Fiscal Year: 2018
1984 The University of Texas at San Antonio (75802)
Principal Investigator: Hermann, Brian (Principal Investigator)
Total Amount of Contract, Award, or Gift (Annual before 2011): $ 1,547,371
Exceeds $250,000 (Is it flagged?): Yes
Start and End Dates: 9/1/16 - 8/31/21
Restricted Research: YES
Academic Discipline: COS BIOLOGY
Department, Center, School, or Institute: San Antonio Cellular Therapeutics Institute (SACTI)
Title of Contract, Award, or Gift: Origin and functional significance of the spermatogonial stem cell transcriptome barcode.
Name of Granting or Contracting Agency/Entity:
Natl Inst of Health
CFDA Link: HHS
CFDA Linked: Child Health and Human Development Extramural Research
Spermatogonial stem cells (SSCs) are undifferentiated male germ cells that maintain spermatogenesis throughout adult life through balanced self-renewing and differentiating fate decisions. The vast majority of cases of male infertility resulting from spermatogenic defects (non-obstructive azoospermia) are of unknown etiology, but possible causes include defective SSC specification or maintenance. Thus, investigation into the molecular and cellular mechanisms of SSC specification and maintenance should reveal novel underlying causes of human male infertility, which affects 11% of the reproductive-age population in the US. SSCs arise from morphologically homogeneous prospermatogonia, though only some prospermatogonia produce SSCs, with the remainder differentiating to A1 spermatogonia that produce a single round of spermatogenesis termed the “first wave.” It follows that SSC specification may occur as a result of molecular divergence among prospermatogonia during an earlier developmental window that establishes subpopulations with higher or lower likelihoods of producing foundational SSCs. We recently performed single-cell RNA-seq which revealed considerable heterogeneity among mouse P6 Id4-eGFP+ spermatogonia and defined discrete subpopulations, on the basis of eGFP epifluorescence and cell surface marker staining, which exhibited differing stemness by transplant. Thus, for the first time, we have produced candidate molecular signatures which allow us to recognize foundational SSCs from among heterogeneous spermatogonial populations, which we will use to uncover the origin of these cells and the responsible mechanisms. In this project, we will test two hypotheses about the origin of SSCs in the testis and the functional significance of gene expression heterogeneity in this process. First, we hypothesize that definitive SSCs are predetermined and emerge from a precursor subpopulation with a unique transcriptome barcode. Second, we hypothesize that SSCs are induced from prospermatogonia and unique transcriptomes emerge as a result of selection. The experiments in this proposal will determine which of these opposing mechanisms is responsible for SSC specification by exploring the full extent, temporal origin, functional significance, and evolutionary conservation of population heterogeneity among foundational SSC precursors. Specific Aim 1: Define the extent and temporal origin(s) of gene expression heterogeneity among fetal/neonatal male germ cells and correlate with emergence of SSCs. Specific Aim 2: Determine whether cells expressing the SSC barcode are required for SSC pool formation. Specific Aim 3: Identify conserved gene expression signatures in higher primates that correlate with formation of the SSC state.
Discussion: No discussion notes