Transgenic mice expressing F3/contactin from the transient axonal glycoprotein promoter undergo developmentally regulated deficits of the cerebellar function.

We have shown that transgenic transient axonal glycoprotein (TAG)/F3 mice, in which the mouse axonal glycoprotein F3/contactin was misexpressed from a regulatory region of the gene encoding the transient axonal glycoprotein TAG-1, exhibit a transient disruption of cerebellar granule and Purkinje cell development [Development 130 (2003) 29]. In the present study we explore the neurobehavioural consequences of this mutation. We report on assays of reproductive parameters (gestation length, litter size and offspring viability) and on somatic and neurobehavioural end-points (sensorimotor development, homing performance, motor activity, motor coordination and motor learning). Compared with wild-type littermates, TAG/F3 mice display delayed sensorimotor development, reduced exploratory activity and impaired motor activity, motor coordination and motor learning. The latter parameters, in particular, were affected also in adult mice, despite the apparent recovery of cerebellar morphology, suggesting that subtle changes of neuronal circuitry persist in these animals after development is complete. These behavioural deficits indicate that the finely coordinated expression of immunoglobulin-like cell adhesion molecules such as TAG-1 and F3/contactin is of key relevance to the functional, as well as morphological maturation of the cerebellum.

Alternative promoters drive the expression of the gene encoding the mouse axonal glycoprotein F3/contactin.

F3/Contactin is a neuronal glycoprotein which mediates axonal growth control via complex interactions with a number of cell surface or matrix components. As part of this developmental role, its expression undergoes differential regulation during the maturation of definite neuronal populations within the central and peripheral nervous tissue. To elucidate the underlying molecular mechanisms we study here the organization of the regulatory region of the mouse F3/Contactin gene. We show that this region displays peculiar features in that it spans more than 80 kb, bears very large introns and includes four untranslated exons which undergo complex splicing events leading to 11 potential arrangements of the F3/Contactin mRNA 5' end. Within this region we identify three alternative neurospecific promoters which, as deduced from the developmental profile of the associated 5' exons (A1,C1,0), drive two different patterns of F3/Contactin gene expression. The activity of the A1 exon-associated promoter displays only minor developmental changes and is likely to contribute to the basal level of the F3/Contactin gene expression; by contrast, the activities of the exon C1- and exon 0-associated promoters are significantly upregulated at the end of the first postnatal week. The data indicate that differential regulation of the F3/Contactin expression during development may depend upon alternative utilization of distinct promoter elements and may involve complex splicing events of the 5' untranslated exons. Several consensuses for homeogene transcription factors are scattered within the identified regulatory region, in agreement with the general assumption of homeotic gene regulation of neural morphoregulatory molecules.