Pax6 is required intrinsically by thalamic progenitors for the normal molecular patterning of thalamic neurons but not the growth and guidance of their axons. Issue 1 (December 2015)

• Record Type: Journal Article
• Authors: Clegg, James; Li, Ziwen; Molinek, Michael; Caballero, Isabel; Manuel, Martine; Price, David
• Is Part Of: Neural development. Volume 10:Issue 1(2015)
• Page Start: 1
• Page End: 12
• Publication Date: 2015-12
• Subjects: Nkx2.2 -- Pax6 -- Robo2 -- Thalamic patterning -- Thalamocortical axons -- Transcription factors; Neurology -- Periodicals; Nervous system -- Growth -- Periodicals; Developmental neurobiology -- Periodicals; 573.8
• DOI: 10.1186/s13064-015-0053-7
• Languages: English
• ISSNs: 1749-8104

Abstract

Abstract Background In mouse embryos, the Pax6 transcription factor is expressed in the progenitors of thalamic neurons but not in thalamic neurons themselves. Its null-mutation causes early mis-patterning of thalamic progenitors. It is known that thalamic neurons generated byPax6 −/− progenitors do not develop their normal connections with the cortex, but it is not clear why. We investigated the extent to which defects intrinsic to the thalamus are responsible. Results We first confirmed that, in constitutivePax6 −/− mutants, the axons of thalamic neurons fail to enter the telencephalon and, instead, many of them take an abnormal path to the hypothalamus, whose expression of Slits would normally repel them. We found that thalamic neurons show reduced expression of the Slit receptorRobo2 inPax6 −/− mutants, which might enhance the ability of their axons to enter the hypothalamus. Remarkably, however, in chimeras comprising a mixture ofPax6 −/− andPax6 +/+ cells, Pax6 −/− thalamic neurons are able to generate axons that exit the diencephalon, take normal trajectories through the telencephalon and avoid the hypothalamus. This occurs despite abnormalities in their molecular patterning (they express Nkx2.2, unlike normal thalamic neurons) and their reduced expression ofRobo2 . In conditional mutants, acute deletion of Pax6 from the forebrain at the time when thalamic axons are starting to grow does not prevent the development of the thalamocortical tract, suggesting that earlier extra-thalamic patterning and /or morphological defects are the main cause of thalamocortical tract failure inPax6 −/− constitutive mutants. Conclusions Our results indicate that Pax6 is required by thalamic progenitors for the normal molecular patterning of the thalamic neurons that they generate but thalamic neurons do not need normal Pax6-dependent patterning to become competent to grow axons that can be guided appropriately.