The human ABL2 (or ARG) gene codes for a nonreceptor tyrosine kinase is involved 
in translocation with the ETV6 gene in human leukemia and has an altered 
expression in several human carcinomas. Two isoforms of Arg with different 
N-termini (1A and 1B) have been described. The C-terminal domain of Arg contains 
two F-actin-binding sequences that perform a number of actions related to cell 
morphology and motility by interacting with actin filaments. We have identified 
different-sized specific cDNAs in hematopoietic, epithelial, nervous, and 
fibroblastic cells by means of the reverse transcription (RT)-polymerase chain 
reaction (PCR) analysis of human Arg mRNA. Some of these cDNAs showed an 
adjunctive alternative splice event involving the 63 bp sequence of exon II, 
thus leading to four cDNA types with different N-termini: 1A long and short, and 
1B long and short. Other cDNAs lacked a 309 bp sequence in the last exon 
involving one of the C-terminal F-actin binding domains, thus giving rise to two 
cDNA types: C-termini long and short. Quantified by real-time PCR-quantitative 
RT-PCR-these Arg transcript isoforms have specific expression patterns not only 
in different normal and tumor cell types, but also during cell differentiation 
and growth arrest. These isoforms maintained the open reading frames, and eight 
putative proteins were predicted. The different C-termini isoforms seem to 
retain the same quantitative reciprocal ratio of their respective transcripts. 
The Arg protein isoforms with different C-terminal actin-binding domains and 
different N-termini might have specific cellular localizations/concentrations, 
and differently regulated catalytic activity with different implications in 
normal and neoplastic cells.