Loss of Mafb and Maf distorts myeloid cell ratios and disrupts fetal mouse testis vascularization and organogenesis†

Uncovering the prominent role of satellite cells in paravertebral muscle development and aging by single-nucleus RNA sequencing

To uncover the role of satellite cells (SCs) in paravertebral muscle development and aging, we constructed a single-nucleus transcriptomic atlas of mouse paravertebral muscle across seven timepoints spanning the embryo (day 16.5) to old (month 24) stages. Eight cell types, including SCs, fast muscle cells, and slow muscle cells, were identified. An energy metabolism-related gene set, TCA CYCLE IN SENESCENCE, was enriched in SCs. Forty-two skeletal muscle disease-related genes were highly expressed in SCs and exhibited similar expression patterns. Among them, Pdha1 was the core gene in the TCA CYCLE IN SENESCENCE; Pgam2, Sod1, and Suclg1 are transcription factors closely associated with skeletal muscle energy metabolism. Transcription factor enrichment analysis of the 42 genes revealed that Myod1 and Mef2a were also highly expressed in SCs, which regulated Pdha1 expression and were associated with skeletal muscle development. These findings hint that energy metabolism may be pivotal in SCs development and aging. Three ligand-receptor pairs of extracellular matrix (ECM)-receptor interactions, Lamc1-Dag1, Lama2-Dag1, and Hspg2-Dag1, may play a vital role in SCs interactions with slow/fast muscle cells and SCs self-renewal. Finally, we built the first database of a skeletal muscle single-cell transcriptome, the Musculoskeletal Cell Atlas (http://www.mskca.tech), which lists 630,040 skeletal muscle cells and provides interactive visualization, a useful resource for revealing skeletal muscle cellular heterogeneity during development and aging. Our study could provide new targets and ideas for developing drugs to inhibit skeletal muscle aging and treat skeletal muscle diseases.

Testicular macrophages are recruited during a narrow fetal time window and promote organ-specific developmental functions

A growing body of evidence demonstrates that fetal-derived tissue-resident macrophages have developmental functions. It has been proposed that macrophages promote testicular functions, but which macrophage populations are involved is unclear. Previous studies showed that macrophages play critical roles in fetal testis morphogenesis and described two adult testicular macrophage populations, interstitial and peritubular. There has been debate regarding the hematopoietic origins of testicular macrophages and whether distinct macrophage populations promote specific testicular functions. Here our hematopoietic lineage-tracing studies in mice show that yolk-sac-derived macrophages comprise the earliest testicular macrophages, while fetal hematopoietic stem cells (HSCs) generate monocytes that colonize the gonad during a narrow time window in a Sertoli-cell-dependent manner and differentiate into adult testicular macrophages. Finally, we show that yolk-sac-derived versus HSC-derived macrophages have distinct functions during testis morphogenesis, while interstitial macrophages specifically promote adult Leydig cell steroidogenesis. Our findings provide insight into testicular macrophage origins and their tissue-specific roles.

Lhx2 in germ cells suppresses endothelial cell migration in the developing ovary

LIM-homeobox genes play multiple roles in developmental processes, but their roles in gonad development are not completely understood. Herein, we report that Lhx2, Ils2, Lmx1a, and Lmx1b are expressed in a sexually dimorphic manner in mouse, rat, and human gonads during sex determination. Amongst these, Lhx2 has female biased expression in the developing gonads of species with environmental and genetic modes of sex determination. Single-cell RNAseq analysis revealed that Lhx2 is exclusively expressed in the germ cells of the developing mouse ovaries. To elucidate the roles of Lhx2 in the germ cells, we analyzed the phenotypes of Lhx2 knockout XX gonads. While the gonads developed appropriately in Lhx2 knockout mice and the somatic cells were correctly specified in the developing ovaries, transcriptome analysis revealed enrichment of genes in the angiogenesis pathway. There was an elevated expression of several pro-angiogenic factors in the Lhx2 knockout ovaries. The elevated expression of pro-angiogenic factors was associated with an increase in numbers of endothelial cells in the Lhx2-/- ovaries at E13.5. Gonad recombination assays revealed that the increased numbers of endothelial cells in the XX gonads in absence of Lhx2 was due to ectopic migration of endothelial cells in a cell non-autonomous manner. We also found that, there was increased expression of several endothelial cell-enriched male-biased genes in Lhx2 knockout ovaries. Also, in absence of Lhx2, the migrated endothelial cells formed an angiogenic network similar to that of the wild type testis, although the coelomic blood vessel did not form. Together, our results suggest that Lhx2 in the germ cells is required to suppress vascularization in the developing ovary. These results suggest a need to explore the roles of germ cells in the control of vascularization in developing gonads. Preprint version of the article is available on BioRxiv at https://doi.org/10.1101/2022.03.07.483280.