The “pipsqueak” family is a new family of eukaryotic proteins that contain a pipsqueak (psq) motif. This motif consists of a 50 amino acid sequence, which is structurally related to the helix-turn-helix domain, known for its role in DNA recognition. However, it lacks the conserved sequence signatures of the classic eukaryotic DNA-binding motifs, thus defining a new family of DNA-binding proteins and potential transcription factors (Lehmann et al., 1998). This family includes proteins from fungi, sea urchins, nematodes, insects, and vertebrates. Their role has been better studied in Drosophila, where 14 proteins, including a psq motif (psq proteins), have been identified. These proteins can be classified into three groups, depending on sequence homologies within the psq motif, the existence of different protein domains, and the position of the psq motif within the proteins (Siegmund and Lehmann, 2002). The first group is composed of members of the BTB (Broad-complex, Tramtrack, Bric à brac) protein family; the second group contains the Drosophila cell death regulator E93, with orthologues in sea urchins, nematodes, and humans; the third group includes the two Drosophila genes fernández (fer)/distal antenna (dan) and hernández (hern)/distal antenna related (danr), the human centromere protein B (CENP-B), a related predicted human protein (CAB66474), and transposases from phytopathogenetic fungi (Siegmund and Lehmann, 2002; Suzanne et al., 2003; Emerald et al., 2003). Among members of this protein group, the psq domain, located at the N-terminus of the protein, is particularly well conserved. Functional analysis of some of the Drosophila genes encoding psq proteins revealed their importance in a variety of fundamental processes: ribbon is required in epithelial migration of the tracheal system and in dorsal closure (Blake et al., 1998; Bradley and Andrew, 2001; Shim et al., 2001); pipsqueak in early oogenesis (Horowitz and Berg, 1996); bric à brac in appendage diversity, morphogenesis, and oogenesis (Godt et al., 1993; Godt and Laski, 1995; Chu et al., 2002); and finally, E93 in programmed cell death during metamorphosis (Lee et al., 2000).
Here, I describe the expression pattern of two of these genes, fer/dan and hern/danr, that belong to the CENP-B/transposase subfamily of psq proteins and have been characterised recently (Emerald et al., 2003; Suzanne et al., 2003). Their expression patterns, however, have only been described in third instar larvae. In the present work, I analyse in more detail their larval and pupal expression by using several Gal4 enhancer traps inserted into the fer and the hern genes and characterise their embryonic expression patterns. Finally, I show that they are required for the correct development of the embryonic nervous system.