Targeted Disruption of Tgif, the Mouse Ortholog of a Human Holoprosencephaly Gene, Does Not Result in Holoprosencephaly in Mice

Abstract

5-TG-3-interacting factor or transforming growth factor beta (TGF-␤)-induced factor (TGIF) belongs to a family of evolutionarily conserved proteins that are characterized by an atypical three-amino-acid loop extension homeodomain. In vitro studies have implicated TGIF as a transcriptional repressor and corepressor in retinoid and TGF-␤ signaling pathways that regulate several important biological processes. Heterozygous nonsense and missense mutations of the human TGIF gene have been associated with holoprosencephaly, the most common congenital malformation of the forebrain. In mice, Tgif mRNA is expressed ubiquitously in the ventricular neuroepithelium at embryonic day 10.5 (E10.5) but displays a medial to lateral gradient in the developing cerebral cortex at E12.5. The expression quickly declines by E14.5. The spatiotemporal expression profile of Tgif is consistent with its involvement in midline forebrain development. To better understand the function of Tgif in forebrain patterning and proliferation in vivo, we generated mice lacking Tgif by targeted deletion of exons 2 and 3, which encode 98% of the amino acids. Tgif ؊/؊ mice had no detectable Tgif protein by Western blotting. Surprisingly, however, these mice were viable and fertile. In addition, there were no discernible derangements in any of the major organ systems, including the forebrain. Overall our results point to a possible functional redundancy of Tgif, potentially provided by the closely related Tgif2.

Expression and functional analysis of Tgif during mouse midline development

“…Moreover, Tgif Ϫ/Ϫ mutant mice are viable and can be bred normally. Our result is consistent with a recent report by Shen and Walsh (2005). This result is strikingly different from the human study, which revealed that loss of Tgif function is associated with human HPE, a typical ventral forebrain malformation (Gripp et al, 2000).…”

“…Since the expression after day 12.5 d.p.c has been reported before (Bertolino et al, 1996;Shen and Walsh, 2005), we focused our Tgif in situ hybridization study on early stages of neural induction and ventral CNS specification during mouse development. We found that Tgif is expressed in the epiblast of the mouse embryo as early as the prestreak stage at day 6.0 d.p.c (E6.0) (Fig.…”

“…It is possible that TGIF, C-Ski, and SnoN play redundant roles in regulating TGF-␤ signaling during mouse CNS development. It is also possible that the loss of TGIF function is compensated for by its related protein, TGIF2, as suggested by Shen and Walsh (2005).…”

TGIF, a gene associated with human brain defects, regulates neuronal development

“…Experiments directly assessing the loss of TGIF function will be important for understanding the role of TGIF in human HPE. Of note, the null mutant mouse for Tgif did not show any abnormalities in the structure of the prosencephalon (Shen and Walsh, 2005). It is possible that the Tgif2 gene provides redundancy for Tgif activity in the forebrain.…”

“…Studies in Drosophila have indicated that Tgif-related genes are required for normal spermatogenesis (Ayyar et al, 2003;Wang and Mann, 2003). However, the Tgif null mutant mouse did not demonstrate abnormalities in neural development (Shen and Walsh, 2005). Overall, the role of TGIF in vertebrate development is not well understood.…”