Developing compound eye in lozenge mutants of Drosophila: lozenge expression in the R7 equivalence group

 The lozenge locus is genetically complex, containing two functionally distinct units, cistrons A and B, that influence the structure of the compound eye. Extreme mutations of either cistron produce adult phenotypes that share similarities and that have striking differences. We have analyzed the expression of several developmentally important eye genes including boss, scabrous, rhomboid, seven-up, and Bar in lozenge mutant backgrounds representing both cistrons. This analysis follows the progressive recruitment of photoreceptor neurons during eye development and has confirmed that the initial development of photoreceptors is normal up to the five cell precluster stage (R8, R2/5 and R3/4). However, when lozenge is mutant, further eye development is perturbed. As cells R1, R6 and R7 are recruited, patterns of gene expression for seven-up and Bar become abnormal. We have also characterized the expression of two different enhancer trap alleles of lozenge. The lozenge product(s) appear to be first expressed in the eye disc in undifferentiated cells shortly after the five cell precluster forms. Then, as distinct cells are recruited to a fate, lozenge expression persists and is refined in those cells. Our data suggests that lozenge functions in cone cells and pigment cells as well as in specific glia. With respect to photoreceptor neurons, lozenge biases the developmental potential of cells R1, R6 and R7, by directly influencing the expression of genes important for establishing cell fate. Received: 26 July 1996 / Accepted: 6 January 1997     

senseless repression of rough is required for R8 photoreceptor differentiation in the developing Drosophila eye.

An outstanding model to study how neurons differentiate from among a field of equipotent undifferentiated cells is the process of R8 photoreceptor differentiation during Drosophila eye development. We show that in senseless mutant tissue, R8 differentiation fails and the presumptive R8 cell adopts the R2/R5 fate. We identify senseless repression of rough in R8 as an essential mechanism of R8 cell fate determination and demonstrate that misexpression of senseless in non-R8 photoreceptors results in repression of rough and induction of the R8 fate. Surprisingly, there is no loss of ommatidial clusters in senseless mutant tissue and all outer photoreceptor subtypes can be recruited, suggesting that other photoreceptors can substitute for R8 to initiate recruitment and that R8-specific signaling is not required for outer photoreceptor subtype assignment. A genetic model of R8 differentiation is presented.     

Over-expression of transglutaminase in the Drosophila eye imaginal disc induces a rough eye phenotype

Transglutaminases (TGs) catalyze the cross-linking of proteins and are involved in various biological processes in mammals. In invertebrates, except for the involvement in the hemolymph clotting, the functions of TG have not been revealed. Drosophila has a single TG gene (CG7356), from which two kinds of mRNAs (dTG-RA and dTG-RB) are formed. RT-PCR analyses indicated that both dTGs-RA and -RB are synthesized in all the developmental stages tested. To reveal the roles of dTG during the development, we examined a phenotype induced through the ectopic expression of dTG by using a GAL4-UAS targeted expression system. Over-expression of dTG-A in the eye imaginal disc of larva induced a rough eye phenotype in adult compound eyes. Co-expression of P35, an inhibitor of apoptosis, suppressed the rough eye phenotype, suggesting that the rough eye phenotype induced by the over-expression of dTG-A in the eye imaginal disc is due to the occurrence of apoptosis. The rough eye phenotype induced by the over-expression of dTG-A was suppressed by the crossing with mutant fly lines lacking Drosophila JNK gene basket (bsk) or Drosophila JNKK gene hemipterous. FLP-out experiments using an enhancer trap line showed that the over-expression of dTG-A in the eye imaginal disc increased the puckered enhancer activity, a reporter of Bsk activity. These results suggested that the rough eye phenotype induced by the over-expression of dTG-A is related to an enhancement of JNK signaling pathway.     

The pineapple eye gene is required for survival of Drosophila imaginal disc cells

Each ommatidium of the Drosophila eye is constructed by precisely 19 specified precursor cells, generated in part during a second mitotic wave of cell divisions that overlaps early stages of ommatidial cell specification. Homozygotes for the pineapple eye mutation lack sufficient precursor cells due to apoptosis during the period of fate specification. In addition development is delayed by apoptosis during earlier imaginal disc growth. Null alleles are recessive lethal and allelic to l(2)31Ek; heteroallelic combinations can show developmental delay, abnormal eye development, and reduced fertility. Mosaic clones autonomously show extensive cell death. The pineapple eye gene was identified and predicted to encode a novel 582-amino-acid protein. The protein contains a novel, cysteine-rich domain of 270 amino acids also found in predicted proteins of unknown function from other animals.     

semang affects the development of a subset of cells in the Drosophila compound eye

semang (sag), a mutation isolated as a suppressor of Drosophila Src42A, has previously been shown to affect some receptor tyrosine kinase mediated embryonic processes. Here we show that sag specifically affects the development of R1, R6 and R7 photoreceptor cells in a cell-autonomous manner. These cells are absent in the mutant at the time when they normally appear in the ommatidial pre-clusters. Genetic analyses suggest that sag functions downstream of, or parallel to, Mapk and Yan in the photoreceptor differentiation pathway. The autonomous requirement of sag for R1/R6/R7 development could be explained by a selective impairment of the late, but not early, rounds of Egfr-induced precursor cell assembly by the sag mutations. Egfr signaling is highly regulated by autocrine or paracrine mechanisms in different cells. Knowing that the photoreceptor cluster formation is a complex process involving dynamic changes in cell-cell contact, our hypothesis is that the sag alleles affected certain special aspects of Egfr-signaling that are unique for the recruitment of R1/R6/R7 cells.     

The embryonic development of larval muscles in Drosophila

Each of the abdominal hemisegments A2-A7 in the Drosophila larva has a stereotyped pattern of 30 muscles. The pattern is complete by 13 h after egg laying, but the development of individual muscles has begun with the definition of precursors at least by the onset of germ band shortening, some 5.5 h earlier. The earliest signs of muscle differentiation are cell fusions, which occur in the ventralmost mesoderm overlying the CNS and at stereotyped positions in the rest of the mesoderm as the germ band shortens. At the end of shortening, the pattern of muscle precursors produced by these fusions is complete. Precursors filled with dye reveal extensive fine processes probably involved initially in cell fusion and, subsequently, in navigation over the epidermis to form attachment points. The muscle pattern is formed before innervation and without cell death. Thus, neither of these processes is involved in determining the distribution of precursors. Evidence is presented for the view that the development of the larval muscle pattern in Drosophila depends on a prior segregation of founder cells at appropriate locations in the mesoderm with which other cells fuse to form the precursors.     

Growing pains: development of the larval nocifensive response in Drosophila

The ability to perceive and avoid harmful substances or stimuli is key to an organism's survival. The neuronal cognate of the perception of pain is known as nociception, and the reflexive motion to avoid pain is termed the nocifensive response. As the nocifensive response is an ancient and evolutionarily conserved behavioral response to nociceptive stimuli, it is amenable to study in relatively simple and genetically tractable model systems such as Drosophila. Recent studies have taken advantage of the useful properties of Drosophila larvae to begin elucidating the neuronal connectivity and molecular machinery underlying the nocifensive response. However, these studies have primarily utilized the third-instar larval stage, and many mutations that potentially influence nociception survive only until earlier larval stages. Here we characterize the nocifensive responses of Drosophila throughout larval development and find dramatic changes in the nature of the behavior. Notably, we find that prior to the third instar, larvae are unable to perform the characteristic "corkscrew-like roll" behavior. Also, we identify an avoidance behavior consistent with a nocifensive response that is present immediately after larval hatching, representing a paradigm that may be useful in examining mutations with an early lethal phenotype.     

Determination and development of the larval muscle pattern in Drosophila melanogaster

This review describes briefly what is known about the early steps of mesoderm differentiation in the fruitfly Drosophila melanogaster. After a summary of general aspects including mesoderm differentiation, mesoderm cell migration and subdivision of the mesoderm, more detail is given about the specification of muscle progenitor cells, due to their role as the earliest obvious landmarks in muscle fiber development in Drosophila. Particular focus is given to recent results on the role of asymmetric cell division in muscle differentiation. Furthermore a short summary of myoblast fusion is provided.     

Adhesion of Drosophila imaginal disc cells in vitro

Summary We have used our imaginal disc cell lines to carry out in vitro studies on the cell-cell and cell-substrate adhesion of Drosophila leg and wing disc cells. Single cells were allowed to reaggregate in roller culture, and this process was found to be partially dependent on the presence of magnesium and calcium ions in the suspension medium. Varying rates of reaggregation were observed in cells from different stages of a passage, correlating with the pattern of morphogenesis which occurs during the passage. We have demonstrated that cloned cell lines can be produced showing certain selected characteristics, such as reduced cell adhesiveness.     

Electron microscopic study of larval eye development in Turbellaria Polycladida

The appearance and development of the embryonic and larval eyes of the polyclad turbellarian Stylochus mediterraneus were studied. In the embryo, the left epidermal eye appears first. Subsequently, the right epidermal eye appears, and within hours it sinks into the parenchyma and turns into a cerebral eye. Newly hatched Götte's larvae possess both the left epidermal and the right cerebral eye. Three days after hatching, an incomplete eye appears adjacent to the left epidermal eye. The left cerebral eye then originates from this incomplete eye as it sinks into the parenchyma. This third eye is believed to originate through a process of induction.     

Lobe mediates Notch signaling to control domain-specific growth in the Drosophila eye disc

Notch (N) activation at the dorsoventral (DV) boundary of the Drosophila eye is required for early eye primordium growth. Despite the apparent DV mirror symmetry, some mutations cause a preferential loss of the ventral domain, suggesting that the growth of individual domains is asymmetrically regulated. We show that the Lobe (L) gene is required non-autonomously for ventral growth but not dorsal growth, and that it mediates the proliferative effect of midline N signaling in a ventral-specific manner. L encodes a novel protein with a conserved domain. Loss of L suppresses the overproliferation phenotype of constitutive N activation in the ventral, but not in the dorsal eye, and gain of L rescues ventral tissue loss in N mutant background. Furthermore, L is necessary and sufficient for the ventral expression of a N ligand, Serrate (Ser), which affects ventral growth. Our data suggest that the control of ventral Ser expression by L represents a molecular mechanism that governs asymmetrical eye growth.     

The influence of morphogene Wg on the formation of an ectopic eye in Drosophila melanogaster

Due to the ectopic expression of the ey gene in the wing imaginal disc under the action of the 1096-Gal4 driver, a part of the wing disc cells change their fate and become eye cells. Ectopic eyes are induced in definite regions of the wing disc and form a stable pattern on the wing of an adult fly. Here, we have shown that the ectopic expression of Wg inhibits the formation of ectopic eyes, and conversely the expression of Wg is reduced in the sites of ectopic Ey expression. Experiments with overexpression of the vesicular traffic protein H rs capable of inhibiting the Wg signaling agree with the notion on antagonism of Wg and Ey in ectopic eyes. Our results confirm that the processes of formation of normal and ectopic eyes are principally similar with regard to genetic control.     

Ectopic expression of BEAF32A in the Drosophila eye imaginal disc inhibits differentiation of photoreceptor cells and induces apoptosis

Transgenic flies were established in which ectopic expression of boundary element-associated factor (BEAF) 32A was targeted to the Drosophila eye imaginal disc. The eyes of the adult fly displayed a severe rough eye phenotype. When these eyes were sectioned, most ommatidia were found to be fused and irregularly shaped rhabdomeres were observed. In the developing eye imaginal disc, expression of BEAF32A inhibited differentiation of photoreceptor cells. Expression of BEAF32A also induced extensive apoptosis of eye imaginal disc cells and, consistent with this, co-expression of baculovirus P35 in the eye imaginal disc suppressed the BEAF32A-induced rough eye phenotype. To investigate the effects of BEAF32A on regulation of chromatin structure, genetic crosses of the BEAF32A-overexpressing flies with loss-of-function mutants for genes encoding other boundary element-binding factors or regulators of chromatin structure were conducted. Interestingly, half-dose reduction of the su(Hw) gene strongly enhanced the rough eye phenotype induced by BEAF32A. Furthermore, genetic crosses of the transgenic flies with loss-of-function mutants for genes interacting with Polycomb revealed specific links between BEAF32A and genes such as Distalless and kohtalo, suggesting a relation to the chromatin insulator function of BEAF. In addition, genetic crosses of transgenic flies expressing BEAF32A with a collection of Drosophila deficiency stocks allowed us to identify several genomic regions, deletions of which caused enhancement or suppression of the BEAF32A-induced rough eye phenotype. The transgenic flies established in this study should be useful to identify targets of BEAF32A and its positive or negative regulators in Drosophila.     

Rickettsiae-like structures in the larval salivary gland cells of Drosophila auraria

Rickettsiae-like structures were found in the salivary gland cells of Drosophila auraria during different larval and prepupal developmental stages, from the early 3rd instar up to 14 hr after spiracle inversion. These microorganisms are surrounded by a membrane, are constantly intracellular, and occur singly or in groups. Their widespread occurrence in various tissues of other Drosophila species indicates that they can be considered as symbionts, but their actual functional significance (if any) is unknown.