Neuroblast pattern formation: Regulatory DNA that confers the vnd/NK-2 homeobox gene pattern on a reporter gene in transgenic lines of Drosophila

DNA fragments −0.57, −2.2, −2.9, −5.3, and −8.4 kb in length from the upstream regulatory region of the vnd/NK-2 gene were cloned in the 5′-flanking region of a β-galactosidase (β-gal) reporter gene in the P-element pCaSpeR-AUG-β-gal, and the effects of the DNA on the pattern and time of expression of β-gal were determined in transgenic embryos. Embryos from 11 lines transformed with −8.4 kb of vnd/NK-2 regulatory DNA expressed β-gal patterns that closely resemble those of vnd/NK-2. In embryos from four lines transformed with −5.3 kb of vnd/NK-2 DNA, β-gal was found in the normal vnd/NK-2 pattern in the nerve cord but not in part of the cephalic region. β-Gal patterns in embryos from transgenic lines containing −0.57, −2.2, or −2.9 kb of vnd/NK-2 DNA did not resemble vnd/NK-2. Null vnd/NK-2 mutant embryos containing the homozygous P-element p[−8.4 to +0.34 β-gal] expressed little β-gal in contrast to siblings with a wild-type vnd/NK-2 gene. We conclude that (i) the 8.4-kb DNA fragment from the vnd/NK-2 gene contains the nucleotide sequences required to generate the normal pattern of vnd/NK-2 gene expression, sequences that may be involved in the switch between neuroblast vs. epidermoblast pathways of development, (ii) the 5′-flanking region of the vnd/NK-2 gene between −5.3 and −8.4 kb is required for vnd/NK-2 gene expression in the most dorsoanterior part of the cephalic region, and (iii) vnd/NK-2 protein is required, directly or indirectly, for maintenance of vnd/NK-2 gene expression.