Advantages of a P-element construct containing MtnA sequences for the identification of patterning and cell determination genes in Drosophila melanogaster

The P[MTW] transposon carries a functional MtnA (metallothionein) gene and a miniwhite reporter gene. When P[MTW] was transformed into Drosophila, man y lines were found to show position-dependent expression patterns of the mi niwhite or the MtnA transgene. Identification of several of the target gene s indicated that this construct behaves as an enhancer or silencer trap. Fo r instance, expression of at least one reporter transgene was shown to corr elate with that of the endogenous gene in the case of insertions in Ultrabi thorax, four jointed. and the iroquois complex. The frequency of patterns r ecovered with P[MTW] is higher than that reported for P[LacW]. suggesting t hat P[MTW] has unusual properties. The possibility of biased insertion of P [MTW] was assayed by screening a sample of 66 MTW lines for modifiers of th e extra sex comb phenotype: caused by a hypomorphic allele of polyhomeotic. Seven modifiers were recovered, which could be ranked in two classes: gene s involved in leg morphogenesis (including four-jointed and spitz), and gen es of the Polycomb- or trithorax-Group, including trithorax and batman, a n ew gene which encodes a product with a BTB/POZ domain. Taken together, thes e results indicate that P[MTW] allows the tagging of patterning and cell de termination genes, and thus provides a useful tool for identifying new deve lopmental functions.