Lrwd1, also known as ORCA, is a nuclear protein involved in multiple biological processes. It interacts with repressive histone marks via its WD40 domain, maintaining heterochromatin region silencing in mammalian cells. It also associates with the origin recognition complex (ORC), facilitating prereplication complex formation at late-replicating origins. Understanding its function is crucial as it likely plays important roles in various cellular and developmental processes [1,2,3,4].

Using a gene-trap approach to generate Lrwd1 knockout mice, it was found that Lrwd1 is ubiquitously expressed in the developing mouse embryo. Depletion of LRWD1 did not impact embryonic development, but the postnatal growth of homozygous mutants was retarded. In vitro, mouse embryonic fibroblasts (MEFs) lacking LRWD1 showed reduced proliferation. Also, the knockout of Lrwd1 in MEFs increased the expression of epigenetically silenced repetitive elements with minimal effect on protein-coding gene expression, suggesting Lrwd1 plays an important role in postnatal development by regulating cell proliferation, likely through modulating DNA replication [1].

In conclusion, Lrwd1 is essential for postnatal development by regulating cell proliferation, potentially through DNA replication modulation. The Lrwd1 knockout mouse model has been instrumental in uncovering these functions, providing insights into its role in normal development and potentially in diseases related to abnormal cell proliferation.

References:

1. Kang, Tze Zhen Evangeline, Wan, Yi Ching Esther, Zhang, Zhiguo, Chan, Kui Ming. 2022. Lrwd1 impacts cell proliferation and the silencing of repetitive DNA elements. In Genesis (New York, N.Y. : 2000), 60, e23475. doi:10.1002/dvg.23475. https://pubmed.ncbi.nlm.nih.gov/35451548/

2. Hsu, Rosaline Y C, Lin, Yo-Chuen, Redon, Christophe, Prasanth, Kannanganattu V, Prasanth, Supriya G. 2020. ORCA/LRWD1 Regulates Homologous Recombination at ALT-Telomeres by Modulating Heterochromatin Organization. In iScience, 23, 101038. doi:10.1016/j.isci.2020.101038. https://pubmed.ncbi.nlm.nih.gov/32344376/

3. Sahu, Sumon, Ekundayo, Babatunde E, Kumar, Ashish, Bleichert, Franziska. 2023. A dual role for the chromatin reader ORCA/LRWD1 in targeting the origin recognition complex to chromatin. In The EMBO journal, 42, e114654. doi:10.15252/embj.2023114654. https://pubmed.ncbi.nlm.nih.gov/37551430/

4. Giri, Sumanprava, Prasanth, Supriya G. 2016. Association of ORCA/LRWD1 with repressive histone methyl transferases mediates heterochromatin organization. In Nucleus (Austin, Tex.), 6, 435-41. doi:10.1080/19491034.2015.1102814. https://pubmed.ncbi.nlm.nih.gov/26765314/