Biomedical subjects

B S Baker

Publications and source records attributed to B S Baker.

At least 19 recordsLinked to original sources

PubMed1998

The evolutionary dynamics of sex determination.

REVIEW There is substantial cytogenetic data indicating that the process of sex determination can evolve relatively rapidly. However, recent molecular studies on the evolution of the regulatory genes that control sex determination in the insect Drosophila melanogaster, the nematode Caenorhabditis elegans, and mammals suggest that, although certain sex determination regulatory genes have evolved relatively rapidly, other sex determination regulatory genes are quite conserved. Thus, studies of the evolution of sex determination, a process that appears to have elements that undergo substantial evolutionary change and others that may be conserved, could provide substantial insights into the kinds of forces that both drive and constrain the evolution of developmental hierarchies.

Animals↗

PubMed1998

Regulation of sex-specific selection of fruitless 5' splice sites by transformer and transformer-2.

In Drosophila melanogaster, the fruitless (fru) gene controls essentially all aspects of male courtship behavior. It does this through sex-specific alternative splicing of the fru pre-mRNA, leading to the production of male-specific fru mRNAs capable of expressing male-specific fru proteins. Sex-specific fru splicing involves the choice between alternative 5' splice sites, one used exclusively in males and the other used only in females. Here we report that the Drosophila sex determination genes transformer (tra) and transformer-2 (tra-2) switch fru splicing from the male-specific pattern to the female-specific pattern through activation of the female-specific fru 5' splice site. Activation of female-specific fru splicing requires cis-acting tra and tra-2 repeat elements that are part of an exonic splicing enhancer located immediately upstream of the female-specific fru 5' splice site and are recognized by the TRA and TRA-2 proteins in vitro. This fru splicing enhancer is sufficient to promote the activation by tra and tra-2 of both a 5' splice site and the female-specific doublesex (dsx) 3' splice site, suggesting that the mechanisms of 5' splice site activation and 3' splice site activation may be similar.

Animals↗

PubMed1998

hermaphrodite and doublesex function both dependently and independently to control various aspects of sexual differentiation in Drosophila.

The hermaphrodite (her) gene is necessary for sexual differentiation in Drosophila. Our characterization of her's zygotic function suggests that one set of female-specific terminal differentiation genes, the yolk protein (yp) genes, is transcriptionally activated by two separate pathways. One is a female-specific pathway, which is positively regulated by the female-specific doublesex protein (DSXF). The other is a non-sex-specific pathway, that is positively regulated by HER. The HER pathway is prevented from functioning in males by the action of the male-specific doublesex protein (DSXM). The HER and DSX pathways also function independently to control downstream target genes in the precursor cells that give rise to the vaginal teeth and dorsal anal plate of females, and the lateral anal plates of males. However, a female-specific pathway that is dependent on both DSXF and HER controls the female-specific differentiation of the foreleg bristles and tergites 5 and 6, and the male-specific differentiation of these tissues does not require the suppression of HER's function by DSXM.

Animals↗

PubMed1998

Her, a gene required for sexual differentiation in Drosophila, encodes a zinc finger protein with characteristics of ZFY-like proteins and is expressed independently of the sex determination hierarchy.

The zygotic function of the hermaphrodite (her) gene of Drosophila plays an important role in sexual differentiation. Our molecular genetic characterization of her suggests that her is expressed sex non-specifically and independently of other known sex determination genes and that it acts together with the last genes in the sex determination hierarchy, doublesex and intersex, to control female sexual differentiation. Consistent with such a terminal function in sexual differentiation, her encodes a protein with C2H2-type zinc fingers. The her zinc fingers are atypical and similar to the even-numbered zinc fingers of ZFY and ZFX proteins in humans and other vertebrates.

Abdominal Muscles↗

PubMed1997

The regulation of the Drosophila msl-2 gene reveals a function for Sex-lethal in translational control.

In Drosophila, dosage compensation occurs by increasing the transcription of the single male X chromosome. Four trans-acting factors encoded by the male-specific lethal genes are required for this process. Dosage compensation is restricted to males by the splicing regulator Sex-lethal, which functions to prevent the production of the MSL-2 protein in females by an unknown mechanism. In this report, we provide evidence that Sex-lethal acts synergistically through sequences in both the 5' and 3' untranslated regions of MSL-2 to mediate repression. We also provide evidence that the repression of MSL-2 is directly regulated by Sex-lethal at the level of translation.

Animals↗

PubMed1997

In vivo analysis of the functional domains of the Drosophila splicing regulator RBP1.

The Drosophila splicing factor RBP1 participates together with TRA and TRA-2 in the regulation of alternative splicing of doublesex (dsx) pre-mRNA. It does so by recognizing RBP1 RNA target sequences in the dsx pre-mRNA. RBP1 belongs to the Ser-Arg-rich (SR) protein family of splicing factors, which have in common a N-terminal RNA recognition motif-type RNA binding domain, a Gly-rich region, and a C-terminal SR domain. Using a tissue culture transfection assay, we demonstrate that the Gly residues within the Gly-rich domain, the ribonucleoprotein motifs within the RNA recognition motif RNA binding domain, and the SR domain are required for regulation of dsx splicing by RBP1 in vivo. Furthermore, using a two-hybrid system, we show protein-protein interactions between RBP1 and itself and between RBP1 and TRA-2. The SR domain and the Gly residues within the Gly-rich domain of RBP1 were found to be involved in these protein-protein interactions. Our results suggest that RBP1 and TRA-2 function in regulation of dsx splicing by forming a complex.

Alternative Splicing↗

PubMed1997

Induction of cutaneous lymphocyte-associated antigen expression by group A streptococcal antigens in psoriasis.

The cutaneous lymphocyte-associated antigen (CLA) has been proposed as a homing receptor for the selective migration of memory T cells into the skin. To investigate the effect of group A streptococci (GAS) on the migration of T cells in psoriasis, CLA expression was assessed by double-staining for CD3 and the HECA-452 epitope on peripheral blood T cells from 13 patients with psoriasis, 10 patients with other inflammatory skin diseases and 12 normal controls before and after 7 days culture with a GAS sonicate, Candida albicans (control antigen) or medium. In addition, CLA+, and CLA-, CD3+ CD45RO+ subsets were isolated from individuals in each group and V beta 2 expression and proliferation to GAS studied. Mean CLA expression by freshly isolated T cells was almost identical in the three groups. After culture with GAS, T cells from the psoriatic patients and control showed a significant increase in mean percentage CLA+ expression compared to medium (P < 0.002, P < 0.05, respectively). This induction was inhibited by the addition of anti-IL-12 antibody. However, in psoriatic patients, but not in controls, the GAS-induced increase was significantly greater than that of C. albicans (P < 0.002) and was accompanied by a decrease in T cells positive for the peripheral lymph node homing receptor, L-selectin (P < 0.05). The percentage of V beta 2+ T cells was markedly higher in the CLA+ than in the CLA- T-cell subset in psoriatic patients (P < 0.01) and controls; both subsets proliferated to GAS, in each group. These findings suggest a differential modulation of specific tissue homing receptors on T cells by GAS in psoriasis.

Adolescent↗

PubMed1997

Evolutionary conservation of regulatory strategies for the sex determination factor transformer-2.

Sex determination in Drosophila melanogaster is regulated by a cascade of splicing factors which direct the sex-specific expression of gene products needed for male and female differentiation. The splicing factor TRA-2 affects sex-specific splicing of multiple pre-mRNAs involved in sexual differentiation. The tra-2 gene itself expresses a complex set of mRNAs generated through alternative processing that collectively encode three distinct protein isoforms. The expression of these isoforms differs in the soma and germ line. In the male germ line the ratio of two isoforms present is governed by autoregulation of splicing. However, the functional significance of multiple TRA-2 isoforms has remained uncertain. Here we have examined whether the structure, function, and regulation of tra-2 are conserved in Drosophila virilis, a species diverged from D. melanogaster by over 60 million years. We find that the D. virilis homolog of tra-2 produces alternatively spliced RNAs encoding a set of protein isoforms analogous to those found in D. melanogaster. When introduced into the genome of D. melanogaster, this homolog can functionally replace the endogenous tra-2 gene for both normal female sexual differentiation and spermatogenesis. Examination of alternative mRNAs produced in D. virilis testes suggests that germ line-specific autoregulation of tra-2 function is accomplished by a strategy similar to that used in D. melanogaster. The similarity in structure and function of the tra-2 genes in these divergent Drosophila species supports the idea that sexual differentiation in D. melanogaster and D. virilis is accomplished under the control of similar regulatory pathways.

Alternative Splicing↗

PubMed1997

Compartmental organization of the Drosophila genital imaginal discs.

We have investigated the anterior and posterior compartmental organization of the genital imaginal disc. Unlike the thoracic discs, the genital disc is a compound disc consisting of three primordia--the female genital, male genital, and anal primordia. Here we provide evidence that each primordium is divided into anterior and posterior compartments. Genes that are known to be expressed in compartment-specific manners in other discs (engrailed, hedgehog, patched, decapentaplegic, wingless and cubitus interruptus) are expressed in analogous patterns in each primordium of the genital disc. Specifically, engrailed and cubitus interruptus are expressed in complementary domains, while patched, decapentaplegic and wingless are expressed along the border between the two domains. Mitotic clones induced at the beginning of the second larval instar do not cross the boundary between the engrailed-expressing and cubitus interruptus-expressing domains, indicating that these domains are true genetic compartments. Furthermore, we examined the phenotypes of mutant clones of the cAMP-dependent protein kinase A and engrailed-invected, genes that are known to play compartment-specific functions in other discs. These experiments demonstrate that the anterior/posterior patterning functions of these genes are conserved in the genital disc. The adult clonal phenotypes of protein kinase A and engrailed-invected mutants also provide a more detailed map of the adult genitalia and analia with respect to the anterior/posterior compartmental subdivision. Our results lead us to propose a new model to describe the anterior and posterior compartmental organization of the genital disc.

Animals↗

PubMed1997

T-cell receptor V beta expression is restricted in dermatitis herpetiformis skin.

An infiltrate of T-cells is found in lesional dermatitis herpetiformis skin, but the role of these cells in the pathogenesis of the skin lesions is unknown. The purpose of this study was to examine T-cell receptor V beta expression in skin biopsies taken from patients with dermatitis herpetiformis. Expression of eleven T-cell receptor V beta families in biopsies obtained from 10 patients was examined by immunoperoxidase staining and compared simultaneously with peripheral blood lymphocytes. Over-representation of V beta 2 (p < 0.02), V beta 5.2/5.3 (p < 0.01) and V beta 5.3 (p < 0.05) was found in lesional dermatitis herpetiformis skin compared with peripheral blood lymphocytes. These results suggest that recognition of an antigen(s) or superantigen is involved in the pathogenesis of dermatitis herpetiformis skin lesions.

Adult↗

PubMed1997

Differential T-cell reactivity to the round and oval forms of Pityrosporum in the skin of patients with psoriasis.

Pityrosporum yeasts have been implicated as a trigger for the initiation of scalp lesions in psoriasis. To determine whether Pityrosporum-reactive T cells are present in lesional psoriatic skin. T-cell lines (TCL) were cultured from the scalps of nine patients with psoriasis and seven with alopecia areata (disease controls), and from non-scalp lesions from six of the psoriatic patients. The psoriatic skin TCL were stained for CD3, CD4, CD8 and TCR alpha beta expression and tested in a proliferation assay with Candida albicans and purified protein derivative (PPD), and cytoplasmic and cell-wall extracts of P. ovale (oval) and P. orbiculare (round). The proliferative responses of corresponding peripheral blood mononuclear cells (PBMC) were also determined. All the PBMC samples responded to the Pityrosporum extracts to variable extents, but no significant difference in the response of the group to the two different forms of yeast was observed. The response was mediated by CD4+ T cells and inhibited by the addition of anti-HLA-DR antibody. In addition, all nine psoriatic scalp TCL, which were predominantly CD3+, CD4+ TCR alpha beta(+), responded to the cytoplasmic, and five of nine TCL to the cell-wall extract of P. orbiculare. In contrast, only three of the nine TCL proliferated to either extract of P. ovale. This difference was significant for both the cytoplasmic (P < 0.01) and cell wall (P = 0.01) extracts. Similarly, the TCL cultured from non-scalp psoriatic lesions also showed a more marked response to the P. orbiculare extracts (P = 0.05). Furthermore, four of seven and two of seven scalp TCL from lesions of alopecia areata responded to the P. orbiculare and P. ovale extracts, respectively; these responses did not differ significantly from those of the psoriatic scalp TCL. None of the skin TCL responded to either Candida albicans or PPD. These findings demonstrate that T cells with differential reactivity to the round and oval forms of Pityrosporum are present in, but are not specific for, psoriatic skin lesions. A role for these cells in the pathogenesis of psoriasis remains speculative.

Adult↗

PubMed1997

Active psoriasis and profound CD4+ lymphocytopenia.

We report the case of a patient with a long-standing history of widespread chronic plaque psoriasis, who was recently found to have a profound CD4+ lymphocytopenia. He is human immunodeficiency virus (HIV) negative. His psoriasis remains active and widespread, and he has had 60 cutaneous malignancies, including many squamous cell carcinomas, excised over the last 10 years. In the past he has had numerous cutaneous viral warts. Despite a low peripheral blood CD4+ T-cell count, similar numbers of activated T cells, identified by double labelling for CD4 and HLA-DR antigens, were found in the epidermis of our patient as other individuals with psoriasis. Thus, there appear to be sufficient activated CD4+ T cells in our patient's psoriatic plaques to maintain the psoriatic process.

Adult↗

PubMed1996

Control of male sexual behavior and sexual orientation in Drosophila by the fruitless gene.

Sexual orientation and courtship behavior in Drosophila are regulated by fruitless (fru), the first gene in a branch of the sex-determination hierarchy functioning specifically in the central nervous system (CNS). The phenotypes of new fru mutants encompass nearly all aspects of male sexual behavior. Alternative splicing of fru transcripts produces sex-specific proteins belonging to the BTB-ZF family of transcriptional regulators. The sex-specific fru products are produced in only about 500 of the 10(5) neurons that comprise the CNS. The properties of neurons expressing these fru products suggest that fru specifies the fates or activities of neurons that carry out higher order control functions to elicit and coordinate the activities comprising male courtship behavior.

Age Factors↗

PubMed1996

The dosage compensation system of Drosophila is co-opted by newly evolved X chromosomes.

In species where males and females differ in number of sex chromosomes, the expression of sex-linked genes is equalized by a process known as dosage compensation. In Drosophila melanogaster, dosage compensation is mediated by the binding of the products of the male-specific lethal (msl) genes to the single male X chromosome. Here we report that the sex- and chromosome-specific binding of three of the msl proteins (MSLs) occurs in other drosophilid species, spanning four genera. Moreover, we show that MSL binding correlates with the evolution of the sex chromosomes: in species that have acquired a second X chromosome arm because of an X-autosome translocation, we observe binding of the MSLs to the 'new' (previously autosomal) arm of the X chromosome, only when its homologue has degenerated. Moreover, in Drosophila miranda, a Y-autosome translocation has produced a new X chromosome (called neo-X), only some regions of which are dosage compensated. In this neo-X chromosome, the pattern of MSL binding correlates with the known pattern of dosage compensation.

Animals↗

PubMed1996

Dominant-negative mutant thyroid hormone receptors prevent transcription from Xenopus thyroid hormone receptor beta gene promoter in response to thyroid hormone in Xenopus tadpoles in vivo.

We describe a dominant-negative approach in vivo to assess the strong, early upregulation of thyroid hormone receptor beta (TR beta) gene in response to thyroid hormone, characteristic of the onset of natural and thyroid hormone-induced amphibian metamorphosis, 3,3',5-Triiodo-thyronine (T3) treatment of organ cultures of premetamorphic Xenopus tadpole tails coinjected in vivo with the wild-type Xenopus TR beta (wt-xTR beta) and three different thyroid responsive element chloramphenicol acetyltransferase (TRE-CAT) reporter constructs, including a direct repeat +4 (DR +4) element in the -200/+87 fragment of the xTR beta promoter, resulted in a 4- to 8-fold enhancement of CAT activity. Two human C-terminal TR beta 1 mutants (delta-hTR beta 1 and Ts-hTR beta 1), an artificial Xenopus C-terminal deletion mutant (mt-xTR beta), and the oncogenic viral homology v-erbA, none of which binds T3, inhibited this T3 response of the endogenous wt-xTR in Xenopus XTC-2 cells cotransfected with the -1600/+87 xTR beta promoter-CAT construct, the potency of the dominant-negative effect of these mutant TRs being a function of the strength of their heterodimerization with Xenopus retinoid X receptor gamma. Coinjection of the dominant-negative Xenopus and human mutant TR beta s into Xenopus tadpole tails totally abolished the T3 responsiveness of the wt-xTR beta with different TREs, including the natural DR +4 TRE of the xTR beta promoter.

Amino Acid Sequence↗

PubMed1996

Cytokine expression in psoriatic skin lesions during PUVA therapy.

To determine whether an improvement in skin lesions as a result of PUVA therapy may be correlated with changes in cytokine patterns, RT-PCR amplification was used to compare the levels of IL-2, IL-6, IL-8, IL-10, TNF-alpha and IFN-gamma cytokine mRNA expression in serial biopsies from three chronic plaque psoriatic patients. In each case, 3-mm punch biopsies were taken from lesional skin before and during 2-28 days of treatment with PUVA. Total mRNA was extracted from each biopsy, cDNA synthesized, and then amplified by 35 cycles of PCR using cytokine-specific primers. The specificity of the PCR products was confirmed by the Southern blot technique. Substantial levels of specific mRNA for each of the cytokines studied was present in the lesions prior to treatment. In two of the three patients who responded well to PUVA, a reduction in all the cytokines including IL-10 was observed compared with baseline levels. In contrast, PUVA proved to be ineffective in clearing the psoriasis of the third patient whose skin lesions worsened during the course of treatment. This was accompanied by an increase in IFN-gamma but not of the other cytokines investigated, above the pretreatment level. This study showed an association between PUVA-induced resolution and decreases in the levels of various cytokines highly expressed in psoriatic lesions.

Adult↗

PubMed1996

Dosage compensation and chromatin structure in Drosophila.

The past year has brought significant advances in our understanding of the male-specific lethal (msl genes and dosage compensation in Drosophila. The molecular characterization of the msl-2 gene has, to a great extent, solved the question of how msl-mediated dosage compensation is restricted to males. Molecular analyses of the msl genes have substantiated the proposal that the MSL proteins function as a multimeric complex to mediate dosage compensation. The finding that MSL-2 protein has a RING finger and the demonstration that an insulator protein facilitates the dosage compensation of X-linked genes inserted into the autosomes have opened promising avenues to identify the cis-acting dosage-compensation determinants.

Acetylation↗

PubMed1996

A negative feedback mechanism revealed by functional analysis of the alternative isoforms of the Drosophila splicing regulator transformer-2.

The Drosophila sex determination gene transformer-2 (tra-2) is a splicing regulator that affects the sex-specific processing of several distinct pre-mRNAs. While the tra-2 gene itself is known to produce alternative mRNAs that together encode three different TRA-2 protein isoforms, the respective roles of these isoforms in affecting individual pre-mRNA targets has remained unclear. We have generated transgenic fly strains with mutations affecting specific TRA-2 isoforms to investigate their individual roles in regulating the alternative processing of doublesex, exuperantia and tra-2 pre-mRNA. Our results indicate that in somatic tissues two different isoforms function redundantly to direct female differentiation and female-specific doublesex pre-mRNA splicing. In the male germline, where tra-2 has an essential role in spermatogenesis, a single isoform was found to uniquely perform all necessary functions. This isoform appears to regulate its own synthesis during spermatogenesis through a negative feedback mechanism involving intron retention.

Alternative Splicing↗