# tRNA and tsRNA: From Heterogeneity to Multifaceted Regulators
## 6 tsRNA: From Sensor of Environment to Epigenetic Inheritance Messenger  
SncRNA profiles (including piRNAs, miRNAs, tsRNAs, rsRNAs, etc.) [133] in male germ cells undergo dramatic remodeling during spermatogenesis in testis and sperm maturation in the epididymis, resulting in a significant special sncRNA profile in mature sperm [168]. The literature shows that the expression and RNA modification profiles of sperm sncRNAs are highly sensitive to environmental perturbations. Environment exposures, such as nutritional alteration stress (high-fat diet or low-protein diet), fetal trauma, chemical toxicants, and aging are capable of shaping sperm sncRNA signatures (including sncRNA expression and RNA modification profiles), thus generating the \"sperm RNA code\" that encodes paternal life experience [169] and further leading to the intergenerational or transgenerational epigenetic inheritance of parenally acquired phenotypes in the offspring [170]. As we propose here, the neural network model of sperm RNA code-mediated paternal intergenerational inheritance is a possible mechanistic model that may help deepen our understanding of sperm RNA-mediated epigenetic inheritance (Figure 3). Under environmental stress, the paternal exposures act as information inputs that are parsed into various sperm RNA signatures, such as tsRNA features, to form a specific \"sperm RNA code\". During fertilization, sperm RNA enters the oocyte along with sperm and targets specific regulatory elements, such as promoters, enhancers, open reading frames (ORFs),UTRs, coding sequences (CDS), and RNA-binding proteins (RBPs) through diverse mechanisms [24] during early embryonic development. The regulatory effects further influence embryonic epigenetic reprogramming and transcriptional and translational activities [25], subsequently affecting specific biological processes and ultimately impacting embryonic development. These acquired traits gradually manifest, completing the process of phenotypic intergenerational inheritance during the development and growth of offspring. As a crucial part of the \"sperm RNA code\", tsRNA is one of the most abundant sncRNAs with an apparent nucleus and mitochondrial localization in sperm. tsRNA is characterized by various RNA modifications and diverse regulatory mechanisms in biological processes, expanding the information coding capacity of tsRNAs during fertilization and embryonic development [133]. Growing evidence confirms that sperm tsRNAs are capable of responding to various environmental stresses, such as nutritional changes, age factors, hypoxic conditions, inflammation, gut microbiota, and chemical toxicity in mammals [132; 169; 171; 172; 173; 174; 175]. In humans, one week of a high-sugar diet is sufficient to alter the expression signature of tsRNA and rsRNA in sperm [176], and the alteration of the sperm RNA code after 6 months of high-fat-diet treatment is capable of independently transmitting the paternal acquired phenotype to the offspring, resulting in metabolic disorders in the progeny [169]. Moreover, aging-induced alterations of sperm tsRNA profiles have been shown to induce anxiety-like behaviors in the offspring [172]. Gut microbiota dysbiosis-induced upregulation of tsRNAGly(GCC) in the sperm increases the risk of impaired placental development and premature death in mice offspring [175]. Additionally, RNA modifications also serve as key components of the sperm RNA code in response to environmental stimuli. We previously found that global modifications in mouse testes and mature sperm underwent significant remodeling under hypoxic conditions [177], while  
Figure 3: Neural network model for transmitting parental traits to offspring through the sperm RNA code. The generally acquired phenotypes are encoded as the sperm RNA code, with various features. It is possible that these features may interact with each other, either directly or indirectly, to influence the biological process in the early embryo and subsequently affect the phenotypes of the offspring. Created in BioRender.