Generation and Characterization of Neuregulin-2-Deficient Mice

Abstract

The neuregulins (NRGs) are a family of four structurally related growth factors that are expressed in the developing and adult brain. NRG-1 is essential for normal heart formation and has been implicated in the development and maintenance of both neurons and glia. NRG-2 was identified on the basis of its homology to NRG-1 and, like NRG-1, is expressed predominantly by neurons in the central nervous system. We have generated mice with the active domain of NRG-2 deleted in an effort to characterize the biological function of NRG-2 in vivo. In contrast to the NRG-1 knockout animals, NRG-2 knockouts have no apparent heart defects and survive embryogenesis. Mutant mice display early growth retardation and reduced reproductive capacity. No obvious histological differences were observed in the major sites of NRG-2 expression. Our results indicate that in vivo NRG-2 activity differs substantially from that of NRG-1 and that it is not essential for normal development in utero.The neuregulin (NRG) family of growth factors comprises numerous glycoproteins that arise via alternative splicing from four distinct genes (NRG-1, NRG-2, NRG-3, and NRG-4). These proteins have a similar mosaic-like structure with a number of recognizable protein domains. The prototypic member of this family, NRG-1, was independently identified as a Schwann cell mitogen (12,19), an activator of erbB2 (15,29), and an inducer of acetylcholine receptor synthesis at the neuromuscular junction (7). The NRG-1 gene gives rise to as many as 15 different splice forms, generated by alternative splicing and differential promoter usage. These variants are also known as heregulin, acetylcholine receptor-inducing activity (ARIA), sensory and motor neuron-derived differentiation factor, Neu differentiation factor, and glial growth factor. More recently, a number of genes encoding proteins related to NRG-1 have been identified. These genes, named NRG-2 (also identified as Don-1 and NTAK) (2-4, 14), NRG-3 (32), and NRG-4 (13), were discovered by using sequences from NRG-1 to either search nucleotide databases or perform low-stringency hybridization and/or PCR.Of the four NRG genes, NRG-1 and NRG-2 are the most closely related, although all members possess a 50-amino-acid region with homology to epidermal growth factor. This domain alone is sufficient for receptor binding and activation (2-4, 15, 32). The epidermal growth factor-like domains of NRGs 1 to 4 are 40 to 48% similar to each other in pairwise comparisons. Despite this low homology, all the NRG epidermal growth factor-like domains bind to either ErbB4 or ErbB3, albeit with different affinities (16). The epidermal growth factor-like domains of NRG-1 and NRG-2 each have two variants, designated ␣ and ␤, arising from alternative exon usage, which also exhibit differential receptor binding affinities (16).

Neuregulin 1 Sustains the Gene Regulatory Network in Both Trabecular and Nontrabecular Myocardium

“…No cardiac phenotype was seen in mutants for Nrg2 or ska (a hypomorphic allele of Nrg3). 37,38 Nevertheless, to assess redundancy in this system, we exploited a mutant mouse line (ErbB4 gt ) in which the ErbB4 gene had been disrupted by insertion of a gene trap vector. 21 Among EGF family receptors, only ErbB4 and its coreceptor ErbB2 are expressed in developing myocardium, and knockout mice for ErbB4 show the same smooth-walled ventricular chamber phenotype as seen in Nrg1 Ϫ/Ϫ and Nrg1 TM/TM embryos.…”

The role of neuregulin–ErbB4 interactions on the proliferation and organization of cells in the subventricular zone

“…The conditional nervous systemspecific loss of the NRG2 receptor ErbB4 resulted in the abrogation of the effects of the infusion of this factor. However, it remains to be determined whether SVZ cell proliferation or neuroblast migration is disrupted in NRG2-deficient mice (38).…”

Schwann cell‐derived neuregulin‐2α can function as a cell‐attached activator of muscle acetylcholine receptor expression

“…Thus, it will be important to carefully evaluate the Nrg-2-deficient mice (Britto et al, 2004), which are viable and fertile, before a more compelling conclusion can be made concerning the role of this factor in synaptic AChR expression in vivo.…”