Yes, there are a few tools—free as well as paid ones—that enable you to search for mRNA and/or protein expression for genes in mouse cell lines. Some of the top free tools are as follows:

1. BioGPS

Link: http://biogps.org

It enables us to search gene expression profiles in a range of mouse tissues and cell lines. It provides both mRNA expression data as well as links to other tools.

2. Expression Atlas (EMBL-EBI)

Link: https://www.ebi.ac.uk/gxa/home

It contains baseline and differential expression data for mouse and other organisms. From this you can query genes and view expression across different cell types and cell lines.

3. Mouse ENCODE Project

Link: https://www.encodeproject.org

It is free. It contains RNA-seq and ChIP-seq data from different mouse tissues and cell lines. With this Data can be filtered to specifically include cell lines.

4. The Human Protein Atlas – Mouse Brain Atlas

Link: https://www.proteinatlas.org

It too is free and more tissue-level expression-oriented but contains cell line data as well for mouse. It is best suited for protein-level expression through antibody-based approaches.

5. GEO (Gene Expression Omnibus)

Link:https://www.ncbi.nlm.nih.gov/geo/

It too is free. With it comes a huge database of expression data, including RNA-seq and microarray data for mouse cell lines. It employs advanced search filters or tools such as GEO2R to contrast expression between samples.

6. DepMap / CCLE (Broad Institute) (Partly human, but applicable)

Link: https://depmap.org/portal/

It had a focus mainly on human cancer cell lines, but could perhaps still be useful depending on experimental context. In mouse models, occasionally RNA-seq datasets do contain mouse xenografts or derived lines.

These are a few paid resources:

Paid Resources:

1. Qiagen's Ingenuity Pathway Analysis (IPA)

Provides gene expression data but is typically used for pathway analysis instead of raw expression profiling.

2. Genevestigator (Free tier + paid plans)

https://genevestigator.com

Features curated gene expression in numerous cell lines, including mouse.

Here are key mouse cell line expression data resources:

1. Public Databases

• ENCODE (encodeproject.org) – RNA-seq/ChIP-seq data for mouse cell lines (e.g., C2C12, ES cells).
• CellXGene (cellxgene.cziscience.com) – Single-cell RNA-seq datasets (search for mouse cell lines).
• GEO (NCBI GEO) – Search "mouse cell line" + "expression" (e.g., datasets like GSE12345).

2. Cell Line Repositories

• ATCC (atcc.org) – Some cell lines include expression profiles.
• DepMap (depmap.org) – Includes some mouse models (focus on cancer).

3. Tools for Analysis

• BioGPS (biogps.org) – Gene expression across mouse cell lines.
• ARCHS4 (maayanlab.cloud/ARCHS4) – RNA-seq data for mouse/human cell lines.