Final answer:
Pre-pro-B cells initially express Immunoglobulin alpha (Igα) and Igβ molecules during their development, which are signaling components of the B-cell receptor complex. Major histocompatibility complex (MHC) molecules and T-cell receptors (TCRs) are not expressed by pre-pro-B cells at this early stage.
Step-by-step explanation:
The molecules initially expressed by pre-pro-B cells during their development are Immunoglobulin alpha (Igα) and Igβ. As precursors to B cells, pre-pro-B cells begin the process of immunoglobulin gene rearrangement for the production of the heavy chain component of the B-cell receptor (BCR), but light chains are not yet produced. This stage is prior to the expression of a complete BCR or secretion of antibodies. The BCR, which is structurally similar to an antibody, will eventually be composed of both heavy and light chains. The Igα and Igβ molecules are important signaling components of the BCR complex, even though the full BCR is not yet present on these immature cells.
The major histocompatibility complex (MHC) molecules, while critical for antigen presentation, are not what is initially expressed by developing pre-pro-B cells. MHC I molecules are found on all nucleated cells and present antigens to T cells, while MHC II molecules are expressed by antigen-presenting cells (APCs) and present antigens to helper T cells. Similarly, T-cell receptors (TCRs), CD3, and CD4, are associated with T-cell development and are not involved in the early stages of B-cell development.