MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by targeting messenger RNAs (mRNAs) for degradation or translational repression. Recent studies have shown that miRNAs also have nuclear functions, including transcriptional control, regulation of the RNA transcriptome, nucleolar function, alternative splicing, and transcriptional activation or inhibition. The biogenesis of miRNAs involves a multi-step process in both the nucleus and cytoplasm, starting with the transcription of primary miRNAs (pri-miRNAs) by RNA polymerases II or III, followed by processing by the Microprocessor complex into precursor miRNAs (pre-miRNAs), and finally by Dicer to generate miRNA duplexes. These miRNAs are then loaded onto Argonaute (AGO) proteins to form the miRNA-induced silencing complex (miRISC), which can either repress translation or promote mRNA degradation. miRISC can also be found in the nucleus, where it may regulate gene expression at the transcriptional level. miRNAs can influence transcription by interacting with non-coding RNAs, such as long non-coding RNAs (lncRNAs), and by modulating chromatin structure. They can also affect nucleolar function, ribosome biogenesis, and the processing of pre-miRNAs. Additionally, miRNAs can regulate alternative splicing by interacting with splicing factors and modifying chromatin structure. Some miRNAs can activate gene transcription (TGA) by interacting with non-coding promoter transcripts, while others can inhibit gene transcription (TGS) by recruiting repressive complexes and modifying chromatin structure. The mechanisms by which miRNAs regulate gene expression in the nucleus are still being investigated, but it is clear that miRNAs have diverse functions in both the cytoplasm and nucleus. These functions include the regulation of mRNA stability, alternative splicing, transcriptional activation or inhibition, and the modulation of chromatin structure. The versatility of miRNAs in regulating gene expression at both the transcriptional and post-transcriptional levels highlights their importance in cellular processes such as differentiation, apoptosis, and development. Dysregulation of miRNAs has been linked to various diseases, including cancer, diabetes, and muscular dystrophy. The study of miRNA functions in the nucleus is an important area of research, as it provides insights into the complex regulatory networks that govern gene expression.MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by targeting messenger RNAs (mRNAs) for degradation or translational repression. Recent studies have shown that miRNAs also have nuclear functions, including transcriptional control, regulation of the RNA transcriptome, nucleolar function, alternative splicing, and transcriptional activation or inhibition. The biogenesis of miRNAs involves a multi-step process in both the nucleus and cytoplasm, starting with the transcription of primary miRNAs (pri-miRNAs) by RNA polymerases II or III, followed by processing by the Microprocessor complex into precursor miRNAs (pre-miRNAs), and finally by Dicer to generate miRNA duplexes. These miRNAs are then loaded onto Argonaute (AGO) proteins to form the miRNA-induced silencing complex (miRISC), which can either repress translation or promote mRNA degradation. miRISC can also be found in the nucleus, where it may regulate gene expression at the transcriptional level. miRNAs can influence transcription by interacting with non-coding RNAs, such as long non-coding RNAs (lncRNAs), and by modulating chromatin structure. They can also affect nucleolar function, ribosome biogenesis, and the processing of pre-miRNAs. Additionally, miRNAs can regulate alternative splicing by interacting with splicing factors and modifying chromatin structure. Some miRNAs can activate gene transcription (TGA) by interacting with non-coding promoter transcripts, while others can inhibit gene transcription (TGS) by recruiting repressive complexes and modifying chromatin structure. The mechanisms by which miRNAs regulate gene expression in the nucleus are still being investigated, but it is clear that miRNAs have diverse functions in both the cytoplasm and nucleus. These functions include the regulation of mRNA stability, alternative splicing, transcriptional activation or inhibition, and the modulation of chromatin structure. The versatility of miRNAs in regulating gene expression at both the transcriptional and post-transcriptional levels highlights their importance in cellular processes such as differentiation, apoptosis, and development. Dysregulation of miRNAs has been linked to various diseases, including cancer, diabetes, and muscular dystrophy. The study of miRNA functions in the nucleus is an important area of research, as it provides insights into the complex regulatory networks that govern gene expression.