Mammalian artificial chromosome formation from circular alphoid input DNA does not require telomere repeats

No prior work had resolved whether specific terminal sequences are strictly necessary for the de novo assembly of synthetic genetic structures in human cells. It was already known that linear constructs containing telomeric repeats typically facilitate the creation of stable artificial chromosomes. That uncertainty drove researchers to examine if alternative DNA architectures could bypass these requirements. Prior research has shown that linear yeast-derived constructs often rely on terminal caps to prevent degradation and promote stability. This gap motivated a deeper look into the structural constraints governing the formation of these engineered entities. Scientists previously assumed that circular inputs might behave differently than their linear counterparts during the integration process. Understanding these mechanisms is vital for advancing gene therapy and synthetic biology applications. This study addresses the fundamental structural prerequisites for successful chromosome generation in mammalian environments.

The aim of this study was to investigate the structural constraints of input DNA during the formation of artificial chromosomes in mammalian cells. Researchers sought to determine if circular DNA molecules require specific terminal sequences to successfully assemble into stable chromosomes. This work addresses the uncertainty surrounding the necessity of telomeric repeats for different DNA topologies. The team specifically examined whether linear constructs and circular molecules follow the same assembly pathways. By varying the orientation and position of telomeric arrays, the investigators aimed to clarify the role of these sequences in linear construct stability. The study also intended to verify if the resulting chromosomes acquire host DNA or form through independent assembly mechanisms. These experiments were motivated by the need to understand the fundamental requirements for synthetic chromosome creation. The findings provide insight into the structural flexibility of DNA inputs in human cell lines.

The team conducted a series of transfection experiments using HT1080 cells to introduce various DNA constructs. They prepared both circular and linear alphoid arrays to test structural requirements for chromosome generation. The researchers systematically varied the presence, orientation, and location of telomeric sequences on the linear input molecules. This review approach involved comparing the formation efficiency of these diverse DNA configurations under controlled laboratory conditions. They monitored the resulting structures to determine if they could segregate properly without ongoing selection pressure. The investigators also performed molecular analyses to detect the presence of telomeres on the final artificial chromosomes. They screened for host DNA integration to verify the de novo nature of the assembly process. This methodology allowed for a comprehensive assessment of how input topology dictates the success of synthetic chromosome formation.

Circular input DNA successfully generated artificial chromosomes with high efficiency regardless of the presence of telomere arrays. Linear constructs capped with telomere arrays produced artificial chromosomes effectively, matching the performance of circular inputs. A severe reduction in formation rates occurred when linear constructs lacked these terminal protective sequences. Human telomere arrays positioned between one and five kilobases from the ends of linear constructs promoted formation with similar efficiencies regardless of orientation. The resulting artificial chromosomes segregated efficiently in the absence of selection, indicating stable maintenance. Telomeres remained undetectable on the artificial chromosomes even when telomere arrays were included on the input DNA. This observation suggests that the final structures likely maintain a circular form. No evidence for the acquisition of host cell DNA appeared, which aligns with the hypothesis of de novo assembly.

The authors propose that circular DNA molecules possess an inherent capacity to form stable artificial chromosomes without requiring telomeric sequences. Their findings suggest that the absence of terminal repeats does not hinder the generation of these structures when using circular inputs. The study indicates that linear constructs lacking such protective caps suffer from significantly reduced formation rates compared to capped versions. Researchers observed that the orientation or precise placement of telomeric arrays on linear molecules does not impact the efficiency of chromosome assembly. The evidence implies that the resulting artificial chromosomes likely maintain a circular topology throughout their existence. The team found no signs of host DNA acquisition, supporting the conclusion that these structures arise through de novo assembly processes. These results demonstrate that the structural configuration of input DNA is a primary determinant of successful artificial chromosome creation. The work clarifies the distinct requirements for circular versus linear DNA substrates in synthetic chromosome engineering.