Experimental Animal Division

An useful cell marker system for hematopoietic cells in transplantation studies
The protein-tyrosine phosphatase, receptor type, C (Ptprc), also known as Ly5 or Cd45 gene of the mouse, encodes a set of transmembrane glycoprotein isoforms expressed only on hematopoietic cells [1, 2]. Ptprc was found to express in multiple forms by alternative splicing of different exons [3], and in allelic forms designated as Ly5.1/Cd45.1 of SJL/J and Ly5.2/Cd45.2/ of C57BL/6J [4, 5]. A Congenic strain, B6.SJL-Ptprc^a/Boy has been generated by backcrossing SJL/J carrying Ptprc^a (Ly5^a/Cd45^a, Ly5.1/Cd45.1) to the C57BL/6 background strain for hematological studies [6]. RIKEN BRC distributes B6.SJL-Ptprc^a/BoyYuoRbrc (C57BL/6-Ly5^a, C57BL/6-Ly5.1, RBRC00126) mice (Fig. 1) as a useful cell marker system in bone marrow transplantation studies. The specific mouse monoclonal antibodies for the Cd45.1 and Cd45.2 have been exploited [4] and widely used to distinguish hematopoitetic cells of donor and recipient mice. A typical transplantation experiment is shown in Fig. 2.

Confusing Ly5 gene nomenclature and its history
Revision of gene and allele names for Ptprc (Ly5/Cd45) have led to much confusion regarding antigen specificity and allelic symbols [7]. Present and past nomenclature of Ly5 gene is summarized in Table 1.
Komura, et al. (1975), described an antigen expressed on T cells, and designated the specificity on C57BL/6 cells as Ly5.1 and on SJL cells as Ly5.2 [1]. According to gene naming convention for alleles, the C57BL/6 allele became Ly5^a and SJL/J allele became Ly5^b.
In 1987, Morse et al. proposed a revision of nomenclature of mouse lymphocyte antigens, which led to a reversed designation [8]. Consequently, the B6 allele became Ly5^b (antigen specificity Ly5.2) and the SJL allele became Ly5^a (antigen specificity Ly5.1).
A further revision was made on the cell surface antigens by Morse in 1992, where Ly5 became Cd45[9].
Finally, the gene name was changed to Ptprc in 1993, based on the work by Charbonneau et al. who demonstrated homology between a tyrosine phosphatase and CD45 protein [2]. This led to the present nomenclature of the B6 as Ptprc^b and the SJL as Ptprc^a.