Informational content of polytene chromosome bands and puffs

Protein composition of interband regions in polytene and cell line chromosomes of Drosophila melanogaster

Background

Despite many efforts, little is known about distribution and interactions of chromatin proteins which contribute to the specificity of chromomeric organization of interphase chromosomes. To address this issue, we used publicly available datasets from several recent Drosophila genome-wide mapping and annotation projects, in particular, those from modENCODE project, and compared molecular organization of 13 interband regions which were accurately mapped previously.

Results

Here we demonstrate that in interphase chromosomes of Drosophila cell lines, the interband regions are enriched for a specific set of proteins generally characteristic of the "open" chromatin (RNA polymerase II, CHRIZ (CHRO), BEAF-32, BRE1, dMI-2, GAF, NURF301, WDS and TRX). These regions also display reduced nucleosome density, histone H1 depletion and pronounced enrichment for ORC2, a pre-replication complex component. Within the 13 interband regions analyzed, most were around 3-4 kb long, particularly those where many of said protein features were present. We estimate there are about 3500 regions with similar properties in chromosomes of D. melanogaster cell lines, which fits quite well the number of cytologically observed interbands in salivary gland polytene chromosomes.

Conclusions

Our observations suggest strikingly similar organization of interband chromatin in polytene chromosomes and in chromosomes from cell lines thereby reflecting the existence of a universal principle of interphase chromosome organization.

Photographic polytene chromosome maps for Glossina morsitans submorsitans (Diptera: Glossinidae): cytogenetic analysis of a colony with sex-ratio distortion

Photographic polytene chromosome maps from trichogen cells of pharate adult Glossina morsitans submorsitans were constructed. Using the standard system employed to map polytene chromosomes of Drosophila, the characteristic landmarks were described for the X chromosome and the two autosomes (L1 and L2). Sex-ratio distortion, which is expressed in male G. m. submorsitans, was found to be associated with an X chromosome (X8) that contains three inversions in each arm. Preliminary data indicate no differences in the fecundity of X(A)X(A) and X(A)X(B) females, but there are indications that G. m. submorsitans in colonies originating from Burkina Faso and Nigeria have genes on the autosomes and (or) the Y chromosome that suppress expression of sex-ratio distortion.

JIL-1: a novel chromosomal tandem kinase implicated in transcriptional regulation in Drosophila

We have cloned and characterized JIL-1, a novel tandem kinase in Drosophila that associates with the chromosomes throughout the cell cycle. Antibody staining and live imaging of JIL-1-GFP transgenic flies show that JIL-1 localizes to the gene-rich interband regions of larval polytene chromosomes and is upregulated almost 2-fold on the hypertranscribed male X chromosome compared to autosomes. Phylogenetic analysis suggests that JIL-1 together with human MSKs defines a separate family of tandem kinases. That JIL-1 is a functional kinase was demonstrated by autophosphorylation and phosphorylation of histone H3 in vitro. Based on these findings, we propose that JIL-1 may play a role in transcriptional control potentially by regulating chromatin structure.

A three-dimensional structural dissection of Drosophila polytene chromosomes

We have analyzed the three-dimensional structural details of Drosophila melanogaster polytene chromosome bands and interbands using three-dimensional light microscopy and a novel method of sample preparation that does not involve flattening or stretching the chromosomes. Bands have been visualized in unfixed chromosomes stained with the DNA specific dye 4,6-Diamidino-2-phenylindole (DAPI). Interbands have been visualized using fixed chromosomes that have been immunostained with an antibody to RNA polymerase II. Additionally, these structures have been analyzed using in situ hybridization with probes from specific genetic loci (Notch and white). Bands are seen to be composed of approximately 36 substructural features that measure 0.2-0.4 micron in diameter. We suggest that these substructural features are in fact longitudinal fibers made up of bundles of chromatids. Band shape can be a reproducible characteristic of a particular band and is dependent on the spatial relationship of these bundles, varying from bands with a uniform distribution of bundles to bands with a peripheral concentration of chromatin. Interbands are composed of bundles of chromatids of a similar size and number as those seen in the bands. The distribution of bundles is similar between a band and the neighboring interband, implying that there is a long range organization to the DNA that includes both the coding and the noncoding portions of genes. Finally, we note that the polytene chromosome has a circular shape when viewed in cross section, whether there are one or two homologs present.

Cloning and molecular genetic analysis of Drosophila melanogaster interband DNA

Interband DNA of Drosophila melanogaster polytene chromosomes was studied using a novel approach based on the electron microscopic (EM) analysis of chromosome regions carrying DNA fragments of known molecular genetic composition, inserted by P element-mediated transformation. Insertion of such fragments predominantly into interbands makes it possible to clone interband DNA by constructing genomic libraries from transformed strains and probing them with the insert DNA. The transformed strain P[H-sp70:Adh](61C) has insertion in the 61C7-8 interband on the left arm of chromosome 3. This DNA consists of part of the hsp70 gene promoter fused to the coding region of the Adh gene, and is flanked on either side by P element sequences. We constructed a genomic library from DNA of this strain and isolated a clone containing the insert and the interband DNA. Subsequently the genomic library of wild-type strain was probed with a subclone composed of interband DNA only. We have thus isolated a clone containing the entire native interband. 1289 bp of interband DNA was sequenced and found to be AT-rich (53.4%) with numerous regions of overlapping direct and inverted repeats, regulatory sites, and two overlapping open reading frames (ORFs).

Molecular analysis of the lethal(1)B214 region at the base of the X chromosome of Drosophila melanogaster

Approximately 50 kb of genomic DNA was isolated from polytene chromosome bands 19F1 and 2 of Drosophila melanogaster. Bands 19F1 and 2 are in the immediate vicinity of the beta-heterochromatin at the base of the X chromosome and encompass the little fly-like and lethal(1)B214 complementation groups. The cloned DNA consists of an approximately 21 kb stretch of unique or low copy number sequence that is bounded by repetitive elements interspersed with further unique sequences. The presence of repeated sequences is characteristic of regions within and adjacent to beta-heterochromatin. At least part of a tRNA gene cluster is present within the 50 kb of cloned DNA. The cloned region also produces at least 18 discrete size classes of developmentally regulated poly(A)+ RNA species. A 2 kb EcoRI fragment (E10), which lies in the 21 kb stretch of unique sequence, generates seven of these transcripts (of sizes 3.5, 3.35, 2.1, 2.0, 1.5, 1.2 and 1.0 kb) in wild-type flies. However, a small deletion of approximately 75 bp in E10 in a lethal(1)B214 mutant allele is associated with alterations in the production or processing of all seven of these transcripts. These data identify E10 sequences as belonging to the lethal(1)B214 gene and suggest that the wild-type lethal(1)B214 gene encodes multiple transcripts. Furthermore, no transcripts of the same size and having the same developmental profile as those generated by the wild-type E10 fragment were identified by probes covering the remainder of the cloned region. This suggests that at least the larger transcripts hybridizing to E10 are partly transcribed from sequences located outside the cloned region, which indicates that the lethal(1)B214 gene extends for more than 20 kb and contains other transcriptionally active sequences within it.

Developmental changes in fat body and midgut chromosomes of Drosophila auraria

Changes in puffing activity of fat body (FB) and midgut (MG) chromosomes of Drosophila auraria during late larval and white prepupal development as well as after in vitro culture with or without ecdysterone were studied and compared with those of the salivary gland (SG). The Balbiani Rings characteristic of the SG chromosomes of D. auraria, are not formed in FB and MG. Most of the inverted tandem chromosomal duplications that have been found to be common to all three tissues showed differentiation of puffing activity of the bands considered to be homologous. The major early ecdysone puffs 73A and 73B (considered to be homologues of D. melanogaster puffs 74EF and 75B, respectively), together with other early ecdysone puffs were present in all three tissues. Clear intermoult and postintermoult puffs were not evident in FB and MG chromosomes. However, a small set of late ecdysone puffs could be scored in FB, while no late ecdysone puffs were abserved in MG. Other tissue-specific puffs were identified, but a very small number of them were limited to MG.

Functional and structural units in the chromomere

Electron microscopic observations demonstrate the existence of several DNA packing levels in the chromomere. A linear DNA molecule forms a big (chromomere) loop anchored to the chromosomal scaffold. The loop forms a set of smaller loops in the rosette pattern. Packing of the DNA by the histone octamer particles results in nucleosomes and nucleomeres. To establish the possible correspondence between the structural units of a chromomere and the genetical units (genes, exons, introns) in it, we compared the lengths of the units. Statistical analysis of the 315 sequenced genes indicate that the average gene size corresponds to the average length of a rosette loop. It means that a chromomere contains one or more genes. Assuming that exon-intron boundaries cannot bind nucleosomes we constructed DNA-packing models of the 88 genes. They demonstrate that the first (in 77.8 per cent of the genes) and the last (in 52.7 per cent) exons of the genes are too short to bind nucleosomes. Many genes contain long (nucleosome binding) pieces of DNA. Long packed pieces are introns in vertebrates; they are exons in invertebrates and plants. The average size gene contains two nucleomeres.

The faint band/interband region 28C2 to 28C4-5(-) of the Drosophila melanogaster salivary gland polytene chromosomes is rich in transcripts

Urate oxidase mRNA and five other transcripts map along 38 kb of DNA in the region 28C on the Drosophila melanogaster second chromosome. Three biotinylated restriction fragments from this 38 kb of DNA, one from each end and one from the middle, were individually hybridized in situ to slightly stretched salivary gland polytene chromosomes. The data from these in situ hybridizations in combination with the transcription map of the 38 kb of DNA indicate that: (i) there are six discrete RNA species encoded along the 38 kb of DNA and (ii) these six transcripts map to the faint band/interband region which includes the proximal edge of 28C1, the three faint bands, 28C2, 28C3 and 28C4-5(-), and the adjacent interband chromatin. Our data are consistent with the few published studies directly demonstrating that faint band/interband regions of the Drosophila melanogaster salivary gland polytene chromosomes code for a high density of transcripts.

Chromomeric organization of polytene chromosomes

This is a review summarizing work carried out at the Laboratory of Molecular Cytogenetics in recent years. Problems of genetic organization of bands, interbands and puffs as well as intercalary heterochromatin and position effect variegation are discussed from the point of view of the dynamic model of polytene chromosome organization.

Optical sectioning and three-dimensional reconstruction of diploid and polytene nuclei

To build a coherent picture of mitosis and cell fates during blastoderm and through the complex movements of gastrulation, it will be important to localize and follow several markers simultaneously in live specimens, ideally in 3D, using high-resolution, specific, noninjurious staining and observation procedures. The study of early Drosophila development has already profited from the use of fluorescent labeling and low-light-level imaging of live embryos using a CCD camera. Chromosomes in fixed samples have been labeled using DNA-specific dyes, making the pattern of mitotic patches visible. In vivo, 3D microscopy of fluorescently tagged chromosomes, in conjunction with computerized image processing, has permitted the first direct cell lineage analysis in the early Drosophila embryo. Moreover, the techniques adapted to study Drosophila development have been used for analysis of Drosophila chromosome structure, mitosis, and cell cycle, and are general enough to be applied to a myriad of problems in cell biology. "Optical sectioning" has always been used to scrutinize everything from onion roots to frog eggs, focusing up and down through the specimen, with the observer's brain responsible for the image processing. However, the volume of raw data generated by the high-resolution approach detailed above requires the use of sophisticated and adaptable computer systems to analyze and organize the results. Software designed to extract information from these complex images, either automatically or through an interactive approach, will become essential tools for cell and developmental biology. The brain of the experimenter remains the most important component in any image-processing system, but the support of technology will be essential.

Comparison of the polytene chromosomes of the salivary gland, the fat body and the midgut nuclei of Drosophila auraria

Photo-maps of the fat body and midgut polytene chromosomes of Drosophila auraria were constructed. These photo-maps are compared with a new, more detailed photo-map of the salivary gland chromosomes of the same species. Seven, not previously described inverted tandem-duplications were detected, raising the number of such structures found in this species to 31. The constancy of the banding pattern based on the analysis of the above chromosomes is discussed.

Genetic and developmental analysis of irreC, a genetic function required for optic chiasm formation in Drosophila

Irregular chiasm C (irreC) is an X-linked genetic function necessary for the correct projection of visual fibers in the optic chiasms of Drosophila optic ganglia. In addition to a severe disorganization of the inner optic chiasm irreC mutants display a subtle phenotype in the outer optic chiasm, in which some bundles of axons that leave the posterior equatorial part of the lamina on their way to the anterior medulla take a long detour before eventually finding their specific targets in the medulla neuropile. Deletion and recombination mapping of two irreC alleles (one P-element induced, the other associated with an inversion) have yielded a precise cytogenetic location in 3C4-5. A complex complementation pattern between roughest (rst) and irreC alleles indicates that both genetic functions are structurally and/or functionally closely interrelated. Flies in which the irreC locus is completely deleted by overlapping deficiencies are viable and their defects in the optic chiasms are similar to those seen in the two alleles. The defects in the outer and inner optic chiasms are not epigenetically connected and mosaic analyses have shown them to be independent from the genotype of the compound eye. Although the larval visual nerve looks normal, we have found that in the optic lobes of irreC mutants a group of early differentiating larval neurons is misplaced, suggesting a pioneering function of these cells during organization of the outer optic chiasms.

Electron microscopical analysis of Drosophila polytene chromosomes. V. Characteristics of structures formed by transposed DNA segments of mobile elements

An electron microscopical (EM) analysis was performed on regions of polytene chromosomes which contained DNA segments of different genetic composition, inserted by P element-mediated transformation into the Drosophila melanogaster genome. In seven of ten regions examined, containing insertions of the hsp28-ry, hsp70-Adh, ryhsp 70-beta-gal genes and of the ry gene tetramer, new bands appeared. Lack of new bands in three other strains is apparently connected with the fusion of the inserted material to preexisting bands. The new bands do not differ morphologically from the usual bands of polytene chromosomes, and their formation is likely due to predominant insertion of DNA segments into interbands. Among the constructs examined, the minimal length of a DNA segment which appears as a new band is about 5 kb; the DNA packing ratio in the new bands varies from 30 to 50. Activation of the inserted genes by heat shock has enabled us to observe the puffing characteristics of new bands. A sequence of some one kb forms a large interband, or micropuff; the puff size is correlated with the length of the genes being activated. If a DNA segment contains a single gene, then its activation causes the decompaction of the whole band; however, when a DNA segment consists of two genes and the promoter element of the activated gene is positioned in the middle of the sequence, the band splits and only part is decompacted and puffed. The DNA packing ratio in the puffs is 1.4-3.5. The subsequent deletion of the hsp70 promoter but retention of 23, 59, and 73 by from the transcription start points leads to failure of puff formation. In all the transformed sites an increase in the total length of the interbands adjacent to the insert as compared with the initial interband was observed. This increase appears to be due to decompaction of the P element DAN flanking the inserted segments. It is shown that a DNA segment, consisting of four tandemly repeated ry gene copies and interspersed by material which includes P DNA, forms a complex of loose chromatin in which, however, four bands can be resolved. We also observed a lengthening of interband regions containing only the P element sequence itself. Insertion of the complete 2.9 kb P element into the large single 10A1-2 bound of the X chromosome (an insertion in the region approximately 10 kb to the right of the v gene) causes splitting of the band into two parts and formation of a new interband.(ABSTRACT TRUNCATED AT 400 WORDS)

Precise determination of the molecular limits of a polytene chromosome band: regulatory sequences for the Notch gene are in the interband

We have aligned the molecular map of the Notch locus to the cytological features of the salivary gland polytene chromosomes of D. melanogaster in order to determine the interphase chromatin structure of this gene. Using high-resolution in situ hybridization and computer-aided optical microscope data collection and image analysis, we have determined that the coding portions and introns of the Notch gene, which is not expressed in this tissue, are all contained within the polytene chromosome band 3C7. The portion of the Notch gene that resides 5' to the start of transcription lies in an open chromatin conformation, the interband between bands 3C6 and 3C7. Our data are most consistent with condensation of the chromosomal DNA into 30 nm fibers in this polytene band.

Gene activity of polytene chromosomes in Drosophila species of the obscura group

The polytene chromosome puffing patterns of Drosophila guanche were established and compared with those of Drosophila subobscura. A total of 150 loci, active in some of the 17 developmental stages studied, were described and 23 of them were found to form the characteristic puffing pattern of D. guanche. Taking into account the number of puffs as well as the gene activity of each chromosome and the total gene activity, D. guanche seems to be less active than D. subobscura. Although both species show a degree of homology in their puffing patterns lower than that found for sibling species, the degree of homology is stronger than that between species belonging to the same group but to different subgroups. Thus, D. guanche and D. subobscura must be considered as phylogenetically closely related species, belonging to the same subgroup.

The banding pattern of polytene chromosomes of Drosophila guanche compared with that of D. subobscura

A detailed map of the salivary gland chromosomes of Drosophila guanche is presented and compared to the standard gene arrangements of D. subobscura. Generally, the polytene chromosome banding patterns of the two species show a high degree of homology. Only Segment I of the sex chromosome (Chromosome A) shows marked differences. The banding pattern proposed for this segment in D. guanche could have originated from a cluster of overlapping inversions including A1 arrangement.

Possible correlations of polypeptides and Balbiani rings in the salivary glands of Drosophila auraria Peng

Salivary glands of various stocks of Drosophila auraria and some of its close relatives were examined with a variety of electrophoretic techniques both from larval and prepupal stages, and after ecdysterone treatments, in an effort to detect possible translation products of the two Balbiani rings (BR1 and BR2) found in the salivary gland chromosomes of these species. Two polypeptides (P2 and P1), with molecular weights of 12,000 and 53,000, respectively, have been detected, the appearance of which coincides with the presence of BR2. The results do not allow the correlation of BR1 action with any specific polypeptide(s).

Chromosome structure in four wild-type polytene tissues of Drosophila melanogaster. The 87A and 87C heat shock loci are induced unequally in the midgut in a manner dependent on growth temperature

A systematic screen of wild-type Drosophila melanogaster larval organs has revealed three tissues besides the salivary gland with suitable polyteny for detailed cytogenetic analysis: the prothoracic gland, hindgut, and middle midgut. Chromosome banding patterns are very similar between tissues, but puffing patterns show considerable differences. In intact nuclei, oblique substructural elements can sometimes be detected in bands from some of the tissues. As a way of exploiting these newly characterized chromosomes, the heat shock puff response in midgut cells has been studied in detail. The puffing pattern is very similar to that in salivary glands, but an unexpected difference is found in the relative activity of the 87A7 and 87C1 loci, which contain the hsp70 genes. When larvae are raised at 16 degrees C, heat shocks ranging from 10 to 60 min induce only a weak midgut puff at 87A7 that is much smaller than that at 87C1, in contrast to other tissues where both are strongly induced. In pulse-labeled nuclei, an approximately five fold difference in transcriptional activity at the two loci is observed. However, when larvae are raised at 25 degrees C, the converse is found: the 87A7 puff is large, and little or no puffing is detectable at 87C1. Thus, in the midgut, heat shock induced puffing at these two loci is inversely modulated by a mechanism dependent on growth temperature.

Genes and loops in 320,000 base-pairs of the Drosophila melanogaster chromosome

We have mapped the DNA sequences bound to the nuclear scaffold along 320,000 base-pairs of a genetically well-defined region of the Drosophila chromosome. We have found that the domains delimited by the scaffold attachment regions are heterogeneous in size (ranging from 26,000 to 112,000 base-pairs in this interval), and that the attachment sites are within unique sequences as judged by blot hybridization. We also found that looped domains contain up to five, or even eight, unrelated genes including, in some cases, more than one transcribed gene. The loop organization unravelled here in cultured cells does not correspond to the banding pattern seen in salivary gland polytene chromosomes.

High resolution mapping of in situ hybridized biotinylated DNA to surface-spread Drosophila polytene chromosomes

We describe a method of mapping genes or transcripts on polytene chromosomes by transmission electron microscopy. We present several applications which illustrate that, in favorable cases, the method has a resolution of ca. 10 kg, and that high resolution mapping of hybridization sites relative to bands and puffs can be achieved. We mapped sites of transcription for poly-(A) RNA and present evidence which shows that these sites are localized in some bands and puffs, but are also found in interbands.

Electron microscopical analysis of Drosophila polytene chromosomes. III. Mapping of puffs developing from one band

Mapping of 16 regions of polytene chromosomes in which 18 one-band puffs develop was carried out with the use of electron microscopy (EM). In most cases a uniform decondensation of the whole band was observed. However, there were examples in which only a part of the band was activated (three puffs) or its right and left parts decondensed simultaneously (three puffs). Splitting of the band into two parts with their further decondensation was also found (one puff). This suggests structural and functional complexity of the bands. On the basis of the data obtained here and those published earlier, a classification of 52 puffs by the number of bands participating in their formation is given. Four classes numbering 22, 21, 7, 2 puffs, developing from 1, 2, 3 and 4 bands, respectively, are revealed. The data show that active chromosome regions are rather diverse in both the pattern of decondensation and expansion of the decondensed region, thus providing evidence of the informational complexity of the majority of active regions.

Electron microscopical analysis of Drosophila polytene chromosomes. II. Development of complex puffs

Data are presented of electron microscopic (EM) analysis of consecutive developmental stages of Drosophila melanogaster complex puffs, formed as a result of simultaneous decondensation of several bands. EM mapping principles proposed by us permitted more exact determination of the banding patterns of 19 regions in which 31 puffs develop. It is shown that 20 of them develop as a result of synchronous decondensation of two bands, 7 of three and 4 of one band. Three cases of two-band puff formation when one or both bands undergo partial decondensation are described. In the 50CF, 62CE, 63F and 71CF regions puffing zones are located closely adjacent to each other but the decondensation of separate band groups occurs at different puff stages (PS). These data are interpreted as activation of independently regulated DNA sequences. The decondensation of two or three adjacent bands during formation of the majority of the puffs occurs simultaneously in the very first stages of their development. It demonstrates synchronous activation of the material of several bands presumably affected by a common inductor. Bands adjacent to puffing centres also lose their clarity as the puff develops, probably due to "passive" decondensation connected with puff growth. The morphological data obtained suggest a complex genetic organisation of many puffs.

Immunofluorescence localization of DNA:RNA hybrids in Drosophila melanogaster polytene chromosomes

Sites of transcriptional activity in the whole set of Drosophila melanogaster polytene chromosomes have been localized by means of fluorescent antibodies against DNA:RNA hybrid molecules and compared with results on 3H-uridine incorporation obtained earlier. The majority of large and small puffs with intensive 3H-uridine incorporation demonstrate bright fluorescence. Moreover, bright fluorescence is also observed for a large number of small puffs though the intensity of 3H-uridine incorporation is low. Some prominent puffs with high levels of 3H-uridine incorporation show weak fluorescence. Condensed bands, as a rule, do not show fluorescence. The regions that look like interbands under the light microscope are not real interbands, but consist of minibands visible only in the electron microscope (EM). However, a region that has been previously studied by EM and proven to be a real interband between two thick dark bands (100B3-100B4-5) showed fluorescence. These data support previous suggestions indicating a substantial contribution of transcriptional products from small puffs and interbands to the whole transcriptional system of polytene chromosomes.

Transcription-dependent localization of U1 and U2 small nuclear ribonucleoproteins at major sites of gene activity in polytene chromosomes

The location and dynamics of small nuclear ribonucleoproteins (snRNPs) were studied in salivary gland polytene chromosomes of Chironomus tentans by immunofluorescence with specific snRNP antibodies. Monoclonal antibody against the snRNP Sm antigens reacted at all sites of transcription (puffs and Balbiani rings). The amount of snRNP immunofluorescence was strictly dependent on transcription, increasing in parallel with gene activation and decreasing upon repression. Identical patterns of localization and transcriptional dependence were observed with antibodies specific for U1 or U2 snRNPs. These latter results show that the involvement of U1 and U2 snRNPs in transcription-related processes involves a high proportion, rather than small subsets, of active gene loci. In addition, the colocalization of U1 and U2 snRNPs at loci known to contain only one messenger RNA transcription unit (e.g. Balbiani ring 2) raises the possibility that both of these snRNPs interact with the same transcript. Finally, the lack of immunofluorescence at repressed loci indicates that snRNPs are not structural components of the chromatin (DNP) fiber, and also shows that unused snRNPs are not stored in chromatin. These latter points, and the growing evidence for the involvement of U1 snRNP in splicing, suggest that nascent pre-mRNA is the major chromosomal binding site for snRNPs.

Genetic interpretation of polytene chromosomes banding pattern

This mini-review covers new data regarding the problem of the functional organization of polytene chromosomes: The localization of RNA synthesis in the polytene chromosome puffs, diffuse bands and interbands; The relative stability of banding pattern and its functional value; The informational content of bands.

Cytogenetic analysis of the 2B3-4--2B11 region of the X chromosome of Drosophila melanogaster. III. Puffing disturbance in salivary gland chromosomes of homozygotes for mutation l(1)pp1t10

Puffing patterns have been studied both in homozygotes t10/t10, a gene located in the area of the early ecdysone puff 2B5, and in a yellow (y) control stock, at the end of the third instar and during prepupal development. In mutants t10 at the end of the third instar puffing develops normally in general, however, 21 puffs (5 early and 16 late ones) underdevelop or do not develop at all, some larval intermoult puffs regressing slower. The next cycle of puffs (mid prepupal) in mutants t10 proceeds normally, but in the late prepupal cycle 21 puffs underdevelop again or are not formed at all. A model for the induction of early ecdysone puffs is proposed, assigning a key role to the 2B5 puff product in stimulating other early puffs. It is suggested that defects in the activity of early puffs in the mutant t10 may cause underdevelopment of late puffs.

Homologous banding patterns in the polytene chromosomes from the larval salivary glands and ovarian nurse cells of Anopheles stephensi Liston (Culicidae)

A comparison of the banding patterns of two homologous polytene chromosome arms from the larval salivary gland and ovarian nurse cell complement of Anopheles stephensi is presented. The homologous chromosomes from the somatic larval salivary glands and germ-line derived ovarian nurse cells have essentially the same band-interband organisation. An analysis of the 3H-uridine labelling patterns of a small chromosome segment from the two tissues indicates that germ-line polytene chromosomes are not radically different from somatic polytene chromosomes in their patterns of gene expression.