Tan, Z. M. | Search bioRxiv

bioRxiv2024

Multi-level transcriptional regulation of embryonic sex determination and dosage compensation by the X-signal element sex-1

The C. elegans nuclear hormone receptor sex-1 is known to be an embryonic X-signal element that represses xol-1, the sex-switch gene that is the master regulator of sex determination and dosage compensation. Several prior studies on sex-1 function have suggested that sex-1 may have additional downstream roles beyond the regulation of xol-1 expression. In this study we characterize some of these additional roles of sex-1 in regulating the dual processes of sex determination and dosage compensation during embryogenesis. Our study reveals that sex-1 acts on many of the downstream targets of xol-1 in a xol-1-independent manner. Further analysis of these shared but independently regulated downstream targets uncovered that sex-1 mediates the expression of hermaphrodite- and male-biased genes during embryogenesis. We validated sex-1 binding on one of these downstream targets, the male-developmental gene her-1. Our data suggests a model where sex-1 exhibits multi-level direct transcriptional regulation on several targets, including xol-1 and genes downstream of xol-1, to reinforce the appropriate expression of sex-biased transcripts in XX embryos. Furthermore, we found that xol-1 sex-1 double mutants show defects in dosage compensation. Our study provides evidence that misregulation of dpy-21, one of the components of the dosage compensation complex, and the subsequent misregulation of H4K20me1 enrichment on the X chromosomes, may contribute to this defect.

developmental biology↗

bioRxiv2024

XOL-1 regulates developmental timing by modulating the H3K9 landscape in C. elegans early embryos

Sex determination in the nematode C. elegans is controlled by the master regulator XOL-1 during embryogenesis. Expression of xol-1 is dependent on the ratio of X chromosomes and autosomes, which differs between XX hermaphrodites and XO males. In males, xol-1 is highly expressed and in hermaphrodites, xol-1 is expressed at very low levels. XOL-1 activity is known to be critical for the proper development of C. elegans males, but its low expression was considered to be of minimal importance in the development of hermaphrodite embryos. Our study reveals that XOL-1 plays an important role as a regulator of developmental timing during hermaphrodite embryogenesis. Using a combination of imaging and bioinformatics techniques, we found that hermaphrodite embryos have an accelerated rate of cell division, as well as a more developmentally advanced transcriptional program when xol-1 is lost. Further analyses reveal that XOL-1 is responsible for regulating the timing of initiation of dosage compensation on the X chromosomes, and the appropriate expression of sex-biased transcriptional programs in hermaphrodites. We found that xol-1 mutant embryos overexpress the H3K9 methyltransferase MET-2 and have an altered H3K9me landscape. Some of these effects of the loss of xol-1 gene were reversed by the loss of met-2. These findings demonstrate that XOL-1 plays an important role as a developmental regulator in embryos of both sexes, and that MET-2 acts as a downstream effector of XOL-1 activity in hermaphrodites. Author SummaryVarious organisms have differing ways of determining, at a molecular level, what the sex of a developing embryo is supposed to be. The two sexes in the nematode C. elegans, hermaphrodite and male, have different numbers of X chromosomes. Hermaphrodites have two X chromosomes and males only have one. This mismatch raises an additional problem as hermaphrodites will have twice the amount of genes expressed from the X compared to males. This is solved by a process called dosage compensation, which equalizes gene expression between the sexes. A molecular sensor called XOL-1 detects the number of X chromosomes in an embryo and kick-starts the process of proper sexual development and/or dosage compensation. XOL-1 was known to be very important for activating male development but was believed to not have any role in the development of the hermaphrodite sex. We show that XOL-1 has some crucial roles in hermaphrodite embryos in controlling the rate of development of the embryo, and regulating the timing of dosage compensation. We also show that MET-2, a protein that deposits repressive methyl marks on DNA-bound histone proteins, is involved in this process.

genetics↗