A dual role of 20-hydroxyecdysone in the control of protein synthesis related to DNA puff activity in the anterior region of Bradysia hygida (Diptera, Sciaridae) salivary gland

Pseudolycoriella hygida (Sauaia and Alves)-An Overview of a Model Organism in Genetics, with New Aspects in Morphology and Systematics

Pseudolycoriella hygida (Sauaia & Alves, 1968) is a sciarid that has been continuously cultured in the laboratory for nearly 60 years. Studies on this species have contributed to the understanding of DNA puffs, which are characteristic of Sciaridae, and to the knowledge of more general aspects of insect biology, including cell death, nucleolar organization, and the role of the hormone ecdysone during molting. The genome of Psl. hygida has now been sequenced, and it is the third publicly available sciarid genome. The aim of this work is to expand the current knowledge on Psl. hygida. The morphology of the adults is revisited. The morphology of larvae and pupae is described, together with the behavior of immature stages under laboratory conditions. Cytogenetic maps of the salivary gland polytene chromosomes are presented, together with a comparative analysis of the mitotic chromosomes of six different sciarid species. Pseudolycoriella hygida was originally described as a species of Bradysia and recently moved to Pseudolycoriella. We examine here the systematic position of Psl. hygida in the latter genus. Our results extend the characterization of an unconventional model organism and constitute an important resource for those working on the cytogenetics, ecology, taxonomy, and phylogenetic systematics of sciarids.

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

Gene amplification occurs in Bradysia hygida salivary glands, at the end of the fourth larval instar. The hormone 20-hydroxyecdysone (20E) triggers this process, which results in DNA puff formation. Amplified genes are activated in two distinct groups. The activity of the first group is dependent on high levels of 20E, while the second group needs low hormone levels. Consequently, the salivary glands of B. hygida constitute an interesting biological model to study how 20E, and its receptors, affect gene amplification and activity. We produced polyclonal antibodies against B. hygida EcR (BhEcR). In western blots a polypeptide of about 66 kDa was detected in salivary gland extracts. The antibodies were also used for indirect immune-localization of BhEcR in polytene chromosomes. RNA-polymerase II was also immune-detected. We did not detect the receptor in chromosome C where the first and second groups of DNA puffs form during DNA puff anlage formation, but it was present during puff expansion. During the active phase of both groups of DNA puffs, RNA polymerase II co-localized with BhEcR. After puff regression, these antigens were not detected. Apparently, EcR plays a direct role in the transcription of amplified genes, but its role in gene amplification remains enigmatic.

Programmed cell death inBradysia hygida (Diptera, Sciaridae) salivary glands presents apoptotic features

In this work, we present biochemical and morphological evidence that the final steps of programmed cell death (PCD) in the salivary glands of the inferior Diptera, Bradysia hygida, present apoptotic characteristics. In B. hygida, elimination of salivary glands is preceded by the establishment of a typical pattern of protein synthesis; increase in caspase activity; decrease in cell volume; nuclear pyknosis; nuclear DNA breakage; changes in the actin cytoskeleton; and most importantly, destruction of giant cells via formation of apoptotic bodies containing broken DNA or cytoplasm remains. Thus, elimination of B. hygida salivary glands by this process suggests that such mode of PCD is also involved in the destruction of entire organs in insects and, therefore, adds more complexity to the regulation of tissue elimination during development.

The control of BhB10-1 gene expression in the salivary gland of Bradysia hygida (Diptera, Sciaridae) is disrupted in vivo by a delayed effect of cycloheximide

BhB10-1 is an amplified gene present in DNA puff B10. This gene is very active in the salivary gland regions S1 and S3 at the end of the larval development. Two transcripts of this gene, 1.3 and 1.1 kb in size, were detected. A secretory protein, SP23, is the product of BhB10-1. In this work, we present evidence supporting the hypothesis that a biphasic process of mRNA degradation is an important component in the control of BhB10-1 gene expression. The 1.3 kb transcript, by a process of poly(A) tail shortening, is converted to the inactive transcript of 1.1 kb which is detected during and after the period of SP23 expression. Cycloheximide in very low concentration, if applied at a proper time, can disrupt this process leading to extended periods of 1.3 kb RNA detection and SP23 synthesis. A tentative model is proposed to explain this phenomenon.

The induction of DNA puff BhC4-1 gene is a late response to the increase in 20-hydroxyecdysone titers in last instar dipteran larvae

The characterization of DNA puff BhC4-1 expression was extended and its response to 20-hydroxyecdysone investigated in Bradysia hygida and in transgenic Drosophila carrying the BhC4-1 gene. In both organisms the activation of BhC4-1 in salivary glands occurs at the end of the larval stage coinciding with the peak in ecdysone titers which induces metamorphosis. Injections of 20-hydroxyecdysone into mid-fourth instar larvae of B. hygida show that the induction of BhC4-1 expression, as well as amplification and puff C4 expansion, are late events induced by the hormone. This late response of BhC4-1 expression was also observed in transgenic salivary glands cultivated in the presence of 20-hydroxyecdysone. In vitro studies using transgenic Drosophila indicate that both repressor and activator factors regulate the timing of BhC4-1 expression in salivary glands.