Isolation and characterization of X-linked lethal mutants affecting differentiation of the imaginal discs in Drosophila melanogaster

Steroid hormone induction of temporal gene expression in Drosophila brain neuroblasts generates neuronal and glial diversity

An important question in neuroscience is how stem cells generate neuronal diversity. During Drosophila embryonic development, neural stem cells (neuroblasts) sequentially express transcription factors that generate neuronal diversity; regulation of the embryonic temporal transcription factor cascade is lineage-intrinsic. In contrast, larval neuroblasts generate longer ~50 division lineages, and currently only one mid-larval molecular transition is known: Chinmo/Imp/Lin-28+ neuroblasts transition to Syncrip+ neuroblasts. Here we show that the hormone ecdysone is required to down-regulate Chinmo/Imp and activate Syncrip, plus two late neuroblast factors, Broad and E93. We show that Seven-up triggers Chinmo/Imp to Syncrip/Broad/E93 transition by inducing expression of the Ecdysone receptor in mid-larval neuroblasts, rendering them competent to respond to the systemic hormone ecdysone. Importantly, late temporal gene expression is essential for proper neuronal and glial cell type specification. This is the first example of hormonal regulation of temporal factor expression in Drosophila embryonic or larval neural progenitors.

Toxic effect of destruxin A on abnormal wing disc-like (SLAWD) in Spodoptera litura fabricius (Lepidoptera: Noctuidae)

BACKGROUND

Destruxin A (DA) is a microbial insecticide with potent bioactivity against Spodoptera litura larvae. A previous proteomic analysis of S. litura (SL-1) cells exposed to DA showed the abnormal expression of wing disc-like protein of S. litura (SLAWD). To further understand the effect of DA on SLAWD expression, a functional study was carried out.

PRINCIPAL FINDINGS

The SLAWD gene (SLAWD) was cloned and an open reading frame of 537 bp encoding a polypeptide of 178 amino acids was detected. Real-time fluorescence quantitative PCR (qRT-PCR) suggested that SLAWD is expressed in all developmental stages of S. litura, but expression was highest during the pupal and adult stages. RNAi knockdown of SLAWD expression in 6th-stage larvae was achieved by the microinjection of a specific double-stranded RNA (dsRNA). The results showed a significant decrease in SLAWD mRNA expression levels between the prepupal and adult stages. Interestingly, SLAWD expression was similarly down-regulated by treating 6th-stage larvae with DA. Growth- and development-related statistics confirmed the observed abnormalities in S. litura development after either RNAi or DA treatment.

CONCLUSIONS

SLAWD appears to have a biosynthetic function in the pupal and adult stages of S. litura. The toxic effect of DA on S. litura development is due the negative effect of DA on SLAWD gene expression.

Broad Complex isoforms have unique distributions during central nervous system metamorphosis in Drosophila melanogaster

Broad Complex (BRC) is a highly conserved, ecdysone-pathway gene essential for metamorphosis in Drosophila melanogaster, and possibly all holometabolous insects. Alternative splicing among duplicated exons produces several BRC isoforms, each with one zinc-finger DNA-binding domain (Z1, Z2, Z3, or Z4), highly expressed at the onset of metamorphosis. BRC-Z1, BRC-Z2, and BRC-Z3 represent distinct genetic functions (BRC complementation groups rbp, br, and 2Bc, respectively) and are required at discrete stages spanning final-instar larva through very young pupa. We showed previously that morphogenetic movements necessary for adult CNS maturation require BRC-Z1, -Z2, and -Z3, but not at the same time: BRC-Z1 is required in the mid-prepupa, BRC-Z2 and -Z3 are required earlier, at the larval-prepupal transition. To explore how BRC isoforms controlling the same morphogenesis events do so at different times, we examined their central nervous system (CNS) expression patterns during the approximately 16 hours bracketing the hormone-regulated start of metamorphosis. Each isoform had a unique pattern, with BRC-Z3 being the most distinctive. There was some colocalization of isoform pairs, but no three-way overlap of BRC-Z1, -Z2, and -Z3. Instead, their most prominent expression was in glia (BRC-Z1), neuroblasts (BRC-Z2), or neurons (BRC-Z3). Despite sequence similarity to BRC-Z1, BRC-Z4 was expressed in a unique subset of neurons. These data suggest a switch in BRC isoform choice, from BRC-Z2 in proliferating cells to BRC-Z1, BRC-Z3, or BRC-Z4 in differentiating cells. Together with isoform-selective temporal requirements and phenotype considerations, this cell-type-selective expression suggests a model of BRC-dependent CNS morphogenesis resulting from intercellular interactions, culminating in BRC-Z1-controlled, glia-mediated CNS movements in late prepupa.

Steroid regulation of glue protein genes in Drosophila melanogaster

Transcript accumulation of the 3C glue protein gene Sgs-4 was induced in cultured salivary glands of Drosophila third instar larvae by supplementing the culture medium with 20-OH-ecdysone. The salivary glands were isolated from hormone-deficient larvae of the temperature-sensitive mutant l(1)su(f)ts67g, which were shifted from permissive (25 degrees C) to restrictive temperature (30 degrees C) at 60 h after oviposition. At the permissive temperature the glue protein are expressed during the latter half of the third instar. At the restrictive temperature there is no detectable or an extremely reduced accumulation of the 3C glue protein gene transcripts in these larvae. Induction of transcript accumulation was demonstrated by increased amounts of glue gene RNAs in the 20-OH-ecdysone supplemented salivary glands. Maximum accumulation was reached within 1 h after supplementation. The induction of accumulation was inhibited by a concentration of cycloheximide that repressed total protein synthesis, suggesting that 20-OH-ecdysone acts indirectly on the 3C glue gene by inducing synthesis of a protein(s) required transcript accumulation. We also show that there is a more rapid disappearance of 3C transcripts from salivary glands cultured in the presence of 20-OH-ecdysone than from glands cultured in its absence. This hormone-induced disappearance is, in contrast to the 68C transcripts, not inhibited by cycloheximide.

Anciently duplicated Broad Complex exons have distinct temporal functions during tissue morphogenesis

Broad Complex (BRC) is an essential ecdysone-pathway gene required for entry into and progression through metamorphosis in Drosophila melanogaster. Mutations of three BRC complementation groups cause numerous phenotypes, including a common suite of morphogenesis defects involving central nervous system (CNS), adult salivary glands (aSG), and male genitalia. These defects are phenocopied by the juvenile hormone mimic methoprene. Four BRC isoforms are produced by alternative splicing of a protein-binding BTB/POZ-encoding exon (BTBBRC) to one of four tandemly duplicated, DNA-binding zinc-finger-encoding exons (Z1BRC, Z2BRC, Z3BRC, Z4BRC). Highly conserved orthologs of BTBBRC and all four ZBRC were found among published cDNA sequences or genome databases from Diptera, Lepidoptera, Hymenoptera, and Coleoptera, indicating that BRC arose and underwent internal exon duplication before the split of holometabolous orders. Tramtrack subfamily members, abrupt, tramtrack, fruitless, longitudinals lacking (lola), and CG31666 were characterized throughout Holometabola and used to root phylogenetic analyses of ZBRC exons, which revealed that the ZBRC clade includes Zabrupt. All four ZBRC domains, including Z4BRC, which has no known essential function, are evolving in a manner consistent with selective constraint. We used transgenic rescue to explore how different BRC isoforms contribute to shared tissue-morphogenesis functions. As predicted from earlier studies, the common CNS and aSG phenotypes were rescued by BRC-Z1 in rbp mutants, BRC-Z2 in br mutants, and BRC-Z3 in 2Bc mutants. However, the isoforms are required at two different developmental stages, with BRC-Z2 and -Z3 required earlier than BRC-Z1. The sequential action of BRC isoforms indicates subfunctionalization of duplicated ZBRC exons even when they contribute to common developmental processes.

Genetic control of cell proliferation in female germ line cells of Drosophila: mosaic analysis of five discless mutations

The 'discless' mutations are zygotic lethals of Drosophila melanogaster with lethal phase at the larva/pupa boundary. They have been shown to identify genes whose functions are required for cell proliferation in the soma. We analysed mosaic females (generated by pole cell transplantation or by the dominant female sterile technique) with mutant germ line and normal soma and concluded that (1) the discless genes are required for the proliferation of the female germ line cells. (2) The discless genes are expressed during oogenesis and (3) as suggested by indirect evidence, the maternally provided gene products are necessary for cell proliferation in the embryo. It is suggested, that the same sets of genes control proliferation in the soma, germ line and-through the maternal effect-embryos in Drosophila.

Role of AWD/nucleoside diphosphate kinase in Drosophila development

The abnormal wing discs gene of Drosophila encodes a soluble protein with nucleoside diphosphate kinase activity. This enzymic activity is necessary for the biological function of the abnormal wing discs gene product. Complete loss of function, i.e., null, mutations cause lethality after the larval stage. Most larval organs in such null mutant larvae appear to be normal, but the imaginal discs are small and incapable of normal differentiation. Killer-of-prune is a neomorphic mutation in the abnormal wing discs gene. It causes dominant lethality in larvae that lack prune gene activity. The Killer-of-prune mutant protein may have altered substrate specificity. Null mutant larvae have a low level of nucleoside diphosphate kinase activity. This suggests that there may be additional Drosophila genes that encode proteins with nucleoside dipthosphate kinase activity. Candidate genes have been found in the Drosophila genome.

Ecdysone pathway is required for furrow progression in the developing Drosophila eye

In Drosophila, secretion of the steroid hormone ecdysone from the prothoracic ring gland coordinates and triggers events such as molting and metamorphosis. In the developing Drosophila compound eye, pattern formation and cell-type specification initiate at a moving boundary known as the morphogenetic furrow. We have investigated the role of ecdysone in eye development and report here that the ecdysone signaling pathway is required for progression of the morphogenetic furrow in the eye imaginal disc of Drosophila. Genetic disruption both of the ecdysone signal in vivo with the ecdysoneless1 (ecd1) mutant and of ecdysone response with a Broad-Complex mutant result in disruption of morphogenetic furrow progression. In addition, we show that ecdysone-dependent gene expression, both of a reporter of transcriptional activity of the Ecdysone Receptor and of the Z1 isoform of the Broad Complex, are localized in and close to the furrow. These results suggest that, in the morphogenetic furrow, temporal hormonal signals are integrated into genetic pathways specifying spatial pattern.

The Drosophila Broad-Complex plays a key role in controlling ecdysone-regulated gene expression at the onset of metamorphosis

During Drosophila third instar larval development, one or more pulses of the steroid hormone ecdysone activate three temporally distinct sets of genes in the salivary glands, represented by puffs in the polytene chromosomes. The intermolt genes are induced first, in mid-third instar larvae; these genes encode a protein glue used by the animal to adhere itself to a solid substrate for metamorphosis. The intermolt genes are repressed at puparium formation as a high titer ecdysone pulse directly induces a small set of early regulatory genes. The early genes both repress their own expression and activate more than 100 late secondary-response genes. The Broad-Complex (BR-C) is an early ecdysone-inducible gene that encodes a family of DNA binding proteins defined by at least three lethal complementation groups: br, rbp, and l(1)2Bc. We have found that the BR-C is critical for the appropriate regulation of all three classes of ecdysone-inducible genes. Both rbp and l(1)2Bc are required for glue gene induction in mid-third instar larvae. In addition, the l(1)2Bc function is required for glue gene repression in prepupae; in l(1)2Bc mutants the glue genes are re-induced by the late prepupal ecdysone pulse, recapitulating a mid-third instar regulatory response at an inappropriate stage in development. The l(1)2Bc function is also required for the complete ecdysone induction of some early mRNAs (E74A, E75A, and BR-C) and efficient repression of most early mRNAs in prepupae. Like the intermolt secondary-response genes, the late secondary-response genes are absolutely dependent on rbp for their induction. An effect of l(1)2Bc mutations on late gene activity can also be detected, but is most likely a secondary consequence of the submaximal ecdysone-induction of a subset of early regulatory products. Our results indicate that the BR-C plays a key role in dictating the stage-specificity of the ecdysone response. In addition, the ecdysone-receptor protein complex alone is not sufficient for appropriate induction of the early primary-response genes, but requires the prior expression of BR-C proteins. These studies define the BR-C as a key regulator of gene activity at the onset of metamorphosis in Drosophila.

Genetic, cytogenetic and developmental analysis of the Drosophila melanogaster tumor suppressor gene lethal(2)tumorous imaginal discs (1(2)tid)

Three of the twenty recessive-lethal tumor suppressor genes of Drosophila cause imaginal disc tumors in the homozygously mutated state. One of these is the lethal(2)tumorous imaginal discs (l(2)tid) gene. Histological preparations show the tumorous imaginal disc epithelium to consist of a mosaic of cells in monolayer and cells in clumped arrangement. In contrast, the wild-type imaginal disc epithelium is comprised exclusively of cells in monolayer arrangement. Mutant imaginal disc tissue pieces implanted into ready-to-pupariate wild-type larvae fail to differentiate. Implantation of l(2)tid imaginal disc tissue pieces in vivo into wild-type adult flies revealed a lethal, tumorous growth comparable to that in situ, thus characterizing the l(2)tid imaginal discs as truly malignant. The phenotypes of double mutants between two l(2)tid alleles and tumor suppressor genes, such as lethal(2)giant larvae and lethal(2)brain tumor, and the epithelial overgrowth mutant lethal(2)fat are described and discussed. Finally, we present the genetic, cytogenetic and molecular localization of the l(2)tid gene to the giant chromosome bands 59F4-6.

apterous, a gene required for imaginal disc development in Drosophila encodes a member of the LIM family of developmental regulatory proteins

The apterous (ap) gene is required for the normal development of the wing and haltere imaginal discs in Drosophila melanogaster. ap encodes a new member of the LIM family of developmental regulatory genes. The deduced amino acid sequence of ap predicts a homeo domain and a cysteine/histidine-rich domain known as the LIM domain. In these domains ap is highly similar to the mec-3 and lin-11 proteins of Caenorhabditis elegans and to the vertebrate insulin enhancer-binding protein isl-1. ap is presumably required for transcriptional regulation of genes involved in wing and haltere development. The nature of the defects in homozygous null mutant flies is consistent with the pattern of ap expression in the larval imaginal discs. ap is also expressed in a complex pattern in the embryo, including portions of the peripheral nervous system (PNS) and central nervous system (CNS). A requirement for ap expression in the larval and adult CNS may be the underlying cause of the defects in hormone production and vitellogenesis described for ap mutations.

Mutations in a steroid hormone-regulated gene disrupt the metamorphosis of the central nervous system in Drosophila

The actions of steroid hormones on vertebrate and invertebrate nervous systems include alterations in neuronal architecture, regulation of neuronal differentiation, and programmed cell death. In particular, central nervous system (CNS) metamorphosis in insects requires a precise pattern of exposure to the steroid molting hormone 20-hydroxyecdysone (ecdysterone). To test whether the effects of steroid hormones on the insect nervous system are due to changes in patterns of gene expression, we examined Drosophila mutants of the ecdysterone-regulated locus, the Broad Complex (BR-C). This report documents aspects of CNS reorganization which are dependent on BR-C function. During wild-type metamorphosis, CNS components undergo dramatic morphogenetic movements relative to each other and to the body wall. These movements, in particular, the separation of the subesophageal ganglion from the thoracic ganglion, the positioning of the developing visual system, and the fusion of right and left brain hemispheres, are deranged in BR-C mutants. In addition, a subset of mutants shows disorganization of optic lobe neuropil, both within and among optic lobe ganglia. Optic lobe disorganization is found in mutants of the br and l(1)2Bc complementation groups, but not in those of the rbp complementation group. This suggests that the three complementation groups of this complex locus represent distinct but overlapping functions necessary for normal CNS reorganization. This study demonstrates that ecdysterone-regulated gene expression is essential for CNS metamorphosis, illustrating the utility of Drosophila as a model system for investigating the genetic basis of steroid hormone action on the nervous system.

Hormonal control of gene expression: interactions between two trans-acting regulators in Drosophila

The steroid hormone 20-hydroxyecdysone (20HE) and the Broad-Complex locus (BRC) are involved in regulating developmental changes in gene expression around the time of metamorphosis in Drosophila. We have investigated the regulatory interactions between 20HE, BRC, and a set of genes expressed in the fat body of third-instar Drosophila larvae. RNA levels for two hormone-inducible genes, Larval Serum Protein-2 and P1, accumulate to normal levels in BRC-mutant larvae. In contrast, RNA levels for the P6 gene were affected by mutations at BRC. On the basis of the results of experiments in which hormone concentrations were varied in BRC-mutant or wild-type larvae, we conclude that 20HE can both increase and decrease P6 RNA levels in the absence of BRC product(s). BRC appears to be a trans-acting modulator of the response of P6 to the hormone. We propose that BRC attenuates the repressive effect of the hormone, expanding the range of hormone concentrations that induce the gene, thus allowing P6 RNA to reach high levels during the third larval instar. The results are discussed in relation to other genes that are regulated by the same two trans-acting factors. A model is presented that refines the model of Ashburner et al. (1974, Cold Spring Harbor Symp. Quant. Biol. 38: 655-662) for the hormonal regulation of gene activity.

Genes controlling essential cell-cycle functions in Drosophila melanogaster

On the basis of the hypothesis that mutants in genes controlling essential cell cycle functions in Drosophila should survive up to the larval-pupal transition, 59 such 'late lethals' were screened for those mutants affecting cell division. Examination of mitosis in brain neuroblasts revealed that 30 of these lethals cause disruptions in mitotic chromosome behavior. These mutants identify genes whose wild-type functions are important for: (1) progression through different steps of interphase, (2) the maintenance of mitotic chromosome integrity, (3) chromosome condensation, (4) spindle formation and/or function, and (5) completion of cytokinesis or completion of chromosome segregation. The presence of mitotic defects in late lethal mutants is correlated tightly with the presence of defective imaginal discs. Thus, the phenotypes of late lethality and poorly developed imaginal discs are together almost diagnostic of mutations in essential cell-cycle functions. The terminal phenotypes exhibited by these Drosophila mitotic mutants are remarkably similar to those observed in mammalian cell-cycle mutants, suggesting that these diverse organisms use a common genetic logic to regulate and integrate the events of the cell cycle.

Developmental consequences of awdb3, a cell-autonomous lethal mutation of Drosophila induced by hybrid dysgenesis

In order to recover mutations affecting imaginal discs in a way which would allow the relevant genes to be readily cloned, a hybrid dysgenic screen was performed for mutations causing late larval/early pupal lethality. This paper describes that mutagenesis procedure and the phenotypes caused by the mutations that were recovered. Of 81 late larval/pupal lethal mutations that were recovered, 20 cause imaginal disc defects. These 20 mutations define 12 different genes. This paper also includes a description of the developmental defects caused by a mutation in one of those 12 genes which we have named abnormal wing discs (awd); the following paper (C. Dearolf, N. Tripoulas, J. Biggs, and A. Shearn, 1988, Dev. Biol. 129, 169-178) describes the cloning of the awd gene and an analysis of its pattern of transcription. awdb3 homozygotes develop at a normal rate until the end of the second larval instar, when their rate of development is reduced. After an extended third larval instar, they form puparia and die. Mutant wing discs have an abnormal morphology and extensive cell death. These abnormal wing discs, and also the leg and eye-antenna discs which appear to be morphologically normal, differentiate poorly or not at all when injected into metamorphosing larvae. Analysis of genetic mosaics indicates that the awdb3 mutation is expressed in a cell-autonomous manner in wing, leg, and eye-antenna discs. The larval brain and proventriculus in awdb3 homozygous third-instar larvae appear to be vacuolated due to the accumulation of lipid droplets. Mutant ovaries are unable to develop when injected into wild-type larvae, although mutant germ cells are capable of producing normal eggs.

The defective dorsal discs gene of Drosophila is required for the growth of specific imaginal discs

The wild-type allele of the gene defective dorsal discs (ddd) is required for the normal development of the dorsal thoracic discs in Drosophila melanogaster. In ddd mutant larvae the dorsal discs (wing, haltere, and humeral) are greatly reduced in size or absent while the ventral discs (leg) are unaffected. We have examined the function of the ddd+ gene in wing development. The ddd+ product is not involved in the initial determination of wing cells but rather is required for their subsequent proliferation during the larval period. Analysis of chimaeras shows that there is a requirement for ddd+ gene expression in wing discs, but it is sufficient for normal development that only some cells in a disc express the gene. We propose that the ddd+ product is involved in the synthesis of a factor which is required for the normal growth of wing discs and which can be transferred between wing disc cells.

Genetic studies of mutations at two loci of Drosophila melanogaster which cause a wide variety of homeotic transformations

The ash-1 locus is in the proximal region of the left arm of the third chromosome of Drosophila melanogaster and the ash-2 locus is in the distal region of the right arm of the third chromosome. Mutations at either locus can cause homeotic transformations of the antenna to leg, proboscis to leg and/or antenna, dorsal prothorax to wing, first and third leg to second leg, haltere to wing, and genitalia to leg and/or antenna. Mutations at the ash-1 locus cause, in addition, transformations of the posterior wing and second leg to anterior wing and second leg, respectively. A similar spectrum of transformations is caused by mutations at yet another third chromosome locus, trithorax. One extraordinary aspect of mutations at all three of these loci is that they cause such a wide variety of transformations. For mutations at both of the loci that we have studied the expression of the homeotic phenotype is both disc-autonomous (as shown by injecting mutant discs into metamorphosing larvae) and cell autonomous (as shown by somatic recombination analysis). The original mutations which identified these two loci, although lethal, manifest variable expressivity and incomplete penetrance of the homeotic phenotype suggesting that they are hypomorphic. The phenotype of double mutants which were synthesized by combining different pairs of those original mutations manifest for two of the four pairs a greater degree of expressivity and slightly more penetrance of the homeotic transformations. This mutual enhancement suggests that the products of both loci interact in the same process. A third double mutant expresses a discless phenotype.Additional alleles have been recovered at both the ash-1 and the ash-2 loci. Some of these alleles as homozygotes or transheterozygotes express the wide range of transformations revealed first by double mutants. One of the alleles at the ash-1 locus when homozygous and several transheterozygous pairs can cause either the homeotic transformation of discs or the absence of those discs. The fact that these two defects, absence of specific discs and homeotic transformations of those same discs can be caused by mutations within a single gene suggests that the activity of the product of this gene is essential for normal imaginal disc cell proliferation. Loss of that activity leads to the absence of discs, whereas, reduction of that activity leads to homeotic transformations.

A trans-acting regulatory product necessary for expression of the Drosophila melanogaster 68C glue gene cluster

The mutation l(1)npr-1 is located at cytological location 2B5 on the X chromosome in Drosophila melanogaster. We have found that this mutation causes absence of the normal product of the 2B5 locus and that it has the following phenotypes: the 68C glue puff on the third chromosome does not regress when mutant salivary glands are cultured in the presence of ecdysterone; the three 68C glue protein mRNAs are not synthesized; and a transformed Drosophila strain carrying both a normal resident 68C Sgs-3 gene and an introduced functional Sgs-3 gene with only a few kb of flanking sequences expresses neither Sgs-3 RNA if the l(1)npr-1 mutation is crossed into the stock. Thus the normal product of the l(1)npr-1 gene is required for regression of the 68C puff, and the l(1)npr-1 gene product allows expression of the Sgs-3 gene by interacting, either directly or indirectly, with DNA sequences near this glue protein gene.

Genetic analysis of transdetermination in Drosophila. II. Transdetermination to wing of leg discs from a mutant which lacks wing discs

Drosophila melanogaster larvae homozygous for lethal mutations at the L6 locus have no wing discs. However, like wild-type leg discs, leg discs from such mutant larvae can transdetermine to wing. Apparently such a transdetermination event bypasses the block to wing disc development caused by mutations at this locus. In order to evaluate the significance of this observation we have examined the cell autonomy of the mutant phenotype and the capacity of mutant larvae to support the growth of normal wing discs. The mutation appears not to be expressed cell autonomously, yet mutant larvae can support the growth of normal wing discs. One way of resolving these paradoxical results is to hypothesize that the normal product of the L6 gene is essential only for an initial step of wing disc development. According to this hypothesis, the fact that mutant leg discs can transdetermine to wing implies that transdetermination does not proceed by recapitulating that step of normal wing disc development.

Cytogenetic analysis of the 2B3-4--2B11 region of the X-chromosome of Drosophila melanogaster. I. Cytology of the region and mutant complementation groups

There are, at least, 11 distinct single bands and one real doublet in the region 2B1-2--2C1-2 of the X-chromosome of Drosophila melanogaster. This figure coincides with that in Bridges' revised map with most of the "doublet" bands being artifacts. Three puffs appear in the region. The early ecdysone-specific puff 2B5-6, small at PS(puffing stage) 1, increases sharply at PS 2. The late ecdysone-specific puff 2C1-2 appears at PS 4--5. At PS 9--10, when 2B5-6 disappears completely and 2C1-2 decreases, a third puff at 2B11 appears. None of these puffs is active at PS 11. Morphological analysis of puff appearance and autoradiographic study of 3H-uridine incorporation into chromosomes carrying rearrangements within the 2B region suggest that the early ecdysone-specific puff derives from bands 2B5 and may be 2B6, while the neighbouring bands 2B1-4, and 2B7-10 do not show appreciable transcription at the investigated stages. There are 42 mutations affecting viability in the region where the 2B5-6 puff is located. The mutations belong to 6 complementation groups; two of the groups dor and swi, are independent while the rest are overlapped by several lethal mutations (overlapping complex.) Mutants of the different groups have series of similar characteristics: temperature sensitivity, dose sensitivity, larva-pupal lethality and similar morphological abnormalities. It can be assumed that there is a functionally linked cluster of genes within the region 2B. Complementation groups br, rbp, l(1)pp-1, l(1)pp-2 (overlapping complex) have been located by rearrangements in very narrow cytological limit 2B3-4--2B5 that is in the area of developing puff. Two other loci dor and swi are situated some to the right of 2B5.