Biology subjects

Maggert, K. A.

Publications and source records attributed to Maggert, K. A..

5 recordsLinked to original sources

bioRxiv2026

Developmental patterning of adipose tissue by abd-A and Abd-B homeotic genes in Drosophila melanogaster

The Bithorax Complex (BX-C) homeobox proteins specify segmental identities along the anterior-posterior axis during Drosophila embryogenesis. Differential expression of the BX-C genes abd-A and Abd-B distinguishes abdominal from thoracic adipocytes, yet the mechanism regulating this heterogeneity remains poorly understood. Here, we identify cis-regulatory elements (CREs) and transcription factors that direct abdominal-specific expression of abd-A and Abd-B in the larval fat body. Fine-mapping analyses identified a 627-bp CRE within the Abd-B locus and a [~]6-kb CRE within the abd-A locus sufficient to drive heterogeneous expression. Yeast one-hybrid screening combined with functional analyses identified Lola, Lolal, and Combgap as key repressors of Abd-B, whereas Piragua (Prg) and Seven up (Svp) function as transcriptional activators, indicating that adipocyte heterogeneity in postembryonic adipose tissue is actively regulated. In turn, lola and prg are repressed by Abd-B, whereas lolal and svp are activated, forming a feedback circuit further modulated by Wnt signaling, which promotes lola and lolal expression while repressing svp. CUT&RUN analyses suggest that these interactions are direct, with dTCF/Pan and Abd-B occupancy detected at target loci. Together, our findings define a transcriptional circuit that regulates Abd-B gene transcription to pattern adipose tissue and may establish the developmental basis of fat depot specialization. One-sentence summaryTranscriptional regulation of abd-A & Abd-B in adipocytes

genetics↗

bioRxiv2024

Insights Into Ribosomal DNA (rDNA) Dominance and Magnification Through Characterization of Isogenic Deletion Alleles

The major loci for the large primary ribosomal RNA genes (35S rRNAs) exist as hundreds to thousands of tandem repeats in all organisms, and dozens to hundreds in Drosophila. The highly repetitive nature of the rDNA makes it intrinsically unstable, and many conditions arise from the reduction or magnification of copy number, but the conditions under which it does so remains unknown. By targeted DNA damage to the rDNA of the Y chromosome, we created and investigated a series of rDNA alleles. We found that complete loss of rDNA leads to lethality after the completion of embryogenesis, blocking larval molting and metamorphosis. We find that the resident retrotransposons - R1 and R2 - are regulated by active rDNA such that reduction in copy number derepresses these elements. Their expression is highest during the early 1st instar, when loss of rDNA is lethal. Regulation of R1 and R2 may be related to their structural arrangement within the rDNA, as we find they are clustered in the flanks of the Nucleolus Organizing Region (NOR; the cytological appearance of the rDNA). We assessed the complex nucleolar dominance relationship between X- and Y-linked rDNA using a Histone H3.3-GFP reporter construct and incorporation at the NOR, and found that dominance is controlled by rDNA copy number as at high multiplicity the Y-linked array is dominant, but at low multiplicity the X-linked array becomes derepressed. Finally, we found that multiple conditions that disrupt nucleolar dominance lead to increased rDNA magnification, suggesting that the phenomena of dominance and magnification are related, and a single mechanism may underly and unify these two longstanding observations in Drosophila.

genetics↗

bioRxiv2021

Symmetric Inheritance of Histones H3 in Drosophila Male Germline Stem Cell Divisions

Mitotically-stable "epigenetic" memory requires a mechanism for the maintenance of gene-regulatory information through the cell division cycle. Typically DNA-protein contacts are disrupted by DNA replication, but in some cases locus-specific association between DNA and overlying histones may appear to be maintained, providing a plausible mechanism for the transmission of histone-associated gene-regulatory information to daughter cells. Male Drosophila melanogaster testis germ stem cell divisions seem a clear example of such inheritance, as previously chromatin-bound Histone H3.2 proteins (presumably with their post-translational modifications intact) have been reported to be retained in the germ stem cell nuclei, while newly synthesized histones are incorporated into daughter spermatogonial chromosomes. To investigate the rate of errors in this selective partitioning that may lead to defects in the epigenetic identity of germ stem cells, we employed a photoswitchable Dendra2 moiety as a C-terminal fusion on Histones H3 (Histone H3.2 and Histone H3.3); we could thereby discriminate histones translated before photoswitching and those translated after. We found instead that male germ line stem cell divisions show no evidence of asymmetric histone partitioning, even after a single division, and thus no evidence for locus-specific retention of either Histone H3.2 or Histone H3.3. We considered alternative hypotheses for the appearance of asymmetry and find that previous reports of asymmetric histone distribution in male germ stem cells can be satisfactorily explained by asynchrony between subsequent sister stem cell and spermatogonial divisions.

genetics↗

bioRxiv2021

Live Analysis of Position Effect Variegation Reveals Different Modes of Action for HP1 and Su(var)3-9

AO_SCPLOWBSTRACTC_SCPLOWPosition Effect Variegation (PEV) results from the juxtaposition of euchromatic and heterochromatic components of eukaryotic genomes, silencing genes near the new euchromatin/heterochromatin junctions. Silencing is itself heritable through S phase, giving rise to distinctive random patterns of cell clones expressing the genes intermixed with clones in which the genes are silenced. Much of what we know about epigenetic inheritance in the soma stems from work on PEV aimed at identifying the components of the silencing machinery and its mechanism of inheritance. The roles of two central gene activities - the Su(var)3-9-encoded histone H3-Lysine-9 methyltransferase and the Su(var)205-encoded methyl-H3-Lysine-9 binding protein HP1a - have been inferred from terminal phenotypes, leaving considerable gaps in understanding how PEV behaves through development. Here, we investigate the PEV phenotypes of Su(var)3-9 and Su(var)205 mutations in live developing tissues. We discovered that mutation in Su(var)205 compromises the initial establishment of PEV in early embryogenesis. Later gains of heterochromatin-induced gene silencing are possible, but are unstable and lost rapidly. In contrast, a strain with mutation in Su(var)3-9 exhibits robust silencing early in development, but fails to maintain it through subsequent cell divisions. Our analyses show that while the terminal phenotypes of these mutations may appear identical, they have arrived at them through different developmental trajectories. We discuss how our findings expand and clarify existing models for epigenetic inheritance of heterochromatin-induced gene silencing. SO_SCPLOWIGNIFICANCEC_SCPLOWCurrent concepts of epigenetic inheritance are exemplified by Position Effect Variegation, a phenomenon whereby heterochromatin can repress genes in clonal cell lineages. Heterochromatin is required for genome protection as it silences toxic transposable elements and prevents instability of repeat sequences. Histone H3 modified by methylation of Lysine-9 and HP1a are critical components of heterochromatin. Using live cell analysis of PEV in mutants in strains with mutations in Su(var)3-9, which encodes the histone methyltransferase, and Su(var)205, which encodes HP1a, we describe an unexpected dynamism in PEV, challenging current models of epigenetics, and revealing unexpectedly different modes of action of these two fundamental components of heterochromatin.

genetics↗

bioRxiv2019

Human rDNA Copy Number Is Unstable in Metastatic Breast Cancers

Epigenetic silencing, including the formation of heterochromatin, silent chromosome territories, and repressed gene promoters, acts to stabilize patterns of gene regulation and the physical structure of the genome. Reduction of epigenetic silencing can result in genome rearrangements, particularly at intrinsically unstable regions of the genome such as transposons, satellite repeats, and repetitive gene clusters including the rRNA gene clusters (rDNA). It is thus expected that mutational or environmental conditions that compromise heterochromatin function might cause genome instability, and diseases associated with decreased epigenetic stability might exhibit genome changes as part of their etiology. We find support of this hypothesis in invasive ductal breast carcinoma, in which reduced epigenetic silencing has been previously described, by using a facile method to quantify rDNA copy number in biopsied breast tumors and pair-matched healthy tissue. We found that rDNA and satellite DNA sequences had significant copy number variation - both losses and gains of copies - compared to healthy tissue, arguing that these genome rearrangements are common in developing breast cancer. Thus, any proposed etiology onset or progression of breast cancer should consider alterations to the epigenome, but must also accommodate concomitant changes to genome sequence at heterochromatic loci.\n\nAuthors StatementOne of the common hallmarks of cancer is genome instability, including hypermutation and changes to chromosome structure. Using tumor tissues obtained from women with invasive ductal carcinoma, we find that a sensitive area of the genome - the ribosomal DNA gene repeat cluster - shows hypervariability in copy number. The patterns we observe as not consistent with an adaptive loss leading to increased tumor growth, but rather we conclude that copy number variation at repeat DNA is a general consequence of reduced heterochromatin function in cancer progression.

cancer biology↗