Isolation, characterization and developmental expression of the ecdysteroid‐induced E75 gene of the wax moth Galleria mellonella

Abstract

Using the cDNA for the Drosophila ecdysteroid-induced member of the steroid-hormone-receptor superfamily, E75A, we isolated a genomic clone from Galleria mellonella that revealed 77% similarity with the region of E75A cDNA encoding the C-terminal zinc-finger motif. A Galleria cDNA clone was isolated that encoded a complete DNA-binding domain composed of two zinc fingers and designated GmE75A. Its deduced amino acid sequence showed 100% and 85% identities within the DNA-binding and ligand-binding domains of Drosophila E75 A, respectively. The Galleria genomic clone did not encode the N-terminal zinc finger, but included a sequence similar to the B1 exon, which is unique to the B isoform of E75. Thus, the cDNA and genomic DNA sequences indicated that the Galleria gene E75 encoded at least two isoforms, GmE75 A and GmE75 B, which differed in their N-termini.Probes specific for GmE75A and B hybridized to two distinct transcripts of 2.6 kb. Both GmE75A and B mRNA levels correlated closely with the ecdysteroid titer during development. At the onset of larval/pupal transformation, both transcripts appeared in high amounts within 4 h of the ecdysteroid rise, then declined concurrently with the hormone titer decline. At the time of pupal ecdysis, there was another peak of GmE75 A expression but not GmE75B expression, coincident with a minor ecdysteroid pulse. In isolated abdomens of final instar larvae, GmE75A mRNA was induced by 20-hydroxyecdysone within 20 min of the injection; the mRNA levels were maximal at 1 h and declined by 3 h following the treatment.Post-embryonic development in insects is a cyclical process punctuated by alternation of molts and intermolt periods followed by metamorphosis. The molts are initiated and coordinated by the steroid hormone 20-hydroxyecdysone (20E) and related ecdysteroids [l]. The intermolt growth periods are characterized by a low ecdysteroid titer, which increases dramatically at the time of the molt. During the last larval instar, low levels of ecdysteroid in the absence of juvenile hormone, a sesquiterpenoid, initiate metamorphosis by causing pupal commitment of tissues. Then, a higher ecdysteroid level triggers a pupal molt.From studies of the effects of 20E on the 'puffing patterns' of the giant polytene chromosomes of Drosophila melanogaster, Ashburner et al. [2] proposed a model for ecdysteroid action. In this model, the ecdysteroid combined with its receptor binds to the target DNA to induce directly the 'early puff' genes and to repress the 'late puff' genes. The protein products encoded by the early genes then activate the late genes while inhibiting their own synthesis. In support ofCorrespondence to M. Jindra, Department of Zoology NJ-15, Fax: +1 206 543 3041.

A novel putative insect chitinase with multiple catalytic domains: hormonal regulation during metamorphosis

“…Although similar patterns of gene expression have also been reported for EcR-B1 in T. molitor [19] and E75A in Galleria mellonella [41], the physiological relevance of TmChit5 increase just before ecdysis remains unknown.…”

The BmE75 Nuclear Receptors Function as Dominant Repressors of the Nuclear Receptor BmHR3A

“…3). Because the B isoform of E75 differs from the other isoforms by a unique N terminus that replaces the first half of the DNA-binding domain (2,25,26), our findings indicate that the unique N-terminal sequences of E75B are not necessary for repression. Based on the structural features of the E75B isoform of B. mori, which has also been described recently (27), we predict that this isoform will also function as an efficient repressor of BmHR3-mediated transactivation.…”

Cloning of a shrimp (Metapenaeus ensis) cDNA encoding a nuclear receptor superfamily member: an insect homologue of E75 gene1

“…Since the DNA binding domain and the P-box of the shrimp E75 (EGCKG) is 100% identical to that of other E75s, the MeE75 may also compete with ecdysone for binding in the response element [14]. The E region of the MeE75 is less homologous to the LBD of insects.…”

“…The deduced amino acid sequence of the cDNA revealed a high level of similarity with that of nuclear receptor superfamily members. Like other nuclear receptors, the deduced amino acid sequence of the [12], Choristoneura CfE75 [13] and Galleria GmE75 [14] showed an overall 100% identity in the DBD region (Table 1). Another region that is conserved among members of the nuclear receptor superfamily is the E region.…”