Production of an aminoterminally truncated, stable type of bioactive mouse fibroblast growth factor 4 in Escherichia coli

Increased thermal stability of FGF10 leads to ectopic signaling during development

Fibroblast growth factors (FGFs) control organ morphogenesis during development as well as tissue homeostasis and repair in the adult organism. Despite their importance, many mechanisms that regulate FGF function are still poorly understood. Interestingly, the thermodynamic stability of 22 mammalian FGFs varies widely, with some FGFs remaining stable at body temperature for more than 24 h, while others lose their activity within minutes. How thermodynamic stability contributes to the function of FGFs during development remains unknown. Here we show that FGF10, an important limb and lung morphogen, exists as an intrinsically unstable protein that is prone to unfolding and is rapidly inactivated at 37 °C. Using rationally driven directed mutagenesis, we have developed several highly stable (STAB) FGF10 variants with a melting temperature of over 19 °C more than that of wildtype FGF10. In cellular assays in vitro, the FGF10-STABs did not differ from wildtype FGF10 in terms of binding to FGF receptors, activation of downstream FGF receptor signaling in cells, and induction of gene expression. In mouse embryonal lung explants, FGF10-STABs, but not wildtype FGF10, suppressed branching, resulting in increased alveolarization and expansion of epithelial tissue. Similarly, FGF10-STAB1, but not FGF10 wildtype, inhibited the growth of mouse embryonic tibias and markedly altered limb morphogenesis when implanted into chicken limb buds, collectively demonstrating that thermal instability should be considered an important regulator of FGF function that prevents ectopic signaling. Furthermore, we show enhanced differentiation of human iPSC-derived lung organoids and improved regeneration in ex vivo lung injury models mediated by FGF10-STABs, suggesting an application in cell therapy.

Suspension culture promotes serosal mesothelial development in human intestinal organoids

Pluripotent-stem-cell-derived human intestinal organoids (HIOs) model some aspects of intestinal development and disease, but current culture methods do not fully recapitulate the diverse cell types and complex organization of the human intestine and are reliant on 3D extracellular matrix or hydrogel systems, which limit experimental control and translational potential for regenerative medicine. We describe suspension culture as a simple, low-maintenance method for culturing HIOs and for promoting in vitro differentiation of an organized serosal mesothelial layer that is similar to primary human intestinal serosal mesothelium based on single-cell RNA sequencing and histological analysis. Functionally, HIO serosal mesothelium has the capacity to differentiate into smooth-muscle-like cells and exhibits fibrinolytic activity. An inhibitor screen identifies Hedgehog and WNT signaling as regulators of human serosal mesothelial differentiation. Collectively, suspension HIOs represent a three-dimensional model to study the human serosal mesothelium.

Charting human development using a multi-endodermal organ atlas and organoid models

Organs are composed of diverse cell types that traverse transient states during organogenesis. To interrogate this diversity during human development, we generate a single-cell transcriptome atlas from multiple developing endodermal organs of the respiratory and gastrointestinal tract. We illuminate cell states, transcription factors, and organ-specific epithelial stem cell and mesenchyme interactions across lineages. We implement the atlas as a high-dimensional search space to benchmark human pluripotent stem cell (hPSC)-derived intestinal organoids (HIOs) under multiple culture conditions. We show that HIOs recapitulate reference cell states and use HIOs to reconstruct the molecular dynamics of intestinal epithelium and mesenchyme emergence. We show that the mesenchyme-derived niche cue NRG1 enhances intestinal stem cell maturation in vitro and that the homeobox transcription factor CDX2 is required for regionalization of intestinal epithelium and mesenchyme in humans. This work combines cell atlases and organoid technologies to understand how human organ development is orchestrated.

Generation of small intestinal organoids for experimental intestinal physiology

Human intestinal organoids (HIOs) derived from pluripotent stem cells were first described almost a decade ago as a method to differentiate intestinal tissue containing both epithelium and supporting mesenchymal cells. The original protocol documents a directed differentiation approach to first induce definitive endoderm from pluripotent stem cells, followed by hindgut specification, resulting in the self-organization of 3D hindgut spheroids. These hindgut spheroids are then embedded in a basement membrane extracellular matrix (ECM) such as Matrigel and mature into HIOs over about 4 weeks in culture. Since the initial HIO protocol was published, the methods to generate HIOs have been updated over time including revisions to the directed differentiation protocol and implementation of new culture methods for spheroids such as embedding in alginate or polyethylene glycol hydrogels as defined alternatives to Matrigel. Additionally, HIOs have been utilized for new applications such as co-culture with bacteria. This protocol compiles the most up to date information on HIO generation and presents alternative experimental applications.

Large-scale production of bioactive recombinant human acidic fibroblast growth factor in transgenic silkworm cocoons

With an increasing clinical demand for functional therapeutic proteins every year, there is an increasing requirement for the massive production of bioactive recombinant human acidic fibroblast growth factor (r-haFGF). In this present study, we delicately explore a strategy for the mass production of r-haFGF protein with biological activity in the transgenic silkworm cocoons. The sequence-optimized haFGF was inserted into an enhanced sericin-1 expression system to generate the original transgenic silkworm strain, which was then further crossed with a PIG jumpstarter strain to achieve the remobilization of the expression cassette to a “safe harbor” locus in the genome for the efficient expression of r-haFGF. In consequence, the expression of r-haFGF protein in the mutant line achieved a 5.6-fold increase compared to the original strain. The high content of r-haFGF facilitated its purification and large-scald yields. Furthermore, the r-haFGF protein bioactively promoted the growth, proliferation and migration of NIH/3T3 cells, suggesting the r-haFGF protein possessed native mitogenic activity and the potential for wound healing. These results show that the silk gland of silkworm could be an efficient bioreactor strategy for recombinant production of bioactive haFGF in silkworm cocoons.

Generation of aminoterminally truncated, stable types of bioactive bovine and porcine fibroblast growth factor 4 in Escherichia coli

Fibroblast growth factor 4 (FGF4) is a crucial growth factor for the development of mammalian embryos. We previously produced hexahistidine-tagged, bovine and porcine FGF4 (Pro(32) to Leu(206) ) proteins without a secretory signal peptide at the aminoterminus in Escherichia coli. Here, we found that these were unstable; site-specific cleavage between Ser(54) and Leu(55) in both FGF4 derivatives was identified. In order to generate stable FGF4 derivatives and to investigate their biological activities, aminoterminally truncated and hexahistidine-tagged bovine and porcine FGF4 (Leu(55) to Leu(206) ) proteins, termed HisbFGF4L and HispFGF4L, respectively, were produced in E. coli. These FGF4 derivatives were sufficiently stable and exerted mitogenic activities in fibroblasts. Treatment with the FGF4 derivatives promoted the phosphorylation of ERK1/2, which are crucial kinases in the FGF signaling pathway. In the presence of PD173074, an FGF receptor inhibitor, the phosphorylation of ERK1/2 was inhibited and resulted in abolition of the growth-promoting activity of FGF4 derivatives. Taken together, we demonstrate that HisbFGF4L and HispFGF4L are capable of promoting the proliferation of bovine- and porcine-derived cells, respectively, via an authentic FGF signaling pathway. These FGF4 derivatives may be applicable for dissecting the roles of FGF4 during embryogenesis in cattle and pigs.