Comparative Expression Analysis of Autism-Associated Cadherin Superfamily Members
Cell adhesion molecules (CAMs) play crucial roles in neural circuit formation. The cadherin superfamily is one of the largest families of CAMs containing more than one hundred molecules, including classical cadherins type I and II, protocadherins, and atypical cadherins. The type I classical cadherin N-cadherin/CDH2 is the most well-studied member to-date. N-cadherin functions throughout the development of nervous system including neurite outgrowth, axon guidance, synaptogenesis, spine morphogenesis and plasticity. Although there is only little known about the function of other cadherins they have been strongly implicated in autism. A genome wide association study performed by the Hussman Institute for Human Genomics identified the classical cadherin type II CDH8, CDH9 and CDH11, the protocadherin family member PCDH9 and the atypical cadherin FAT1 as candidate risk genes. This suggests that cadherin signaling pathways could be disrupted and may display increased vulnerability in autism.
As a first step toward understanding the central role of cadherins in the etiology of autism, we focus on CDH8, CDH9, CDH11, PCDH9 as well as FAT1 and investigate the expression pattern of these cadherins in specific brain areas, cell types and their subcellular localization during development. This comparative expression analysis could provide novel insights into common and distinct functions of these cadherins in neural circuit formation.
SDS-PAGE and Western blot analyses were performed to evaluate the protein expression of CDH8, CDH9, CDH11, PCDH9 and FAT1 in the developing mouse brain of embryonic day 14 (E14), postnatal day 0 (P0), P7, P14 and P21 and adult as well as in different brain areas. To analyze the cellular localization, primary neurons from different brain regions were cultured for 4 days in vitro and co-stained for cadherins and neuronal marker MAP2.
Temporal expression analysis in the developing mouse brain revealed increased expression of CDH8, CDH11 and PCDH9 from stages P7 to P14. In contrast, CDH9 expression peaked earlier in development between E14 and P7. The expression pattern of FAT1 was distinct from the other cadherins as its level was high at E14, decreased at P0 and was elevated again from P7 throughout P21. Analysis of specific brain areas showed that CDH8, CDH11 and PCDH9 were prominently expressed in the cortex, hippocampus and midbrain/striatum whereas FAT1 expression was restricted to the cerebellum. In line with these results, cellular localization of CDH8, CDH9, CDH11, PCDH9 and FAT1 expression was observed in the dendrites of cortical and cerebellar granule neurons, respectively.
Our results revealed similar expression profile among CDH8, CDH11 and PCDH9, with distinct expression patterns for CDH9 and FAT1. A peak of cadherin expression between P7 and P14 as well as cellular localization in dendrites is consistent with the proposed functions of cadherins in dendritogenesis and synaptogenesis. The brain areas that revealed the highest cadherin levels overlap those reported as associated with autism. Taken together, this analysis highlights that cadherins of different subfamilies are expressed in a developmental time window and in brain areas that are often affected in autism.