43. The blastopore region of amphibian embryo that secretes BMP inhibitors and dorsalizes the surrounding tissue is known as
(1) Brachet’s cleft                                            (2) Nieuwkoop center
(3) Hensen’s node                                           (4) Spemann’s organizer

 

The blastopore region of the amphibian embryo that secretes BMP inhibitors and dorsalizes the surrounding tissue is known as the Spemann’s organizer. This region, located in the dorsal lip of the blastopore, plays a crucial role in embryonic development by secreting molecules like chordin, noggin, and follistatin that inhibit bone morphogenetic proteins (BMPs). By blocking BMP signaling in nearby ectodermal cells, the Spemann organizer prevents them from becoming epidermis (skin) and instead directs them to form neural tissue, thereby dorsalizing the embryo and establishing the body axis.

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The Spemann’s organizer is a fundamental region in the amphibian embryo located at the dorsal lip of the blastopore during gastrulation. Discovered by Hans Spemann and Hilde Mangold in the early 20th century, this organizer region profoundly influences embryonic development by secreting signaling molecules that modulate the fate of surrounding cells.

One of the key functions of the Spemann organizer is to secrete inhibitors of bone morphogenetic proteins (BMPs), a group of growth factors that normally promote the formation of ventral and epidermal tissues. The main BMP inhibitors secreted by the organizer include chordin, noggin, and follistatin. These proteins bind to BMPs, preventing them from interacting with their receptors on neighboring ectodermal cells.

By blocking BMP signaling, the organizer induces the dorsalization of the ectoderm, causing these cells to adopt a neural fate rather than an epidermal fate. This process is crucial for the formation of the central nervous system and proper axial patterning of the embryo.

The organizer does not operate in isolation; it works closely with other signaling centers such as the Nieuwkoop center, which lies in the vegetal region of the embryo and induces the organizer itself. While the Nieuwkoop center provides the signals necessary for organizer formation, it is the Spemann organizer that actively patterns the embryonic axis by directing mesoderm differentiation and neural induction.

The discovery of the Spemann organizer cemented the concept of embryonic induction, showing how a group of cells can direct the developmental fate of another group of cells. This organizer is specific to amphibians, but analogous structures exist in other vertebrates; for example, Hensen’s node in birds and the embryonic node in mammals serve similar organizational roles.

Understanding the function of the Spemann organizer illuminates critical aspects of developmental biology and congenital disorders linked to early patterning defects. The balance of BMP signaling and its inhibition by the organizer exemplifies the intricate molecular dialogue that shapes early embryonic development.

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Final Answer:
The blastopore region of the amphibian embryo that secretes BMP inhibitors and dorsalizes the surrounding tissue is called (4) Spemann’s organizer. It is located at the dorsal lip of the blastopore and secretes molecules like chordin and noggin that inhibit BMP signaling, inducing dorsal structures and neural tissue formation during embryogenesis