Biology subjects

Alexander, A. K.

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

5 recordsLinked to original sources

bioRxiv2025

Meiotic prophase I disruption as a strategy for non-hormonal male contraception using small-molecule inhibitor JQ1

Long-acting non-hormonal male contraceptives are urgently needed but developing strategies that are both effective and reversible presents significant challenges. Here, we investigated the potential of meiotic prophase I blockade as a promising and potentially reversible approach to male contraception. To do this, we utilized (+)-JQ1, a small-molecule inhibitor of the testis-specific protein, BRDT. Daily injections of (+)-JQ1 for three weeks resulted in disrupted spermatogenesis resulting in loss of spermatozoa and an inability to sire pups. While spermatogenic cells repopulated the testis within six weeks post drug cessation, full fertility restoration required a longer recovery period. We attribute this delay in full recovery to persistent issues with the pachytene transcriptional program, which is crucial for meiotic progression and spermatid development. These findings underscore the potential of pharmacological approaches to disrupt meiotic prophase I as a targeted, reversible male contraceptive strategy, providing new insights into developing effective non-hormonal contraceptive approaches.

cell biology↗

bioRxiv2025

Single-nucleus multiomics of murine gonadal cells reveals transcriptional regulatory network underlying supporting lineage differentiation

Sex determination of mammalian gonads hinges upon sex-specific differentiation of gonadal supporting cells: Sertoli cells in the testis and granulosa cells in the ovary. To gain insights into how supporting cells acquire their identities, we performed joint single-nucleus transcriptomics and chromatin accessibility assays on murine gonadal cells across sex determination. By contrasting sex-specific gene expression and corresponding chromatin accessibility among progenitor and differentiated cells, we discovered that sex-specific chromatin regions in supporting cells are established shortly after sex determination, accompanied by the acquisition of active histone marks. The presence of potential transcription factor binding motifs in the open chromatin regions revealed regulatory networks underlying ovary-enriched factors LEF1 and MSX1, which promote granulosa fate by inducing granulosa-specific genes such as Foxl2 and Fst. Our results not only identify the gene regulatory framework underlying supporting cell sex differentiation, but also provide invaluable resources for the field. TeaserSex-specific changes in chromatin and gene expression underly the divergent developmental fates of the bipotential gonadal primordium.

developmental biology↗

bioRxiv2024

Single-nucleus multiomics reveals the gene-regulatory networks underlying sex determination of murine primordial germ cells

Accurate specification of female and male germ cells during embryonic development is critical for sexual reproduction. Primordial germ cells (PGCs) are the bipotential precursors of mature gametes that commit to an oogenic or spermatogenic fate in response to sex-determining cues from the fetal gonad. The critical processes required for PGCs to integrate and respond to signals from the somatic environment in gonads are not understood. In this study, we developed the first single-nucleus multiomics map of chromatin accessibility and gene expression during murine PGC development in both XX and XY embryos. Profiling of cell-type specific transcriptomes and regions of open chromatin from the same cell captured the molecular signatures and gene networks underlying PGC sex determination. Joint RNA and ATAC data for single PGCs resolved previously unreported PGC subpopulations and cataloged a multimodal reference atlas of differentiating PGC clusters. We discovered that regulatory element accessibility precedes gene expression during PGC development, suggesting that changes in chromatin accessibility may prime PGC lineage commitment prior to differentiation. Similarly, we found that sexual dimorphism in chromatin accessibility and gene expression increased temporally in PGCs. Combining single-nucleus sequencing data, we computationally mapped the cohort of transcription factors that regulate the expression of sexually dimorphic genes in PGCs. For example, the gene regulatory networks of XX PGCs are enriched for the transcription factors, TFAP2c, TCFL5, GATA2, MGA, NR6A1, TBX4, and ZFX. Sex-specific enrichment of the forkhead-box and POU6 families of transcription factors was also observed in XY PGCs. Finally, we determined the temporal expression patterns of WNT, BMP, and RA signaling during PGC sex determination, and our discovery analyses identified potentially new cell communication pathways between supporting cells and PGCs. Our results illustrate the diversity of factors involved in programming PGCs towards a sex-specific fate.

developmental biology↗

bioRxiv2022

Meiotic gene transcription programs are mediated by A-MYB and BRDT-dependent RNA polymerase II pause release during mammalian prophase I

During meiotic prophase I, germ cells must balance transcriptional activation with meiotic recombination and chromosome synapsis, biological processes requiring extensive changes to chromatin state and structure. Here we explored the interplay between chromatin accessibility and transcription across a detailed time-course of murine male meiosis by measuring genome-wide patterns of chromatin accessibility, nascent transcription, and processed mRNA. To understand the relationship between these parameters of gene regulation and recombination, we integrated these data with maps of double-strand break formation. Maps of nascent transcription show that Pol II is loaded on chromatin and maintained in a paused state early during prophase I. In later stages of prophase I, paused Pol II is released in a coordinated transcriptional burst resulting in [~]3-fold increase in transcription. Release from pause is mediated by the transcription factor A-MYB and the testis-specific bromodomain protein, BRDT. The burst of transcriptional activity is both temporally and spatially segregated from key steps of meiotic recombination: double strand breaks show evidence of chromatin accessibility earlier during prophase I and at distinct loci from those undergoing transcriptional activation, despite shared chromatin marks. Our findings reveal the mechanism underlying chromatin specialization in either transcription or recombination in meiotic cells.

genomics↗

bioRxiv2021

Genetic Dissection of the RNA Polymerase II Transcription Cycle

How DNA sequence affects the dynamics and position of RNA Polymerase II (Pol II) during transcription remains poorly understood. Here we used naturally occurring genetic variation in F1 hybrid mice to explore how DNA sequence differences affect the genome-wide distribution of Pol II. We measured the position and orientation of Pol II in eight organs collected from heterozygous F1 hybrid mice using ChRO-seq. Our data revealed a strong genetic basis for the precise coordinates of transcription initiation and promoter proximal pause, allowing us to redefine molecular models of core transcriptional processes. Our results implicate the strength of base pairing between A-T or G-C dinucleotides as key determinants to the position of Pol II initiation and pause. We report evidence that initiation site selection follows a stochastic process similar to brownian motion along the DNA template. We found widespread differences in the position of transcription termination, which impact the primary structure and stability of mature mRNA. Finally, we report evidence that allelic changes in transcription often affect mRNA and ncRNA expression across broad genomic domains. Collectively, we reveal how DNA sequences shape core transcriptional processes at single nucleotide resolution in mammals.

genomics↗