Avian Primordial Germ Cells Contribute to and Interact With the Extracellular Matrix During Early Migration

Abstract

During early avian development, primordial germ cells (PGC) are highly migratory, moving from the central area pellucida of the blastoderm to the anterior extra-embryonic germinal crescent. The PGCs soon move into the forming blood vessels by intravasation and travel in the circulatory system to the genital ridges where they participate in the organogenesis of the gonads. This complex cellular migration takes place in close association with a nascent extracellular matrix that matures in a precise spatio-temporal pattern. We first compiled a list of quail matrisome genes by bioinformatic screening of human matrisome orthologs. Next, we used single cell RNA-seq analysis (scRNAseq) to determine that PGCs express numerous ECM and ECM-associated genes in early embryos. The expression of select ECM transcripts and proteins in PGCs were verified by fluorescent in situ hybridization (FISH) and immunofluorescence (IF). Live imaging of transgenic quail embryos injected with fluorescent antibodies against fibronectin and laminin, showed that germinal crescent PGCs display rapid shape changes and morphological properties such as blebbing and filopodia while surrounded by, or in close contact with, an ECM fibril meshwork that is itself in constant motion. Injection of anti-β1 integrin CSAT antibodies resulted in a reduction of mature fibronectin and laminin fibril meshwork in the germinal crescent at HH4-5 but did not alter the active motility of the PGCs or their ability to populate the germinal crescent. These results suggest that integrin β1 receptors are important, but not required, for PGCs to successfully migrate during embryonic development, but instead play a vital role in ECM fibrillogenesis and assembly.

Envelopment by endothelial cells initiates translocation of avian primordial germ cell into vascular tissue

“…PGCs that did not associate with ECs (free PGCs) exhibited cell protrusions like lamellipodia and membrane blebs (Figure 4; yellow arrows), suggesting that free PGCs, as well as ECs, are motile in the L‐GC. Previous studies also reported that some PGCs in the germinal crescent exhibited a motile appearance 9,28,31 . By contrast, we captured images in which EC‐associated PGCs exhibited spherical shapes rather than amoeboid shapes with protrusions (Figure 4; yellow arrowheads), suggesting that EC‐associated PGCs are static.…”

Single-Cell RNA Sequencing Revealed the Heterogeneity of Gonadal Primordial Germ Cells in Zebra Finch (Taeniopygia guttata)

“…For chicken or quail, which are representative model species of birds, there are commercially available antibodies such as DAZL and SSEA-1 (Stage-Specific Embryonic Antigen-1) that distinguish PGCs from gonads; however, few antibodies are optimized for zebra finch PGCs, and commercialized antibodies are lacking ( Jung et al, 2005 ; Huss et al, 2019 ; Ioannidis et al, 2021 ). Accordingly, it is necessary to discover a marker that is expressed specifically in PGCs.…”

The quail genome: insights into social behaviour, seasonal biology and infectious disease response

“…The avian embryo has long been a popular model for studying developmental biology due to the accessibility of the embryo, which permits fate mapping studies [5,6] and dynamic imaging of embryogenesis [7][8][9]. Several transgenic lines that express fluorescent proteins now exist, which greatly facilitates time-lapse imaging and tissue transplantation [7,[10][11][12][13].…”