Tissue morphogenesis and vascular stability require the Frem2 protein, product of the mouse myelencephalic blebs gene

Abstract

Adhesive properties of cells undergoing morphogenetic rearrangements can be regulated either at the cellular level or by altering the environment in which rearrangements occur. Here, we describe the identification of a mutation (my F11 ) in the mouse extracellular matrix component Frem2, and provide evidence that suggests Frem2 expression creates an environment conducive to morphogenetic events. Loss of Frem2 function results in defects in developmental events associated with morphogenetic rearrangements of the vasculature and of tissues arising from all germ layers. The Frem2 transcript is restricted both spatially and temporally and appears in advance of cell rearrangement events. Thus, expression of Frem2 may dynamically alter the extracellular matrix to provide a substrate for cell migration and rearrangements during embryogenesis. extracellular matrix ͉ hemorrhage ͉ Frem ͉ CALX␤ ͉ neural tube defect

Breakdown of the reciprocal stabilization of QBRICK/Frem1, Fras1, and Frem2 at the basement membrane provokes Fraser syndrome-like defects

“…7, which is published as supporting information on the PNAS web site). These results are consistent with recent reports that Frem2 is dysfunctional in mice bearing the my KST and my F11 alleles, both of which cause Fraser syndrome-like phenotypes similar to those observed in my mice (5,9). Because we failed to detect any deletion or missense͞ nonsense mutation in the exons encoding the Frem2 protein (see Table 1, which is published as supporting information on the PNAS web site), the reduced expression of Frem2 may result from either mutation(s) affecting the activity of cistranscriptional elements or the stability of Frem2 transcripts.…”

“…Although disruption of Frem2 is reported in my KST and my UCL mutants, both of which are thought to be allelic to my, the original my allele has not been fully investigated (5,9,11). In my͞my mutant embryos and newborns, Frem2 immunoreactivity was reduced in the epidermal basement membrane zone when compared with my͞ϩ animals (Fig.…”

“…Discussion Four mouse models of Fraser syndrome, bearing mutations in Fras1, Frem2, Qbrick͞Frem1, and Grip1, exhibit closely overlapping phenotypes of subepidermal blistering, cryptophthalmos, syndactyly, and renal agenesis (4)(5)(6)(7)(8)(9)(11)(12)(13). The similarities in their phenotypes and the expression patterns of their causative genes (4)(5)(6)(7)(8)(9) imply that the protein products of these genes function cooperatively, although little has been known about such cooperativity, except that the intracellular adaptor protein GRIP1 is required for the transport of Fras1 (7). Our results clearly show that the three Fraser syndrome-associated ECM proteins, Fras1, Frem2, and QBRICK͞Frem1, each characterized by the presence of 12 CSPG repeats and variable Calx-␤ motif(s), exhibit mutually dependent basement membrane deposition; their basement membrane localization strongly depends on intact expression of all three proteins.…”

“…The developmental defects observed in Fraser syndrome and the associated mouse models suggest that these defects arise from disruption of the epithelial-mesenchymal interactions required for normal morphogenetic processes. Recently, two novel genes, FRAS1 and FREM2, have been identified as the causative genes in human Fraser syndrome, and Fras1, Frem2, Grip1, and Qbrick͞Frem1 have been recognized as the genes mutated in bl, my, eb, and heb mice, respectively (4)(5)(6)(7)(8)(9). Grip1 encodes an intracellular adaptor protein containing multiple PDZ domains, whereas Fras1, Qbrick͞Frem1, and Frem2 encode members of a novel family of ECM proteins characterized by 12 consecutive CSPG repeats and a varying number of Calx-␤ domains (refs.…”

Uncovering the uncharacterized and unexpected: Unbiased phenotype‐driven screens in the mouse

“…In some cases, these screens have been carried out in individual labs (Kasarskis et al, 1998;Herron et al, 2002;Zarbalis et al, 2004;Garcia-Garcia et al, 2005;Papathanasiou and Goodnow, 2005). In other cases, collaborations among neighboring labs that are interested in complementary phenotypes have been particularly productive (Pask et al, 2005;Timmer et al, 2005;Kennedy et al, 2006). Based on our rough calculations, the time and cost to generate one mutation is about the same in forward and reverse genetic approaches.…”