Preserving the Pineal Gland in Perinatal Mouse Brain Preparations

The pineal gland, a neuroendocrine structure that secretes melatonin, forms from an anlage at the dorsal midline in the embryonic forebrain. At embryonic day (E) 14.5 in the mouse, a pineal diverticulum is seen out-pouching from the roof of the diencephalon between the paired telencephalic vesicles. This diverticulum is in close contact with overlying cartilage, meningeal, and vascular tissue. It is easily lost when the cranial vault is opened to extract the brain at late embryonic/ early postnatal stages. Despite its important neuroendocrine role, the early development of the pineal gland and the signaling mechanisms that regulate this process remain poorly understood, partly due to the difficulty of preserving this structure intact during embryonic stages of mouse brain development. This article presents an innovative dissection procedure that preserves the pineal gland while maintaining its structural integrity and its attachment to the roof of the diencephalon during brain isolation from embryonic stages through postnatal day (P) 7. The procedure is demonstrated using an E18.5 mouse brain and is therefore suitable for downstream applications requiring preservation of tissue architecture, including in situ hybridization, immunohistochemistry, and spatial transcriptomics. The protocol may also be used to isolate the developing pineal gland, thereby improving pineal-specific representation in transcriptomic and proteomic analyses, which is otherwise challenging because of its small size.