Imprinted Cdkn1c genomic locus cell-autonomously promotes cell survival in cerebral cortex development

Abstract

The cyclin-dependent kinase inhibitor p57 KIP2 is encoded by the imprinted Cdkn1c locus, exhibits maternal expression, and is essential for cerebral cortex development. How Cdkn1c regulates corticogenesis is however not clear. To this end we employ Mosaic Analysis with Double Markers (MADM) technology to genetically dissect Cdkn1c gene function in corticogenesis at single cell resolution. We find that the previously described growth-inhibitory Cdkn1c function is a non-cell-autonomous one, acting on the whole organism. In contrast we reveal a growth-promoting cell-autonomous Cdkn1c function which at the mechanistic level mediates radial glial progenitor cell and nascent projection neuron survival. Strikingly, the growth-promoting function of Cdkn1c is highly dosage sensitive but not subject to genomic imprinting. Collectively, our results suggest that the Cdkn1c locus regulates cortical development through distinct cell-autonomous and non-cell-autonomous mechanisms. More generally, our study highlights the importance to probe the relative contributions of cell intrinsic gene function and tissue-wide mechanisms to the overall phenotype.

A Genome-wide Library of MADM Mice for Single-Cell Genetic Mosaic Analysis

“…In order to genetically link a mutant allele of a candidate gene to the corresponding chromosome containing the MADM cassette, meiotic recombination in germline can be utilized [e.g. (Hippenmeyer et al 2010;Laukoter et al 2020)] ( Figure 1E-F). The probability for meiotic recombination that results in the linkage of the mutant allele with the MADM cassette can be estimated ( Figure 1F) once the location (cM) of the mutant allele (genomic locus) has been determined by using for example Mouse Genome Informatics (MGI) database (www.informatics.jax.org).…”

“…MADM can create uniparental chromosome disomy (UPD, cells that carry two chromosomes from mother and maternally expressed imprinted genes are thus overexpressed whereas paternally expressed genes are not expressed and vice versa) ( Figure 3A). This feature has been utilized to analyze imprinting phenotypes at single cell level that result from the imbalanced expression of imprinted genes in UPD Laukoter et al 2020). Importantly, the analysis of candidate gene function, i.e.…”

“…MADM technology has recently emerged as a unique approach to probe genomic imprinting and the function of individual imprinted genes Laukoter et al 2020). Genomic imprinting is a prevalent epigenetic phenomenon in placental mammals and results in the preferential expression of either the maternal or paternal inherited allele of a subset of genes (Barlow and Bartolomei 2014;Ferguson-Smith 2011;Tucci et al 2019).…”

“…Genomic imprinting is a prevalent epigenetic phenomenon in placental mammals and results in the preferential expression of either the maternal or paternal inherited allele of a subset of genes (Barlow and Bartolomei 2014;Ferguson-Smith 2011;Tucci et al 2019). MADM can be applied to create uniparental chromosome disomy (UPD, somatic cells with two copies of either the maternal or paternal chromosome) and visualize imprinting effects at morphological and transcriptional level with single cell resolution (Hippenmeyer et al 2013;Laukoter et al 2020).…”

“…The candidate gene function can be either ablated in just very sparse mosaic and/or single clones (see above), or tissue-wide in all cells. However in both paradigms, single cell MADM labeling enables the high resolution quantitative phenotypic analysis (Beattie et al 2017;Joo et al 2014;Laukoter et al 2020). The above paradigms thus potentially permit systematic dissection of the level of cell-autonomy of any gene function in a given tissue, provided appropriate Cre-driver lines exist.…”