sry h-1, a new Drosophila melanogaster multifingered protein gene showing maternal and zygotic expression

Collier, a novel regulator of Drosophila head development, is expressed in a single mitotic domain

BACKGROUND

Segmentation of the Drosophila embryo is based on a cascade of hierarchical gene interactions that is initiated by maternal morphogens; these interactions define spatially restricted domains of zygotic gene expression within the blastoderm. Although the hierarchy of the segmentation genes that subdivide the trunk is well established, the patterning of the head is less well understood. Seven head segments can be assigned on the basis of metameric patterns of segment-polarity gene expression and internal sensory organs. The domains of expression of head gap-like genes broadly overlap, with their posterior margins out of phase by one segment. Taken together with the lack of pair-rule gene expression in the head, these observations led to the suggestion that head gap genes act in a combinatorial manner, determining head segmental borders and segmental identity at the same time.

RESULTS

We have identified a new Drosophila gene, collier (col), whose expression at the blastoderm stage is restricted to a single stripe of cells corresponding to part of the intercalary and mandibular segment primordia, possibly parasegment O. Reduction of col activity in early gastrula embryos by antisense RNA expression results in a specific lack of head structures derived from these segments. The expression of col coincides with a mitotic domain, which supports the proposal that cells in this domain undergo a concerted mitotic and differentiation program that is orchestrated at the transcriptional level. Col is an ortholog of mammalian early B-cell factor/Olfactory-1. These proteins define a new family of transcription factors that contain a helix-loop-helix dimerization motif and a new type of DNA-binding domain that is highly conserved during evolution.

CONCLUSIONS

Here we describe Col, the first Drosophila member of a new family of transcription factors. Col may act as a "second-level regulator' of head patterning. The structural conservation of Col during evolution raises the questions of its conservation of function in head specification and its interactions with other factors conserved between insects and vertebrates.

Evolutionarily conserved positive and negative cis-acting elements control the blastoderm-specific expression of the Drosophila serendipity alpha cellularisation gene

The serendipity alpha (sry alpha) cellularisation gene is only transcribed at the blastoderm stage, when this morphogenetic event takes place. We show that a 95 bp sry alpha upstream region is sufficient for blastoderm-specific expression of a lacZ reporter gene. This region encompasses four nucleotide motifs (I-IV, 5' to 3') conserved at similar relative positions in several Drosophila species. Removal of motif I leads to ectopic expression of lacZ in precursor cells of the PNS. Deletion of motif IV decreases the level of lacZ transcripts and modifies their banded pattern of accumulation late in cycle 14, whereas deletion of motifs II and III abolishes the sry alpha promoter activity. Motif III includes a consensus recognition site for b-HLH proteins. A point mutation in this E-box both severely reduces lacZ expression at blastoderm and prevents its ectopic expression in the PNS upon deleting motif I. These two effects depend upon da+ activity, suggesting that daughterless may positively control sry alpha transcription.

Dissection of the Drosophila pourquoi-pas? promoter: complex ovarian expression is driven by distinct follicle cell- and germ line-specific enhancers

The pourquoi-pas? (pqp) gene of Drosophila melanogaster encodes a zinc finger protein present in the oocyte nucleus, the nurse cells and, at a lower level, in the follicle cells. Null mutations of the pqp gene lead to female sterility. We have undertaken a functional dissection of the pqp promoter by following the expression of the lacZ reporter gene in the ovaries of transgenic flies. pqp sequences, necessary for expression of the lacZ gene in a pattern similar to that of the endogenous pqp gene, are located between positions -210 and +30, relative to the transcription start site. These sequences, subdivided in follicle cell- and germ line-specific regions, appear to function in a direction-independent and distance-sensitive manner. The -210/-40 region, sharing stretches of sequence similarity with 5' sequences of follicle cell-specific genes, promotes lacZ expression only in the follicle cells. The -80/+30 region is germ line-specific. The promoter limits, deduced from the deletion experiments presented here, are in accordance with the molecular analysis of pqp mutants.

Physical characterization and sequence identification of the ovary maturating parsin. A new neurohormone purified from the nervous corpora cardiaca of the African locust (Locusta migratoria migratorioides

A novel neurohormone, which anticipates ovarian maturation, was recently purified using liquid chromatography from the African locust nervous corpora cardiaca. Both its function and production by the pars intercerebralis of Locusta migratoria lead to its name, the ovary maturating parsin (Lom OMP). In this study, the Lom OMP was physically and chemically characterized. Its multiply charged ion spectrum was interpreted as two peaks of quite equal size having molecular masses of 6923.4 Da (major peak) and 6907.3 Da. The Lom OMP presented no periodic secondary structure according to the far ultraviolet circular dichroism spectrum obtained. It is composed of 65 amino acids and included a high concentration of alanine but is devoid of cysteine, isoleucine, methionine, lysine and threonine. The amino acid sequence indicated only one microheterogeneity, observed at position 26, consisted in the replacement of serine by alanine. The calculated Mr of the two acidic isoforms (calculated pHi = 4.87) were found to be in agreement with mass spectrometry measurements. When compared to the sequence libraries, the Lom OMP, the first insect gonadotropic neurohormone, was revealed as an unique protein.

Serendipity delta, a Drosophila zinc finger protein present in embryonic nuclei at the onset of zygotic gene transcription

Serendipity delta (sry delta) is a member of a set of Drosophila zinc finger protein genes showing maximal transcription during oogenesis. By using transformant lines, we monitored the zygotic expression of the sry delta gene and characterized some biochemical properties of a sry delta/beta-galactosidase fusion protein-containing fingers. Further analysis made use of anti-sry delta specific antibodies. During oogenesis, while sry delta mRNAs transcribed by nurse cells are transferred to the oocyte starting in stage 10, translation into protein occurs in the ooplasm starting in stage 12. The maternally inherited protein concentrates in embryonic nuclei during early cleavages, prior to the onset of zygotic transcription. At the blastoderm stage, the sry delta protein is localized in all somatic nuclei. Later in embryogenesis and up to the adult stage, the zygotic protein is present in nuclei of transcriptionally active cells (both somatic and germ line). These data are consistent with the sry delta protein being a transcription factor, with a role in zygotic activation of general cellular functions.