Current state of in situ gene expression studiesin animal tissues

Morphological studies of farm animals are most often conducted using simple preparation and staining techniques. The study of the processes of embryogenesis, postembryonic features of the development of organs and tissues, as well as the effect of various substances remains to be elucidated not only using histochemical and immunohistochemical staining methods, but also using RNA in situ hybridization and transcriptome in situ sequencing. Aspects of many cellular and tissue processes for cattle, pigs and chickens in the context of comparative physiology have not yet been studied. The high productivity of farm animals is associated with the intensive functioning of all organs and systems of the body. The influence of the agricultural management of farm animals and its consequences on the development of an organism in ontogeny deserve a separate area of research from the point of in situ gene expression. Despite rapid development of transcriptome sequencing technologies, which result in the discovery of new candidate genes for many processes, RNA in situ hybridization remains the gold standard for their validation. This review briefly presents modern techniques and their modifications for studying in situ gene expression. Transcriptome studies that have been implemented in cattle, pigs and chickens as model organisms include: in situ RNA hybridization using ZZ-probes, tyramide signal amplification, hybridization chain reaction, digoxigenin-labeled probes, RT-PCR, single cell transcriptome sequencing, in situ transciptome sequencing. This paper is a review of the results of studies on cattle, pigs and chickens. The results of research in this area are relevant for understanding the features of adaptation mechanisms at the transcriptomic level in highly productive animals under industrial conditions in order to search for new markers of valuable agricultural traits. It should be noted that in literature there are very few studies using RNA in situ hybridization, despite the availability and simplicity of the method.