Genomic analysis of human and mouse TCL1 loci reveals a complex of tightly clustered genes

Abstract

TCL1 and TCL1b genes on human chromosome 14q23.1 are activated in T cell leukemias by translocations and inversions at 14q32.1, juxtaposing them to regulatory elements of T cell receptor genes. In this report we present the cloning, mapping, and expression analysis of the human and murine TCL1/Tcl1 locus. In addition to TCL1 and TCL1b, the human locus contains two additional genes, TCL1-neighboring genes (TNG) 1 and 2, encoding proteins of 141 and 110 aa, respectively. Both genes show no homology to any known genes, but their expression profiles are very similar to those of TCL1 and TCL1b. TNG1 and TNG2 also are activated in T cell leukemias with rearrangements at 14q32.1. To aid in the development of a mouse model we also have characterized the murine Tcl1 locus and found five genes homologous to human TCL1b. Tcl1b1-Tcl1b5 proteins range from 117 to 123 aa and are 65-80% similar, but they show only a 30-40% similarity to human TCL1b. All five mouse Tcl1b and murine Tcl1 mRNAs are abundant in mouse oocytes and two-cell embryos but rare in various adult tissues and lymphoid cell lines. These data suggest a similar or complementary function of these proteins in early embryogenesis.

Figure 1

Genomic organization of human and mouse TCL1 loci. (A) Human TCL1 locus. Vertical arrows refer to cloned 14q32.1 breakpoints (1, 7). Restriction sites are given for BssHII (B), ClaI (C), EagI (E), SfiI (F), KspI (K), MluI (M), NotI (N), and SalI (S). Solid boxes represent exons of the four genes. (B) Striped boxes indicate translated parts of exons, and open boxes indicate untranslated regions. Bold lines under the exons show various splicing products of TNG1, TNG2, and TCL1b genes. (C) Murine Tcl1 locus. Restriction sites and exons are indicated as in A.

Figure 2

RT-PCR analysis of TNG1 and TNG2 genes. (A) Leukemia cell lines. Lanes: 1–3, T-ALL cell lines MOLT3, MOLT4, and CEM; 4, pre-B-ALL cell line 697; 5, T-ALL cell line SupT11; 6–8, Burkitt’s lymphoma cell lines CA-46, Raji, and Daudi; 9 and 10, bone marrow and peripheral blood lymphocytes (PBL). Top gel, TCL1 primers; second, TCL1b primers; third, TNG1 primers; fourth, TNG2 primers; bottom, control G3PDH primers (B) Normal human tissues. Lanes 1–23: heart, liver, brain, muscle, placenta, kidney, lung, pancreas, spleen, lymph node, thymus, tonsil, PBL, fetal liver, fetal brain, fetal lung, fetal kidney, fetal heart, fetal skeletal muscle, fetal spleen, fetal thymus, negative control. (C) Lanes: 1–4, T cell PLL samples 3047, 3046, 3050, and 3048; 5 and 6, bone marrow and PBL. (B and C) (Top) TNG1 primers. (Middle) TNG2 primers. (Bottom) Control G3PDH primers.

Figure 3

Northern analysis of TNG1 and TNG2 genes. Lanes: 1–3, Burkitt’s lymphomas Raji, Daudi, and CA-46; 4, T-ALL SupT11; 5 and 6, bone marrow and placenta. (Top) TNG1 probe. (Middle) TNG2 probe. (Bottom) Actin probe. Each lane contains 3 μg of poly(A)⁺ RNA.

Figure 4

RT-PCR analysis of murine Tcl1b genes. (A and B) Nested PCR, except β-actin. The gels are in the same order. (A) Normal mouse tissues. Lanes 1–13: heart, brain, spleen, lung, liver, skeletal muscle, kidney, testis, 7-day embryo, 11-day embryo, 15-day embryo, 17-day embryo, negative control. (B) Lymphoid cell lines. Lanes: 1–5, B cell lines NFS-5, NFS-70, WEHI-279, MOPC-31C, and MPC-11; 6 and 7, T cell lines S49.1 and BW5147; 8 and 9, embryonic stem cells and negative control. (C) Single round of PCR. Lanes 1–4: ES cells, mouse oocytes, two-cell embryos, and negative control.

Figure 5

Sequence comparison of human and murine Tcl1, Tcl1b, and Mtcp1 proteins. Identities are shown in black boxes, and similarities are indicated by shaded boxes. *, Conserved residues of the inner hydrophobic core.

Figure 6

Location of the insertion in human and murine Tcl1b proteins. A side view of human TCL1 (14) is shown in green. The proposed TCL1b insert into the C-D loop is shown in blue.