Developmental control elements in the promoter of a Drosophila vitelline membrane gene

Following the 'tracks': Tramtrack69 regulates epithelial tube expansion in the Drosophila ovary through Paxillin, Dynamin, and the homeobox protein Mirror

Epithelial tubes are the infrastructure for organs and tissues, and tube morphogenesis requires precise orchestration of cell signaling, shape, migration, and adhesion. Follicle cells in the Drosophila ovary form a pair of epithelial tubes whose lumens act as molds for the eggshell respiratory filaments, or dorsal appendages (DAs). DA formation is a robust and accessible model for studying the patterning, formation, and expansion of epithelial tubes. Tramtrack69 (TTK69), a transcription factor that exhibits a variable embryonic DNA-binding preference, controls DA lumen volume and shape by promoting tube expansion; the tramtrack mutation twin peaks (ttk(twk)) reduces TTK69 levels late in oogenesis, inhibiting this expansion. Microarray analysis of wild-type and ttk(twk) ovaries, followed by in situ hybridization and RNAi of candidate genes, identified the Phospholipase B-like protein Lamina ancestor (LAMA), the scaffold protein Paxillin, the endocytotic regulator Shibire (Dynamin), and the homeodomain transcription factor Mirror, as TTK69 effectors of DA-tube expansion. These genes displayed enriched expression in DA-tube cells, except lama, which was expressed in all follicle cells. All four genes showed reduced expression in ttk(twk) mutants and exhibited RNAi phenotypes that were enhanced in a ttk(twk)/+ background, indicating ttk(twk) genetic interactions. Although previous studies show that Mirror patterns the follicular epithelium prior to DA tubulogenesis, we show that Mirror has an independent, novel role in tube expansion, involving positive regulation of Paxillin. Thus, characterization of ttk(twk)-differentially expressed genes expands the network of TTK69 effectors, identifies novel epithelial tube-expansion regulators, and significantly advances our understanding of this vital developmental process.

Specific domains drive VM32E protein distribution and integration in Drosophila eggshell layers

A study was made of the localization and assembly of the VM32E protein, a putative vitelline membrane component of the Drosophila eggshell. The results highlight some unique features of this protein compared with the other proteins of the same gene family. At the time of its synthesis (stage 10), the VM32E protein is not detectable in polar follicle cells. However, it is able to move in the extracellular space around the oocyte and, by stage 11 is uniformly distributed in the vitelline membrane. During the terminal stages of oogenesis the VM32E protein is partially released from the vitelline membrane and becomes localized in the endochorion layer also. By analyzing transgenic flies carrying variously truncated VM32E proteins, we could identify the protein domains required for the proper assembly of the VM32E protein in the eggshell. The highly conserved vitelline membrane domain is implicated in the early interactions with other components and is required for cross-linking VM32E protein in the vitelline membrane. The terminal carboxylic domain is necessary for localization to the endochorion layer. Protein with the C-end domain deleted is localized solely to the vitelline membrane and cross-linked only in laid eggs, as occurs for the other vitelline membrane proteins.

Spatial activation and repression of the drosophila vitelline membrane gene VM32E are switched by a complex cis-regulatory system

The VM32E gene is differently expressed in the distinct cell domains composing the follicular epithelium. Our previous work on the VM32E gene defined the promoter regions required for the control of gene expression in the ventral and dorsal follicle domains. In this report, we present data from a finer dissection of each upstream regulatory region, allowing to draw the functional interactions among different regulatory elements. A 73-bp proximal region (-112/-39) contains regulatory element(s) to dictate the activation of the gene in the follicular epithelium. This region interacts with two other cis-regulatory elements and is absolutely required for their output. The first element (-206/ -113), individually unable to raise reporter expression, elicits gene activity in the ventral domain when joined to the proximal fragment; a second element (-348/-254) joined to the same proximal fragment sustains the full dorsal and ventral activity. Moreover, the ectopic expression driven by some promoter fragments in border or posterior cells uncovers the existence of specific negative regulatory elements. So, the follicular domain specificity of VM32E gene expression is achieved through the combined activities of cell-type specific positive and negative elements.

Vitelline envelope genes of the yellow fever mosquito, Aedes aegypti

Vitelline envelope genes from the mosquito Aedes aegypti were analyzed with respect to their DNA sequences, genomic representation, temporal and spatial expression profiles and response to 20-hydroxyecdysone. Genomic clones of three vitelline envelope genes, 15a-1, 15a-2 and 15a-3 were isolated. Southern analysis indicates that all three genes are represented by a single copy in the genome. The deduced amino acid sequences of all three vitelline envelope genes contain a conserved region of 46 residues that overlaps with a region that is conserved in four Drosophila melanogaster vitelline envelope genes. DNA was sequenced flanking the 15a-1, 15a-2 and 15a-3 coding regions. A 360 bp sequence 5' of the 15a-2 coding region was identified with 72% identity to a sequence upstream of the Ae. aegypti VgA1 vitellogenin gene. The temporal patterns of 15a-1, 15a-2 and 15a-3 expression, as determined by Northern analysis, were similar. The spatial patterns of expression, as determined by whole-mount in situ hybridization, differed between the three genes. 15a-1 and 15a-3 were only expressed in the middle and posterior regions of the follicle, while 15a-2 was also expressed at the anterior region. Vitelline envelope gene expression was higher in ovaries that were dissected at 0, 2 and 10 h following a blood meal and then incubated in vitro for 10 h in medium containing 10(-5) M 20-hydroxyecdysone, compared to ovaries that were incubated without hormone.

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.

Cell functions in Drosophila oogenesis

We are studying Drosophila oogenesis by analysing at genetic and molecular levels several female-sterile mutations. Some (hold up, wavoid-like and abnormal oocyte) have been isolated by L. Sandler in region 32 of the second chromosome; others have been isolated by us and their phenotype is presented for the first time in this paper. We performed chromosome walking in 32D-32E-F(250 Kb) and 32A-B(100 Kb) and in the last years we molecularly identified several genes with specific maternal expression patterns. We will review here our studies on two of these genes: the Vitelline Membrane Protein gene 32E and the gene coding for a receptor form of Guanylate Cyclase.

Comparative analysis of the sequence and structure of two Drosophila melanogaster genes encoding vitelline membrane proteins

Two Drosophila melanogaster vitelline membrane protein-encoding genes (VM), located at polytene band positions 26A and 34C, have been cloned and comparatively characterized at the nucleotide level. Sequence analysis of genomic and cDNA clones for the two genes, VM26A.1 and VM34C.1, indicates that both are similarly organized with a central highly conserved domain [Scherer et al., Dev. Biol. 130 (1988) 786-788] which is flanked by unrelated regions, and that both genes lack introns. Comparison of the upstream regions reveals that both VM genes contain a hepatmeric element identical to one associated with the D. melanogaster yolk protein-encoding genes (YP). This heptamer occurs in the specific 5' flanking region responsible for ovarian temporal- and tissue-specific control in both VM and YP genes. A putative chorion transcription factor 2 site is also associated with an upstream control element of VM26A.1, but not with any sequenced portion of VM34C.1.

The regulation of sex determination and sexually dimorphic differentiation in Drosophila

Sex determination and sexually dimorphic differentiation in Drosophila involve multiple regulatory mechanisms, including alternative splicing, transcriptional control, subcellular compartmentalization, and intercellular signal transduction. Regulatory interactions occur throughout the development of the fly, some requiring the continuous function of the genes involved, and others being temporally limited, but having permanent consequences. The control of sexual differentiation in Drosophila is, for the most part, subject to the continuous active control of numerous regulatory proteins operating at many levels.