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Thomas W Cline

Publications and source records attributed to Thomas W Cline.

6 recordsLinked to original sources
PubMed2006

Drosophila melanogaster male somatic cells feminized solely by TraF can collaborate with female germ cells to make functional eggs.

Female differentiation of Drosophila germ cells is induced by cell-nonautonomous signals generated in the gonadal soma that work with germ-cell-autonomous signals determined by germ-cell X chromosome dose. Generation of the nonautonomous feminizing signals was known to involve female-specific protein encoded by the master sex-determination gene Sex-lethal (Sxl) acting on its switch-gene target transformer (tra) to produce Tra(F) protein. However, it was not known whether Sxl's action on tra alone would suffice to trigger a fully feminizing nonautonomous signal. We developed a constitutively feminizing tra transgene that allowed us to answer this question. In gynanders (XX//XO mosaics) feminized by this Tra(F) transgene, functionally Sxl- haplo-X (chromosomally male) somatic cells collaborated successfully with diplo-X (chromosomally female) germ cells to make functional eggs. The fertility of such gynanders shows not only that Tra(F) is sufficient to elicit a fully feminizing nonautonomous signal, but also that haplo-X somatic cells can execute all other somatic functions required for oogenesis, despite the fact that their genome is not expected to be dosage compensated for such diplo-X-specific functions. The unexpected observation that some Tra(F)-feminized gynanders failed to lay their eggs showed there to be diplo-X cells outside the gonad for which Tra(F)-feminized haplo-X cells cannot substitute.

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PubMed2006

The TAGteam DNA motif controls the timing of Drosophila pre-blastoderm transcription.

The Drosophila sex-determination switch gene Sex-lethal (Sxl) and the X-chromosome signal element genes (XSEs) that induce the female-specific expression of Sxl are transcribed extremely early in development when most of the genome of this organism is still silent. The DNA sequence CAGGTAG had been implicated in this pre-cellular blastoderm activation of sex-determination genes. A genome-wide computational search, reported here, suggested that CAGGTAG is not specific to early sex-determination genes, since it is over-represented upstream of most genes that are transcribed pre-cellular blastoderm, not just those involved in sex determination. The same search identified similarly over-represented, one-base-pair degenerate sequences as possible functional synonyms of CAGGTAG. We call these heptamers collectively, the TAGteam. Relevance of the TAGteam sequences to pre-cellular blastoderm transcription was established through analysis of TAGteam changes in Sxl, scute (an XSE), and the ;ventral repression element' of the pattern-formation gene zerknüllt. Decreasing the number of TAGteam sites retarded the onset of pre-blastoderm transcription, whereas increasing their number correlated with an advanced onset. Titration of repressors was thought to be the rate-limiting step determining the onset of such early transcription, but this TAGteam dose effect shows that activators must also play an important role in the timing of pre-blastoderm gene expression.

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PubMed2003

The Drosophila melanogaster sir2+ gene is nonessential and has only minor effects on position-effect variegation.

Five Drosophila melanogaster genes belong to the highly conserved sir2 family, which encodes NAD(+)-dependent protein deacetylases. Of these five, dsir2(+) (CG5216) is most similar to the Saccharomyces cerevisiae SIR2 gene, which has profound effects on chromatin structure and life span. Four independent Drosophila strains were found with P-element insertions near the dsir2 transcriptional start site as well as extraneous linked recessive lethal mutations. Imprecise excision of one of these P elements (PlacW07223) from a chromosome freed of extraneous lethal mutations produced dsir2(17), a null intragenic deletion allele that generates no DSIR2 protein. Contrary to expectations from the report by Rosenberg and Parkhurst on their P-mobilization allele dSir2(ex10), homozygosity for dsir2(17) had no apparent deleterious effects on viability, developmental rate, or sex ratio, and it fully complemented sir2(ex10). Moreover, through a genetic test, we ruled out the reported effect of dSir2(ex10) on Sex-lethal expression. We did observe a modest, strictly recessive suppression of white(m4) position-effect variegation and a shortening of life span in dsir2 homozygous mutants, suggesting that dsir2 has some functions in common with yeast SIR2.

Amino Acid Sequence↗
PubMed2003

Recruitment of the proneural gene scute to the Drosophila sex-determination pathway.

In flies, scute (sc) works with its paralogs in the achaete-scute-complex (ASC) to direct neuronal development. However, in the family Drosophilidae, sc also acquired a role in the primary event of sex determination, X chromosome counting, by becoming an X chromosome signal element (XSE)-an evolutionary step shown here to have occurred after sc diverged from its closest paralog, achaete (ac). Two temperature-sensitive alleles, sc(sisB2) and sc(sisB3), which disrupt only sex determination, were recovered in a powerful F1 genetic selection and used to investigate how sc was recruited to the sex-determination pathway. sc(sisB2) revealed 3' nontranscribed regulatory sequences likely to be involved. The sc(sisB2) lesion abolished XSE activity when combined with mutations engineered in a sequence upstream of all XSEs. In contrast, changes in Sc protein sequence seem not to have been important for recruitment. The observation that the other new allele, sc(sisB3), eliminates the C-terminal half of Sc without affecting neurogenesis and that sc(sisB1), the most XSE-specific allele previously available, is a nonsense mutant, would seem to suggest the opposite, but we show that housefly Sc can substitute for fruit fly Sc in sex determination, despite lacking Drosophilidae-specific conserved residues in its C-terminal half. Lack of synergistic lethality among mutations in sc, twist, and dorsal argue against a proposed role for sc in mesoderm formation that had seemed potentially relevant to sex-pathway recruitment. The screen that yielded new sc alleles also generated autosomal duplications that argue against the textbook view that fruit fly sex signal evolution recruited a set of autosomal signal elements comparable to the XSEs.

Amino Acid Sequence↗
PubMed2002

A host parasite interaction rescues Drosophila oogenesis defects.

The cytoplasmically inherited bacterium Wolbachia pipientis is a widespread parasite of arthropods that manipulates the reproductive biology of its hosts, often to their detriment, in order to foster its own transmission through egg cytoplasm. Here we report that infection by Wolbachia restores fertility to Drosophila melanogaster mutant females prevented from making eggs by protein-coding lesions in Sex-lethal (Sxl), the master regulator of sex determination. Suppression of sterility by Wolbachia discriminates markedly among similar germline-specific Sxl alleles, and is not observed for mutations in other genes that produce similar 'tumorous ovary' phenotypes, including one that blocks Sxl germline expression. This allele and gene specificity indicates that suppression probably results from a specific interaction with Sxl protein, rather than from a bypass of the normal germline requirement for this developmental regulator or from an effect on Sxl expression. The Sxl-Wolbachia interaction provides a rare opportunity to explore host-parasite relationships at the molecular level in a model insect. Furthermore, demonstration that a parasite infection can counteract the deleterious effects of mutations in host genes illustrates how hosts might become dependent on parasites.

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