Mechanisms Regulating Gonadal Morphogenesis and Distal Tip Cell Migration in C. elegans

Organ morphogenesis requires precise coordination among stem cell niches, surrounding somatic tissues, and extracellular guidance cues. In C. elegans, the hermaphrodite’s gonad provides a powerful model for investigating stem cell maintenance, differentiation, migration, and associated morphogenetics. The distal tip cell (DTC) serves as the stem cell niche by balancing self-renewal and differentiation through GLP-1/Notch signaling. At the same time, DTC also functions as a leader cell that guides gonad arms elongation through long-range, stereotyped migration during larval development.This dissertation investigates two major aspects of distal gonad development: the structural organization of the distal germline niche and the genetic regulation of DTC migration. In Chapter 2, we investigated the spatial relationship between the DTC and the most distal pair of somatic gonadal sheath cells (Sh1). Previous models proposed that a germline “bare region” exists between the DTC and Sh1. However, our observations challenged this; the most distal part of Sh1 exhibits morphological overlap with the elaborated DTC beginning in the late L4 stages. This spatial arrangement forms a functional interface that influences how germ cells shift from self-renewal to differentiation. We further investigate the structural stability of this organization. We also compared several fluorescence-tagged sheath cell strains and revealed potential limitations of the commonly used Sh1 reporter strain. These results provide a new angle on somatic cell organization in the distal gonad and strengthen our previous model in which the DTC and Sh1 form a closely associated interface rather than a separate niche.In Chapter 3, we used published single-cell RNA sequencing (scRNA-seq) datasets to select the new regulator mig-21, which is highly and specifically enriched in young adult DTCs. Genetic analyses show that loss of mig-21 causes a low penetrance but constant DTC migration defect. Additional experiments indicated that mig-21 functions cell-autonomously in the DTC and interacts with both Wnt and Netrin signaling, acting as an integrator to fine-tune how DTCs interpret multiple guidance cues during development and regulate migration decisions.In summary, this dissertation broadens our understanding of the distal gonad architecture and provides additional insights into how migrating cells coordinate guidance cues during development.