The myelin basic protein gene is expressed in differentiated blood cell lineages and in hemopoietic progenitors

Abstract

Myelin basic proteins (MBP) are major constituents of the myelin sheath of oligodendrocytes and Schwann cells in the central nervous system and the peripheral nervous system, respectively. We previously showed that MBP-related transcripts are present in the bone marrow and the immune system. These mRNAs are transcribed from a region called 0', consisting of three exons, located upstream of the classical MBP exons; these three exons belong to the long MBP gene otherwise called "Golli-MBP." The most abundant of these mRNAs, now called HMBP (hemopoietic MBP), encompasses the sequence encoded by the region 0' plus exon 1 and part of intron 1 of the classic MBP gene. Antisera to recombinant HMBP proteins are immunoreactive with proteins of about 26-28 kDa in brain, thymus, and spleen. This report demonstrates that HMBP proteins are present in the vast majority (>95%) of thymic T cells, which express the corresponding transcripts, as do mature T cells from lymph nodes and spleen. HMBP mRNAs and proteins are also manifest in the majority of spleen B lymphocytes and in B cell lines. In addition to lymphoid cells, HMBP proteins are in all types of myeloid lineage cells, i.e., macrophages, dendritic cells, and granulocytes, as well as in megakaryocytes and erythroblasts. Finally, HMBP proteins are present in CD34+ bone marrow cells, and, furthermore, in highly proliferative cultures, these CD34+ cells express HMBP RNAs and proteins. Thus, MBP gene products are present both in the nervous system and in the entire hemopoietic system.

Figure 1

Thymic T cells produce HMBP proteins. Western blots of proteins from thymic T cells extracts with anti-HMBP antisera 1130 and 025. PI, Preimmune sera; I, crude antisera to HMBP; IP, immunopurified antisera.

Figure 2

HMBP AND MBP2 mRNA expression in hemopoietic cell lineages. Lane 1, thymus CD4⁺CD8⁻ cells; lane 2, thymus CD4⁻CD8⁺ cells; lane 3, lymph node CD4⁺ cells; lane 4, lymph node CD8⁺ cells; lane 5, spleen CD4⁺ cells; lane 6, spleen CD8⁺ cells; lane 7, spleen CD19⁺ cells; lane 8, peritoneal macrophage F4/80⁺ cells; lane 9, Shiverer thymus; lane C, control, no DNA; lane L, 100-bp DNA ladder.

Figure 3

T cells from wild-type mice and from Shiverer produce HMBP proteins. Western blots of 20- to 30-kDa proteins of thymus T cells extracts from wild-type mice (a) as compared with Shiverer mice (b) immunodetected with an immunopurifed antiserum. (Upper) Monodimensional gels; (Lower) bidimensional IEF gels with 2% Biolyte 3/10.

Figure 4

Thymic CD4⁺ T cells are immunoreactive to HMBP antisera. (A) Thymic cell suspensions were immunolabeled with an anti-CD4 mAb and an HMBP antiserum. (B) Electron micrograph of a thymic T cell immunolabeled with an HMBP antiserum.

Figure 5

HMBP proteins are present in B cells. (A) Western blots of 20- to 30-kDa proteins with an HMBP antiserum. (Aa) T cells; (Ab) spleen cells; (Ac) X-24 B cell line; (Ad) P388 B cell line; (Ae) T 1165 B cell line. (B) Spleen B cells were double labeled with an anti-CD19 and an HMBP antiserum.

Figure 6

Myeloid cells produce HMBP proteins. (A) Western blots of 20- to 30-kDa proteins with an HMBP antiserum. (Aa) Peritoneal cells; (Ab) P388 macrophage cell line; (Ac) bone marrow. (B) Double labeling of (Ba) peritoneal cells (F4/80) and (Bb) granulocytes (Gr1) with an HMBP antiserum.

Figure 7

Bone marrow CD34⁺ cells express HMBP proteins. (A) Western blots of protein extracts of CD34⁺ cells from bone marrow cultures (Ab) as compared with T cell extracts (Aa). (B) All CD34⁺ cells from bone marrow cultures are HMBP⁺ as shown by double labeling with a CD34 mAb and an HMBP antiserum. (C) RT-PCR of bone marrow (Ca) and CD34⁺ cell cultures (Cb).

Figure 8

Western blots of two-dimensional IEF gels of 20- to 30-kDa protein extracts were prepared as in Materials and Methods and probed with an immunopurified HMBP antiserum. (a) T cells; (b) X-24 B cells; (c) peritoneal macrophages; (d) bone marrow; (e) in vitro CD34⁺ cells.