## **Core Concept**
Mullerian inhibiting substance (MIS), also known as anti-Mullerian hormone (AMH), plays a crucial role in the development of the reproductive system. It is responsible for the regression of Mullerian ducts in male embryos, preventing the development of female reproductive structures. This process is essential for the normal development of male genitalia.

## **Why the Correct Answer is Right**
The correct answer, ** Sertoli cells**, is right because these cells in the testes of the male fetus produce Mullerian inhibiting substance (MIS). MIS causes the regression of Mullerian ducts, which if present, would develop into female reproductive structures such as the fallopian tubes, uterus, and upper part of the vagina. The production of MIS by Sertoli cells is critical for the male differentiation of the reproductive system.

## **Why Each Wrong Option is Incorrect**
- **Option A: Leydig cells** - These cells are involved in the production of testosterone, which is crucial for the development of male secondary sexual characteristics and the promotion of Wolffian duct development into male reproductive structures. However, they do not produce MIS.
- **Option B: Germ cells** - While germ cells are essential for the development of gametes (sperm in males and eggs in females), they do not produce MIS.
- **Option D: Peritubular myoid cells** - These cells are involved in the structure and function of the seminiferous tubules but are not responsible for producing MIS.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that Mullerian inhibiting substance (MIS or AMH) is not only crucial for fetal development but also has a role in adult females. In females, AMH is produced by granulosa cells of small antral follicles and serves as a marker of ovarian reserve. Low levels of AMH can indicate diminished ovarian reserve.

## **Correct Answer: C. Sertoli cells**