Transgenic Mouse Services


Transgenic Mouse Production

The generation of genetically modified mice can be divided into two categories; insertion of foreign DNA into a targeted loci or random integration into the mouse genome. The first category (gene targeting) is typically performed in cell culture and is ideally suited to deletion (or modification) of endogenous alleles. In contrast, pronuclear injection generates mutant mice with a random pattern of integration sites. Each model has several strengths and weaknesses for studying in vivo.


Plasmid DNA & Bacterial Artificial Chromosomes (BAC’s)

Single gene constructs with constitutively expressed promoter elements have the highest rates of random integrations with typically 10-30% of all live born progeny containing, though not necessarily expressing the gene construct. This class of construct is usually ~10kb in size and is ideal for the study of ubiquitously expressed foreign DNA from either mouse or other species in vivo. Plasmid DNA is directly injected into the pronucleus of a mouse zygote as a single gene construct or co-injection of two or more constructs. Plasmid DNA frequently integrates as concatemers with head to tail repeats that may interrupt endogenous gene function(s), integrate in unexpressed regions or undergo gene silencing by acetylation. For these reasons, several transgenic founders must be generated, examined and potential founders selected for consistency of gene expression. This type of construct inherently lacks complex regulatory elements typical of native genes environments and is best suited for overexpression of gene products.

In contrast, BAC’s can be as large as 500kb in size and may contain many genes with complete regulatory elements. BAC constructs are ideally suited for the study of regional or tissue specific transcription of gene products for both coding and regulatory genes. Due to their size, BAC’s have a slightly lower efficiency of integration into the mouse genome (~5-10% of live births) and fragments of the original construct may integrate if degradation or shearing takes place prior to or during the micro-injection procedure. However, BAC’s rarely form concatemers at insertion sites and once two or more potential founders are identified, gene expression levels tends to be stable and readily transmitted to subsequent progeny.



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