Two New Pseudopod Morphologies Displayed by the Human Hematopoietic KG1a Progenitor Cell Line and by Primary Human CD34+Cells

Abstract

A primitive human hematopoietic myeloid progenitor cell line, KG1a, characterized by high expression of the CD34 surface antigen has been observed to extend long, thin pseudopodia. Once extended, these pseudopods may take on one of two newly described morphologies, tenupodia or magnupodia. Tenupodia are very thin and form in linear segments. They adhere to the substrate, can bifurcate multiple times, and often appear to connect the membranes of cells more than 300 μm apart. Magnupodia are much thicker and have been observed to extend more than 330 μm away from the cell. Magnupods are flexible and can exhibit rapid dynamic motion, extending or retracting in a few seconds. During retraction, the extended material often pools into a bulb located on the pod. Both morphologies can adhere to substrates coated with fibronectin, collagen IV, and laminin as well as plastic. The CD34 and CD44 antigens are also present on the surface of these podia. Primary human CD34+ cells from fetal liver, umbilical cord blood, adult bone marrow, and mobilized peripheral blood extend these podia as well. The morphology that these pseudopods exhibit suggest that they may play both sensory and mechanical roles during cell migration and homing after bone marrow transplantation.

Hematopoietic progenitors polarize in contact with bone marrow stromal cells in response to SDF1

“…1 E ), as well as in bone marrow in vivo ( Coutu et al, 2017 ). HSPCs appeared to be attached to stromal cells by a pseudopod of variable size that has been previously described and named a “magnupodium” ( Francis et al, 1998 ; Freund et al, 2006 ), similar to the stalk-like projection documented in B lymphoblastoid cells ( Dustin et al, 1992 ). The contact site of this magnupodium was restricted to a small area estimated to be ∼1–2 µm 2 .…”

“…Several lines of experimental evidence, in living organisms and in cultured cells, have revealed that, in addition to diffusible signals, direct cell-to-cell contact is involved in the regulation of HSPC fate ( Wagner et al, 2007 ; Bruns et al, 2014 ; Alakel et al, 2009 ; Ceafalan et al, 2018 ; Walenda et al, 2010 ). In cocultures of human CD34 + , HSPCs isolated from newborn cord blood and mesenchymal stromal cells from bone marrow aspirates ( Wagner et al, 2007 ), HSPCs can adopt elongated and asymmetric morphologies, with several types of protrusions of various lengths and widths ( Francis et al, 1998 ) that can have specific impact on proliferation and differentiation ( Freund et al, 2006 ; Frimberger et al, 2001 ; Holloway et al, 1999 ). Similar polarized HSPC morphologies have also been observed in vivo ( Coutu et al, 2017 ), but the stromal cells and signaling pathways that give rise to these morphologies remain to be deciphered.…”

Decoding Single Cell Morphology in Osteotropic Breast Cancer Cells for Dissecting Their Migratory, Molecular and Biophysical Heterogeneity

“…Aside from the migrating cells, poorly motile cells are also of interest since they are differentially detected. Cells exhibiting Morphotype 2 harbor a magnupodium, as previously observed in a subpopulation of hematopoietic stem cells [24,91,92] and cancer cells [91,93]. In a previous study, one of our laboratories has shown that CD9 participates in their formation by stabilizing the lamellipodium at the free end [94], and it remains to be determined whether the differential CD9 expression explains the presence or absence of these types of protrusions in a given cell line.…”

Membrane-bound SCF and VCAM-1 synergistically regulate the morphology of hematopoietic stem cells

“…The membrane protrusions we observed resemble these microspikes and/or podia but under the distinct context of membrane-bound HSC–stromal interactions, which has not been described in mouse HSCs before. The existence of long podia has also been seen in human CD34 + HPCs in culture ( Francis et al, 1998 ; Wagner et al, 2004 ). Notably, the more primitive fraction of human CD34 + /CD38 − HPCs has a higher frequency of polarized morphology ( Wagner et al, 2004 ), and these cells seek contact with a mouse stromal cell line (AFT024) through protrusions ( Wagner et al, 2005 ).…”

“…The two structures differ in cytoskeletal composition; pseudopods are enriched with newly synthesized actin, and uropods are composed of contractile actin–myosin complexes ( Sánchez-Madrid and Serrador, 2009 ; Xu et al, 2003 ). While studies on HSC morphologies are relatively few, researchers have described the microspikes or protrusions of mouse HSCs or human HPCs with various terms (e.g., magnupodia, tenupodia, proteopodia, and uropods), which resemble morphological and functional features of pseudopods and/or uropods ( Francis et al, 1998 ; Frimberger et al, 2001 ; Wagner et al, 2005 ). However, little is known about the cytoskeletal nature of these structures and the signaling components that regulate them in HSCs.…”