Abstract：Abstract MicroRNAs (miRNAs) are a class of recently identified regulatory RNAs which are short non-coding RNA. They participate in diverse biological functions including embryogenesis, development, metabolism, and oncogenesis. Let-7 family members (Let-7s) are a fundamental tumor suppressor miRNA, which was first identified as a heterochronic gene in Caenorhabditis elegans. In recent years, studies have shown that Let-7s plays an important regulatory role in the growth and development of animals. It is not only related to tumor development, but also participates in the reproduction of females. In order to analyze the sequence of let-7s and to study its expression pattern during the goose reproductive cycle, the current literature and miRBase were used to search the let-7s. The NCBI and Ensembl databases were used to identify the location of let-7s in the genome of each species. At the same time, qRT-PCR was used to detect the expression of let-7s in geese's ovary tissues at the reproductive cycle. A total of 300 vertebrate let-7s sequences were found, containing 11 members (let-7a, let-7b, let-7c, let-7d, let-7e, let-7f-5p, let-7g, let-7h, let-7i, let-7j, let-7k) widely distributed and highly conserved in eukaryotes. Most of the members were located in the intergenic region (IGR), only let-7e, let-7f-5p and let-7g were located in the gene region in mammals. The multiple sequence alignment of the mature sequences of let-7s showed that let-7s have high homology of mature sequences with similar length of sequences. And there is nearly half of the conserved bases in the let-7s which indicating that let-7s is highly conserved across species. In addition, the let-7s family may have mutated during evolution. The results of qRT-PCR showed that there was no significant difference in the expression levels of let-7a, let-7b, let-7c and let-7f-5p between ovulation and broody phase (P＞0.05). However, the expression levels of let-7g and let-7h in broody phase were significantly less than those at pre-laying stage, ovulation and oviposition (P＜0.01). Therefore, let-7s were highly conserved in evolution, and let-7g and let-7h played a regulatory role in reproductive cycle of geese. This study will provide a reference for investigating the regulation of let-7 family in geese.
