Ecdysone induces transcription and amplification in Sciara coprophila DNA puff II/9A

Abstract

DNA replication is normally tightly regulated to ensure the production of only one copy of the genome per cell cycle. However, DNA puffs of the salivary gland giant polytene chromosomes of Sciara coprophila undergo DNA amplification during the normal course of development, overriding this control. This developmental strategy provides more template for the production of large amounts of protein needed for pupation. We have focused on DNA puff II/9A, which amplifies approximately 17-fold over the rest of the genome. Evidence presented here suggests that DNA amplification at this locus is controlled by the steroid hormone ecdysone, the master regulator of insect development. Explanted, pre-amplification stage salivary glands undergo premature amplification when incubated with ecdysone. Injection of ecdysone into pre-amplification stage larvae induces amplification. Ecdysone also induces transcription of the II/9A genes. We report the presence of a putative ecdysone response element directly adjacent to the origin recognition complex (ORC)-binding site in the II/9A origin and demonstrate that it is efficiently bound by the Sciara ecdysone receptor. These results implicate ecdysone in the regulation of DNA amplification in Sciara and suggest the ecdysone receptor may be the elusive amplification factor. This would be a new role for this transcription factor.

Ras signaling modulates activity of the ecdysone receptor EcR during cell migration in the drosophila ovary

“…While reduced amplification of the chorion loci in EcR-DN egg chambers is sufficient to explain reduced chorion protein accumulation and gene expression, it has been shown that sequence elements that regulate Cp18 amplification are discrete from sequences controlling transcription (Austin et al, 1999). Recent work from the Sciarid fly Sciara coprophila (Foulk et al, 2006) has shown that EcR, which regulates transcription of the II/9a genes (Bienz-Tadmor et al, 1991), also binds to the ORC site in the II/9a locus, suggesting that the mechanism of hormonal control of amplification may be conserved in insects. Thus, EcR regulation of amplification and transcriptional activation of the Cp18 gene via its nearby EcRE likely are stimulated independently by ecdysone.…”

Functional and bioinformatics analyses reveal conservation of cis‐regulatory elements between sciaridae and drosophilidae

“…V INTRODUCTION DNA puffs are a feature of the Sciaridae family and are formed at discrete sites during the fourth larval instar in the salivary gland polytene chromosomes. These genomic regions constitute sites of developmentally regulated gene amplification and transcription (Basso et al, 2002;Foulk et al, 2006;Gerbi et al, 1993;Lara et al, 1991;Stocker et al, 1996). The formation of DNA puffs is induced by ecdysone and is concomitant with the transcription of the genes which present the highest levels of amplification within the amplicons (Fontes et al, 1992;Gerbi et al, 1993;Glover et al, 1982;Paçó-Larson et al, 1992;Penalva et al, 1997;Santelli et al, 1991Santelli et al, , 2004Wu et al, 1993;Yokosawa et al, 1999).…”

Indirect immune detection of ecdysone receptor (EcR) during the formation of DNA puffs in Bradysia hygida (Diptera, Sciaridae)

“…The hormone 20-hydroxyecdysone (20E) induces transcription at Drosophila RNA puffs (Ashburner 1972, Ashburner et al 1974) through its interaction with the ecdysone receptor (EcR) and its heterodimeric partner ultraspiracle (USP) (Koelle et al 1991, Yao et al 1992, Talbot et al 1993, Thomas et al 1993. 20E also induces DNA puffs in sciarid larvae (Crouse & Keyl 1968, Stocker & Pavan 1974, Amabis & Amabis 1984a, and EcR/USP binds to DNA puff response elements (EcRE) (Foulk et al 2006). However, the molecular mechanisms of the action of 20E in these processes are still largely unknown de Carvalho et al 2000, Basso et al 2002, Foulk et al 2006.…”

“…20E also induces DNA puffs in sciarid larvae (Crouse & Keyl 1968, Stocker & Pavan 1974, Amabis & Amabis 1984a, and EcR/USP binds to DNA puff response elements (EcRE) (Foulk et al 2006). However, the molecular mechanisms of the action of 20E in these processes are still largely unknown de Carvalho et al 2000, Basso et al 2002, Foulk et al 2006.…”