Biomedical subjects

T C Kaufman

Publications and source records attributed to T C Kaufman.

At least 73 records · Page 4Linked to original sources

PubMed1988

Characterization of amalgam: a member of the immunoglobulin superfamily from Drosophila.

The immunoglobulin superfamily is a diverse group of proteins that are involved in various aspects of cell surface recognition. Here, we report the characterization of amalgam (ama), a gene in the Antennapedia complex (ANT-C) of D. melanogaster that exhibits amino acid similarity to vertebrate neural cell adhesion molecules and other members of the immunoglobulin superfamily. The putative 333 amino acid ama protein consists of a signal sequence, three immunoglobulin-like domains, and a short slightly hydrophobic carboxy-terminal region. Antibodies against the ama protein reveal that it accumulates on the surface of various mesodermal and neural cells during embryogenesis. The function of this protein remains elusive, as no mutations have been recovered for ama during saturation EMS mutagenesis of this chromosomal region.

Amino Acid Sequence↗

PubMed1988

Identification and expression of the gap segmentation gene hunchback in Drosophila melanogaster.

Genetic analysis has shown that the gap segmentation gene hunchback (hb) is a member of the genetic hierarchy involved in pattern formation in Drosophila. To identify the hb gene, we have mapped the position of hb mutant breakpoints within a chromosomal walk of the 85A region by genomic Southern blots and determined the transcription pattern of DNA from the walk. We detect a single gene within the domain defined by breakpoint mapping. We conclude that we have identified the hunchback gene because three mutations that inactivate hb physically interrupt or delete this gene. Northern analysis shows that the hb gene gives rise to at least five overlapping transcripts ranging in length from 2.6 to 3.5 kilobases. S1 nuclease and primer extension experiments demonstrate that the gene employs two promoters and three polyadenylation sites. The two hb promoters have different temporal specificities. Transcripts arising from the upstream promoter are detected from 0-12 hours of embryogenesis as well as in adult female and male RNA preparations. Transcripts arising from the downstream promoter accumulate only from 0-6 hours of embryogenesis. During the syncytial blastoderm stage, transcripts from the hb gene accumulate over a broad anterior and a narrow posterior domain. This pattern sharpens during the late blastoderm/early gastrula stage to produce an embryo with two stripes of hybridization anterior and one stripe posterior. Later, hb transcripts are detected within the ventral hypoderm in extended germ band stage embryos.

Animals↗

PubMed1988

Mutations that encode partially functional beta 2 tubulin subunits have different effects on structurally different microtubule arrays.

The testis-specific beta 2 tubulin of Drosophila is required for assembly and function of at least three architecturally different microtubule arrays (Kemphues et al., 1982). Two recessive male-sterile mutations in the B2t locus that encode partially functional, stable, variant forms of beta 2 tubulin cause defects in only certain microtubule-based processes during spermatogenesis. These mutations could thus identify aspects of beta tubulin primary structure critical for function only in specific microtubule arrays. In males carrying the B2t6 mutation, meiotic chromosome segregation and nuclear shaping are normal and flagellar axonemes are formed, but there is a subtle defect in axoneme structure; the outer doublet microtubules fill in with a central core normally seen only in the central pair and accessory microtubules. In homozygous B2t7 males, chromosome movement is usually normal during meiosis but cytokinesis often fails, cytoplasmic microtubules are assembled and nuclear shaping appears to be normal, but the flagellar axoneme lacks structural integrity. In contrast, the B2t8 allele affects a general property of tubulin, the ability to form normal side-to-side association of protofilaments (Fuller et al., 1987), and causes defects in meiosis, axoneme assembly and nuclear shaping. Certain combinations of these beta 2 tubulin mutations show interallelic complementation; in B2t6/B2t8 males functional sperm are produced and both variant subunits are incorporated into mature sperm, in the absence of wild-type beta 2 tubulin. Comparison of the phenotypes of the three partially functional beta 2 tubulin alleles reveals some aspects of tubulin primary structure more important for function in specific subsets of microtubule arrays, and other aspects required for the construction of microtubules in general.

Alleles↗

PubMed1988

The proboscipedia locus of the Antennapedia complex: a molecular and genetic analysis.

The homeotic proboscipedia (pb) locus of the Antennapedia Complex (ANT-C) directs the differentiation of adult labial and maxillary structures. Loss-of-function pb alleles show a transformation of adult mouth parts to legs and affect maxillary palp morphology. We have identified the pb transcription unit by inducing and analyzing a series of pb null chromosomal breakpoints. In addition, we describe a variegating pb phenotype associated with two rearrangement breakpoints. Having identified the pb locus, we describe the expression of its RNA and protein products. Unlike the other homeotic genes of the ANT-C, pb has no obvious role in embryonic development. Nevertheless, pb protein is detected during embryogenesis in nuclei of the labial and maxillary lobes and in part of the mandibular segment. In this respect, pb expression parallels the early segment-specific expression of neighboring, embryonically essential homeotic genes. Accumulation of pb protein is also detected in mesodermal cells and in a unique subset of nuclei throughout the central nervous system. We also describe a transcription unit very close to pb, which is expressed dorsally during embryogenesis in a pattern resembling that of the nearby zygotic lethal zerknüllt (zen) locus. This transcription unit has been shown to contain a homeo box and has been designated z2. Surprisingly, we find that individuals deleted for both the pb and z2 transcription units survive to adulthood and produce normal larval cuticular structures. Thus, pb and z2 show similarities to neighboring ANT-C genes in their expression patterns, yet these similarities are not manifested in comparable loss-of-function embryonic phenotypes.

Alleles↗

PubMed1987

A development genetic analysis of the gene regulator of postbithorax in Drosophila melanogaster.

We report the characterization of loss-of-function alleles of the homoeotic mutation Regulator of postbithorax (Rg-pbx) in Drosophila melanogaster. Rg-pbx is a dominant gain-of-function mutation which shows a transformation of posterior haltere to wing in the adult cuticle. This mutant phenotype mimics that of the bithorax complex lesion postbithorax (pbx). Loss-of-function alleles described here are lethal in the embryonic stage and affect the pattern of segmentation of the embryo. Examination of the terminal phenotype of null and hypomorphic alleles of Rg-pbx has shown that inactivation of the Rg-pbx gene leads to loss of the thoracic segments and the adjacent labial segment of the Drosophila embryo. An effect of the mutations is also seen in the seventh and eighth abdominal segments of embryos. The loss-of-function phenotype is similar to that described for the segmentation mutant hunchback (hb). Complementation tests show that Rg-pbx and hb are allelic. Temperature shift experiments using a temperature-sensitive loss-of-function allele show that the Rg-pbx gene product is required early in embryogenesis. We further report that the dominant Rg-pbx phenotype is sensitive to the gene dosage of another segmentation-controlling gene, fushi tarazu (ftz). Flies carrying a mutant copy of the ftz gene in trans to Rg-pbx show a dramatic enhancement of the penetrance of the homoeotic mutant phenotype. We were also able to demonstrate a suppression of the Rg-pbx phenotype by the addition of a duplication for the ftz+ gene to an Rg-pbx stock. Examination of the phenotype of ftz Rg-pbx- double-mutant embryos did not reveal a clear pattern of epistasis between the genes nor was absolute additivity of phenotype seen. A possible formal relationship between Rg-pbx, ftz, and the postbithorax (pbx) locus is proposed.

Abdomen↗

PubMed1987

Developmental consequences of mutations in the 84B alpha-tubulin gene of Drosophila melanogaster.

Developmental effects of six mutations in the gene encoding the majority of alpha-tubulin in all tissues at all stages of Drosophila melanogaster development have been examined. All six alleles produce at least partially stable alpha 84B protein. In genetic assays, two of these alleles approximate the null condition. The other four alleles appear to form a graded series of hypomorphs. The two most severe alleles produce a semidominant maternal-effect polyphasic lethality, plus a predominantly larval recessive zygotic lethality. Clonal analysis of one of these alleles suggests it is a cell lethal. Worsening of the lethal phenotype (negative complementation) occurs in most interallelic heterozygotes involving these two mutations. As hemizygotes, the other four alleles are predominantly larval/pupal lethals. Partial complementation is achieved by most interallelic heterozygotes involving these four alleles. Phenotypic defects associated with the six tubulin mutation include disrupted embryos, pseudopupae, pharate adults with defects in various cuticular pattern elements, pharate adults with retarded head development, adults with leg tremors and extremely short life spans, and viable but sterile adults with bristle defects.

Alleles↗

PubMed1987

A genetic and developmental analysis of mutations in the Deformed locus in Drosophila melanogaster.

Individuals expressing recessive mutations in the Deformed (Dfd) locus of Drosophila melanogaster were examined for embryonic and adult defects. Mutant embryos were examined in both scanning electron microscope and light microscope preparations. The adult Dfd recessive mutant phenotype was assessed in somatic clones and in survivors homozygous for hypomorphic alleles of the gene. The time of Dfd+ action was determined by studying a temperature conditional allele. Dfd+ is required in three embryonic cephalic segments to form a normal head. Mutant embryos of Dfd display defects in derivatives of the maxillary segment, of the mandibular segment, and of some more anterior segments. In the adult fly, defects are seen in the posterior aspect of the head when the gene is mutant. A transformation from head to thoracic-like tissue is seen dorsally and a deletion of structures is seen ventrally. Shift studies utilizing a temperature conditional allele have shown that the gene product is necessary during at least two periods of development, during embryonic segmentation and head involution and during the late larval and pupal stages. From these studies we conclude that Dfd is a homeotic gene necessary for proper specification of both the embryonic and the adult head.

Alleles↗

PubMed1987

Genetic analysis of microtubule structure: a beta-tubulin mutation causes the formation of aberrant microtubules in vivo and in vitro.

A recessive male sterile mutation (B2t8) that encodes a stable variant of the testis-specific beta 2-tubulin of Drosophila causes the assembly of aberrant microtubules both in vivo and in vitro. The B2t8 mutation appears to cause defects in the formation of interprotofilament bonds. In testes from homozygous mutant males, the most commonly observed aberrant structures were sheets of protofilaments curved to form an S in cross section rather than a normal, closed microtubule. These characteristic S-shaped structures appear in the meiotic spindle, in place of axonemes in differentiating spermatids, and in cytoplasmic microtubules, including those that lie next to the nucleus during nuclear elongation. Homozygous mutant males exhibit defects in chromosome movement and cytokinesis during meiosis, flagellar elongation, and nuclear shaping, indicating that the ability to form normal closed microtubules is required for each of these events. The presence of the aberrant microtubules in three architecturally different microtubule arrays demonstrates conclusively the multifunctional nature of the beta 2-tubulin gene product. Although the mutant beta 2-tubulin subunit causes assembly of aberrant microtubules in vitro and in homozygous males, in the presence of wild-type beta 2-tubulin in heterozygous males, the variant subunit coassembles with the wild-type subunit into functional sperm.

Alleles↗

PubMed1987

Distribution of the Sex combs reduced gene products in Drosophila melanogaster.

The spatial and temporal distribution of RNA and protein encoded by the homeotic Sex combs reduced (Scr) gene were examined during Drosophila development. The gene products are present in the epidermis of both the labial and first thoracic segments as would be predicted from prior genetic studies. However, the pattern in the central nervous system (CNS) and mesoderm is further restricted; the major expression located in the labial neuromere of the CNS and the mesoderm of the first thoracic segment. The spatial restriction within the CNS is correlated with and may be due to a differential timing of expression in the labial and first thoracic ectoderm. The labial ectoderm accumulates the Scr RNA prior to segregation of the neuroblasts while expression in the first thoracic ectoderm occurs after neuroblast segregation. The protein is also observed in the subesophageal ganglia of both larvae and adults, as well as in the labial and first thoracic imaginal discs. Surprisingly, the protein is also present to a lesser extent in second and third thoracic leg discs.

Animals↗

PubMed1986

A rehabilitation of the genetic map of the 84B-D region in Drosophila melanogaster.

A reanalysis of the 84B3 to 84D3,5 region of the polytene chromosomes of Drosophila melanogaster has led to the identification and localization of 16 genes. These genes include 11 vital loci, four genes exhibiting nonlethal visible mutant phenotypes and one gene encoding a nonessential enzyme. The identity of the gene products of two of the vital genes has been determined to be alpha-tubulin and glucose dehydrogenase (Gld). Three newly identified genes, sticking (stk), half out (hat) and trapped (ted), as well as Gld are required for eclosion. Among the nonessential genes are roughened eye (roe) and ruffed eye (rue), which affect eye texture. The roe phenotype is greatly enhanced by deletions that simultaneously remove roe and an unidentified locus in 84E. Mutations in another nonessential gene, rotund (rn), are characterized by pattern deletions of most adult appendages.

Animals↗

PubMed1986

The relationship between the functional complexity and the molecular organization of the Antennapedia locus of Drosophila melanogaster.

The Antp locus is involved in the development of the thorax of the larval and adult Drosophila. The absence of Antp+ function during embryogenesis results in the larval mesothorax exhibiting characteristics of the prothorax and an ensuing lethality; the loss of Antp+ function in the development of the adult thorax causes specific portions of the leg, wing and humeral imaginal discs to develop abnormally. Every Antp mutation, however, does not cause all of these developmental defects. Certain mutant alleles disrupt humeral and wing disc development without affecting leg development, and they are not deficient for the wild-type function required during embryogenesis. Other Antp mutations result in abnormal legs, but do not alter dorsal thoracic development. Mutations of each type can complement to produce a normal adult fly, which suggests that there are at least two discrete functional units within the locus. This hypothesis is supported by the fact that each of the developmental defects arises from the alteration of a different physical region within the Antp DNA. These observations indicate that the complete developmental role of the Antp locus is defined by the spatial and temporal regulation of the expression of several individual functional units.

Animals↗

PubMed1984

Defects in embryogenesis in mutants associated with the antennapedia gene complex of Drosophila melanogaster.

Embryogenesis in individuals with mutations or deficiencies of the genes in the polytene interval 84A-84B1,2 of Drosophila melanogaster was examined using scanning electron microscopy (SEM). The developmental function of this region of chromosome 3 is of particular interest since it contains the Antennapedia Gene Complex (ANT-C), a gene cluster that includes the homoeotic proboscipedia (pb), Sex combs reduced (Scr), and Antennapedia (Antp) loci. The results of SEM studies, clonal analyses, and temperature-shift experiments show that the fushi tarazu (ftz) and zerknullt (zen) genes, which map between pb and Scr, are involved in processes initiated during embryogenesis. The activity of ftz+ appears to be required within the first 4 hr of development for the establishment of the proper number of segments in the embryonic germ band. Individuals with ftz mutations or deficiencies produce only half the normal number of segments. Each of the segments is twice the normal width and is apparently comprised of cells that would normally form two separate metameres. The zen allele is required from about 2-4 hr of embryogenesis. Mutations of this gene result in disturbances of morphogenetic movements during gastrulation. The mutant phenotype is characterized by the absence of the optic lobe, defects in involution of the head segments, and in some cases, failure of germ band elongation. A requirement during embryogenesis for the activities of other genes residing in the 84A-84B1,2 polytene interval is suggested by the phenotypes of individuals heterozygous or homozygous for chromosomal deficiencies. Using the deficiencies Df(3R)AntpNs+R17, Df(3R)Scr, and Df(3R)ScxW+RX2, we examined the effects of deleting the distal portions or all of the 84A-84B1,2 interval. The defects in deletion heterozygotes suggest that the wild-type activity of some gene(s) other than zen, within or just adjacent to the 84B1,2 doublet, is required to complete normal head involution. The deletion of all the loci in the 84A5-84B1,2 interval results in grossly abnormal morphology and morphogenesis of the gnathocephalic appendages of the embryo. From these studies we conclude that mutations and deficiencies of genes associated with the ANT-C have profound effects on embryogenesis. The mutant phenotypes suggest, in addition to ensuring proper segment identity, the wild-type alleles of the 84A-84B1,2 genes are necessary for normal segmentation and elongation of the germ band and normal head involution.

Animals↗

PubMed1984

Developmental effects of a temperature-sensitive RNA polymerase II mutation in Drosophila melanogaster.

Drosophila melanogaster possessing a temperature-sensitive (ts) mutation that maps to an X-linked locus ( RpII215 ) (the locus has also been called l(1)L5 and Ultrabithorax -like or Ubl ) encoding a subunit of RNA polymerase II are fertile at 22 degrees C but become sterile when shifted to 29 degrees C. Homozygous RpII215ts adult females shifted to 29 degrees C lay structurally normal eggs for 24 hr, after which increasing numbers of eggs are abnormal. Eggs left to develop at 29 degrees C die as morphologically normal late embryos or first instar larvae when produced by females maintained at 29 degrees C for less than 6 hr. However, eggs produced by females undergoing oogenesis at 29 degrees C for longer than 6 hr develop abnormally, displaying holes primarily in their ventral cuticle and possessing an abnormal pharyngeal apparatus. As exposure of females to 29 degrees C lengthens there is an increase in the severity of these defects. Some of the eggs can be rescued by either mating RpII215ts females to wild-type males or shifting the eggs to 22 degrees C. The percentage of eggs rescued decreases with increased length of oogenesis at 29 degrees C, up to 20 hr, at which point they are no longer rescuable. The terminal phenotype of eggs that fail to be rescued by the above procedure is less extreme than that of eggs for which no rescue attempt was made. Holes in the ventral cuticle are reduced or absent, but pattern formation is disrupted such that segments are often missing, incorrectly oriented or fused. Because the RpII215 locus encodes a subunit of RNA polymerase II, the developmental defects described above are most likely due to reduced or aberrant transcription during oogenesis and early embryogenesis. This postulated effect on transcription results, in part, from the maternal loading of a gene product(s) that is thermolabile in eggs.

Animals↗

PubMed1984

A molecular analysis of fushi tarazu, a gene in Drosophila melanogaster that encodes a product affecting embryonic segment number and cell fate.

Mutations at the fushi tarazu locus in Drosophila melanogaster affect both segment number and the pattern of cuticular structures on alternating segments of embryos. The ftz gene has been cloned and characterized. Two mutations, ftzw20 and ftzRpl are associated with lesions in a 3.2 kb fragment of DNA cloned in the Antennepedia Complex (ANT-C) chromosome "walk." The structure of DNA isolated from the ftzw20 and ftzRpl chromosomes indicates that the mutations are associated with a 4.9 kb insertion of DNA and a chromosomal rearrangement breakpoint, respectively. The 3.2 kb genomic DNA fragment hybridizes to a 1.8 kb polyadenylated transcript which accumulates maximally at 2-4 hr of embryonic development. The ftzw20 and ftzRpl mutations have different phenotypic consequences for the developing embryo, although both mutations interrupt the 1.8 kb transcription unit. The genetic and molecular data indicate that the 1.8 kb transcript derives from the ftz locus. The gene products are synthesized and utilized several hours prior to the visibly detectable morphogenetic events which the gene apparently regulates.

Age Factors↗

PubMed1983

The molecular organization of the Antennapedia locus of Drosophila.

The Antennapedia complex (ANT-C) of Drosophila is a cluster of genes involved in the regulation of morphogenesis, including at least three homoeotic loci (Antp, Scr, and pb), in which mutations cause switches of cell fates from one developmental pathway to another. We have isolated DNA clones containing most of the ANT-C, a region of about 300 kb. Antp mutations are distributed across more than 100 kb of the ANT-C. Dominant Antp mutations are associated with certain chromosome rearrangements and insertions that interrupt the 100 kb region; other chromosome breaks within the region cause recessive lethality and have no dominant effects. Two prominent transcripts (3.5 and 5.0 kb) are derived from exons within and at the two ends of the 100 kb region.

Alleles↗

PubMed1983

Genetic analysis of B2t, the structural gene for a testis-specific beta-tubulin subunit in Drosophila melanogaster.

Genetic analysis of the B2t locus has resulted in the recovery of four recessive mutations in the B2t structural gene and a deficiency that deletes the locus. Two of the mutations were recovered as suppressors of B2tD, a dominant male sterile mutation at the locus, and two were induced on wild-type chromosomes. All four mutant genes encode beta 2-tubulin subunits that are synthesized at normal rates but do not accumulate. All mutants are completely male sterile as homozygotes.

Animals↗

PubMed1982

Developmental genetics of a temperature-sensitive RNA polymerase II mutation in Drosophila melanogaster.

Purified RNA polymerase II (RNA nucleotidyl-transferase; EC 2.7.7.6) extracted from flies possessing lesions in the Ultrabithorax-like (Ubl) locus of Drosophila melanogaster has altered activity in vitro (Greenleaf et al. 1979, 1980; Coulter and Greenleaf 1982). This strongly suggests that the Ubl locus encodes a subunit of RNA polymerase II. Ethyl methanesulfonate was used to induce a temperature-sensitive mutation in this locus. Flies either homozygous or hemizygous for this new X-linked mutation (Ublts) display viability comparable to that of wild-type flies at 22 degrees C but are lethal at 29 degrees C. The temperature-sensitive period for Ublts flies is between gastrulation (6 h, 29 degrees C) and pupation (9-10 days, 22 degrees C). Zygotes shifted from 22 degrees C to 29 degrees C die at either the late embryonic or first larval instar stage while temperature shifts of second and third instar larvae result in the lethal phase occurring at the pupal stage. Most pupae shifted from 22 degrees C to 29 degrees C undergo metamorphosis and eclose as adults. Adults are viable if placed at 29 degrees C; however, all females and some males become sterile if maintained at this temperature. Somatic recombination was used to induce clones homozygous for a null allele of Ubl at different stages of development. Clones of this null allele appear to be cell lethal indicating that the Ubl+ gene product is required at all stages of development. The viability of Ublts pupae and adults at 29 degrees C may result from only a partial reduction in activity caused by the mutation at this nonpermissive temperature.

Alleles↗

PubMed1982

The testis-specific beta-tubulin subunit in Drosophila melanogaster has multiple functions in spermatogenesis.

We have isolated four recessive male sterile mutations in the structural gene for the testis-specific Drosophila beta 2-tubulin. Each of these mutations encodes a variant beta 2-tubulin subunit synthesized at normal levels, but which is subsequently unstable and rapidly degraded within the testis. In such testes, the normal alpha tubulins are also synthesized at normal levels and then degraded. Thus in mutant males the testis tubulin pool is drastically reduced relative to wild-type. In males homozygous for any of the recessive beta 2-tubulin mutations, the early mitotic divisions, which are completed before the time of synthesis of beta 2-tubulin, are normal. Thereafter, however, all microtubule-mediated events subsequent to the expression of the altered subunit are defective: meiosis, nuclear shaping and assembly of the axoneme all fail to occur. We thus conclude that the beta 2-tubulin subunit that forms the Drosophila sperm axoneme is not functionally restricted but serves multiple functions in spermatogenesis, including the assembly of both singlet and doublet tubules.

Animals↗