Le, T. N. U. | Search bioRxiv

bioRxiv2023

Y chromosome damage underlies testicular abnormalities in ATR-X syndrome

ATR-X (alpha thalassemia, mental retardation, X-linked) syndrome is a severe developmental disorder affecting males caused by mutations in the chromatin remodelling gene ATRX. Genital abnormalities in affected boys include hypospadias and ambiguous genitalia, and patients show small poorly formed testes with only a few seminiferous tubules. Our mouse model recapitulated these testicular defects when Atrx was specifically deleted in Sertoli cells (ScAtrxKO). ScAtrxKO mice develop small testes with fewer and discontinuous tubules due to G2/M arrest and apoptosis of Sertoli cells. Here, we investigated the mechanism underlying the Sertoli cell defects in ATR-X syndrome. In healthy male control mice, Sertoli cell nuclei contain a single novel "GATA4 PML nuclear body (NB)" that strongly expresses the transcription factor GATA4, as well as ATRX and its binding partner DAXX. The GATA4 PML NB co-localizes with heterochromatin protein HP1 and PH3 (a marker of chromosome condensation), and with the short arm of the Y chromosome (Yp). In contrast, ScAtrxKO Sertoli cells contain a single giant GATA4 PML NB, frequently associated with DNA double-strand breaks in G2/M-arrested Sertoli cells that underwent apoptosis. HP1 and PH3 were absent from the giant GATA4 foci suggesting a local failure in heterochromatin formation and chromosome condensation. Our data indicate that in Sertoli cells, ATRX protects a chromosomal region of Yp from DNA damage, probably during replication stress, and thus protects Sertoli cells from cell death. We discuss Y chromosome damage as a novel mechanism for testicular failure and the potential role of GATA4 during this process. Disclosure SummaryThe authors have nothing to disclose.

developmental biology↗

bioRxiv2021

Mfsd2b and Spns2 are essential for maintenance of blood vessels during development and protection of anaphylaxis

Sphingosine-1-phosphate (S1P) is a potent lipid mediator that is secreted by several cell types to induce signaling. We recently showed that Mfsd2b is an S1P transporter from hematopoietic cells, which contributes approximately 50% plasma S1P. To further determine the sources of plasma S1P, here, we report the characterizations of compound deletions of Mfsd2b and Spns2, another S1P transporter from endothelial cells. Global deletion of Mfsd2b and Spns2 (gDKO) resulted in embryonic lethality between E13.5 and E14.5 with severe hemorrhage that largely recapitulated the phenotypes from global S1P1 knockout mice, indicating that together with Mfsd2b, Spns2 also provides embryonic source of S1P for S1P1 stimulation. The hemorrhagic phenotypes in gDKO embryos were accompanied by increased angiogenesis and defects of tight junction proteins, indicating that S1P from Mfsd2b and Spns2 is essential for blood vessel integrity and maturation. The various sources of S1P in postnatal stages are yet to be fully understood. Postnatal ablation of S1P synthesis enzymes using Mx1Cre shows that Mx1Cre-sensitive cells provide most of plasma S1P. Interestingly, we showed that compound postnatal deletion of Mfsd2b and Spns2 using Mx1Cre (ctDKO-Mx1Cre) resulted in maximal reduction of 80% plasma S1P. Thus, a small amount of plasma S1P is supplied from other sources independent of Mfsd2b and Spns2. Nevertheless, the vasculature in the lung of ctDKO-Mx1Cre mice was compromised. Furthermore, ctDKO-Mx1Cre mice also exhibited severe susceptibility to anaphylaxis, indicating that S1P from Mfsd2b and Spns2 is indispensable during vascular stress. Together, our results show that Mfsd2b and Spns2 provide a critical source of S1P for embryonic development and they also provide a majority of plasma S1P for vascular homeostasis.

molecular biology↗