Maternal regulation of zerknüllt: a homoeobox gene controlling differentiation of dorsal tissues in Drosophila

Abstract

The homoeobox gene zerknüllt (zen) plays an important role in the differentiation of dorsal tissues during Drosophila development. zen- embryos show transformations in the dorsal-most regions of the fate map, and lack several tissues that normally derive from these regions, including the amnioserosa and optic lobe. zen displays a simple dorsal on/ventral off pattern as early as cleavage cycle 10-11 (ref. 2). We have prepared a polyclonal antibody against a full-length zen protein, and used this to examine its pattern of expression in mutants that disrupt dorsal-ventral polarity. Most or all of the maternally expressed genes that are involved in this process have been previously identified and fall into two classes, so called 'dorsalizers' and 'ventralizers' (see refs 4-7, reviewed in ref. 8). On the basis of our analysis of zen expression in each of these maternal mutants we propose that one or more of the dorsalizing genes encodes a repressor which inhibits the expression of zen in ventral regions of developing embryos. The ventralizing gene cactus might play an important role in restricting the activity of this repressor to ventral regions, thereby permitting the activation of zen in those dorsal tissues where its function is critically required.

Conversion of a silencer into an enhancer: evidence for a co-repressor in dorsal-mediated repression in Drosophila

“…In contrast to its role as an activator, dl can also function as a repressor. Genes such as zerknullt (zen), decapentaplegic (dpp) and tolloid (tld) are normally expressed only in the dorsal part of the embryo (Rushlow et al, 1987b;St Johnston and Gelbart, 1987;Shimell et al, 1991). In the absence of dl protein, these genes are expressed uniformly along the DV axis, indicating that dl protein normally represses their transcription (Rushlow et al, 1987a;Ray et al, 1991).…”

Conversion of a dorsal-dependent silencer into an enhancer: evidence for dorsal corepressors

“…High levels of dl activate the mesoderm determinants twist (twi) and snail (sna) Ip et al, 1992a,b;Jiang and Levine, 1993). dl also functions as a transcriptional repressor that restricts the expression of decapentaplegic (dpp) and zerknutt (zen) to dorsal regions, where they are responsible for the differentiation of the dorsal epidermis and amnioserosa, respectively (Rushlow et al, 1987;St Johnston and Gelbart, 1987;Ip et al, 1991).…”

Head involution in Drosophila: Genetic and morphogenetic connections to dorsal closure

“…Dorsal fates are then partitioned along the AP axis such that cells acquire head epidermal fates in anterior domains (Tan et al, 2001) and amnioserosal fates more posteriorly (Ferguson and Anderson, 1992). Animals homozygous for null alleles of dpp or zen are completely ventralized, lacking all dorsal fates including the optic lobe in anterior domains and the amnioserosa more posteriorly (Rushlow et al, 1987). In contrast, animals homozygous for hypomorphic alleles of dpp and zen can exhibit defects in just one subset of dorsally fated cells.…”