Paul M. Bingham

The molecular basis of P-M hybrid dysgenesis: The role of the P element, a P-strain-specific transposon family

We have shown previously that four of five white mutant alleles arising in P-M dysgenic hybrids result from the insertion of strongly homologous DNA sequence elements. We have named these P elements. We report that P elements are present in 30-50 copies per haploid genome in all P strains examined and apparently are missing entirely from all M strains examined, with one exception. Furthermore, members of the P family apparently transpose frequently in P-M dysgenic hybrids; chromosomes descendant from P-M dysgenic hybrids frequently show newly acquired P elements. Finally, the strain-specific breakpoint hotspots for the rearrangement of the pi 2 P X chromosome occurring in P-M dysgenic hybrids are apparently sites of residence of P elements. These observations strongly support the P factor hypothesis for the mechanistic basis of P-M hybrid dysgenesis.

The molecular basis of P-M hybrid dysgenesis: The nature of induced mutations

The molecular nature of mutations arising in dysgenic hybrids between P and M Drosophila melanogaster strains has been investigated. Seven independent mutations at the white locus were examined, and these fell into two classes on the basis of their genetic and structural properties. The five mutations comprising the first class were caused by DNA insertions of 0.5, 0.5, 0.6, 1.2 and 1.4 kb, respectively. The DNA insertions in four of these mutations were examined in detail. Although heterogeneous in size and pattern of restriction enzyme sites, they were homologous in sequence. We refer to members of this sequence family as P elements. Mutations caused by P elements appeared to be stable in the P cytotype, but had reversion rates greater than 10(-3) in the M cytotype. Phenotypic reversion to wild-type was accompanied by excision of the P element. The two mutations comprising the second class were caused by insertion of the 5.0 kb copia element and appeared to be stable in both P and M cytotypes.

Cloning of DNA sequences from the white locus of D. melanogaster by a novel and general method

We describe the isolation of a cloned DNA segment carrying unique sequences from the white locus of Drosophila melanogaster. Sequences within the cloned segment are shown to hybridize in situ to the white locus region on the polytene chromosomes of both wild-type strains and strains carrying chromosomal rearrangements whose breakpoints bracket the white locus. We further show that two small deficiency mutations, deleting white locus genetic elements but not those of complementation groups contiguous to white, delete the genomic sequences corresponding to a portion of the cloned segment. The strategy we have employed to isolate this cloned segment exploits the existence of an allele at the white locus containing a copy of a previously cloned transposable, reiterated DNA sequence element. We describe a simple, rapid method for retrieving cloned segments carrying a copy of the transposable element together with contiguous sequences corresponding to this allele. The strategy described is potentially general and we discuss its application to the cloning of the DNA sequences of other genes in Drosophila, including those identified only by genetic analysis and for which no RNA product is known.

Arginine/serine-rich domains of the su(wa) and tra RNA processing regulators target proteins to a subnuclear compartment implicated in splicing

Two unrelated pre-mRNA splicing regulators-suppressor-of-white-apricot (su(wa)) and transformer (tra)-contain distinctive, approximately 120 amino acid arginine/serine (RS)-rich domains. Deletion of the su(wa) RS domain eliminates function. Replacement with the tra RS domain restores su(wa) function to nearly wild-type levels. Replacement with a 10 amino acid simple nuclear entry signal allows partial, inefficient function. Thus, the su(wa) RS domain apparently serves a generic function(s) subsuming nuclear entry. Moreover, immunocytochemical studies demonstrate that both RS domains specifically direct localization of a fused reporter protein to a punctate subnuclear compartment shown previously to be enriched in several constitutive splicing components. We propose that RS domains are a new class of targeting signals directing concentration of proteins in a subnuclear compartment implicated in splicing metabolism.

Regulation of white locus expression: The structure of mutant alleles at the white locus of Drosophila melanogaster

We have analyzed the structures of 19 mutant alleles at the white locus of Drosophila melanogaster. Thirteen of the mutant alleles in our selected sample arose spontaneously, and of these, seven are associated with insertions of non-white-region DNA sequence elements. Several lines of evidence strongly suggest that these insertions are responsible for their associated mutant alleles, and further suggest that most or all of these insertions are transposons. Moreover, the white locus DNA sequences can be divided into two nonoverlapping domains on the basis of the properties of the two domains as mutational targets. One of these domains behaves, in this regard, in the manner expected of functional coding sequences, whereas the other does not. We propose a model for the nature and function of the presumptive noncoding white locus genetic elements. The two domains of the white locus defined by our studies are approximately coextensive with the functionally distinct subintervals of the locus defined by previous genetic analysis. Lastly, our results strongly suggest that the dominant, mutable wDZL allele results from the insertion of a transposon outside of, but near, the white locus. This putative transposon apparently carries genetic elements that act at a distance to repress expression of the white locus.

On/off regulation of gene expression at the level of splicing

Abstract The past two years have seen the discovery of three independent cases in which expression of a eukaryotic protein gene product is turned on and off by controlling splicing events necessary to produce the corresponding mRNA. Various considerations suggest that such on/off regulation at the level of splicing may be unexpectedly common.

Developmental expression of a regulatory gene is programmed at the level of splicing.

We report sequence and transcript structures for a 6191‐base chromosomal segment containing the presumptive regulatory gene from Drosophila, suppressor‐of‐white‐apricot [su(wa)]. Our results indicate that su(wa) expression is controlled by regulating occurrence of specific splices. Seven introns are removed from the su(wa) primary transcript during precellular blastoderm development. The sequence of this mature RNA indicates that it is a conventional messenger RNA. In contrast, after cellular blastoderm the first two of these introns cease to be efficiently removed. The mature RNAs resulting from this failure to remove the first two introns have structures quite unexpected of mRNAs. We propose that postcellular blastoderm su(wa) expression is repressed by preventing splices necessary to produce a functional mRNA. Implications and mechanisms are discussed.

Molecular cloning of sequences from a Drosophila RNA polymerase II locus by P element transposon tagging.

We have identified a lethal mutation in the D. melanogaster RNA polymerase II locus, RpIIC4, caused by insertion of a transposable element associated with the phenomenon of hybrid dysgenesis (P element). Using previously cloned P element sequences as a hybridization probe we have isolated a hybrid lambda phage clone carrying a 10 kb genomic DNA fragment containing a 1.3 kb P element insert and flanking sequences from the RpII locus. The non-P sequences in this clone (lambda DmRpII-1) hybridize to polytene chromosome band region 10C, the cytogenetic location of RpIIC4, and revertants which lose the lethal RNA polymerase II mutation also lose P element sequences from the locus. We have generated several additional P element insertions into the locus and shown that they can occur at two or more different sites. These experiments illustrate that mutagenesis by P element insertion and use of cloned P DNA to retrieve the DNA sequences into which insertion has occurred may be a general method for cloning genetically defined loci in Drosophila.

Evidence that a regulatory gene autoregulates splicing of its transcript.

Expression of the presumptive regulatory gene, suppressor‐of‐white‐apricot [su(wa)], is controlled at the level of splicing. Results reported here indicate that this control represents autorepression of su(wa) expression. Specifically, reverse genetic studies demonstrate that the 3.5 kb mature su(wa) RNA (produced by removal of seven introns) is a message essential for su(wa)+ function and indicate that the abundant 4.4 kb and 5.2 kb mature su(wa) RNAs (resulting when the first or first and second of the seven introns are not removed) are, unexpectedly, byproducts of repression of production of the functional 3.5 kb RNA. Moreover, several experiments indicate that this repression of splices necessary to produce the 3.5 kb RNA is dependent on the translation product of the 3.5 kb RNA itself. We propose that this regulatory gene autoregulates its expression by controlling splicing of its primary transcript.

Human evolution and human history: A complete theory

Since Darwin we have been in possession of two superficially dissonant facts. On one hand, humans are merely one of millions of animal species, all products of common ancestry. On the other, humans enjoy a level of ecological dominance that is spectacularly, qualitatively greater than that of any other animal that ever lived, including our closest relatives. Moreover, this unique ascendancy results from a complex suite of attributes that are each individually also unprecedented, including cognitive virtuosity, complex language, and an expanded ethical sense. Collectively, these facts constitute the human uniqueness problem. In spite of its importance, the superficial complexity of this problem has frustrated attempts to resolve it. Though a vast body of earlier work produced important isolated insights, no earlier theory has proven complete or convincing. I briefly review here a new resolution of the human uniqueness problem.1 This new hypothesis appears to be the necessary theory-of-everything. It ostensibly accounts parsimoniously for every major nonstochastic feature of the human story from the origin of Homo approximately 2.0 to 2.5 million years ago through the present instant. I use secondary, review literature where possible here to improve interdisciplinary accessibility. As well, I apologize to the many investigators whose important work could not be directly referenced because of length constraints.