ALAS1 associated with goat kidding number trait was regulated by the transcription factor ASCL2 to affect granulosa cell proliferation

ALAS1 is a member of the α-oxoamine synthase family, which is the first rate-limiting enzyme for heme synthesis and is important for maintaining intracellular heme levels. In the ovary, ALAS1 is associated with the regulation of ovulation-related mitochondrial P450 cytochromes, steroid metabolism, and steroid hormone production. However, there are few studies on the relationship between ALAS1 and reproductive traits in goats. In this study, a mutation located in the promoter region of ALAS1 (g.48791372C>A) was found to be significantly (p < 0.05) associated with the kidding number of Yunshang black goats. Specifically, the mean kidding number in the first three litters and the kidding numbers of all three litters were significantly (p < 0.05) higher in individuals with the CA genotype or AA genotype than in those with the CC genotype. To further investigate the regulatory mechanism of ALAS1, the expression of ALAS1 in goat ovarian tissues with different genotypes was verified by real-time quantitative PCR. The results showed that the expression of ALAS1 was significantly higher in the ovaries of individuals with AA genotype than those with AC and CC genotypes (p < 0.01), and the expression trend of transcription factor ASCL2 was consistent with ALAS1. Additionally, the ALAS1 g.48791372C>A mutation created a new binding site for the transcription factor ASCL2. The luciferase activity assay indicated that the mutation increased the promoter activity of ALAS1. Overexpression of the transcription factor ASCL2 induced increased expression of ALAS1 in goat granulosa cells (p < 0.05). The opposite trend was shown for the inhibition of ASCL2 expression. The results of real-time quantitative PCR, EdU and Cell Counting Kit-8 assays indicated that the transcription factor ASCL2 increased the proliferation of goat granulosa cells by mediating the expression of ALAS1. In conclusion, the transcription factor ASCL2 positively regulated the transcriptional activity and expression levels of ALAS1, altering granulosa cell proliferation and the kidding number in goats.