THY 1 ( Thy - 1 cell surface antigen )

Transcription of THY1 is initiated at multiple sites producing an approximately 5591 bp transcript. After splicing, the transcript is reduced to 2143 bp. Transcriptional regulation for tissue-specific expression of Thy-1, as well as for controlling expression in cell sub-populations, and in some cancers, is governed by a number of mechanisms. For tissue-specific transcriptional regulation, the regulatory elements are found exclusively downstream of the transcription initiation site within the gene itself. Differential tissue expression of Thy1 exists between species as closely related as mouse and rat. For example, Thy1 is expressed in mouse thymocytes and splenocytes, but only thymocytes in rat. The absence of Thy1 in rat splenocytes is attributed to a three nucleotide difference in a conserved 36 bp region within the third intron. In mice, this 36 bp region can bind an Ets-l-like nuclear factor expressed by both mouse thymocytes and splenocytes. In rats, the three nucleotide difference renders the 36 bp region no longer capable of binding the similar Ets-l-like nuclear factor expressed by rats. However, rat thymocytes but not splenocytes express another nuclear factor which does recognize the 36 bp region and this is thought to account for the expression of Thy1 in rat thymocytes but not splenocytes. In humans, THY1 is detected in the brain, spleen, kidneys, but not thymus. In mouse, Thy1 is detected in the brain, spleen, thymus, but not kidneys. In transgenic mice, deletion of half the 3' end of intron 1 prevents expression of Thy1 in the brain but allows for its expression in the thymus. The control elements within the first intron of Thy-1 are conserved in human and mouse, as replacement of the first intron in mouse with that from human causes no detectable change in Thy1 expression in the brain.