in terms of the frequency distributions of miRNA lengths, number of expressed miRNAs, and specifically and highly expressed miRNAs in each reproductive stage. KEGG analysis of the differentially expressed (DE) miRNAs between anestrus and the breeding season indicated that they are significantly enriched in pathways related to protein synthesis, secretion and uptake. Furthermore, transcriptome analysis revealed that many target genes of DE miRNAs in the ribosome pathway showed relatively low expression in the breeding season. On the other hand, analyses combining miRNA-gene expression data with target relationship validation in vitro implied that miR-89 may participate in the negative regulation of aralkylamine N-acetyltransferase (AANAT) mRNA expression by targeting its 3’UTR at a unique binding site.Conclusions: Our results provide new insights into the expression characteristics of sheep pineal miRNAs at different reproductive stages and into the negative regulatory effects of pineal miRNAs onAANATmRNA expression.

Lin28a and Lin28b, homologs of the Caenorhabditis elegans Lin28 gene, play important roles in cell pluripotency, reprogramming, and tumorigenicity. Recently, genome‐wide association and transgenic studies showed that Lin28a and/or Lin28b gene were involved in the onset of mammalian puberty, the stage representing the attainment of reproduction capacity; however, the detailed mechanism of these genes in mammalian puberty remains largely unknown. The present paper reviews the research progress on the roles of Lin28a/b genes in the onset of mammalian puberty by analyzing the results coming from gene expression patterns, mutations, and transgenic studies, and put forward possible pathways for further studies on their roles in animal reproduction.

The Jining Gray goat is famous for its sexual precocity; however, the exact regulatory mechanism is still unknown. The hypothalamus is the key centrum in the process of animal reproduction, especially in signal transduction, and the initiation of puberty. The identification of potential genes and pathways in the hypothalamus of Jining Gray goat is critical to understanding the regulatory mechanism of sexual precocity in these goats. In this study, mRNA transcriptome analysis of the hypothalamus of juvenile and pubertal goats revealed eight genes (NTS, ADORA1, CRH, UCN3, E2F2, PDGFRB, GNRH1, and CACNA1C) and three pathways [neuroactive ligand-receptor interaction; gonadotropin-releasing hormone (GnRH) signal; melanoma] that are involved in this regulation. Subsequent methylation analysis on differentially methylated region (DMR) genes revealed the potential regulation network that influences pubertal onset. Correlation analysis verified the methylation level of some DMR genes correlates negatively with expression level. Integrated analysis between transcriptomes and methylomes identified 80 candidate genes involved in GnRH and neuroactive ligand signal pathways, of which CACNA1C and CRH were differentially expressed genes (DEGs) influenced by methylation level. The GnRH gene was the only DEG not affected by its methylation level. In summary, in this study, we identified eight genes and three pathways that are related to pubertal onset in Jining Gray goats, and the expression of CACNA1C and CRH genes of the GnRH and neuroactive ligand signal pathways were influenced by DNA methylation, while that of the GnRH gene was not affected.