Sphingomyelin synthase genes (Sgms1 and Sgms2) encode the vital enzymes that participate in the processes of membrane
transport, cell proliferation and apoptosis. We previously determined the exon–intron structure of Sgms1 and some features of its
expression in human and rodent tissues. The circular RNAs (circRNAs) emerging from exons of the 5′-untranslated region (5′-
UTR) of Sgms1 were determined. These circRNAs are represented at a high level in the adult brain. Here, we demonstrate that, in
contrast to Sgms1, Sgms2 does not contain the multi-exon 5′-UTR but encodes circRNAs, which are composed of the coding
region of the gene and are expressed at a low level. We present a study of the expression of sphingomyelin synthase genes in rat
brain at embryonic days 7, 9, 13, 17 and 21 and in adult rat brain. In contrast to Sgms1, Sgms2 is expressed at a significantly low
level in adult brain. In embryonic rat brain, the mRNA expression of sphingomyelin synthase genes is varied in a developmental
stage-specific manner. The level of Sgms1 mRNAs, differing by 5′-UTR—in the formation of which alternative promoters can
participate—changes significantly during the process of embryonic development. The expression of circRNAs of Sgms1 was
significantly raised during rat embryonic brain development. We assume that the circRNAs are involved in the regulation of
sphingomyelin synthase activity in rat brain in different developmental stages.

• Developmental stage-specific expression of genes for sphingomyelin synthase in rat brain