EXPRESSION OF BETA-1 TUBULIN (BETA-TUB56D) IN DROSOPHILA TESTIS STEM-CELLS IS REGULATED BY A SHORT UPSTREAM SEQUENCE WHILE INTRON ELEMENTS GUIDE EXPRESSION IN SOMATIC-CELLS

Stem cell differentiation to mature spermatozoa is a morphogenetic process that is highly dependent on microtubular arrays. In the early, mitotically active stages of spermatogenesis, only the beta1 tubulin isotype is expressed. Analysis of transgenic flies containing beta1-lacZ gene fusions revealed that this expression is regulated by sequences located between positions -45 and -191 upstream of the transcription initiation site. Furthermore, beta1 tubulin is a major component of cyst cells. Expression in these cells is driven by enhancer elements located in the beta1 tubulin gene intron. These enhancer elements also guide expression in combination with the hsp70 basal promoter. In addition, redundant enhancer elements in the intron drive expression in the testis wall. Our data show that within a single tissue, the male gonad, expression of the beta1 tubulin gene is under cell-type-specific control mediated by independent cis-acting elements. Therefore in the germ line, control of beta1 tubulin expression is strictly governed by promoter-proximal elements, while for the somatic parts of the testis, enhancer elements confer less stringent expression control.