Magic embryology: origin of the pituitary (Introduction)

by David Turell , Saturday, February 03, 2024, 19:56 (294 days ago) @ David Turell

Surprising for a tiny organ with many functions:

https://phys.org/news/2024-02-pituitary-gland-embryonic-insights-growth.html

"Situated at the base of the brain, this pea-sized organ, also known as the hypophysis, plays a central role in maintaining body metabolism. Interfacing between the brain and the blood, it can be described as the control center of the endocrine system, which releases hormones into the bloodstream.

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"The structure of the pituitary, which contains two separate lobes that serve different physiological functions, has been highly conserved throughout evolution, meaning that fish, mouse and human pituitary glands are largely similar. For many years researchers took great interest in a fundamental question: Where do the two lobes originate during embryonic development?

"The early embryo consists of three primary cell layers, from which the entire body ultimately arises: The endoderm (the inner layer), the mesoderm (middle layer) and the ectoderm (outer layer). Until now, the generally accepted view was that the cells making up each of the two lobes of the pituitary originated from separate embryonic subdivisions of the ectoderm.

"The frontal, or anterior lobe, which releases six major hormones—including the thyroid-stimulating and growth hormones—was thought to originate solely from the early embryo's exterior tissue layer, the oral ectoderm. The posterior lobe, which releases two major brain-derived hormones—oxytocin, a regulator of reproduction and behavior, and vasopressin, which controls various aspects of body fluid balance—was thought to originate from the neural ectoderm, a tissue that eventually also forms the nervous system.

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"In line with the prevalent dogma, she expected the frontal lobe of the fish's pituitary to contain only cells with genetic labels from the early embryo's oral ectoderm, and the posterior lobe, from the embryo's neural ectoderm. Instead, she found that some of the cells in the frontal lobe were descendants of the embryo's neural ectoderm.

"'This finding contradicted the idea that the two parts of the pituitary gland have entirely separate origins," Levkowitz says. "There had been hints in research by other scientists that these origins might be mixed, but before our study, no one had produced the smoking gun."

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"By identifying the exact molecular signatures of the major cell types in the pituitary, the project also led to an additional finding: Previously unknown cross-talk between different cells belonging to the frontal and posterior parts of the gland.

"The researchers discovered that certain cells in the posterior lobe, called pituicytes, influence the development of hormone-producing cells in the frontal lobe. The pituicytes, a subtype of the astroglia—star-shaped cells of the nervous system—were known to facilitate the release of oxytocin and vasopressin hormones from the posterior pituitary lobe.

"'Our finding was a surprise—in addition to their previously known function, pituicytes play a role in the development of the frontal pituitary," says Chen."

Comment: as the master central controller of our endocrine system, the fact that some of the
anterior lobe of the pituitary has a neural origin suggests that fibers from the brain, probably the hypothalamus, are monitoring the pituitary actions. This was designed. Imagine all the very many fortuitous cooperative mutations to achieve this result.