Hand1 gene replacement with Hand2 reveals overlap in function with unique occurrence of omphalocele and heart defects [Spatial Transcriptomics]

The bHLH transcription factors HAND1 and HAND2 are expressed in partially overlapping patterns during development. Studies have established evidence for significant functional redundancy between HAND1 and HAND2. To test redundancy fully, we engineered a Hand1 allele where we directly replace the exons and intron with those of Hand2. Results show that 2% of Hand1Hand2/ Hand2 mice are viable, and fertile. The remaining Hand1Hand2/Hand2 embryos exhibit neonatal lethality due to omphalocele, ventricular septal defects and conduction anomalies. Omphalocele can occur due to altered gut rotation and transcriptomic expression analysis reveals that established gene expression patterns associated with normal gut rotation are compromised. Interrogation of cardiac function in surviving Hand1Hand2/Hand2 mice reveals QRS abnormalities and accompanies cardiac morphogenic defects. These data support previous findings that HAND factors exhibit extensive functional overlap but do reveal that unique functions for HAND1 and HAND2 proteins within the Hand1 expression domain that are required for normal embryonic development. Four Control E13.5 day embryos that were sectioned transverse at the level of the umbilicus and four Hand1^Hand2/Hand2 E13.5 day embryos that were sectioned transverse at the level of the umbilicus were transferred onto Visisum slides (10X Genomics) with 11mm capture area with 55 um diameter "spots" using a CytAssist (10X genomics). Four to six sections depending on the individual emrbyo were transfered to both the A side and B side of a single slide yeilding 8 to 12 section replicates per sample. The A side of one of the Hand1^Hand2/Hand2 Mutants (V52L19-098_A1) failed and was not included in this study.