A Conserved Notochord Enhancer Controls Pancreas Development in Vertebrates

Organizing activities of axial mesoderm

For almost a century, developmental biologists have appreciated that the ability of the embryonic organizer to induce and pattern the body plan is intertwined with its differentiation into axial mesoderm. Despite this, we still have a relatively poor understanding of the contribution of axial mesoderm to induction and patterning of different body regions, and the manner in which axial mesoderm-derived information is interpreted in tissues of changing competence. Here, with a particular focus on the nervous system, we review the evidence that axial mesoderm notochord and prechordal mesoderm/mesendoderm act as organizers, discuss how their influence extends through the different axes of the developing organism, and describe how the ability of axial mesoderm to direct morphogenesis impacts on its role as a local organizer.

Manipulation of Sonic Hedgehog Signaling Pathway in Maintenance, Differentiation, and Endocrine Activity of Insulin-Producing Cells: A Systematic Review

Background

Some studies have evaluated the manipulation of the sonic hedgehog (Shh) signaling pathway to generate more efficient insulin-producing cells (IPCs). In a systematic review, we evaluated in vitro and in vivo studies on the effect of inhibition or activation of the Shh pathway on the production, differentiation, maintenance, and endocrine activity of IPCs.

Methods

A systematic review was conducted using all available experimental studies published between January 2000 and November 2022. The review aimed at determining the effect of Shh manipulation on the differentiation of stem cells (SCs) into IPCs. Keywords and phrases using medical subject headings were extracted, and a complete search was performed in Web of Science, Embase, ProQuest, PubMed, Scopus, and Cochrane Library databases. The inclusion criteria were manipulation of Shh in SCs, SCs differentiation into IPCs, and endocrine activity of mature IPCs. Articles with incomplete data and duplications were excluded.

Results

A total of 208 articles were initially identified, out of which 11 articles were included in the study. The effect of Shh inhibition in the definitive endoderm stage to produce functional IPCs were confirmed. Some studies showed the importance of Shh re-activation at late-stage differentiation for the generation of efficient IPCs. It is proposed that baseline concentrations of Shh in mature pancreatic β-cells affect insulin secretion and endocrine activities of the cells. However, Shh overexpression in pancreatic β-cells ultimately leads to improper endocrine function and inadequate glucose-sensing insulin secretion.

Conclusion

Accurate manipulation of the Shh signaling pathway can be an effective approach in the production and maintenance of functional IPCs.

Efficient knock-in method enabling lineage tracing in zebrafish

Here, we devised a cloning-free 3' knock-in strategy for zebrafish using PCR amplified dsDNA donors that avoids disrupting the targeted genes. The dsDNA donors carry genetic cassettes coding for fluorescent proteins and Cre recombinase in frame with the endogenous gene but separated from it by self-cleavable peptides. Primers with 5' AmC6 end-protections generated PCR amplicons with increased integration efficiency that were coinjected with preassembled Cas9/gRNA ribonucleoprotein complexes for early integration. We targeted four genetic loci (krt92, nkx6.1, krt4, and id2a) and generated 10 knock-in lines, which function as reporters for the endogenous gene expression. The knocked-in iCre or CreERT2 lines were used for lineage tracing, which suggested that nkx6.1 + cells are multipotent pancreatic progenitors that gradually restrict to the bipotent duct, whereas id2a + cells are multipotent in both liver and pancreas and gradually restrict to ductal cells. In addition, the hepatic id2a + duct show progenitor properties upon extreme hepatocyte loss. Thus, we present an efficient and straightforward knock-in technique with widespread use for cellular labelling and lineage tracing.

Ptf1a function and transcriptional cis-regulation, a cornerstone in vertebrate pancreas development

Vertebrate pancreas organogenesis is a stepwise process regulated by a complex network of signaling and transcriptional events, progressively steering the early endoderm toward pancreatic fate. Many crucial players of this process have been identified, including signaling pathways, cis‐regulatory elements, and transcription factors (TFs). Pancreas‐associated transcription factor 1a (PTF1A) is one such TF, crucial for pancreas development. PTF1A mutations result in dramatic pancreatic phenotypes associated with severe complications, such as neonatal diabetes and impaired food digestion due to exocrine pancreatic insufficiency. Here, we present a brief overview of vertebrate pancreas development, centered on Ptf1a function and transcriptional regulation, covering similarities and divergences in three broadly studied organisms: human, mouse and zebrafish.

CRISPR-Cas9-Mediated Genomic Deletions Protocol in Zebrafish

Since its first application for site-directed mutagenesis, the CRISPR-Cas9 system has revolutionized genome engineering. Here, we present a validated workflow for the generation of targeted genomic deletions in zebrafish, including the design, cloning, and synthesis of single-guide RNAs and Cas9 mRNA, followed by microinjection in zebrafish embryos and subsequent genotype screening for the establishment of a mutant line. The versatility and efficiency of this pipeline makes the generation of zebrafish models a widely used approach in functional genetics. For complete details on the use and execution of this protocol, please refer to Amorim et al. (2020).