The Study On The Developmental Dynamics Of The Mouse Transcriptome In Spermiogenesis

After meiosis, round spermatid mature into sperm through metamorphosis. During this time, mostcytoplasm in the germ cell is gradually lost, histones associated with chromatin are replaced bytransition proteins, and eventually transformed into protamines. Thus the spermatid chromatin isstringently packaged and highly concentrated. The dynamics transcriptomic variation of haploid germcell from round spermatid to spermatozoa in mouse has been not clear, which is not conducive tounderstand genetic characteristics and provide the theoretic basis for reproductive control using malegamete. Using Laser Capture Microdissection(LCM), new ultra-high-throughput sequencing andbioinformatics, three kinds of mouse developmental spermatid cells (round spermatid, elongatingspermatid, and mature spermatid) were selected to sequence. Two biological replicate and twotechnogical replicates were performed for each sample. Summing the reads over an entire transcriptome,the obtained sequence reads represent31-fold mouse genome (mm9) length.. The mouse genome-widetranscriptome was described according to the reads matched in mouse genome. We identified47588expressed genes for each samples based on the RPKM value.The read map rate was up to80%for each sample when reads has been mapped to mm9.The genicdistribution of reads in each round and elongating spermatid sample showed that the majority (70%)mapped to known and predicted exons. While the distribution of reads in the mature sperm was verydifferent: about32-35%reads were maped within introns, amazingly51-52%mapped to intergenics andonly9-13%fell in the exons, which suggest that the alternative splicing in the mature sperm is morecomplicated than the round and elongating spermatid and more novo genes can be founded. We detectedthe expression of5104novo genes.Alternative splicing (AS) in mouse spermatids was ananalyed on the genome scale based on theRNA-seq data. We detected aternative splicing at19127genes (~40.2%of the expressed transcriptome).Compared with the mammal somatic cell, the observed instance-rate of splice events in spermatid weredifferent: the most freqence appearance of event are TSS and TTS.We identified12105differentially expressed genes(DEGs)（p-value <0.05）, among which1318significant genes (538up-regulated and780down-regulated) were differentially expressed between theround spermatid and the elongated spermatid,7881genes (3679up-regulated and4202down-regulated)between the elongated spermatid and the mature sperm, and10899genes (5209up-regulated and5690down-regulated) between the round spermatid and the mature sperm. Gene-enrichment analysis,including Gene Ontology(GO), InterPro domains, and KEGG pathways, illustrated that acitivities ofgene transcription, mitochondria protein translation, cell component, and energy metabolism, etc, werechanged during the whole developing time.By RNA-seq, the model organism—mouse transcriptome variation during spermiogenesis may befully elucidated. The results provided much information about alternative splicing events, DEGs, noveltrascriptions, and the mechanism of protein translation and so on, which exploxed the dynamicstranscriptomic variation of haploid germ cell from round spermatid to spermatozoa in mouse. On the transcriptome level, we do a massive study on the trascription activity and regulation duringspermiogenesis, which initially revealed dynamics transcriptomic variation and made a foudation forresearching the molecular mechanism of sperm maturation.