Estudios de antropología en Castilla-La Mancha

1.3.1.1.1. Behavioural and cognitive phenotypes in Df1 mice models

Mice models with homozygous deletions (Df1-/-) did not survive and had embryonic

lethality (Lindsay et al. 1999). On the other hand, although those with heterozygous

deletions Df1+/- were viable; however, they showed congenital heart defects similar

to those seen in 22q11.2DS (Lindsay et al. 1999), In addition to the congenital

abnormalities observed in these mice, they also expressed behavioural abnormalities

(Lindsay et al. 1999) (Figure 1- 9).

Due to difficulties in studying 22q11.2DS behavioural deficit in mice models,

cognitive functions that can be tested in 22q11.2DS patients as well as in Df1 mice

models were examined. These functions encompassing attention, executive function,

working memory, and short-term verbal memory which can represent the activity of

the prefrontal cortex and hippocampus (Sobin et al. 2006). Paylor and colleagues

reported anomalies of sensorimotor gating in the Df1+/- mice, which was

demonstrated by impaired pre-pulse inhibition (PPI) (Paylor et al. 2001). This

phenotypic feature was also described in patients with schizophrenia and patients with

22q11.2DS (Sobin et al. 2006). Moreover, these mice also expressed memory and

learning impairments (Paylor et al. 2001). Lgdel+/- mice also showed similar impaired

PPI in addition to abnormality in grip strength and nociception (Long et al. 2006).

Conversely, mice that are heterozygous for a deletion of proximal 150Kb region of

29 1.3.1.1.2. Gene expression in Df1 mice models

The gene expression studies on the Df1 mice models showed that MMU16qA13 genes

begin to express in mouse embryos and undergo several dynamic expression changes

among different embryonic development stages (Amati et al. 2007).

The effect of haploinsufficiency on gene expression was thought to account for the

cardiac defects in these Df1+/- mice, therefore, they had been studied to investigate

gene expression by using microarray and Real Time Quantitative PCR (RTqPCR).

Prescott and colleagues extracted RNA from dissected branchial arch region and heart

of Df1+/- embryos at embryonic day (E) 10.5, during which the arch-artery phenotype

is fully penetrant (Prescott et al. 2005). 12 of the genes mapping to the Df1 deletion

were covered by MG-U74a microarray used in this study. 75% (n= 9) of the 12 Df1

genes were identified as significantly down regulated in Df1+/- mice (FDR <0.05).

Figure 1- 9: Pre-pulse inhibition phenotypes in 22q11.2DS mice models.

Grey bars indicate generated 22q11.2DS mice models with various sizes of deletions spanning the homologous 22q11.2 multi genes in mice. The gene content of the various deletions is depicted. Along with each mice model, PPI phenotypes, either impaired indicated by a downward arrow or increased indicated by an upward arrow, and references for studies investigated these 22q11.2 mice models. Original figure based on the information from (Paylor & Lindsay 2006).

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33.3% of the 75% genes were validated by RTqPCR and showed reduced hemizygous

expression. Genome-wide, the analysis showed some of the downregulated genes have

a role in vasculogenesis and cardiogenesis including Connexin 45 and Dnajb9

(Prescott et al. 2005). These findings confirmed that the cardiac abnormality seen in

by Df1+/- mice is resulted possibly by some dosage sensitive genes within the Df1

deletion and some other genes that have a key role in the cardiac pathogenesis

(Prescott et al. 2005).

Although the mice with a hemizygous Df1 deletion have cardiac anomalies similar to

those seen in 22q11.2DS patients; however, Lindsay and colleagues noticed that mice

with a deletion in one 22q11.2 chromosome and a duplication in the other chromosome

(Df1/Dp1) have no abnormal cardiac phenotypes (Lindsay et al. 1999). This finding

indicated that cardiac defects seen in 22q11.2DS are possibly resulted by the

haploinsufficiency of dosage sensitive genes in 22q11.2 region (Lindsay et al. 1999).

To identify what particular genes in 22q11.2 region that is associated with cardiac

defects, Lindsay and colleagues further investigated Tbx1 knockout mice. The results

showed a defective development of the 4th pharyngeal arch artery observed in Tbx1+/- mice, which suggested that Tbx1 gene is responsible for heart abnormality in

22q11.2DS (Lindsay et al. 2001). In humans, this finding was confirmed by observing

a series of individuals with typical 22q11.2DS cardiac phenotypes; however, no

22q11.2 deletion in these individuals. However, these individuals were found to have

a point mutation in the TBX1 gene (Yagi et al. 2003).

A number of studies have investigated gene expression in the central nervous system

of Df1+/- mice. Hippocampal sections of 10 week-old Df1+/- and wild-type mice

were used for RNA extraction for microarray and RTqPCR analyses. The results

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reduction in gene expression with an average expression reduction equal to 33%. The

dosage sensitive genes included Prodh and Comt (Jurata et al. 2006).

Sivagnanasundaram and colleagues confirmed these findings by using RNA samples

extracted from the brain of adult Df1+/- and wild-type mice (Sivagnanasundaram et

al. 2007). 41.7% of the Df1 genes expressed in the hippocampus (n= 5/12) and were

significantly down regulated in the Df1+/- hippocampus (p-value <0.05). Globally,

159 other genes were identified to be differentially expressed in the hippocampus of

these mice (p-value <0.05) (Sivagnanasundaram et al. 2007).

In another study, the expression of nine 22q11.2 orthologues genes (Idd, Prodh,

Zdhhc8, Ranbp1, T10, Comt, Tbx1, Ufd1l, and Hira) were investigated in the brains

or dissected brain regions from later fetal (E10.5 embryos), postnatal, adolescent, and

adult Df1+/- mice. The results revealed a diminished expression of these genes in

these models by 40-60% (Meechan et al. 2006).